Adding upstream version 5.10.209.upstream/5.10.209upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

34 files changed, 13458 insertions, 0 deletions

diff --git a/net/dccp/Kconfig b/net/dccp/Kconfig
new file mode 100644
index 000000000..0c7d2f66b
--- /dev/null
+++ b/net/dccp/Kconfig
@@ -0,0 +1,46 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menuconfig IP_DCCP
+	tristate "The DCCP Protocol"
+	depends on INET
+	help
+	  Datagram Congestion Control Protocol (RFC 4340)
+
+	  From https://www.ietf.org/rfc/rfc4340.txt:
+
+	  The Datagram Congestion Control Protocol (DCCP) is a transport
+	  protocol that implements bidirectional, unicast connections of
+	  congestion-controlled, unreliable datagrams. It should be suitable
+	  for use by applications such as streaming media, Internet telephony,
+	  and on-line games.
+
+	  To compile this protocol support as a module, choose M here: the
+	  module will be called dccp.
+
+	  If in doubt, say N.
+
+if IP_DCCP
+
+config INET_DCCP_DIAG
+	depends on INET_DIAG
+	def_tristate y if (IP_DCCP = y && INET_DIAG = y)
+	def_tristate m
+
+source "net/dccp/ccids/Kconfig"
+
+menu "DCCP Kernel Hacking"
+	depends on DEBUG_KERNEL=y
+
+config IP_DCCP_DEBUG
+	bool "DCCP debug messages"
+	help
+	  Only use this if you're hacking DCCP.
+
+	  When compiling DCCP as a module, this debugging output can be toggled
+	  by setting the parameter dccp_debug of the `dccp' module to 0 or 1.
+
+	  Just say N.
+
+
+endmenu
+
+endif # IP_DDCP
diff --git a/net/dccp/Makefile b/net/dccp/Makefile
new file mode 100644
index 000000000..5b4ff37bc
--- /dev/null
+++ b/net/dccp/Makefile
@@ -0,0 +1,30 @@
+# SPDX-License-Identifier: GPL-2.0
+obj-$(CONFIG_IP_DCCP) += dccp.o dccp_ipv4.o
+
+dccp-y := ccid.o feat.o input.o minisocks.o options.o output.o proto.o timer.o \
+	  qpolicy.o
+#
+# CCID algorithms to be used by dccp.ko
+#
+# CCID-2 is default (RFC 4340, p. 77) and has Ack Vectors as dependency
+dccp-y += ccids/ccid2.o ackvec.o
+dccp-$(CONFIG_IP_DCCP_CCID3)	+= ccids/ccid3.o
+dccp-$(CONFIG_IP_DCCP_TFRC_LIB) += ccids/lib/tfrc.o		\
+				   ccids/lib/tfrc_equation.o	\
+				   ccids/lib/packet_history.o	\
+				   ccids/lib/loss_interval.o
+
+dccp_ipv4-y := ipv4.o
+
+# build dccp_ipv6 as module whenever either IPv6 or DCCP is a module
+obj-$(subst y,$(CONFIG_IP_DCCP),$(CONFIG_IPV6)) += dccp_ipv6.o
+dccp_ipv6-y := ipv6.o
+
+obj-$(CONFIG_INET_DCCP_DIAG) += dccp_diag.o
+
+dccp-$(CONFIG_SYSCTL) += sysctl.o
+
+dccp_diag-y := diag.o
+
+# build with local directory for trace.h
+CFLAGS_proto.o := -I$(src)
diff --git a/net/dccp/ackvec.c b/net/dccp/ackvec.c
new file mode 100644
index 000000000..8f3dd3b1d
--- /dev/null
+++ b/net/dccp/ackvec.c
@@ -0,0 +1,402 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/ackvec.c
+ *
+ *  An implementation of Ack Vectors for the DCCP protocol
+ *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
+ */
+#include "dccp.h"
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/export.h>
+
+static struct kmem_cache *dccp_ackvec_slab;
+static struct kmem_cache *dccp_ackvec_record_slab;
+
+struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority)
+{
+	struct dccp_ackvec *av = kmem_cache_zalloc(dccp_ackvec_slab, priority);
+
+	if (av != NULL) {
+		av->av_buf_head	= av->av_buf_tail = DCCPAV_MAX_ACKVEC_LEN - 1;
+		INIT_LIST_HEAD(&av->av_records);
+	}
+	return av;
+}
+
+static void dccp_ackvec_purge_records(struct dccp_ackvec *av)
+{
+	struct dccp_ackvec_record *cur, *next;
+
+	list_for_each_entry_safe(cur, next, &av->av_records, avr_node)
+		kmem_cache_free(dccp_ackvec_record_slab, cur);
+	INIT_LIST_HEAD(&av->av_records);
+}
+
+void dccp_ackvec_free(struct dccp_ackvec *av)
+{
+	if (likely(av != NULL)) {
+		dccp_ackvec_purge_records(av);
+		kmem_cache_free(dccp_ackvec_slab, av);
+	}
+}
+
+/**
+ * dccp_ackvec_update_records  -  Record information about sent Ack Vectors
+ * @av:		Ack Vector records to update
+ * @seqno:	Sequence number of the packet carrying the Ack Vector just sent
+ * @nonce_sum:	The sum of all buffer nonces contained in the Ack Vector
+ */
+int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seqno, u8 nonce_sum)
+{
+	struct dccp_ackvec_record *avr;
+
+	avr = kmem_cache_alloc(dccp_ackvec_record_slab, GFP_ATOMIC);
+	if (avr == NULL)
+		return -ENOBUFS;
+
+	avr->avr_ack_seqno  = seqno;
+	avr->avr_ack_ptr    = av->av_buf_head;
+	avr->avr_ack_ackno  = av->av_buf_ackno;
+	avr->avr_ack_nonce  = nonce_sum;
+	avr->avr_ack_runlen = dccp_ackvec_runlen(av->av_buf + av->av_buf_head);
+	/*
+	 * When the buffer overflows, we keep no more than one record. This is
+	 * the simplest way of disambiguating sender-Acks dating from before the
+	 * overflow from sender-Acks which refer to after the overflow; a simple
+	 * solution is preferable here since we are handling an exception.
+	 */
+	if (av->av_overflow)
+		dccp_ackvec_purge_records(av);
+	/*
+	 * Since GSS is incremented for each packet, the list is automatically
+	 * arranged in descending order of @ack_seqno.
+	 */
+	list_add(&avr->avr_node, &av->av_records);
+
+	dccp_pr_debug("Added Vector, ack_seqno=%llu, ack_ackno=%llu (rl=%u)\n",
+		      (unsigned long long)avr->avr_ack_seqno,
+		      (unsigned long long)avr->avr_ack_ackno,
+		      avr->avr_ack_runlen);
+	return 0;
+}
+
+static struct dccp_ackvec_record *dccp_ackvec_lookup(struct list_head *av_list,
+						     const u64 ackno)
+{
+	struct dccp_ackvec_record *avr;
+	/*
+	 * Exploit that records are inserted in descending order of sequence
+	 * number, start with the oldest record first. If @ackno is `before'
+	 * the earliest ack_ackno, the packet is too old to be considered.
+	 */
+	list_for_each_entry_reverse(avr, av_list, avr_node) {
+		if (avr->avr_ack_seqno == ackno)
+			return avr;
+		if (before48(ackno, avr->avr_ack_seqno))
+			break;
+	}
+	return NULL;
+}
+
+/*
+ * Buffer index and length computation using modulo-buffersize arithmetic.
+ * Note that, as pointers move from right to left, head is `before' tail.
+ */
+static inline u16 __ackvec_idx_add(const u16 a, const u16 b)
+{
+	return (a + b) % DCCPAV_MAX_ACKVEC_LEN;
+}
+
+static inline u16 __ackvec_idx_sub(const u16 a, const u16 b)
+{
+	return __ackvec_idx_add(a, DCCPAV_MAX_ACKVEC_LEN - b);
+}
+
+u16 dccp_ackvec_buflen(const struct dccp_ackvec *av)
+{
+	if (unlikely(av->av_overflow))
+		return DCCPAV_MAX_ACKVEC_LEN;
+	return __ackvec_idx_sub(av->av_buf_tail, av->av_buf_head);
+}
+
+/**
+ * dccp_ackvec_update_old  -  Update previous state as per RFC 4340, 11.4.1
+ * @av:		non-empty buffer to update
+ * @distance:   negative or zero distance of @seqno from buf_ackno downward
+ * @seqno:	the (old) sequence number whose record is to be updated
+ * @state:	state in which packet carrying @seqno was received
+ */
+static void dccp_ackvec_update_old(struct dccp_ackvec *av, s64 distance,
+				   u64 seqno, enum dccp_ackvec_states state)
+{
+	u16 ptr = av->av_buf_head;
+
+	BUG_ON(distance > 0);
+	if (unlikely(dccp_ackvec_is_empty(av)))
+		return;
+
+	do {
+		u8 runlen = dccp_ackvec_runlen(av->av_buf + ptr);
+
+		if (distance + runlen >= 0) {
+			/*
+			 * Only update the state if packet has not been received
+			 * yet. This is OK as per the second table in RFC 4340,
+			 * 11.4.1; i.e. here we are using the following table:
+			 *                     RECEIVED
+			 *                      0   1   3
+			 *              S     +---+---+---+
+			 *              T   0 | 0 | 0 | 0 |
+			 *              O     +---+---+---+
+			 *              R   1 | 1 | 1 | 1 |
+			 *              E     +---+---+---+
+			 *              D   3 | 0 | 1 | 3 |
+			 *                    +---+---+---+
+			 * The "Not Received" state was set by reserve_seats().
+			 */
+			if (av->av_buf[ptr] == DCCPAV_NOT_RECEIVED)
+				av->av_buf[ptr] = state;
+			else
+				dccp_pr_debug("Not changing %llu state to %u\n",
+					      (unsigned long long)seqno, state);
+			break;
+		}
+
+		distance += runlen + 1;
+		ptr	  = __ackvec_idx_add(ptr, 1);
+
+	} while (ptr != av->av_buf_tail);
+}
+
+/* Mark @num entries after buf_head as "Not yet received". */
+static void dccp_ackvec_reserve_seats(struct dccp_ackvec *av, u16 num)
+{
+	u16 start = __ackvec_idx_add(av->av_buf_head, 1),
+	    len	  = DCCPAV_MAX_ACKVEC_LEN - start;
+
+	/* check for buffer wrap-around */
+	if (num > len) {
+		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, len);
+		start = 0;
+		num  -= len;
+	}
+	if (num)
+		memset(av->av_buf + start, DCCPAV_NOT_RECEIVED, num);
+}
+
+/**
+ * dccp_ackvec_add_new  -  Record one or more new entries in Ack Vector buffer
+ * @av:		 container of buffer to update (can be empty or non-empty)
+ * @num_packets: number of packets to register (must be >= 1)
+ * @seqno:	 sequence number of the first packet in @num_packets
+ * @state:	 state in which packet carrying @seqno was received
+ */
+static void dccp_ackvec_add_new(struct dccp_ackvec *av, u32 num_packets,
+				u64 seqno, enum dccp_ackvec_states state)
+{
+	u32 num_cells = num_packets;
+
+	if (num_packets > DCCPAV_BURST_THRESH) {
+		u32 lost_packets = num_packets - 1;
+
+		DCCP_WARN("Warning: large burst loss (%u)\n", lost_packets);
+		/*
+		 * We received 1 packet and have a loss of size "num_packets-1"
+		 * which we squeeze into num_cells-1 rather than reserving an
+		 * entire byte for each lost packet.
+		 * The reason is that the vector grows in O(burst_length); when
+		 * it grows too large there will no room left for the payload.
+		 * This is a trade-off: if a few packets out of the burst show
+		 * up later, their state will not be changed; it is simply too
+		 * costly to reshuffle/reallocate/copy the buffer each time.
+		 * Should such problems persist, we will need to switch to a
+		 * different underlying data structure.
+		 */
+		for (num_packets = num_cells = 1; lost_packets; ++num_cells) {
+			u8 len = min_t(u32, lost_packets, DCCPAV_MAX_RUNLEN);
+
+			av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, 1);
+			av->av_buf[av->av_buf_head] = DCCPAV_NOT_RECEIVED | len;
+
+			lost_packets -= len;
+		}
+	}
+
+	if (num_cells + dccp_ackvec_buflen(av) >= DCCPAV_MAX_ACKVEC_LEN) {
+		DCCP_CRIT("Ack Vector buffer overflow: dropping old entries");
+		av->av_overflow = true;
+	}
+
+	av->av_buf_head = __ackvec_idx_sub(av->av_buf_head, num_packets);
+	if (av->av_overflow)
+		av->av_buf_tail = av->av_buf_head;
+
+	av->av_buf[av->av_buf_head] = state;
+	av->av_buf_ackno	    = seqno;
+
+	if (num_packets > 1)
+		dccp_ackvec_reserve_seats(av, num_packets - 1);
+}
+
+/**
+ * dccp_ackvec_input  -  Register incoming packet in the buffer
+ */
+void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb)
+{
+	u64 seqno = DCCP_SKB_CB(skb)->dccpd_seq;
+	enum dccp_ackvec_states state = DCCPAV_RECEIVED;
+
+	if (dccp_ackvec_is_empty(av)) {
+		dccp_ackvec_add_new(av, 1, seqno, state);
+		av->av_tail_ackno = seqno;
+
+	} else {
+		s64 num_packets = dccp_delta_seqno(av->av_buf_ackno, seqno);
+		u8 *current_head = av->av_buf + av->av_buf_head;
+
+		if (num_packets == 1 &&
+		    dccp_ackvec_state(current_head) == state &&
+		    dccp_ackvec_runlen(current_head) < DCCPAV_MAX_RUNLEN) {
+
+			*current_head   += 1;
+			av->av_buf_ackno = seqno;
+
+		} else if (num_packets > 0) {
+			dccp_ackvec_add_new(av, num_packets, seqno, state);
+		} else {
+			dccp_ackvec_update_old(av, num_packets, seqno, state);
+		}
+	}
+}
+
+/**
+ * dccp_ackvec_clear_state  -  Perform house-keeping / garbage-collection
+ * This routine is called when the peer acknowledges the receipt of Ack Vectors
+ * up to and including @ackno. While based on section A.3 of RFC 4340, here
+ * are additional precautions to prevent corrupted buffer state. In particular,
+ * we use tail_ackno to identify outdated records; it always marks the earliest
+ * packet of group (2) in 11.4.2.
+ */
+void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno)
+{
+	struct dccp_ackvec_record *avr, *next;
+	u8 runlen_now, eff_runlen;
+	s64 delta;
+
+	avr = dccp_ackvec_lookup(&av->av_records, ackno);
+	if (avr == NULL)
+		return;
+	/*
+	 * Deal with outdated acknowledgments: this arises when e.g. there are
+	 * several old records and the acks from the peer come in slowly. In
+	 * that case we may still have records that pre-date tail_ackno.
+	 */
+	delta = dccp_delta_seqno(av->av_tail_ackno, avr->avr_ack_ackno);
+	if (delta < 0)
+		goto free_records;
+	/*
+	 * Deal with overlapping Ack Vectors: don't subtract more than the
+	 * number of packets between tail_ackno and ack_ackno.
+	 */
+	eff_runlen = delta < avr->avr_ack_runlen ? delta : avr->avr_ack_runlen;
+
+	runlen_now = dccp_ackvec_runlen(av->av_buf + avr->avr_ack_ptr);
+	/*
+	 * The run length of Ack Vector cells does not decrease over time. If
+	 * the run length is the same as at the time the Ack Vector was sent, we
+	 * free the ack_ptr cell. That cell can however not be freed if the run
+	 * length has increased: in this case we need to move the tail pointer
+	 * backwards (towards higher indices), to its next-oldest neighbour.
+	 */
+	if (runlen_now > eff_runlen) {
+
+		av->av_buf[avr->avr_ack_ptr] -= eff_runlen + 1;
+		av->av_buf_tail = __ackvec_idx_add(avr->avr_ack_ptr, 1);
+
+		/* This move may not have cleared the overflow flag. */
+		if (av->av_overflow)
+			av->av_overflow = (av->av_buf_head == av->av_buf_tail);
+	} else {
+		av->av_buf_tail	= avr->avr_ack_ptr;
+		/*
+		 * We have made sure that avr points to a valid cell within the
+		 * buffer. This cell is either older than head, or equals head
+		 * (empty buffer): in both cases we no longer have any overflow.
+		 */
+		av->av_overflow	= 0;
+	}
+
+	/*
+	 * The peer has acknowledged up to and including ack_ackno. Hence the
+	 * first packet in group (2) of 11.4.2 is the successor of ack_ackno.
+	 */
+	av->av_tail_ackno = ADD48(avr->avr_ack_ackno, 1);
+
+free_records:
+	list_for_each_entry_safe_from(avr, next, &av->av_records, avr_node) {
+		list_del(&avr->avr_node);
+		kmem_cache_free(dccp_ackvec_record_slab, avr);
+	}
+}
+
+/*
+ *	Routines to keep track of Ack Vectors received in an skb
+ */
+int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce)
+{
+	struct dccp_ackvec_parsed *new = kmalloc(sizeof(*new), GFP_ATOMIC);
+
+	if (new == NULL)
+		return -ENOBUFS;
+	new->vec   = vec;
+	new->len   = len;
+	new->nonce = nonce;
+
+	list_add_tail(&new->node, head);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_add);
+
+void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks)
+{
+	struct dccp_ackvec_parsed *cur, *next;
+
+	list_for_each_entry_safe(cur, next, parsed_chunks, node)
+		kfree(cur);
+	INIT_LIST_HEAD(parsed_chunks);
+}
+EXPORT_SYMBOL_GPL(dccp_ackvec_parsed_cleanup);
+
+int __init dccp_ackvec_init(void)
+{
+	dccp_ackvec_slab = kmem_cache_create("dccp_ackvec",
+					     sizeof(struct dccp_ackvec), 0,
+					     SLAB_HWCACHE_ALIGN, NULL);
+	if (dccp_ackvec_slab == NULL)
+		goto out_err;
+
+	dccp_ackvec_record_slab = kmem_cache_create("dccp_ackvec_record",
+					     sizeof(struct dccp_ackvec_record),
+					     0, SLAB_HWCACHE_ALIGN, NULL);
+	if (dccp_ackvec_record_slab == NULL)
+		goto out_destroy_slab;
+
+	return 0;
+
+out_destroy_slab:
+	kmem_cache_destroy(dccp_ackvec_slab);
+	dccp_ackvec_slab = NULL;
+out_err:
+	DCCP_CRIT("Unable to create Ack Vector slab cache");
+	return -ENOBUFS;
+}
+
+void dccp_ackvec_exit(void)
+{
+	kmem_cache_destroy(dccp_ackvec_slab);
+	dccp_ackvec_slab = NULL;
+	kmem_cache_destroy(dccp_ackvec_record_slab);
+	dccp_ackvec_record_slab = NULL;
+}
diff --git a/net/dccp/ackvec.h b/net/dccp/ackvec.h
new file mode 100644
index 000000000..d2c4220fb
--- /dev/null
+++ b/net/dccp/ackvec.h
@@ -0,0 +1,136 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _ACKVEC_H
+#define _ACKVEC_H
+/*
+ *  net/dccp/ackvec.h
+ *
+ *  An implementation of Ack Vectors for the DCCP protocol
+ *  Copyright (c) 2007 University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@mandriva.com>
+ */
+
+#include <linux/dccp.h>
+#include <linux/compiler.h>
+#include <linux/list.h>
+#include <linux/types.h>
+
+/*
+ * Ack Vector buffer space is static, in multiples of %DCCP_SINGLE_OPT_MAXLEN,
+ * the maximum size of a single Ack Vector. Setting %DCCPAV_NUM_ACKVECS to 1
+ * will be sufficient for most cases of low Ack Ratios, using a value of 2 gives
+ * more headroom if Ack Ratio is higher or when the sender acknowledges slowly.
+ * The maximum value is bounded by the u16 types for indices and functions.
+ */
+#define DCCPAV_NUM_ACKVECS	2
+#define DCCPAV_MAX_ACKVEC_LEN	(DCCP_SINGLE_OPT_MAXLEN * DCCPAV_NUM_ACKVECS)
+
+/* Estimated minimum average Ack Vector length - used for updating MPS */
+#define DCCPAV_MIN_OPTLEN	16
+
+/* Threshold for coping with large bursts of losses */
+#define DCCPAV_BURST_THRESH	(DCCPAV_MAX_ACKVEC_LEN / 8)
+
+enum dccp_ackvec_states {
+	DCCPAV_RECEIVED =	0x00,
+	DCCPAV_ECN_MARKED =	0x40,
+	DCCPAV_RESERVED =	0x80,
+	DCCPAV_NOT_RECEIVED =	0xC0
+};
+#define DCCPAV_MAX_RUNLEN	0x3F
+
+static inline u8 dccp_ackvec_runlen(const u8 *cell)
+{
+	return *cell & DCCPAV_MAX_RUNLEN;
+}
+
+static inline u8 dccp_ackvec_state(const u8 *cell)
+{
+	return *cell & ~DCCPAV_MAX_RUNLEN;
+}
+
+/**
+ * struct dccp_ackvec - Ack Vector main data structure
+ *
+ * This implements a fixed-size circular buffer within an array and is largely
+ * based on Appendix A of RFC 4340.
+ *
+ * @av_buf:	   circular buffer storage area
+ * @av_buf_head:   head index; begin of live portion in @av_buf
+ * @av_buf_tail:   tail index; first index _after_ the live portion in @av_buf
+ * @av_buf_ackno:  highest seqno of acknowledgeable packet recorded in @av_buf
+ * @av_tail_ackno: lowest  seqno of acknowledgeable packet recorded in @av_buf
+ * @av_buf_nonce:  ECN nonce sums, each covering subsequent segments of up to
+ *		   %DCCP_SINGLE_OPT_MAXLEN cells in the live portion of @av_buf
+ * @av_overflow:   if 1 then buf_head == buf_tail indicates buffer wraparound
+ * @av_records:	   list of %dccp_ackvec_record (Ack Vectors sent previously)
+ */
+struct dccp_ackvec {
+	u8			av_buf[DCCPAV_MAX_ACKVEC_LEN];
+	u16			av_buf_head;
+	u16			av_buf_tail;
+	u64			av_buf_ackno:48;
+	u64			av_tail_ackno:48;
+	bool			av_buf_nonce[DCCPAV_NUM_ACKVECS];
+	u8			av_overflow:1;
+	struct list_head	av_records;
+};
+
+/**
+ * struct dccp_ackvec_record - Records information about sent Ack Vectors
+ *
+ * These list entries define the additional information which the HC-Receiver
+ * keeps about recently-sent Ack Vectors; again refer to RFC 4340, Appendix A.
+ *
+ * @avr_node:	    the list node in @av_records
+ * @avr_ack_seqno:  sequence number of the packet the Ack Vector was sent on
+ * @avr_ack_ackno:  the Ack number that this record/Ack Vector refers to
+ * @avr_ack_ptr:    pointer into @av_buf where this record starts
+ * @avr_ack_runlen: run length of @avr_ack_ptr at the time of sending
+ * @avr_ack_nonce:  the sum of @av_buf_nonce's at the time this record was sent
+ *
+ * The list as a whole is sorted in descending order by @avr_ack_seqno.
+ */
+struct dccp_ackvec_record {
+	struct list_head avr_node;
+	u64		 avr_ack_seqno:48;
+	u64		 avr_ack_ackno:48;
+	u16		 avr_ack_ptr;
+	u8		 avr_ack_runlen;
+	u8		 avr_ack_nonce:1;
+};
+
+int dccp_ackvec_init(void);
+void dccp_ackvec_exit(void);
+
+struct dccp_ackvec *dccp_ackvec_alloc(const gfp_t priority);
+void dccp_ackvec_free(struct dccp_ackvec *av);
+
+void dccp_ackvec_input(struct dccp_ackvec *av, struct sk_buff *skb);
+int dccp_ackvec_update_records(struct dccp_ackvec *av, u64 seq, u8 sum);
+void dccp_ackvec_clear_state(struct dccp_ackvec *av, const u64 ackno);
+u16 dccp_ackvec_buflen(const struct dccp_ackvec *av);
+
+static inline bool dccp_ackvec_is_empty(const struct dccp_ackvec *av)
+{
+	return av->av_overflow == 0 && av->av_buf_head == av->av_buf_tail;
+}
+
+/**
+ * struct dccp_ackvec_parsed  -  Record offsets of Ack Vectors in skb
+ * @vec:	start of vector (offset into skb)
+ * @len:	length of @vec
+ * @nonce:	whether @vec had an ECN nonce of 0 or 1
+ * @node:	FIFO - arranged in descending order of ack_ackno
+ *
+ * This structure is used by CCIDs to access Ack Vectors in a received skb.
+ */
+struct dccp_ackvec_parsed {
+	u8		 *vec,
+			 len,
+			 nonce:1;
+	struct list_head node;
+};
+
+int dccp_ackvec_parsed_add(struct list_head *head, u8 *vec, u8 len, u8 nonce);
+void dccp_ackvec_parsed_cleanup(struct list_head *parsed_chunks);
+#endif /* _ACKVEC_H */
diff --git a/net/dccp/ccid.c b/net/dccp/ccid.c
new file mode 100644
index 000000000..1e9bb121b
--- /dev/null
+++ b/net/dccp/ccid.c
@@ -0,0 +1,219 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/ccid.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ *  CCID infrastructure
+ */
+
+#include <linux/slab.h>
+
+#include "ccid.h"
+#include "ccids/lib/tfrc.h"
+
+static struct ccid_operations *ccids[] = {
+	&ccid2_ops,
+#ifdef CONFIG_IP_DCCP_CCID3
+	&ccid3_ops,
+#endif
+};
+
+static struct ccid_operations *ccid_by_number(const u8 id)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ccids); i++)
+		if (ccids[i]->ccid_id == id)
+			return ccids[i];
+	return NULL;
+}
+
+/* check that up to @array_len members in @ccid_array are supported */
+bool ccid_support_check(u8 const *ccid_array, u8 array_len)
+{
+	while (array_len > 0)
+		if (ccid_by_number(ccid_array[--array_len]) == NULL)
+			return false;
+	return true;
+}
+
+/**
+ * ccid_get_builtin_ccids  -  Populate a list of built-in CCIDs
+ * @ccid_array: pointer to copy into
+ * @array_len: value to return length into
+ *
+ * This function allocates memory - caller must see that it is freed after use.
+ */
+int ccid_get_builtin_ccids(u8 **ccid_array, u8 *array_len)
+{
+	*ccid_array = kmalloc(ARRAY_SIZE(ccids), gfp_any());
+	if (*ccid_array == NULL)
+		return -ENOBUFS;
+
+	for (*array_len = 0; *array_len < ARRAY_SIZE(ccids); *array_len += 1)
+		(*ccid_array)[*array_len] = ccids[*array_len]->ccid_id;
+	return 0;
+}
+
+int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
+				  char __user *optval, int __user *optlen)
+{
+	u8 *ccid_array, array_len;
+	int err = 0;
+
+	if (ccid_get_builtin_ccids(&ccid_array, &array_len))
+		return -ENOBUFS;
+
+	if (put_user(array_len, optlen))
+		err = -EFAULT;
+	else if (len > 0 && copy_to_user(optval, ccid_array,
+					 len > array_len ? array_len : len))
+		err = -EFAULT;
+
+	kfree(ccid_array);
+	return err;
+}
+
+static struct kmem_cache *ccid_kmem_cache_create(int obj_size, char *slab_name_fmt, const char *fmt,...)
+{
+	struct kmem_cache *slab;
+	va_list args;
+
+	va_start(args, fmt);
+	vsnprintf(slab_name_fmt, CCID_SLAB_NAME_LENGTH, fmt, args);
+	va_end(args);
+
+	slab = kmem_cache_create(slab_name_fmt, sizeof(struct ccid) + obj_size, 0,
+				 SLAB_HWCACHE_ALIGN, NULL);
+	return slab;
+}
+
+static void ccid_kmem_cache_destroy(struct kmem_cache *slab)
+{
+	kmem_cache_destroy(slab);
+}
+
+static int __init ccid_activate(struct ccid_operations *ccid_ops)
+{
+	int err = -ENOBUFS;
+
+	ccid_ops->ccid_hc_rx_slab =
+			ccid_kmem_cache_create(ccid_ops->ccid_hc_rx_obj_size,
+					       ccid_ops->ccid_hc_rx_slab_name,
+					       "ccid%u_hc_rx_sock",
+					       ccid_ops->ccid_id);
+	if (ccid_ops->ccid_hc_rx_slab == NULL)
+		goto out;
+
+	ccid_ops->ccid_hc_tx_slab =
+			ccid_kmem_cache_create(ccid_ops->ccid_hc_tx_obj_size,
+					       ccid_ops->ccid_hc_tx_slab_name,
+					       "ccid%u_hc_tx_sock",
+					       ccid_ops->ccid_id);
+	if (ccid_ops->ccid_hc_tx_slab == NULL)
+		goto out_free_rx_slab;
+
+	pr_info("DCCP: Activated CCID %d (%s)\n",
+		ccid_ops->ccid_id, ccid_ops->ccid_name);
+	err = 0;
+out:
+	return err;
+out_free_rx_slab:
+	ccid_kmem_cache_destroy(ccid_ops->ccid_hc_rx_slab);
+	ccid_ops->ccid_hc_rx_slab = NULL;
+	goto out;
+}
+
+static void ccid_deactivate(struct ccid_operations *ccid_ops)
+{
+	ccid_kmem_cache_destroy(ccid_ops->ccid_hc_tx_slab);
+	ccid_ops->ccid_hc_tx_slab = NULL;
+	ccid_kmem_cache_destroy(ccid_ops->ccid_hc_rx_slab);
+	ccid_ops->ccid_hc_rx_slab = NULL;
+
+	pr_info("DCCP: Deactivated CCID %d (%s)\n",
+		ccid_ops->ccid_id, ccid_ops->ccid_name);
+}
+
+struct ccid *ccid_new(const u8 id, struct sock *sk, bool rx)
+{
+	struct ccid_operations *ccid_ops = ccid_by_number(id);
+	struct ccid *ccid = NULL;
+
+	if (ccid_ops == NULL)
+		goto out;
+
+	ccid = kmem_cache_alloc(rx ? ccid_ops->ccid_hc_rx_slab :
+				     ccid_ops->ccid_hc_tx_slab, gfp_any());
+	if (ccid == NULL)
+		goto out;
+	ccid->ccid_ops = ccid_ops;
+	if (rx) {
+		memset(ccid + 1, 0, ccid_ops->ccid_hc_rx_obj_size);
+		if (ccid->ccid_ops->ccid_hc_rx_init != NULL &&
+		    ccid->ccid_ops->ccid_hc_rx_init(ccid, sk) != 0)
+			goto out_free_ccid;
+	} else {
+		memset(ccid + 1, 0, ccid_ops->ccid_hc_tx_obj_size);
+		if (ccid->ccid_ops->ccid_hc_tx_init != NULL &&
+		    ccid->ccid_ops->ccid_hc_tx_init(ccid, sk) != 0)
+			goto out_free_ccid;
+	}
+out:
+	return ccid;
+out_free_ccid:
+	kmem_cache_free(rx ? ccid_ops->ccid_hc_rx_slab :
+			ccid_ops->ccid_hc_tx_slab, ccid);
+	ccid = NULL;
+	goto out;
+}
+
+void ccid_hc_rx_delete(struct ccid *ccid, struct sock *sk)
+{
+	if (ccid != NULL) {
+		if (ccid->ccid_ops->ccid_hc_rx_exit != NULL)
+			ccid->ccid_ops->ccid_hc_rx_exit(sk);
+		kmem_cache_free(ccid->ccid_ops->ccid_hc_rx_slab, ccid);
+	}
+}
+
+void ccid_hc_tx_delete(struct ccid *ccid, struct sock *sk)
+{
+	if (ccid != NULL) {
+		if (ccid->ccid_ops->ccid_hc_tx_exit != NULL)
+			ccid->ccid_ops->ccid_hc_tx_exit(sk);
+		kmem_cache_free(ccid->ccid_ops->ccid_hc_tx_slab, ccid);
+	}
+}
+
+int __init ccid_initialize_builtins(void)
+{
+	int i, err = tfrc_lib_init();
+
+	if (err)
+		return err;
+
+	for (i = 0; i < ARRAY_SIZE(ccids); i++) {
+		err = ccid_activate(ccids[i]);
+		if (err)
+			goto unwind_registrations;
+	}
+	return 0;
+
+unwind_registrations:
+	while(--i >= 0)
+		ccid_deactivate(ccids[i]);
+	tfrc_lib_exit();
+	return err;
+}
+
+void ccid_cleanup_builtins(void)
+{
+	int i;
+
+	for (i = 0; i < ARRAY_SIZE(ccids); i++)
+		ccid_deactivate(ccids[i]);
+	tfrc_lib_exit();
+}
diff --git a/net/dccp/ccid.h b/net/dccp/ccid.h
new file mode 100644
index 000000000..105f3734d
--- /dev/null
+++ b/net/dccp/ccid.h
@@ -0,0 +1,262 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _CCID_H
+#define _CCID_H
+/*
+ *  net/dccp/ccid.h
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *
+ *  CCID infrastructure
+ */
+
+#include <net/sock.h>
+#include <linux/compiler.h>
+#include <linux/dccp.h>
+#include <linux/list.h>
+#include <linux/module.h>
+
+/* maximum value for a CCID (RFC 4340, 19.5) */
+#define CCID_MAX		255
+#define CCID_SLAB_NAME_LENGTH	32
+
+struct tcp_info;
+
+/**
+ *  struct ccid_operations  -  Interface to Congestion-Control Infrastructure
+ *
+ *  @ccid_id: numerical CCID ID (up to %CCID_MAX, cf. table 5 in RFC 4340, 10.)
+ *  @ccid_ccmps: the CCMPS including network/transport headers (0 when disabled)
+ *  @ccid_name: alphabetical identifier string for @ccid_id
+ *  @ccid_hc_{r,t}x_slab: memory pool for the receiver/sender half-connection
+ *  @ccid_hc_{r,t}x_obj_size: size of the receiver/sender half-connection socket
+ *
+ *  @ccid_hc_{r,t}x_init: CCID-specific initialisation routine (before startup)
+ *  @ccid_hc_{r,t}x_exit: CCID-specific cleanup routine (before destruction)
+ *  @ccid_hc_rx_packet_recv: implements the HC-receiver side
+ *  @ccid_hc_{r,t}x_parse_options: parsing routine for CCID/HC-specific options
+ *  @ccid_hc_{r,t}x_insert_options: insert routine for CCID/HC-specific options
+ *  @ccid_hc_tx_packet_recv: implements feedback processing for the HC-sender
+ *  @ccid_hc_tx_send_packet: implements the sending part of the HC-sender
+ *  @ccid_hc_tx_packet_sent: does accounting for packets in flight by HC-sender
+ *  @ccid_hc_{r,t}x_get_info: INET_DIAG information for HC-receiver/sender
+ *  @ccid_hc_{r,t}x_getsockopt: socket options specific to HC-receiver/sender
+ */
+struct ccid_operations {
+	unsigned char		ccid_id;
+	__u32			ccid_ccmps;
+	const char		*ccid_name;
+	struct kmem_cache	*ccid_hc_rx_slab,
+				*ccid_hc_tx_slab;
+	char			ccid_hc_rx_slab_name[CCID_SLAB_NAME_LENGTH];
+	char			ccid_hc_tx_slab_name[CCID_SLAB_NAME_LENGTH];
+	__u32			ccid_hc_rx_obj_size,
+				ccid_hc_tx_obj_size;
+	/* Interface Routines */
+	int		(*ccid_hc_rx_init)(struct ccid *ccid, struct sock *sk);
+	int		(*ccid_hc_tx_init)(struct ccid *ccid, struct sock *sk);
+	void		(*ccid_hc_rx_exit)(struct sock *sk);
+	void		(*ccid_hc_tx_exit)(struct sock *sk);
+	void		(*ccid_hc_rx_packet_recv)(struct sock *sk,
+						  struct sk_buff *skb);
+	int		(*ccid_hc_rx_parse_options)(struct sock *sk, u8 pkt,
+						    u8 opt, u8 *val, u8 len);
+	int		(*ccid_hc_rx_insert_options)(struct sock *sk,
+						     struct sk_buff *skb);
+	void		(*ccid_hc_tx_packet_recv)(struct sock *sk,
+						  struct sk_buff *skb);
+	int		(*ccid_hc_tx_parse_options)(struct sock *sk, u8 pkt,
+						    u8 opt, u8 *val, u8 len);
+	int		(*ccid_hc_tx_send_packet)(struct sock *sk,
+						  struct sk_buff *skb);
+	void		(*ccid_hc_tx_packet_sent)(struct sock *sk,
+						  unsigned int len);
+	void		(*ccid_hc_rx_get_info)(struct sock *sk,
+					       struct tcp_info *info);
+	void		(*ccid_hc_tx_get_info)(struct sock *sk,
+					       struct tcp_info *info);
+	int		(*ccid_hc_rx_getsockopt)(struct sock *sk,
+						 const int optname, int len,
+						 u32 __user *optval,
+						 int __user *optlen);
+	int		(*ccid_hc_tx_getsockopt)(struct sock *sk,
+						 const int optname, int len,
+						 u32 __user *optval,
+						 int __user *optlen);
+};
+
+extern struct ccid_operations ccid2_ops;
+#ifdef CONFIG_IP_DCCP_CCID3
+extern struct ccid_operations ccid3_ops;
+#endif
+
+int ccid_initialize_builtins(void);
+void ccid_cleanup_builtins(void);
+
+struct ccid {
+	struct ccid_operations *ccid_ops;
+	char		       ccid_priv[];
+};
+
+static inline void *ccid_priv(const struct ccid *ccid)
+{
+	return (void *)ccid->ccid_priv;
+}
+
+bool ccid_support_check(u8 const *ccid_array, u8 array_len);
+int ccid_get_builtin_ccids(u8 **ccid_array, u8 *array_len);
+int ccid_getsockopt_builtin_ccids(struct sock *sk, int len,
+				  char __user *, int __user *);
+
+struct ccid *ccid_new(const u8 id, struct sock *sk, bool rx);
+
+static inline int ccid_get_current_rx_ccid(struct dccp_sock *dp)
+{
+	struct ccid *ccid = dp->dccps_hc_rx_ccid;
+
+	if (ccid == NULL || ccid->ccid_ops == NULL)
+		return -1;
+	return ccid->ccid_ops->ccid_id;
+}
+
+static inline int ccid_get_current_tx_ccid(struct dccp_sock *dp)
+{
+	struct ccid *ccid = dp->dccps_hc_tx_ccid;
+
+	if (ccid == NULL || ccid->ccid_ops == NULL)
+		return -1;
+	return ccid->ccid_ops->ccid_id;
+}
+
+void ccid_hc_rx_delete(struct ccid *ccid, struct sock *sk);
+void ccid_hc_tx_delete(struct ccid *ccid, struct sock *sk);
+
+/*
+ * Congestion control of queued data packets via CCID decision.
+ *
+ * The TX CCID performs its congestion-control by indicating whether and when a
+ * queued packet may be sent, using the return code of ccid_hc_tx_send_packet().
+ * The following modes are supported via the symbolic constants below:
+ * - timer-based pacing    (CCID returns a delay value in milliseconds);
+ * - autonomous dequeueing (CCID internally schedules dccps_xmitlet).
+ */
+
+enum ccid_dequeueing_decision {
+	CCID_PACKET_SEND_AT_ONCE =	 0x00000,  /* "green light": no delay */
+	CCID_PACKET_DELAY_MAX =		 0x0FFFF,  /* maximum delay in msecs  */
+	CCID_PACKET_DELAY =		 0x10000,  /* CCID msec-delay mode */
+	CCID_PACKET_WILL_DEQUEUE_LATER = 0x20000,  /* CCID autonomous mode */
+	CCID_PACKET_ERR =		 0xF0000,  /* error condition */
+};
+
+static inline int ccid_packet_dequeue_eval(const int return_code)
+{
+	if (return_code < 0)
+		return CCID_PACKET_ERR;
+	if (return_code == 0)
+		return CCID_PACKET_SEND_AT_ONCE;
+	if (return_code <= CCID_PACKET_DELAY_MAX)
+		return CCID_PACKET_DELAY;
+	return return_code;
+}
+
+static inline int ccid_hc_tx_send_packet(struct ccid *ccid, struct sock *sk,
+					 struct sk_buff *skb)
+{
+	if (ccid->ccid_ops->ccid_hc_tx_send_packet != NULL)
+		return ccid->ccid_ops->ccid_hc_tx_send_packet(sk, skb);
+	return CCID_PACKET_SEND_AT_ONCE;
+}
+
+static inline void ccid_hc_tx_packet_sent(struct ccid *ccid, struct sock *sk,
+					  unsigned int len)
+{
+	if (ccid->ccid_ops->ccid_hc_tx_packet_sent != NULL)
+		ccid->ccid_ops->ccid_hc_tx_packet_sent(sk, len);
+}
+
+static inline void ccid_hc_rx_packet_recv(struct ccid *ccid, struct sock *sk,
+					  struct sk_buff *skb)
+{
+	if (ccid->ccid_ops->ccid_hc_rx_packet_recv != NULL)
+		ccid->ccid_ops->ccid_hc_rx_packet_recv(sk, skb);
+}
+
+static inline void ccid_hc_tx_packet_recv(struct ccid *ccid, struct sock *sk,
+					  struct sk_buff *skb)
+{
+	if (ccid->ccid_ops->ccid_hc_tx_packet_recv != NULL)
+		ccid->ccid_ops->ccid_hc_tx_packet_recv(sk, skb);
+}
+
+/**
+ * ccid_hc_tx_parse_options  -  Parse CCID-specific options sent by the receiver
+ * @pkt: type of packet that @opt appears on (RFC 4340, 5.1)
+ * @opt: the CCID-specific option type (RFC 4340, 5.8 and 10.3)
+ * @val: value of @opt
+ * @len: length of @val in bytes
+ */
+static inline int ccid_hc_tx_parse_options(struct ccid *ccid, struct sock *sk,
+					   u8 pkt, u8 opt, u8 *val, u8 len)
+{
+	if (!ccid || !ccid->ccid_ops->ccid_hc_tx_parse_options)
+		return 0;
+	return ccid->ccid_ops->ccid_hc_tx_parse_options(sk, pkt, opt, val, len);
+}
+
+/**
+ * ccid_hc_rx_parse_options  -  Parse CCID-specific options sent by the sender
+ * Arguments are analogous to ccid_hc_tx_parse_options()
+ */
+static inline int ccid_hc_rx_parse_options(struct ccid *ccid, struct sock *sk,
+					   u8 pkt, u8 opt, u8 *val, u8 len)
+{
+	if (!ccid || !ccid->ccid_ops->ccid_hc_rx_parse_options)
+		return 0;
+	return ccid->ccid_ops->ccid_hc_rx_parse_options(sk, pkt, opt, val, len);
+}
+
+static inline int ccid_hc_rx_insert_options(struct ccid *ccid, struct sock *sk,
+					    struct sk_buff *skb)
+{
+	if (ccid->ccid_ops->ccid_hc_rx_insert_options != NULL)
+		return ccid->ccid_ops->ccid_hc_rx_insert_options(sk, skb);
+	return 0;
+}
+
+static inline void ccid_hc_rx_get_info(struct ccid *ccid, struct sock *sk,
+				       struct tcp_info *info)
+{
+	if (ccid->ccid_ops->ccid_hc_rx_get_info != NULL)
+		ccid->ccid_ops->ccid_hc_rx_get_info(sk, info);
+}
+
+static inline void ccid_hc_tx_get_info(struct ccid *ccid, struct sock *sk,
+				       struct tcp_info *info)
+{
+	if (ccid->ccid_ops->ccid_hc_tx_get_info != NULL)
+		ccid->ccid_ops->ccid_hc_tx_get_info(sk, info);
+}
+
+static inline int ccid_hc_rx_getsockopt(struct ccid *ccid, struct sock *sk,
+					const int optname, int len,
+					u32 __user *optval, int __user *optlen)
+{
+	int rc = -ENOPROTOOPT;
+	if (ccid != NULL && ccid->ccid_ops->ccid_hc_rx_getsockopt != NULL)
+		rc = ccid->ccid_ops->ccid_hc_rx_getsockopt(sk, optname, len,
+						 optval, optlen);
+	return rc;
+}
+
+static inline int ccid_hc_tx_getsockopt(struct ccid *ccid, struct sock *sk,
+					const int optname, int len,
+					u32 __user *optval, int __user *optlen)
+{
+	int rc = -ENOPROTOOPT;
+	if (ccid != NULL && ccid->ccid_ops->ccid_hc_tx_getsockopt != NULL)
+		rc = ccid->ccid_ops->ccid_hc_tx_getsockopt(sk, optname, len,
+						 optval, optlen);
+	return rc;
+}
+#endif /* _CCID_H */
diff --git a/net/dccp/ccids/Kconfig b/net/dccp/ccids/Kconfig
new file mode 100644
index 000000000..a3eeb84d1
--- /dev/null
+++ b/net/dccp/ccids/Kconfig
@@ -0,0 +1,55 @@
+# SPDX-License-Identifier: GPL-2.0-only
+menu "DCCP CCIDs Configuration"
+
+config IP_DCCP_CCID2_DEBUG
+	bool "CCID-2 debugging messages"
+	help
+	  Enable CCID-2 specific debugging messages.
+
+	  The debugging output can additionally be toggled by setting the
+	  ccid2_debug parameter to 0 or 1.
+
+	  If in doubt, say N.
+
+config IP_DCCP_CCID3
+	bool "CCID-3 (TCP-Friendly)"
+	def_bool y if (IP_DCCP = y || IP_DCCP = m)
+	help
+	  CCID-3 denotes TCP-Friendly Rate Control (TFRC), an equation-based
+	  rate-controlled congestion control mechanism.  TFRC is designed to
+	  be reasonably fair when competing for bandwidth with TCP-like flows,
+	  where a flow is "reasonably fair" if its sending rate is generally
+	  within a factor of two of the sending rate of a TCP flow under the
+	  same conditions.  However, TFRC has a much lower variation of
+	  throughput over time compared with TCP, which makes CCID-3 more
+	  suitable than CCID-2 for applications such streaming media where a
+	  relatively smooth sending rate is of importance.
+
+	  CCID-3 is further described in RFC 4342,
+	  https://www.ietf.org/rfc/rfc4342.txt
+
+	  The TFRC congestion control algorithms were initially described in
+	  RFC 5348.
+
+	  This text was extracted from RFC 4340 (sec. 10.2),
+	  https://www.ietf.org/rfc/rfc4340.txt
+
+	  If in doubt, say N.
+
+config IP_DCCP_CCID3_DEBUG
+	bool "CCID-3 debugging messages"
+	depends on IP_DCCP_CCID3
+	help
+	  Enable CCID-3 specific debugging messages.
+
+	  The debugging output can additionally be toggled by setting the
+	  ccid3_debug parameter to 0 or 1.
+
+	  If in doubt, say N.
+
+config IP_DCCP_TFRC_LIB
+	def_bool y if IP_DCCP_CCID3
+
+config IP_DCCP_TFRC_DEBUG
+	def_bool y if IP_DCCP_CCID3_DEBUG
+endmenu
diff --git a/net/dccp/ccids/ccid2.c b/net/dccp/ccids/ccid2.c
new file mode 100644
index 000000000..3da1f77bd
--- /dev/null
+++ b/net/dccp/ccids/ccid2.c
@@ -0,0 +1,788 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2005, 2006 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
+ *
+ *  Changes to meet Linux coding standards, and DCCP infrastructure fixes.
+ *
+ *  Copyright (c) 2006 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+/*
+ * This implementation should follow RFC 4341
+ */
+#include <linux/slab.h>
+#include "../feat.h"
+#include "ccid2.h"
+
+
+#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
+static bool ccid2_debug;
+#define ccid2_pr_debug(format, a...)	DCCP_PR_DEBUG(ccid2_debug, format, ##a)
+#else
+#define ccid2_pr_debug(format, a...)
+#endif
+
+static int ccid2_hc_tx_alloc_seq(struct ccid2_hc_tx_sock *hc)
+{
+	struct ccid2_seq *seqp;
+	int i;
+
+	/* check if we have space to preserve the pointer to the buffer */
+	if (hc->tx_seqbufc >= (sizeof(hc->tx_seqbuf) /
+			       sizeof(struct ccid2_seq *)))
+		return -ENOMEM;
+
+	/* allocate buffer and initialize linked list */
+	seqp = kmalloc_array(CCID2_SEQBUF_LEN, sizeof(struct ccid2_seq),
+			     gfp_any());
+	if (seqp == NULL)
+		return -ENOMEM;
+
+	for (i = 0; i < (CCID2_SEQBUF_LEN - 1); i++) {
+		seqp[i].ccid2s_next = &seqp[i + 1];
+		seqp[i + 1].ccid2s_prev = &seqp[i];
+	}
+	seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = seqp;
+	seqp->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
+
+	/* This is the first allocation.  Initiate the head and tail.  */
+	if (hc->tx_seqbufc == 0)
+		hc->tx_seqh = hc->tx_seqt = seqp;
+	else {
+		/* link the existing list with the one we just created */
+		hc->tx_seqh->ccid2s_next = seqp;
+		seqp->ccid2s_prev = hc->tx_seqh;
+
+		hc->tx_seqt->ccid2s_prev = &seqp[CCID2_SEQBUF_LEN - 1];
+		seqp[CCID2_SEQBUF_LEN - 1].ccid2s_next = hc->tx_seqt;
+	}
+
+	/* store the original pointer to the buffer so we can free it */
+	hc->tx_seqbuf[hc->tx_seqbufc] = seqp;
+	hc->tx_seqbufc++;
+
+	return 0;
+}
+
+static int ccid2_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
+{
+	if (ccid2_cwnd_network_limited(ccid2_hc_tx_sk(sk)))
+		return CCID_PACKET_WILL_DEQUEUE_LATER;
+	return CCID_PACKET_SEND_AT_ONCE;
+}
+
+static void ccid2_change_l_ack_ratio(struct sock *sk, u32 val)
+{
+	u32 max_ratio = DIV_ROUND_UP(ccid2_hc_tx_sk(sk)->tx_cwnd, 2);
+
+	/*
+	 * Ensure that Ack Ratio does not exceed ceil(cwnd/2), which is (2) from
+	 * RFC 4341, 6.1.2. We ignore the statement that Ack Ratio 2 is always
+	 * acceptable since this causes starvation/deadlock whenever cwnd < 2.
+	 * The same problem arises when Ack Ratio is 0 (ie. Ack Ratio disabled).
+	 */
+	if (val == 0 || val > max_ratio) {
+		DCCP_WARN("Limiting Ack Ratio (%u) to %u\n", val, max_ratio);
+		val = max_ratio;
+	}
+	dccp_feat_signal_nn_change(sk, DCCPF_ACK_RATIO,
+				   min_t(u32, val, DCCPF_ACK_RATIO_MAX));
+}
+
+static void ccid2_check_l_ack_ratio(struct sock *sk)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+
+	/*
+	 * After a loss, idle period, application limited period, or RTO we
+	 * need to check that the ack ratio is still less than the congestion
+	 * window. Otherwise, we will send an entire congestion window of
+	 * packets and got no response because we haven't sent ack ratio
+	 * packets yet.
+	 * If the ack ratio does need to be reduced, we reduce it to half of
+	 * the congestion window (or 1 if that's zero) instead of to the
+	 * congestion window. This prevents problems if one ack is lost.
+	 */
+	if (dccp_feat_nn_get(sk, DCCPF_ACK_RATIO) > hc->tx_cwnd)
+		ccid2_change_l_ack_ratio(sk, hc->tx_cwnd/2 ? : 1U);
+}
+
+static void ccid2_change_l_seq_window(struct sock *sk, u64 val)
+{
+	dccp_feat_signal_nn_change(sk, DCCPF_SEQUENCE_WINDOW,
+				   clamp_val(val, DCCPF_SEQ_WMIN,
+						  DCCPF_SEQ_WMAX));
+}
+
+static void dccp_tasklet_schedule(struct sock *sk)
+{
+	struct tasklet_struct *t = &dccp_sk(sk)->dccps_xmitlet;
+
+	if (!test_and_set_bit(TASKLET_STATE_SCHED, &t->state)) {
+		sock_hold(sk);
+		__tasklet_schedule(t);
+	}
+}
+
+static void ccid2_hc_tx_rto_expire(struct timer_list *t)
+{
+	struct ccid2_hc_tx_sock *hc = from_timer(hc, t, tx_rtotimer);
+	struct sock *sk = hc->sk;
+	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + HZ / 5);
+		goto out;
+	}
+
+	ccid2_pr_debug("RTO_EXPIRE\n");
+
+	if (sk->sk_state == DCCP_CLOSED)
+		goto out;
+
+	/* back-off timer */
+	hc->tx_rto <<= 1;
+	if (hc->tx_rto > DCCP_RTO_MAX)
+		hc->tx_rto = DCCP_RTO_MAX;
+
+	/* adjust pipe, cwnd etc */
+	hc->tx_ssthresh = hc->tx_cwnd / 2;
+	if (hc->tx_ssthresh < 2)
+		hc->tx_ssthresh = 2;
+	hc->tx_cwnd	= 1;
+	hc->tx_pipe	= 0;
+
+	/* clear state about stuff we sent */
+	hc->tx_seqt = hc->tx_seqh;
+	hc->tx_packets_acked = 0;
+
+	/* clear ack ratio state. */
+	hc->tx_rpseq    = 0;
+	hc->tx_rpdupack = -1;
+	ccid2_change_l_ack_ratio(sk, 1);
+
+	/* if we were blocked before, we may now send cwnd=1 packet */
+	if (sender_was_blocked)
+		dccp_tasklet_schedule(sk);
+	/* restart backed-off timer */
+	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+/*
+ *	Congestion window validation (RFC 2861).
+ */
+static bool ccid2_do_cwv = true;
+module_param(ccid2_do_cwv, bool, 0644);
+MODULE_PARM_DESC(ccid2_do_cwv, "Perform RFC2861 Congestion Window Validation");
+
+/**
+ * ccid2_update_used_window  -  Track how much of cwnd is actually used
+ * This is done in addition to CWV. The sender needs to have an idea of how many
+ * packets may be in flight, to set the local Sequence Window value accordingly
+ * (RFC 4340, 7.5.2). The CWV mechanism is exploited to keep track of the
+ * maximum-used window. We use an EWMA low-pass filter to filter out noise.
+ */
+static void ccid2_update_used_window(struct ccid2_hc_tx_sock *hc, u32 new_wnd)
+{
+	hc->tx_expected_wnd = (3 * hc->tx_expected_wnd + new_wnd) / 4;
+}
+
+/* This borrows the code of tcp_cwnd_application_limited() */
+static void ccid2_cwnd_application_limited(struct sock *sk, const u32 now)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	/* don't reduce cwnd below the initial window (IW) */
+	u32 init_win = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache),
+	    win_used = max(hc->tx_cwnd_used, init_win);
+
+	if (win_used < hc->tx_cwnd) {
+		hc->tx_ssthresh = max(hc->tx_ssthresh,
+				     (hc->tx_cwnd >> 1) + (hc->tx_cwnd >> 2));
+		hc->tx_cwnd = (hc->tx_cwnd + win_used) >> 1;
+	}
+	hc->tx_cwnd_used  = 0;
+	hc->tx_cwnd_stamp = now;
+
+	ccid2_check_l_ack_ratio(sk);
+}
+
+/* This borrows the code of tcp_cwnd_restart() */
+static void ccid2_cwnd_restart(struct sock *sk, const u32 now)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	u32 cwnd = hc->tx_cwnd, restart_cwnd,
+	    iwnd = rfc3390_bytes_to_packets(dccp_sk(sk)->dccps_mss_cache);
+	s32 delta = now - hc->tx_lsndtime;
+
+	hc->tx_ssthresh = max(hc->tx_ssthresh, (cwnd >> 1) + (cwnd >> 2));
+
+	/* don't reduce cwnd below the initial window (IW) */
+	restart_cwnd = min(cwnd, iwnd);
+
+	while ((delta -= hc->tx_rto) >= 0 && cwnd > restart_cwnd)
+		cwnd >>= 1;
+	hc->tx_cwnd = max(cwnd, restart_cwnd);
+	hc->tx_cwnd_stamp = now;
+	hc->tx_cwnd_used  = 0;
+
+	ccid2_check_l_ack_ratio(sk);
+}
+
+static void ccid2_hc_tx_packet_sent(struct sock *sk, unsigned int len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	const u32 now = ccid2_jiffies32;
+	struct ccid2_seq *next;
+
+	/* slow-start after idle periods (RFC 2581, RFC 2861) */
+	if (ccid2_do_cwv && !hc->tx_pipe &&
+	    (s32)(now - hc->tx_lsndtime) >= hc->tx_rto)
+		ccid2_cwnd_restart(sk, now);
+
+	hc->tx_lsndtime = now;
+	hc->tx_pipe    += 1;
+
+	/* see whether cwnd was fully used (RFC 2861), update expected window */
+	if (ccid2_cwnd_network_limited(hc)) {
+		ccid2_update_used_window(hc, hc->tx_cwnd);
+		hc->tx_cwnd_used  = 0;
+		hc->tx_cwnd_stamp = now;
+	} else {
+		if (hc->tx_pipe > hc->tx_cwnd_used)
+			hc->tx_cwnd_used = hc->tx_pipe;
+
+		ccid2_update_used_window(hc, hc->tx_cwnd_used);
+
+		if (ccid2_do_cwv && (s32)(now - hc->tx_cwnd_stamp) >= hc->tx_rto)
+			ccid2_cwnd_application_limited(sk, now);
+	}
+
+	hc->tx_seqh->ccid2s_seq   = dp->dccps_gss;
+	hc->tx_seqh->ccid2s_acked = 0;
+	hc->tx_seqh->ccid2s_sent  = now;
+
+	next = hc->tx_seqh->ccid2s_next;
+	/* check if we need to alloc more space */
+	if (next == hc->tx_seqt) {
+		if (ccid2_hc_tx_alloc_seq(hc)) {
+			DCCP_CRIT("packet history - out of memory!");
+			/* FIXME: find a more graceful way to bail out */
+			return;
+		}
+		next = hc->tx_seqh->ccid2s_next;
+		BUG_ON(next == hc->tx_seqt);
+	}
+	hc->tx_seqh = next;
+
+	ccid2_pr_debug("cwnd=%d pipe=%d\n", hc->tx_cwnd, hc->tx_pipe);
+
+	/*
+	 * FIXME: The code below is broken and the variables have been removed
+	 * from the socket struct. The `ackloss' variable was always set to 0,
+	 * and with arsent there are several problems:
+	 *  (i) it doesn't just count the number of Acks, but all sent packets;
+	 *  (ii) it is expressed in # of packets, not # of windows, so the
+	 *  comparison below uses the wrong formula: Appendix A of RFC 4341
+	 *  comes up with the number K = cwnd / (R^2 - R) of consecutive windows
+	 *  of data with no lost or marked Ack packets. If arsent were the # of
+	 *  consecutive Acks received without loss, then Ack Ratio needs to be
+	 *  decreased by 1 when
+	 *	      arsent >=  K * cwnd / R  =  cwnd^2 / (R^3 - R^2)
+	 *  where cwnd / R is the number of Acks received per window of data
+	 *  (cf. RFC 4341, App. A). The problems are that
+	 *  - arsent counts other packets as well;
+	 *  - the comparison uses a formula different from RFC 4341;
+	 *  - computing a cubic/quadratic equation each time is too complicated.
+	 *  Hence a different algorithm is needed.
+	 */
+#if 0
+	/* Ack Ratio.  Need to maintain a concept of how many windows we sent */
+	hc->tx_arsent++;
+	/* We had an ack loss in this window... */
+	if (hc->tx_ackloss) {
+		if (hc->tx_arsent >= hc->tx_cwnd) {
+			hc->tx_arsent  = 0;
+			hc->tx_ackloss = 0;
+		}
+	} else {
+		/* No acks lost up to now... */
+		/* decrease ack ratio if enough packets were sent */
+		if (dp->dccps_l_ack_ratio > 1) {
+			/* XXX don't calculate denominator each time */
+			int denom = dp->dccps_l_ack_ratio * dp->dccps_l_ack_ratio -
+				    dp->dccps_l_ack_ratio;
+
+			denom = hc->tx_cwnd * hc->tx_cwnd / denom;
+
+			if (hc->tx_arsent >= denom) {
+				ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio - 1);
+				hc->tx_arsent = 0;
+			}
+		} else {
+			/* we can't increase ack ratio further [1] */
+			hc->tx_arsent = 0; /* or maybe set it to cwnd*/
+		}
+	}
+#endif
+
+	sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+
+#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
+	do {
+		struct ccid2_seq *seqp = hc->tx_seqt;
+
+		while (seqp != hc->tx_seqh) {
+			ccid2_pr_debug("out seq=%llu acked=%d time=%u\n",
+				       (unsigned long long)seqp->ccid2s_seq,
+				       seqp->ccid2s_acked, seqp->ccid2s_sent);
+			seqp = seqp->ccid2s_next;
+		}
+	} while (0);
+	ccid2_pr_debug("=========\n");
+#endif
+}
+
+/**
+ * ccid2_rtt_estimator - Sample RTT and compute RTO using RFC2988 algorithm
+ * This code is almost identical with TCP's tcp_rtt_estimator(), since
+ * - it has a higher sampling frequency (recommended by RFC 1323),
+ * - the RTO does not collapse into RTT due to RTTVAR going towards zero,
+ * - it is simple (cf. more complex proposals such as Eifel timer or research
+ *   which suggests that the gain should be set according to window size),
+ * - in tests it was found to work well with CCID2 [gerrit].
+ */
+static void ccid2_rtt_estimator(struct sock *sk, const long mrtt)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	long m = mrtt ? : 1;
+
+	if (hc->tx_srtt == 0) {
+		/* First measurement m */
+		hc->tx_srtt = m << 3;
+		hc->tx_mdev = m << 1;
+
+		hc->tx_mdev_max = max(hc->tx_mdev, tcp_rto_min(sk));
+		hc->tx_rttvar   = hc->tx_mdev_max;
+
+		hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
+	} else {
+		/* Update scaled SRTT as SRTT += 1/8 * (m - SRTT) */
+		m -= (hc->tx_srtt >> 3);
+		hc->tx_srtt += m;
+
+		/* Similarly, update scaled mdev with regard to |m| */
+		if (m < 0) {
+			m = -m;
+			m -= (hc->tx_mdev >> 2);
+			/*
+			 * This neutralises RTO increase when RTT < SRTT - mdev
+			 * (see P. Sarolahti, A. Kuznetsov,"Congestion Control
+			 * in Linux TCP", USENIX 2002, pp. 49-62).
+			 */
+			if (m > 0)
+				m >>= 3;
+		} else {
+			m -= (hc->tx_mdev >> 2);
+		}
+		hc->tx_mdev += m;
+
+		if (hc->tx_mdev > hc->tx_mdev_max) {
+			hc->tx_mdev_max = hc->tx_mdev;
+			if (hc->tx_mdev_max > hc->tx_rttvar)
+				hc->tx_rttvar = hc->tx_mdev_max;
+		}
+
+		/*
+		 * Decay RTTVAR at most once per flight, exploiting that
+		 *  1) pipe <= cwnd <= Sequence_Window = W  (RFC 4340, 7.5.2)
+		 *  2) AWL = GSS-W+1 <= GAR <= GSS          (RFC 4340, 7.5.1)
+		 * GAR is a useful bound for FlightSize = pipe.
+		 * AWL is probably too low here, as it over-estimates pipe.
+		 */
+		if (after48(dccp_sk(sk)->dccps_gar, hc->tx_rtt_seq)) {
+			if (hc->tx_mdev_max < hc->tx_rttvar)
+				hc->tx_rttvar -= (hc->tx_rttvar -
+						  hc->tx_mdev_max) >> 2;
+			hc->tx_rtt_seq  = dccp_sk(sk)->dccps_gss;
+			hc->tx_mdev_max = tcp_rto_min(sk);
+		}
+	}
+
+	/*
+	 * Set RTO from SRTT and RTTVAR
+	 * As in TCP, 4 * RTTVAR >= TCP_RTO_MIN, giving a minimum RTO of 200 ms.
+	 * This agrees with RFC 4341, 5:
+	 *	"Because DCCP does not retransmit data, DCCP does not require
+	 *	 TCP's recommended minimum timeout of one second".
+	 */
+	hc->tx_rto = (hc->tx_srtt >> 3) + hc->tx_rttvar;
+
+	if (hc->tx_rto > DCCP_RTO_MAX)
+		hc->tx_rto = DCCP_RTO_MAX;
+}
+
+static void ccid2_new_ack(struct sock *sk, struct ccid2_seq *seqp,
+			  unsigned int *maxincr)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	int r_seq_used = hc->tx_cwnd / dp->dccps_l_ack_ratio;
+
+	if (hc->tx_cwnd < dp->dccps_l_seq_win &&
+	    r_seq_used < dp->dccps_r_seq_win) {
+		if (hc->tx_cwnd < hc->tx_ssthresh) {
+			if (*maxincr > 0 && ++hc->tx_packets_acked >= 2) {
+				hc->tx_cwnd += 1;
+				*maxincr    -= 1;
+				hc->tx_packets_acked = 0;
+			}
+		} else if (++hc->tx_packets_acked >= hc->tx_cwnd) {
+			hc->tx_cwnd += 1;
+			hc->tx_packets_acked = 0;
+		}
+	}
+
+	/*
+	 * Adjust the local sequence window and the ack ratio to allow about
+	 * 5 times the number of packets in the network (RFC 4340 7.5.2)
+	 */
+	if (r_seq_used * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_r_seq_win)
+		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio * 2);
+	else if (r_seq_used * CCID2_WIN_CHANGE_FACTOR < dp->dccps_r_seq_win/2)
+		ccid2_change_l_ack_ratio(sk, dp->dccps_l_ack_ratio / 2 ? : 1U);
+
+	if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR >= dp->dccps_l_seq_win)
+		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win * 2);
+	else if (hc->tx_cwnd * CCID2_WIN_CHANGE_FACTOR < dp->dccps_l_seq_win/2)
+		ccid2_change_l_seq_window(sk, dp->dccps_l_seq_win / 2);
+
+	/*
+	 * FIXME: RTT is sampled several times per acknowledgment (for each
+	 * entry in the Ack Vector), instead of once per Ack (as in TCP SACK).
+	 * This causes the RTT to be over-estimated, since the older entries
+	 * in the Ack Vector have earlier sending times.
+	 * The cleanest solution is to not use the ccid2s_sent field at all
+	 * and instead use DCCP timestamps: requires changes in other places.
+	 */
+	ccid2_rtt_estimator(sk, ccid2_jiffies32 - seqp->ccid2s_sent);
+}
+
+static void ccid2_congestion_event(struct sock *sk, struct ccid2_seq *seqp)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+
+	if ((s32)(seqp->ccid2s_sent - hc->tx_last_cong) < 0) {
+		ccid2_pr_debug("Multiple losses in an RTT---treating as one\n");
+		return;
+	}
+
+	hc->tx_last_cong = ccid2_jiffies32;
+
+	hc->tx_cwnd      = hc->tx_cwnd / 2 ? : 1U;
+	hc->tx_ssthresh  = max(hc->tx_cwnd, 2U);
+
+	ccid2_check_l_ack_ratio(sk);
+}
+
+static int ccid2_hc_tx_parse_options(struct sock *sk, u8 packet_type,
+				     u8 option, u8 *optval, u8 optlen)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+
+	switch (option) {
+	case DCCPO_ACK_VECTOR_0:
+	case DCCPO_ACK_VECTOR_1:
+		return dccp_ackvec_parsed_add(&hc->tx_av_chunks, optval, optlen,
+					      option - DCCPO_ACK_VECTOR_0);
+	}
+	return 0;
+}
+
+static void ccid2_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	const bool sender_was_blocked = ccid2_cwnd_network_limited(hc);
+	struct dccp_ackvec_parsed *avp;
+	u64 ackno, seqno;
+	struct ccid2_seq *seqp;
+	int done = 0;
+	unsigned int maxincr = 0;
+
+	/* check reverse path congestion */
+	seqno = DCCP_SKB_CB(skb)->dccpd_seq;
+
+	/* XXX this whole "algorithm" is broken.  Need to fix it to keep track
+	 * of the seqnos of the dupacks so that rpseq and rpdupack are correct
+	 * -sorbo.
+	 */
+	/* need to bootstrap */
+	if (hc->tx_rpdupack == -1) {
+		hc->tx_rpdupack = 0;
+		hc->tx_rpseq    = seqno;
+	} else {
+		/* check if packet is consecutive */
+		if (dccp_delta_seqno(hc->tx_rpseq, seqno) == 1)
+			hc->tx_rpseq = seqno;
+		/* it's a later packet */
+		else if (after48(seqno, hc->tx_rpseq)) {
+			hc->tx_rpdupack++;
+
+			/* check if we got enough dupacks */
+			if (hc->tx_rpdupack >= NUMDUPACK) {
+				hc->tx_rpdupack = -1; /* XXX lame */
+				hc->tx_rpseq    = 0;
+#ifdef __CCID2_COPES_GRACEFULLY_WITH_ACK_CONGESTION_CONTROL__
+				/*
+				 * FIXME: Ack Congestion Control is broken; in
+				 * the current state instabilities occurred with
+				 * Ack Ratios greater than 1; causing hang-ups
+				 * and long RTO timeouts. This needs to be fixed
+				 * before opening up dynamic changes. -- gerrit
+				 */
+				ccid2_change_l_ack_ratio(sk, 2 * dp->dccps_l_ack_ratio);
+#endif
+			}
+		}
+	}
+
+	/* check forward path congestion */
+	if (dccp_packet_without_ack(skb))
+		return;
+
+	/* still didn't send out new data packets */
+	if (hc->tx_seqh == hc->tx_seqt)
+		goto done;
+
+	ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
+	if (after48(ackno, hc->tx_high_ack))
+		hc->tx_high_ack = ackno;
+
+	seqp = hc->tx_seqt;
+	while (before48(seqp->ccid2s_seq, ackno)) {
+		seqp = seqp->ccid2s_next;
+		if (seqp == hc->tx_seqh) {
+			seqp = hc->tx_seqh->ccid2s_prev;
+			break;
+		}
+	}
+
+	/*
+	 * In slow-start, cwnd can increase up to a maximum of Ack Ratio/2
+	 * packets per acknowledgement. Rounding up avoids that cwnd is not
+	 * advanced when Ack Ratio is 1 and gives a slight edge otherwise.
+	 */
+	if (hc->tx_cwnd < hc->tx_ssthresh)
+		maxincr = DIV_ROUND_UP(dp->dccps_l_ack_ratio, 2);
+
+	/* go through all ack vectors */
+	list_for_each_entry(avp, &hc->tx_av_chunks, node) {
+		/* go through this ack vector */
+		for (; avp->len--; avp->vec++) {
+			u64 ackno_end_rl = SUB48(ackno,
+						 dccp_ackvec_runlen(avp->vec));
+
+			ccid2_pr_debug("ackvec %llu |%u,%u|\n",
+				       (unsigned long long)ackno,
+				       dccp_ackvec_state(avp->vec) >> 6,
+				       dccp_ackvec_runlen(avp->vec));
+			/* if the seqno we are analyzing is larger than the
+			 * current ackno, then move towards the tail of our
+			 * seqnos.
+			 */
+			while (after48(seqp->ccid2s_seq, ackno)) {
+				if (seqp == hc->tx_seqt) {
+					done = 1;
+					break;
+				}
+				seqp = seqp->ccid2s_prev;
+			}
+			if (done)
+				break;
+
+			/* check all seqnos in the range of the vector
+			 * run length
+			 */
+			while (between48(seqp->ccid2s_seq,ackno_end_rl,ackno)) {
+				const u8 state = dccp_ackvec_state(avp->vec);
+
+				/* new packet received or marked */
+				if (state != DCCPAV_NOT_RECEIVED &&
+				    !seqp->ccid2s_acked) {
+					if (state == DCCPAV_ECN_MARKED)
+						ccid2_congestion_event(sk,
+								       seqp);
+					else
+						ccid2_new_ack(sk, seqp,
+							      &maxincr);
+
+					seqp->ccid2s_acked = 1;
+					ccid2_pr_debug("Got ack for %llu\n",
+						       (unsigned long long)seqp->ccid2s_seq);
+					hc->tx_pipe--;
+				}
+				if (seqp == hc->tx_seqt) {
+					done = 1;
+					break;
+				}
+				seqp = seqp->ccid2s_prev;
+			}
+			if (done)
+				break;
+
+			ackno = SUB48(ackno_end_rl, 1);
+		}
+		if (done)
+			break;
+	}
+
+	/* The state about what is acked should be correct now
+	 * Check for NUMDUPACK
+	 */
+	seqp = hc->tx_seqt;
+	while (before48(seqp->ccid2s_seq, hc->tx_high_ack)) {
+		seqp = seqp->ccid2s_next;
+		if (seqp == hc->tx_seqh) {
+			seqp = hc->tx_seqh->ccid2s_prev;
+			break;
+		}
+	}
+	done = 0;
+	while (1) {
+		if (seqp->ccid2s_acked) {
+			done++;
+			if (done == NUMDUPACK)
+				break;
+		}
+		if (seqp == hc->tx_seqt)
+			break;
+		seqp = seqp->ccid2s_prev;
+	}
+
+	/* If there are at least 3 acknowledgements, anything unacknowledged
+	 * below the last sequence number is considered lost
+	 */
+	if (done == NUMDUPACK) {
+		struct ccid2_seq *last_acked = seqp;
+
+		/* check for lost packets */
+		while (1) {
+			if (!seqp->ccid2s_acked) {
+				ccid2_pr_debug("Packet lost: %llu\n",
+					       (unsigned long long)seqp->ccid2s_seq);
+				/* XXX need to traverse from tail -> head in
+				 * order to detect multiple congestion events in
+				 * one ack vector.
+				 */
+				ccid2_congestion_event(sk, seqp);
+				hc->tx_pipe--;
+			}
+			if (seqp == hc->tx_seqt)
+				break;
+			seqp = seqp->ccid2s_prev;
+		}
+
+		hc->tx_seqt = last_acked;
+	}
+
+	/* trim acked packets in tail */
+	while (hc->tx_seqt != hc->tx_seqh) {
+		if (!hc->tx_seqt->ccid2s_acked)
+			break;
+
+		hc->tx_seqt = hc->tx_seqt->ccid2s_next;
+	}
+
+	/* restart RTO timer if not all outstanding data has been acked */
+	if (hc->tx_pipe == 0)
+		sk_stop_timer(sk, &hc->tx_rtotimer);
+	else
+		sk_reset_timer(sk, &hc->tx_rtotimer, jiffies + hc->tx_rto);
+done:
+	/* check if incoming Acks allow pending packets to be sent */
+	if (sender_was_blocked && !ccid2_cwnd_network_limited(hc))
+		dccp_tasklet_schedule(sk);
+	dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
+}
+
+static int ccid2_hc_tx_init(struct ccid *ccid, struct sock *sk)
+{
+	struct ccid2_hc_tx_sock *hc = ccid_priv(ccid);
+	struct dccp_sock *dp = dccp_sk(sk);
+	u32 max_ratio;
+
+	/* RFC 4341, 5: initialise ssthresh to arbitrarily high (max) value */
+	hc->tx_ssthresh = ~0U;
+
+	/* Use larger initial windows (RFC 4341, section 5). */
+	hc->tx_cwnd = rfc3390_bytes_to_packets(dp->dccps_mss_cache);
+	hc->tx_expected_wnd = hc->tx_cwnd;
+
+	/* Make sure that Ack Ratio is enabled and within bounds. */
+	max_ratio = DIV_ROUND_UP(hc->tx_cwnd, 2);
+	if (dp->dccps_l_ack_ratio == 0 || dp->dccps_l_ack_ratio > max_ratio)
+		dp->dccps_l_ack_ratio = max_ratio;
+
+	/* XXX init ~ to window size... */
+	if (ccid2_hc_tx_alloc_seq(hc))
+		return -ENOMEM;
+
+	hc->tx_rto	 = DCCP_TIMEOUT_INIT;
+	hc->tx_rpdupack  = -1;
+	hc->tx_last_cong = hc->tx_lsndtime = hc->tx_cwnd_stamp = ccid2_jiffies32;
+	hc->tx_cwnd_used = 0;
+	hc->sk		 = sk;
+	timer_setup(&hc->tx_rtotimer, ccid2_hc_tx_rto_expire, 0);
+	INIT_LIST_HEAD(&hc->tx_av_chunks);
+	return 0;
+}
+
+static void ccid2_hc_tx_exit(struct sock *sk)
+{
+	struct ccid2_hc_tx_sock *hc = ccid2_hc_tx_sk(sk);
+	int i;
+
+	sk_stop_timer(sk, &hc->tx_rtotimer);
+
+	for (i = 0; i < hc->tx_seqbufc; i++)
+		kfree(hc->tx_seqbuf[i]);
+	hc->tx_seqbufc = 0;
+	dccp_ackvec_parsed_cleanup(&hc->tx_av_chunks);
+}
+
+static void ccid2_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct ccid2_hc_rx_sock *hc = ccid2_hc_rx_sk(sk);
+
+	if (!dccp_data_packet(skb))
+		return;
+
+	if (++hc->rx_num_data_pkts >= dccp_sk(sk)->dccps_r_ack_ratio) {
+		dccp_send_ack(sk);
+		hc->rx_num_data_pkts = 0;
+	}
+}
+
+struct ccid_operations ccid2_ops = {
+	.ccid_id		  = DCCPC_CCID2,
+	.ccid_name		  = "TCP-like",
+	.ccid_hc_tx_obj_size	  = sizeof(struct ccid2_hc_tx_sock),
+	.ccid_hc_tx_init	  = ccid2_hc_tx_init,
+	.ccid_hc_tx_exit	  = ccid2_hc_tx_exit,
+	.ccid_hc_tx_send_packet	  = ccid2_hc_tx_send_packet,
+	.ccid_hc_tx_packet_sent	  = ccid2_hc_tx_packet_sent,
+	.ccid_hc_tx_parse_options = ccid2_hc_tx_parse_options,
+	.ccid_hc_tx_packet_recv	  = ccid2_hc_tx_packet_recv,
+	.ccid_hc_rx_obj_size	  = sizeof(struct ccid2_hc_rx_sock),
+	.ccid_hc_rx_packet_recv	  = ccid2_hc_rx_packet_recv,
+};
+
+#ifdef CONFIG_IP_DCCP_CCID2_DEBUG
+module_param(ccid2_debug, bool, 0644);
+MODULE_PARM_DESC(ccid2_debug, "Enable CCID-2 debug messages");
+#endif
diff --git a/net/dccp/ccids/ccid2.h b/net/dccp/ccids/ccid2.h
new file mode 100644
index 000000000..330c7b4ec
--- /dev/null
+++ b/net/dccp/ccids/ccid2.h
@@ -0,0 +1,121 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
+ */
+#ifndef _DCCP_CCID2_H_
+#define _DCCP_CCID2_H_
+
+#include <linux/timer.h>
+#include <linux/types.h>
+#include "../ccid.h"
+#include "../dccp.h"
+
+/*
+ * CCID-2 timestamping faces the same issues as TCP timestamping.
+ * Hence we reuse/share as much of the code as possible.
+ */
+#define ccid2_jiffies32	((u32)jiffies)
+
+/* NUMDUPACK parameter from RFC 4341, p. 6 */
+#define NUMDUPACK	3
+
+struct ccid2_seq {
+	u64			ccid2s_seq;
+	u32			ccid2s_sent;
+	int			ccid2s_acked;
+	struct ccid2_seq	*ccid2s_prev;
+	struct ccid2_seq	*ccid2s_next;
+};
+
+#define CCID2_SEQBUF_LEN 1024
+#define CCID2_SEQBUF_MAX 128
+
+/*
+ * Multiple of congestion window to keep the sequence window at
+ * (RFC 4340 7.5.2)
+ */
+#define CCID2_WIN_CHANGE_FACTOR 5
+
+/**
+ * struct ccid2_hc_tx_sock - CCID2 TX half connection
+ * @tx_{cwnd,ssthresh,pipe}: as per RFC 4341, section 5
+ * @tx_packets_acked:	     Ack counter for deriving cwnd growth (RFC 3465)
+ * @tx_srtt:		     smoothed RTT estimate, scaled by 2^3
+ * @tx_mdev:		     smoothed RTT variation, scaled by 2^2
+ * @tx_mdev_max:	     maximum of @mdev during one flight
+ * @tx_rttvar:		     moving average/maximum of @mdev_max
+ * @tx_rto:		     RTO value deriving from SRTT and RTTVAR (RFC 2988)
+ * @tx_rtt_seq:		     to decay RTTVAR at most once per flight
+ * @tx_cwnd_used:	     actually used cwnd, W_used of RFC 2861
+ * @tx_expected_wnd:	     moving average of @tx_cwnd_used
+ * @tx_cwnd_stamp:	     to track idle periods in CWV
+ * @tx_lsndtime:	     last time (in jiffies) a data packet was sent
+ * @tx_rpseq:		     last consecutive seqno
+ * @tx_rpdupack:	     dupacks since rpseq
+ * @tx_av_chunks:	     list of Ack Vectors received on current skb
+ */
+struct ccid2_hc_tx_sock {
+	u32			tx_cwnd;
+	u32			tx_ssthresh;
+	u32			tx_pipe;
+	u32			tx_packets_acked;
+	struct ccid2_seq	*tx_seqbuf[CCID2_SEQBUF_MAX];
+	int			tx_seqbufc;
+	struct ccid2_seq	*tx_seqh;
+	struct ccid2_seq	*tx_seqt;
+
+	/* RTT measurement: variables/principles are the same as in TCP */
+	u32			tx_srtt,
+				tx_mdev,
+				tx_mdev_max,
+				tx_rttvar,
+				tx_rto;
+	u64			tx_rtt_seq:48;
+	struct timer_list	tx_rtotimer;
+	struct sock		*sk;
+
+	/* Congestion Window validation (optional, RFC 2861) */
+	u32			tx_cwnd_used,
+				tx_expected_wnd,
+				tx_cwnd_stamp,
+				tx_lsndtime;
+
+	u64			tx_rpseq;
+	int			tx_rpdupack;
+	u32			tx_last_cong;
+	u64			tx_high_ack;
+	struct list_head	tx_av_chunks;
+};
+
+static inline bool ccid2_cwnd_network_limited(struct ccid2_hc_tx_sock *hc)
+{
+	return hc->tx_pipe >= hc->tx_cwnd;
+}
+
+/*
+ * Convert RFC 3390 larger initial window into an equivalent number of packets.
+ * This is based on the numbers specified in RFC 5681, 3.1.
+ */
+static inline u32 rfc3390_bytes_to_packets(const u32 smss)
+{
+	return smss <= 1095 ? 4 : (smss > 2190 ? 2 : 3);
+}
+
+/**
+ * struct ccid2_hc_rx_sock  -  Receiving end of CCID-2 half-connection
+ * @rx_num_data_pkts: number of data packets received since last feedback
+ */
+struct ccid2_hc_rx_sock {
+	u32	rx_num_data_pkts;
+};
+
+static inline struct ccid2_hc_tx_sock *ccid2_hc_tx_sk(const struct sock *sk)
+{
+	return ccid_priv(dccp_sk(sk)->dccps_hc_tx_ccid);
+}
+
+static inline struct ccid2_hc_rx_sock *ccid2_hc_rx_sk(const struct sock *sk)
+{
+	return ccid_priv(dccp_sk(sk)->dccps_hc_rx_ccid);
+}
+#endif /* _DCCP_CCID2_H_ */
diff --git a/net/dccp/ccids/ccid3.c b/net/dccp/ccids/ccid3.c
new file mode 100644
index 000000000..b9ee1a4a8
--- /dev/null
+++ b/net/dccp/ccids/ccid3.c
@@ -0,0 +1,860 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ *
+ *  An implementation of the DCCP protocol
+ *
+ *  This code has been developed by the University of Waikato WAND
+ *  research group. For further information please see https://www.wand.net.nz/
+ *
+ *  This code also uses code from Lulea University, rereleased as GPL by its
+ *  authors:
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ *
+ *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
+ *  and to make it work as a loadable module in the DCCP stack written by
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
+ *
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#include "../dccp.h"
+#include "ccid3.h"
+
+#include <asm/unaligned.h>
+
+#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
+static bool ccid3_debug;
+#define ccid3_pr_debug(format, a...)	DCCP_PR_DEBUG(ccid3_debug, format, ##a)
+#else
+#define ccid3_pr_debug(format, a...)
+#endif
+
+/*
+ *	Transmitter Half-Connection Routines
+ */
+#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
+static const char *ccid3_tx_state_name(enum ccid3_hc_tx_states state)
+{
+	static const char *const ccid3_state_names[] = {
+	[TFRC_SSTATE_NO_SENT]  = "NO_SENT",
+	[TFRC_SSTATE_NO_FBACK] = "NO_FBACK",
+	[TFRC_SSTATE_FBACK]    = "FBACK",
+	};
+
+	return ccid3_state_names[state];
+}
+#endif
+
+static void ccid3_hc_tx_set_state(struct sock *sk,
+				  enum ccid3_hc_tx_states state)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	enum ccid3_hc_tx_states oldstate = hc->tx_state;
+
+	ccid3_pr_debug("%s(%p) %-8.8s -> %s\n",
+		       dccp_role(sk), sk, ccid3_tx_state_name(oldstate),
+		       ccid3_tx_state_name(state));
+	WARN_ON(state == oldstate);
+	hc->tx_state = state;
+}
+
+/*
+ * Compute the initial sending rate X_init in the manner of RFC 3390:
+ *
+ *	X_init  =  min(4 * s, max(2 * s, 4380 bytes)) / RTT
+ *
+ * Note that RFC 3390 uses MSS, RFC 4342 refers to RFC 3390, and rfc3448bis
+ * (rev-02) clarifies the use of RFC 3390 with regard to the above formula.
+ * For consistency with other parts of the code, X_init is scaled by 2^6.
+ */
+static inline u64 rfc3390_initial_rate(struct sock *sk)
+{
+	const struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	const __u32 w_init = clamp_t(__u32, 4380U, 2 * hc->tx_s, 4 * hc->tx_s);
+
+	return scaled_div(w_init << 6, hc->tx_rtt);
+}
+
+/**
+ * ccid3_update_send_interval  -  Calculate new t_ipi = s / X_inst
+ * This respects the granularity of X_inst (64 * bytes/second).
+ */
+static void ccid3_update_send_interval(struct ccid3_hc_tx_sock *hc)
+{
+	hc->tx_t_ipi = scaled_div32(((u64)hc->tx_s) << 6, hc->tx_x);
+
+	DCCP_BUG_ON(hc->tx_t_ipi == 0);
+	ccid3_pr_debug("t_ipi=%u, s=%u, X=%u\n", hc->tx_t_ipi,
+		       hc->tx_s, (unsigned int)(hc->tx_x >> 6));
+}
+
+static u32 ccid3_hc_tx_idle_rtt(struct ccid3_hc_tx_sock *hc, ktime_t now)
+{
+	u32 delta = ktime_us_delta(now, hc->tx_t_last_win_count);
+
+	return delta / hc->tx_rtt;
+}
+
+/**
+ * ccid3_hc_tx_update_x  -  Update allowed sending rate X
+ * @stamp: most recent time if available - can be left NULL.
+ *
+ * This function tracks draft rfc3448bis, check there for latest details.
+ *
+ * Note: X and X_recv are both stored in units of 64 * bytes/second, to support
+ *       fine-grained resolution of sending rates. This requires scaling by 2^6
+ *       throughout the code. Only X_calc is unscaled (in bytes/second).
+ *
+ */
+static void ccid3_hc_tx_update_x(struct sock *sk, ktime_t *stamp)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	__u64 min_rate = 2 * hc->tx_x_recv;
+	const __u64 old_x = hc->tx_x;
+	ktime_t now = stamp ? *stamp : ktime_get_real();
+
+	/*
+	 * Handle IDLE periods: do not reduce below RFC3390 initial sending rate
+	 * when idling [RFC 4342, 5.1]. Definition of idling is from rfc3448bis:
+	 * a sender is idle if it has not sent anything over a 2-RTT-period.
+	 * For consistency with X and X_recv, min_rate is also scaled by 2^6.
+	 */
+	if (ccid3_hc_tx_idle_rtt(hc, now) >= 2) {
+		min_rate = rfc3390_initial_rate(sk);
+		min_rate = max(min_rate, 2 * hc->tx_x_recv);
+	}
+
+	if (hc->tx_p > 0) {
+
+		hc->tx_x = min(((__u64)hc->tx_x_calc) << 6, min_rate);
+		hc->tx_x = max(hc->tx_x, (((__u64)hc->tx_s) << 6) / TFRC_T_MBI);
+
+	} else if (ktime_us_delta(now, hc->tx_t_ld) - (s64)hc->tx_rtt >= 0) {
+
+		hc->tx_x = min(2 * hc->tx_x, min_rate);
+		hc->tx_x = max(hc->tx_x,
+			       scaled_div(((__u64)hc->tx_s) << 6, hc->tx_rtt));
+		hc->tx_t_ld = now;
+	}
+
+	if (hc->tx_x != old_x) {
+		ccid3_pr_debug("X_prev=%u, X_now=%u, X_calc=%u, "
+			       "X_recv=%u\n", (unsigned int)(old_x >> 6),
+			       (unsigned int)(hc->tx_x >> 6), hc->tx_x_calc,
+			       (unsigned int)(hc->tx_x_recv >> 6));
+
+		ccid3_update_send_interval(hc);
+	}
+}
+
+/**
+ *	ccid3_hc_tx_update_s - Track the mean packet size `s'
+ *	@len: DCCP packet payload size in bytes
+ *
+ *	cf. RFC 4342, 5.3 and  RFC 3448, 4.1
+ */
+static inline void ccid3_hc_tx_update_s(struct ccid3_hc_tx_sock *hc, int len)
+{
+	const u16 old_s = hc->tx_s;
+
+	hc->tx_s = tfrc_ewma(hc->tx_s, len, 9);
+
+	if (hc->tx_s != old_s)
+		ccid3_update_send_interval(hc);
+}
+
+/*
+ *	Update Window Counter using the algorithm from [RFC 4342, 8.1].
+ *	As elsewhere, RTT > 0 is assumed by using dccp_sample_rtt().
+ */
+static inline void ccid3_hc_tx_update_win_count(struct ccid3_hc_tx_sock *hc,
+						ktime_t now)
+{
+	u32 delta = ktime_us_delta(now, hc->tx_t_last_win_count),
+	    quarter_rtts = (4 * delta) / hc->tx_rtt;
+
+	if (quarter_rtts > 0) {
+		hc->tx_t_last_win_count = now;
+		hc->tx_last_win_count  += min(quarter_rtts, 5U);
+		hc->tx_last_win_count  &= 0xF;		/* mod 16 */
+	}
+}
+
+static void ccid3_hc_tx_no_feedback_timer(struct timer_list *t)
+{
+	struct ccid3_hc_tx_sock *hc = from_timer(hc, t, tx_no_feedback_timer);
+	struct sock *sk = hc->sk;
+	unsigned long t_nfb = USEC_PER_SEC / 5;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later. */
+		/* XXX: set some sensible MIB */
+		goto restart_timer;
+	}
+
+	ccid3_pr_debug("%s(%p, state=%s) - entry\n", dccp_role(sk), sk,
+		       ccid3_tx_state_name(hc->tx_state));
+
+	/* Ignore and do not restart after leaving the established state */
+	if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN))
+		goto out;
+
+	/* Reset feedback state to "no feedback received" */
+	if (hc->tx_state == TFRC_SSTATE_FBACK)
+		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
+
+	/*
+	 * Determine new allowed sending rate X as per draft rfc3448bis-00, 4.4
+	 * RTO is 0 if and only if no feedback has been received yet.
+	 */
+	if (hc->tx_t_rto == 0 || hc->tx_p == 0) {
+
+		/* halve send rate directly */
+		hc->tx_x = max(hc->tx_x / 2,
+			       (((__u64)hc->tx_s) << 6) / TFRC_T_MBI);
+		ccid3_update_send_interval(hc);
+	} else {
+		/*
+		 *  Modify the cached value of X_recv
+		 *
+		 *  If (X_calc > 2 * X_recv)
+		 *    X_recv = max(X_recv / 2, s / (2 * t_mbi));
+		 *  Else
+		 *    X_recv = X_calc / 4;
+		 *
+		 *  Note that X_recv is scaled by 2^6 while X_calc is not
+		 */
+		if (hc->tx_x_calc > (hc->tx_x_recv >> 5))
+			hc->tx_x_recv =
+				max(hc->tx_x_recv / 2,
+				    (((__u64)hc->tx_s) << 6) / (2*TFRC_T_MBI));
+		else {
+			hc->tx_x_recv = hc->tx_x_calc;
+			hc->tx_x_recv <<= 4;
+		}
+		ccid3_hc_tx_update_x(sk, NULL);
+	}
+	ccid3_pr_debug("Reduced X to %llu/64 bytes/sec\n",
+			(unsigned long long)hc->tx_x);
+
+	/*
+	 * Set new timeout for the nofeedback timer.
+	 * See comments in packet_recv() regarding the value of t_RTO.
+	 */
+	if (unlikely(hc->tx_t_rto == 0))	/* no feedback received yet */
+		t_nfb = TFRC_INITIAL_TIMEOUT;
+	else
+		t_nfb = max(hc->tx_t_rto, 2 * hc->tx_t_ipi);
+
+restart_timer:
+	sk_reset_timer(sk, &hc->tx_no_feedback_timer,
+			   jiffies + usecs_to_jiffies(t_nfb));
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+/**
+ * ccid3_hc_tx_send_packet  -  Delay-based dequeueing of TX packets
+ * @skb: next packet candidate to send on @sk
+ *
+ * This function uses the convention of ccid_packet_dequeue_eval() and
+ * returns a millisecond-delay value between 0 and t_mbi = 64000 msec.
+ */
+static int ccid3_hc_tx_send_packet(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	ktime_t now = ktime_get_real();
+	s64 delay;
+
+	/*
+	 * This function is called only for Data and DataAck packets. Sending
+	 * zero-sized Data(Ack)s is theoretically possible, but for congestion
+	 * control this case is pathological - ignore it.
+	 */
+	if (unlikely(skb->len == 0))
+		return -EBADMSG;
+
+	if (hc->tx_state == TFRC_SSTATE_NO_SENT) {
+		sk_reset_timer(sk, &hc->tx_no_feedback_timer, (jiffies +
+			       usecs_to_jiffies(TFRC_INITIAL_TIMEOUT)));
+		hc->tx_last_win_count	= 0;
+		hc->tx_t_last_win_count = now;
+
+		/* Set t_0 for initial packet */
+		hc->tx_t_nom = now;
+
+		hc->tx_s = skb->len;
+
+		/*
+		 * Use initial RTT sample when available: recommended by erratum
+		 * to RFC 4342. This implements the initialisation procedure of
+		 * draft rfc3448bis, section 4.2. Remember, X is scaled by 2^6.
+		 */
+		if (dp->dccps_syn_rtt) {
+			ccid3_pr_debug("SYN RTT = %uus\n", dp->dccps_syn_rtt);
+			hc->tx_rtt  = dp->dccps_syn_rtt;
+			hc->tx_x    = rfc3390_initial_rate(sk);
+			hc->tx_t_ld = now;
+		} else {
+			/*
+			 * Sender does not have RTT sample:
+			 * - set fallback RTT (RFC 4340, 3.4) since a RTT value
+			 *   is needed in several parts (e.g.  window counter);
+			 * - set sending rate X_pps = 1pps as per RFC 3448, 4.2.
+			 */
+			hc->tx_rtt = DCCP_FALLBACK_RTT;
+			hc->tx_x   = hc->tx_s;
+			hc->tx_x <<= 6;
+		}
+		ccid3_update_send_interval(hc);
+
+		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_NO_FBACK);
+
+	} else {
+		delay = ktime_us_delta(hc->tx_t_nom, now);
+		ccid3_pr_debug("delay=%ld\n", (long)delay);
+		/*
+		 *	Scheduling of packet transmissions (RFC 5348, 8.3)
+		 *
+		 * if (t_now > t_nom - delta)
+		 *       // send the packet now
+		 * else
+		 *       // send the packet in (t_nom - t_now) milliseconds.
+		 */
+		if (delay >= TFRC_T_DELTA)
+			return (u32)delay / USEC_PER_MSEC;
+
+		ccid3_hc_tx_update_win_count(hc, now);
+	}
+
+	/* prepare to send now (add options etc.) */
+	dp->dccps_hc_tx_insert_options = 1;
+	DCCP_SKB_CB(skb)->dccpd_ccval  = hc->tx_last_win_count;
+
+	/* set the nominal send time for the next following packet */
+	hc->tx_t_nom = ktime_add_us(hc->tx_t_nom, hc->tx_t_ipi);
+	return CCID_PACKET_SEND_AT_ONCE;
+}
+
+static void ccid3_hc_tx_packet_sent(struct sock *sk, unsigned int len)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+
+	ccid3_hc_tx_update_s(hc, len);
+
+	if (tfrc_tx_hist_add(&hc->tx_hist, dccp_sk(sk)->dccps_gss))
+		DCCP_CRIT("packet history - out of memory!");
+}
+
+static void ccid3_hc_tx_packet_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	struct tfrc_tx_hist_entry *acked;
+	ktime_t now;
+	unsigned long t_nfb;
+	u32 r_sample;
+
+	/* we are only interested in ACKs */
+	if (!(DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_ACK ||
+	      DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_DATAACK))
+		return;
+	/*
+	 * Locate the acknowledged packet in the TX history.
+	 *
+	 * Returning "entry not found" here can for instance happen when
+	 *  - the host has not sent out anything (e.g. a passive server),
+	 *  - the Ack is outdated (packet with higher Ack number was received),
+	 *  - it is a bogus Ack (for a packet not sent on this connection).
+	 */
+	acked = tfrc_tx_hist_find_entry(hc->tx_hist, dccp_hdr_ack_seq(skb));
+	if (acked == NULL)
+		return;
+	/* For the sake of RTT sampling, ignore/remove all older entries */
+	tfrc_tx_hist_purge(&acked->next);
+
+	/* Update the moving average for the RTT estimate (RFC 3448, 4.3) */
+	now	  = ktime_get_real();
+	r_sample  = dccp_sample_rtt(sk, ktime_us_delta(now, acked->stamp));
+	hc->tx_rtt = tfrc_ewma(hc->tx_rtt, r_sample, 9);
+
+	/*
+	 * Update allowed sending rate X as per draft rfc3448bis-00, 4.2/3
+	 */
+	if (hc->tx_state == TFRC_SSTATE_NO_FBACK) {
+		ccid3_hc_tx_set_state(sk, TFRC_SSTATE_FBACK);
+
+		if (hc->tx_t_rto == 0) {
+			/*
+			 * Initial feedback packet: Larger Initial Windows (4.2)
+			 */
+			hc->tx_x    = rfc3390_initial_rate(sk);
+			hc->tx_t_ld = now;
+
+			ccid3_update_send_interval(hc);
+
+			goto done_computing_x;
+		} else if (hc->tx_p == 0) {
+			/*
+			 * First feedback after nofeedback timer expiry (4.3)
+			 */
+			goto done_computing_x;
+		}
+	}
+
+	/* Update sending rate (step 4 of [RFC 3448, 4.3]) */
+	if (hc->tx_p > 0)
+		hc->tx_x_calc = tfrc_calc_x(hc->tx_s, hc->tx_rtt, hc->tx_p);
+	ccid3_hc_tx_update_x(sk, &now);
+
+done_computing_x:
+	ccid3_pr_debug("%s(%p), RTT=%uus (sample=%uus), s=%u, "
+			       "p=%u, X_calc=%u, X_recv=%u, X=%u\n",
+			       dccp_role(sk), sk, hc->tx_rtt, r_sample,
+			       hc->tx_s, hc->tx_p, hc->tx_x_calc,
+			       (unsigned int)(hc->tx_x_recv >> 6),
+			       (unsigned int)(hc->tx_x >> 6));
+
+	/* unschedule no feedback timer */
+	sk_stop_timer(sk, &hc->tx_no_feedback_timer);
+
+	/*
+	 * As we have calculated new ipi, delta, t_nom it is possible
+	 * that we now can send a packet, so wake up dccp_wait_for_ccid
+	 */
+	sk->sk_write_space(sk);
+
+	/*
+	 * Update timeout interval for the nofeedback timer. In order to control
+	 * rate halving on networks with very low RTTs (<= 1 ms), use per-route
+	 * tunable RTAX_RTO_MIN value as the lower bound.
+	 */
+	hc->tx_t_rto = max_t(u32, 4 * hc->tx_rtt,
+				  USEC_PER_SEC/HZ * tcp_rto_min(sk));
+	/*
+	 * Schedule no feedback timer to expire in
+	 * max(t_RTO, 2 * s/X)  =  max(t_RTO, 2 * t_ipi)
+	 */
+	t_nfb = max(hc->tx_t_rto, 2 * hc->tx_t_ipi);
+
+	ccid3_pr_debug("%s(%p), Scheduled no feedback timer to "
+		       "expire in %lu jiffies (%luus)\n",
+		       dccp_role(sk), sk, usecs_to_jiffies(t_nfb), t_nfb);
+
+	sk_reset_timer(sk, &hc->tx_no_feedback_timer,
+			   jiffies + usecs_to_jiffies(t_nfb));
+}
+
+static int ccid3_hc_tx_parse_options(struct sock *sk, u8 packet_type,
+				     u8 option, u8 *optval, u8 optlen)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	__be32 opt_val;
+
+	switch (option) {
+	case TFRC_OPT_RECEIVE_RATE:
+	case TFRC_OPT_LOSS_EVENT_RATE:
+		/* Must be ignored on Data packets, cf. RFC 4342 8.3 and 8.5 */
+		if (packet_type == DCCP_PKT_DATA)
+			break;
+		if (unlikely(optlen != 4)) {
+			DCCP_WARN("%s(%p), invalid len %d for %u\n",
+				  dccp_role(sk), sk, optlen, option);
+			return -EINVAL;
+		}
+		opt_val = ntohl(get_unaligned((__be32 *)optval));
+
+		if (option == TFRC_OPT_RECEIVE_RATE) {
+			/* Receive Rate is kept in units of 64 bytes/second */
+			hc->tx_x_recv = opt_val;
+			hc->tx_x_recv <<= 6;
+
+			ccid3_pr_debug("%s(%p), RECEIVE_RATE=%u\n",
+				       dccp_role(sk), sk, opt_val);
+		} else {
+			/* Update the fixpoint Loss Event Rate fraction */
+			hc->tx_p = tfrc_invert_loss_event_rate(opt_val);
+
+			ccid3_pr_debug("%s(%p), LOSS_EVENT_RATE=%u\n",
+				       dccp_role(sk), sk, opt_val);
+		}
+	}
+	return 0;
+}
+
+static int ccid3_hc_tx_init(struct ccid *ccid, struct sock *sk)
+{
+	struct ccid3_hc_tx_sock *hc = ccid_priv(ccid);
+
+	hc->tx_state = TFRC_SSTATE_NO_SENT;
+	hc->tx_hist  = NULL;
+	hc->sk	     = sk;
+	timer_setup(&hc->tx_no_feedback_timer,
+		    ccid3_hc_tx_no_feedback_timer, 0);
+	return 0;
+}
+
+static void ccid3_hc_tx_exit(struct sock *sk)
+{
+	struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+
+	sk_stop_timer(sk, &hc->tx_no_feedback_timer);
+	tfrc_tx_hist_purge(&hc->tx_hist);
+}
+
+static void ccid3_hc_tx_get_info(struct sock *sk, struct tcp_info *info)
+{
+	info->tcpi_rto = ccid3_hc_tx_sk(sk)->tx_t_rto;
+	info->tcpi_rtt = ccid3_hc_tx_sk(sk)->tx_rtt;
+}
+
+static int ccid3_hc_tx_getsockopt(struct sock *sk, const int optname, int len,
+				  u32 __user *optval, int __user *optlen)
+{
+	const struct ccid3_hc_tx_sock *hc = ccid3_hc_tx_sk(sk);
+	struct tfrc_tx_info tfrc;
+	const void *val;
+
+	switch (optname) {
+	case DCCP_SOCKOPT_CCID_TX_INFO:
+		if (len < sizeof(tfrc))
+			return -EINVAL;
+		memset(&tfrc, 0, sizeof(tfrc));
+		tfrc.tfrctx_x	   = hc->tx_x;
+		tfrc.tfrctx_x_recv = hc->tx_x_recv;
+		tfrc.tfrctx_x_calc = hc->tx_x_calc;
+		tfrc.tfrctx_rtt	   = hc->tx_rtt;
+		tfrc.tfrctx_p	   = hc->tx_p;
+		tfrc.tfrctx_rto	   = hc->tx_t_rto;
+		tfrc.tfrctx_ipi	   = hc->tx_t_ipi;
+		len = sizeof(tfrc);
+		val = &tfrc;
+		break;
+	default:
+		return -ENOPROTOOPT;
+	}
+
+	if (put_user(len, optlen) || copy_to_user(optval, val, len))
+		return -EFAULT;
+
+	return 0;
+}
+
+/*
+ *	Receiver Half-Connection Routines
+ */
+
+/* CCID3 feedback types */
+enum ccid3_fback_type {
+	CCID3_FBACK_NONE = 0,
+	CCID3_FBACK_INITIAL,
+	CCID3_FBACK_PERIODIC,
+	CCID3_FBACK_PARAM_CHANGE
+};
+
+#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
+static const char *ccid3_rx_state_name(enum ccid3_hc_rx_states state)
+{
+	static const char *const ccid3_rx_state_names[] = {
+	[TFRC_RSTATE_NO_DATA] = "NO_DATA",
+	[TFRC_RSTATE_DATA]    = "DATA",
+	};
+
+	return ccid3_rx_state_names[state];
+}
+#endif
+
+static void ccid3_hc_rx_set_state(struct sock *sk,
+				  enum ccid3_hc_rx_states state)
+{
+	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	enum ccid3_hc_rx_states oldstate = hc->rx_state;
+
+	ccid3_pr_debug("%s(%p) %-8.8s -> %s\n",
+		       dccp_role(sk), sk, ccid3_rx_state_name(oldstate),
+		       ccid3_rx_state_name(state));
+	WARN_ON(state == oldstate);
+	hc->rx_state = state;
+}
+
+static void ccid3_hc_rx_send_feedback(struct sock *sk,
+				      const struct sk_buff *skb,
+				      enum ccid3_fback_type fbtype)
+{
+	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	ktime_t now = ktime_get();
+	s64 delta = 0;
+
+	switch (fbtype) {
+	case CCID3_FBACK_INITIAL:
+		hc->rx_x_recv = 0;
+		hc->rx_pinv   = ~0U;   /* see RFC 4342, 8.5 */
+		break;
+	case CCID3_FBACK_PARAM_CHANGE:
+		/*
+		 * When parameters change (new loss or p > p_prev), we do not
+		 * have a reliable estimate for R_m of [RFC 3448, 6.2] and so
+		 * need to  reuse the previous value of X_recv. However, when
+		 * X_recv was 0 (due to early loss), this would kill X down to
+		 * s/t_mbi (i.e. one packet in 64 seconds).
+		 * To avoid such drastic reduction, we approximate X_recv as
+		 * the number of bytes since last feedback.
+		 * This is a safe fallback, since X is bounded above by X_calc.
+		 */
+		if (hc->rx_x_recv > 0)
+			break;
+		fallthrough;
+	case CCID3_FBACK_PERIODIC:
+		delta = ktime_us_delta(now, hc->rx_tstamp_last_feedback);
+		if (delta <= 0)
+			delta = 1;
+		hc->rx_x_recv = scaled_div32(hc->rx_bytes_recv, delta);
+		break;
+	default:
+		return;
+	}
+
+	ccid3_pr_debug("Interval %lldusec, X_recv=%u, 1/p=%u\n", delta,
+		       hc->rx_x_recv, hc->rx_pinv);
+
+	hc->rx_tstamp_last_feedback = now;
+	hc->rx_last_counter	    = dccp_hdr(skb)->dccph_ccval;
+	hc->rx_bytes_recv	    = 0;
+
+	dp->dccps_hc_rx_insert_options = 1;
+	dccp_send_ack(sk);
+}
+
+static int ccid3_hc_rx_insert_options(struct sock *sk, struct sk_buff *skb)
+{
+	const struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	__be32 x_recv, pinv;
+
+	if (!(sk->sk_state == DCCP_OPEN || sk->sk_state == DCCP_PARTOPEN))
+		return 0;
+
+	if (dccp_packet_without_ack(skb))
+		return 0;
+
+	x_recv = htonl(hc->rx_x_recv);
+	pinv   = htonl(hc->rx_pinv);
+
+	if (dccp_insert_option(skb, TFRC_OPT_LOSS_EVENT_RATE,
+			       &pinv, sizeof(pinv)) ||
+	    dccp_insert_option(skb, TFRC_OPT_RECEIVE_RATE,
+			       &x_recv, sizeof(x_recv)))
+		return -1;
+
+	return 0;
+}
+
+/**
+ * ccid3_first_li  -  Implements [RFC 5348, 6.3.1]
+ *
+ * Determine the length of the first loss interval via inverse lookup.
+ * Assume that X_recv can be computed by the throughput equation
+ *		    s
+ *	X_recv = --------
+ *		 R * fval
+ * Find some p such that f(p) = fval; return 1/p (scaled).
+ */
+static u32 ccid3_first_li(struct sock *sk)
+{
+	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	u32 x_recv, p;
+	s64 delta;
+	u64 fval;
+
+	if (hc->rx_rtt == 0) {
+		DCCP_WARN("No RTT estimate available, using fallback RTT\n");
+		hc->rx_rtt = DCCP_FALLBACK_RTT;
+	}
+
+	delta = ktime_us_delta(ktime_get(), hc->rx_tstamp_last_feedback);
+	if (delta <= 0)
+		delta = 1;
+	x_recv = scaled_div32(hc->rx_bytes_recv, delta);
+	if (x_recv == 0) {		/* would also trigger divide-by-zero */
+		DCCP_WARN("X_recv==0\n");
+		if (hc->rx_x_recv == 0) {
+			DCCP_BUG("stored value of X_recv is zero");
+			return ~0U;
+		}
+		x_recv = hc->rx_x_recv;
+	}
+
+	fval = scaled_div(hc->rx_s, hc->rx_rtt);
+	fval = scaled_div32(fval, x_recv);
+	p = tfrc_calc_x_reverse_lookup(fval);
+
+	ccid3_pr_debug("%s(%p), receive rate=%u bytes/s, implied "
+		       "loss rate=%u\n", dccp_role(sk), sk, x_recv, p);
+
+	return p == 0 ? ~0U : scaled_div(1, p);
+}
+
+static void ccid3_hc_rx_packet_recv(struct sock *sk, struct sk_buff *skb)
+{
+	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	enum ccid3_fback_type do_feedback = CCID3_FBACK_NONE;
+	const u64 ndp = dccp_sk(sk)->dccps_options_received.dccpor_ndp;
+	const bool is_data_packet = dccp_data_packet(skb);
+
+	if (unlikely(hc->rx_state == TFRC_RSTATE_NO_DATA)) {
+		if (is_data_packet) {
+			const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
+			do_feedback = CCID3_FBACK_INITIAL;
+			ccid3_hc_rx_set_state(sk, TFRC_RSTATE_DATA);
+			hc->rx_s = payload;
+			/*
+			 * Not necessary to update rx_bytes_recv here,
+			 * since X_recv = 0 for the first feedback packet (cf.
+			 * RFC 3448, 6.3) -- gerrit
+			 */
+		}
+		goto update_records;
+	}
+
+	if (tfrc_rx_hist_duplicate(&hc->rx_hist, skb))
+		return; /* done receiving */
+
+	if (is_data_packet) {
+		const u32 payload = skb->len - dccp_hdr(skb)->dccph_doff * 4;
+		/*
+		 * Update moving-average of s and the sum of received payload bytes
+		 */
+		hc->rx_s = tfrc_ewma(hc->rx_s, payload, 9);
+		hc->rx_bytes_recv += payload;
+	}
+
+	/*
+	 * Perform loss detection and handle pending losses
+	 */
+	if (tfrc_rx_handle_loss(&hc->rx_hist, &hc->rx_li_hist,
+				skb, ndp, ccid3_first_li, sk)) {
+		do_feedback = CCID3_FBACK_PARAM_CHANGE;
+		goto done_receiving;
+	}
+
+	if (tfrc_rx_hist_loss_pending(&hc->rx_hist))
+		return; /* done receiving */
+
+	/*
+	 * Handle data packets: RTT sampling and monitoring p
+	 */
+	if (unlikely(!is_data_packet))
+		goto update_records;
+
+	if (!tfrc_lh_is_initialised(&hc->rx_li_hist)) {
+		const u32 sample = tfrc_rx_hist_sample_rtt(&hc->rx_hist, skb);
+		/*
+		 * Empty loss history: no loss so far, hence p stays 0.
+		 * Sample RTT values, since an RTT estimate is required for the
+		 * computation of p when the first loss occurs; RFC 3448, 6.3.1.
+		 */
+		if (sample != 0)
+			hc->rx_rtt = tfrc_ewma(hc->rx_rtt, sample, 9);
+
+	} else if (tfrc_lh_update_i_mean(&hc->rx_li_hist, skb)) {
+		/*
+		 * Step (3) of [RFC 3448, 6.1]: Recompute I_mean and, if I_mean
+		 * has decreased (resp. p has increased), send feedback now.
+		 */
+		do_feedback = CCID3_FBACK_PARAM_CHANGE;
+	}
+
+	/*
+	 * Check if the periodic once-per-RTT feedback is due; RFC 4342, 10.3
+	 */
+	if (SUB16(dccp_hdr(skb)->dccph_ccval, hc->rx_last_counter) > 3)
+		do_feedback = CCID3_FBACK_PERIODIC;
+
+update_records:
+	tfrc_rx_hist_add_packet(&hc->rx_hist, skb, ndp);
+
+done_receiving:
+	if (do_feedback)
+		ccid3_hc_rx_send_feedback(sk, skb, do_feedback);
+}
+
+static int ccid3_hc_rx_init(struct ccid *ccid, struct sock *sk)
+{
+	struct ccid3_hc_rx_sock *hc = ccid_priv(ccid);
+
+	hc->rx_state = TFRC_RSTATE_NO_DATA;
+	tfrc_lh_init(&hc->rx_li_hist);
+	return tfrc_rx_hist_alloc(&hc->rx_hist);
+}
+
+static void ccid3_hc_rx_exit(struct sock *sk)
+{
+	struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+
+	tfrc_rx_hist_purge(&hc->rx_hist);
+	tfrc_lh_cleanup(&hc->rx_li_hist);
+}
+
+static void ccid3_hc_rx_get_info(struct sock *sk, struct tcp_info *info)
+{
+	info->tcpi_ca_state = ccid3_hc_rx_sk(sk)->rx_state;
+	info->tcpi_options  |= TCPI_OPT_TIMESTAMPS;
+	info->tcpi_rcv_rtt  = ccid3_hc_rx_sk(sk)->rx_rtt;
+}
+
+static int ccid3_hc_rx_getsockopt(struct sock *sk, const int optname, int len,
+				  u32 __user *optval, int __user *optlen)
+{
+	const struct ccid3_hc_rx_sock *hc = ccid3_hc_rx_sk(sk);
+	struct tfrc_rx_info rx_info;
+	const void *val;
+
+	switch (optname) {
+	case DCCP_SOCKOPT_CCID_RX_INFO:
+		if (len < sizeof(rx_info))
+			return -EINVAL;
+		rx_info.tfrcrx_x_recv = hc->rx_x_recv;
+		rx_info.tfrcrx_rtt    = hc->rx_rtt;
+		rx_info.tfrcrx_p      = tfrc_invert_loss_event_rate(hc->rx_pinv);
+		len = sizeof(rx_info);
+		val = &rx_info;
+		break;
+	default:
+		return -ENOPROTOOPT;
+	}
+
+	if (put_user(len, optlen) || copy_to_user(optval, val, len))
+		return -EFAULT;
+
+	return 0;
+}
+
+struct ccid_operations ccid3_ops = {
+	.ccid_id		   = DCCPC_CCID3,
+	.ccid_name		   = "TCP-Friendly Rate Control",
+	.ccid_hc_tx_obj_size	   = sizeof(struct ccid3_hc_tx_sock),
+	.ccid_hc_tx_init	   = ccid3_hc_tx_init,
+	.ccid_hc_tx_exit	   = ccid3_hc_tx_exit,
+	.ccid_hc_tx_send_packet	   = ccid3_hc_tx_send_packet,
+	.ccid_hc_tx_packet_sent	   = ccid3_hc_tx_packet_sent,
+	.ccid_hc_tx_packet_recv	   = ccid3_hc_tx_packet_recv,
+	.ccid_hc_tx_parse_options  = ccid3_hc_tx_parse_options,
+	.ccid_hc_rx_obj_size	   = sizeof(struct ccid3_hc_rx_sock),
+	.ccid_hc_rx_init	   = ccid3_hc_rx_init,
+	.ccid_hc_rx_exit	   = ccid3_hc_rx_exit,
+	.ccid_hc_rx_insert_options = ccid3_hc_rx_insert_options,
+	.ccid_hc_rx_packet_recv	   = ccid3_hc_rx_packet_recv,
+	.ccid_hc_rx_get_info	   = ccid3_hc_rx_get_info,
+	.ccid_hc_tx_get_info	   = ccid3_hc_tx_get_info,
+	.ccid_hc_rx_getsockopt	   = ccid3_hc_rx_getsockopt,
+	.ccid_hc_tx_getsockopt	   = ccid3_hc_tx_getsockopt,
+};
+
+#ifdef CONFIG_IP_DCCP_CCID3_DEBUG
+module_param(ccid3_debug, bool, 0644);
+MODULE_PARM_DESC(ccid3_debug, "Enable CCID-3 debug messages");
+#endif
diff --git a/net/dccp/ccids/ccid3.h b/net/dccp/ccids/ccid3.h
new file mode 100644
index 000000000..02e0fc9f6
--- /dev/null
+++ b/net/dccp/ccids/ccid3.h
@@ -0,0 +1,148 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *
+ *  An implementation of the DCCP protocol
+ *
+ *  This code has been developed by the University of Waikato WAND
+ *  research group. For further information please see https://www.wand.net.nz/
+ *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
+ *
+ *  This code also uses code from Lulea University, rereleased as GPL by its
+ *  authors:
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ *
+ *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
+ *  and to make it work as a loadable module in the DCCP stack written by
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
+ *
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#ifndef _DCCP_CCID3_H_
+#define _DCCP_CCID3_H_
+
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/types.h>
+#include <linux/tfrc.h>
+#include "lib/tfrc.h"
+#include "../ccid.h"
+
+/* Two seconds as per RFC 5348, 4.2 */
+#define TFRC_INITIAL_TIMEOUT	   (2 * USEC_PER_SEC)
+
+/* Parameter t_mbi from [RFC 3448, 4.3]: backoff interval in seconds */
+#define TFRC_T_MBI		   64
+
+/*
+ * The t_delta parameter (RFC 5348, 8.3): delays of less than %USEC_PER_MSEC are
+ * rounded down to 0, since sk_reset_timer() here uses millisecond granularity.
+ * Hence we can use a constant t_delta = %USEC_PER_MSEC when HZ >= 500. A coarse
+ * resolution of HZ < 500 means that the error is below one timer tick (t_gran)
+ * when using the constant t_delta  =  t_gran / 2  =  %USEC_PER_SEC / (2 * HZ).
+ */
+#if (HZ >= 500)
+# define TFRC_T_DELTA		   USEC_PER_MSEC
+#else
+# define TFRC_T_DELTA		   (USEC_PER_SEC / (2 * HZ))
+#endif
+
+enum ccid3_options {
+	TFRC_OPT_LOSS_EVENT_RATE = 192,
+	TFRC_OPT_LOSS_INTERVALS	 = 193,
+	TFRC_OPT_RECEIVE_RATE	 = 194,
+};
+
+/* TFRC sender states */
+enum ccid3_hc_tx_states {
+	TFRC_SSTATE_NO_SENT = 1,
+	TFRC_SSTATE_NO_FBACK,
+	TFRC_SSTATE_FBACK,
+};
+
+/**
+ * struct ccid3_hc_tx_sock - CCID3 sender half-connection socket
+ * @tx_x:		  Current sending rate in 64 * bytes per second
+ * @tx_x_recv:		  Receive rate in 64 * bytes per second
+ * @tx_x_calc:		  Calculated rate in bytes per second
+ * @tx_rtt:		  Estimate of current round trip time in usecs
+ * @tx_p:		  Current loss event rate (0-1) scaled by 1000000
+ * @tx_s:		  Packet size in bytes
+ * @tx_t_rto:		  Nofeedback Timer setting in usecs
+ * @tx_t_ipi:		  Interpacket (send) interval (RFC 3448, 4.6) in usecs
+ * @tx_state:		  Sender state, one of %ccid3_hc_tx_states
+ * @tx_last_win_count:	  Last window counter sent
+ * @tx_t_last_win_count:  Timestamp of earliest packet
+ *			  with last_win_count value sent
+ * @tx_no_feedback_timer: Handle to no feedback timer
+ * @tx_t_ld:		  Time last doubled during slow start
+ * @tx_t_nom:		  Nominal send time of next packet
+ * @tx_hist:		  Packet history
+ */
+struct ccid3_hc_tx_sock {
+	u64				tx_x;
+	u64				tx_x_recv;
+	u32				tx_x_calc;
+	u32				tx_rtt;
+	u32				tx_p;
+	u32				tx_t_rto;
+	u32				tx_t_ipi;
+	u16				tx_s;
+	enum ccid3_hc_tx_states		tx_state:8;
+	u8				tx_last_win_count;
+	ktime_t				tx_t_last_win_count;
+	struct timer_list		tx_no_feedback_timer;
+	struct sock			*sk;
+	ktime_t				tx_t_ld;
+	ktime_t				tx_t_nom;
+	struct tfrc_tx_hist_entry	*tx_hist;
+};
+
+static inline struct ccid3_hc_tx_sock *ccid3_hc_tx_sk(const struct sock *sk)
+{
+	struct ccid3_hc_tx_sock *hctx = ccid_priv(dccp_sk(sk)->dccps_hc_tx_ccid);
+	BUG_ON(hctx == NULL);
+	return hctx;
+}
+
+/* TFRC receiver states */
+enum ccid3_hc_rx_states {
+	TFRC_RSTATE_NO_DATA = 1,
+	TFRC_RSTATE_DATA,
+};
+
+/**
+ * struct ccid3_hc_rx_sock - CCID3 receiver half-connection socket
+ * @rx_last_counter:	     Tracks window counter (RFC 4342, 8.1)
+ * @rx_state:		     Receiver state, one of %ccid3_hc_rx_states
+ * @rx_bytes_recv:	     Total sum of DCCP payload bytes
+ * @rx_x_recv:		     Receiver estimate of send rate (RFC 3448, sec. 4.3)
+ * @rx_rtt:		     Receiver estimate of RTT
+ * @rx_tstamp_last_feedback: Time at which last feedback was sent
+ * @rx_hist:		     Packet history (loss detection + RTT sampling)
+ * @rx_li_hist:		     Loss Interval database
+ * @rx_s:		     Received packet size in bytes
+ * @rx_pinv:		     Inverse of Loss Event Rate (RFC 4342, sec. 8.5)
+ */
+struct ccid3_hc_rx_sock {
+	u8				rx_last_counter:4;
+	enum ccid3_hc_rx_states		rx_state:8;
+	u32				rx_bytes_recv;
+	u32				rx_x_recv;
+	u32				rx_rtt;
+	ktime_t				rx_tstamp_last_feedback;
+	struct tfrc_rx_hist		rx_hist;
+	struct tfrc_loss_hist		rx_li_hist;
+	u16				rx_s;
+#define rx_pinv				rx_li_hist.i_mean
+};
+
+static inline struct ccid3_hc_rx_sock *ccid3_hc_rx_sk(const struct sock *sk)
+{
+	struct ccid3_hc_rx_sock *hcrx = ccid_priv(dccp_sk(sk)->dccps_hc_rx_ccid);
+	BUG_ON(hcrx == NULL);
+	return hcrx;
+}
+
+#endif /* _DCCP_CCID3_H_ */
diff --git a/net/dccp/ccids/lib/loss_interval.c b/net/dccp/ccids/lib/loss_interval.c
new file mode 100644
index 000000000..67abad695
--- /dev/null
+++ b/net/dccp/ccids/lib/loss_interval.c
@@ -0,0 +1,181 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#include <net/sock.h>
+#include "tfrc.h"
+
+static struct kmem_cache  *tfrc_lh_slab  __read_mostly;
+/* Loss Interval weights from [RFC 3448, 5.4], scaled by 10 */
+static const int tfrc_lh_weights[NINTERVAL] = { 10, 10, 10, 10, 8, 6, 4, 2 };
+
+/* implements LIFO semantics on the array */
+static inline u8 LIH_INDEX(const u8 ctr)
+{
+	return LIH_SIZE - 1 - (ctr % LIH_SIZE);
+}
+
+/* the `counter' index always points at the next entry to be populated */
+static inline struct tfrc_loss_interval *tfrc_lh_peek(struct tfrc_loss_hist *lh)
+{
+	return lh->counter ? lh->ring[LIH_INDEX(lh->counter - 1)] : NULL;
+}
+
+/* given i with 0 <= i <= k, return I_i as per the rfc3448bis notation */
+static inline u32 tfrc_lh_get_interval(struct tfrc_loss_hist *lh, const u8 i)
+{
+	BUG_ON(i >= lh->counter);
+	return lh->ring[LIH_INDEX(lh->counter - i - 1)]->li_length;
+}
+
+/*
+ *	On-demand allocation and de-allocation of entries
+ */
+static struct tfrc_loss_interval *tfrc_lh_demand_next(struct tfrc_loss_hist *lh)
+{
+	if (lh->ring[LIH_INDEX(lh->counter)] == NULL)
+		lh->ring[LIH_INDEX(lh->counter)] = kmem_cache_alloc(tfrc_lh_slab,
+								    GFP_ATOMIC);
+	return lh->ring[LIH_INDEX(lh->counter)];
+}
+
+void tfrc_lh_cleanup(struct tfrc_loss_hist *lh)
+{
+	if (!tfrc_lh_is_initialised(lh))
+		return;
+
+	for (lh->counter = 0; lh->counter < LIH_SIZE; lh->counter++)
+		if (lh->ring[LIH_INDEX(lh->counter)] != NULL) {
+			kmem_cache_free(tfrc_lh_slab,
+					lh->ring[LIH_INDEX(lh->counter)]);
+			lh->ring[LIH_INDEX(lh->counter)] = NULL;
+		}
+}
+
+static void tfrc_lh_calc_i_mean(struct tfrc_loss_hist *lh)
+{
+	u32 i_i, i_tot0 = 0, i_tot1 = 0, w_tot = 0;
+	int i, k = tfrc_lh_length(lh) - 1; /* k is as in rfc3448bis, 5.4 */
+
+	if (k <= 0)
+		return;
+
+	for (i = 0; i <= k; i++) {
+		i_i = tfrc_lh_get_interval(lh, i);
+
+		if (i < k) {
+			i_tot0 += i_i * tfrc_lh_weights[i];
+			w_tot  += tfrc_lh_weights[i];
+		}
+		if (i > 0)
+			i_tot1 += i_i * tfrc_lh_weights[i-1];
+	}
+
+	lh->i_mean = max(i_tot0, i_tot1) / w_tot;
+}
+
+/**
+ * tfrc_lh_update_i_mean  -  Update the `open' loss interval I_0
+ * For recomputing p: returns `true' if p > p_prev  <=>  1/p < 1/p_prev
+ */
+u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *skb)
+{
+	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh);
+	u32 old_i_mean = lh->i_mean;
+	s64 len;
+
+	if (cur == NULL)			/* not initialised */
+		return 0;
+
+	len = dccp_delta_seqno(cur->li_seqno, DCCP_SKB_CB(skb)->dccpd_seq) + 1;
+
+	if (len - (s64)cur->li_length <= 0)	/* duplicate or reordered */
+		return 0;
+
+	if (SUB16(dccp_hdr(skb)->dccph_ccval, cur->li_ccval) > 4)
+		/*
+		 * Implements RFC 4342, 10.2:
+		 * If a packet S (skb) exists whose seqno comes `after' the one
+		 * starting the current loss interval (cur) and if the modulo-16
+		 * distance from C(cur) to C(S) is greater than 4, consider all
+		 * subsequent packets as belonging to a new loss interval. This
+		 * test is necessary since CCVal may wrap between intervals.
+		 */
+		cur->li_is_closed = 1;
+
+	if (tfrc_lh_length(lh) == 1)		/* due to RFC 3448, 6.3.1 */
+		return 0;
+
+	cur->li_length = len;
+	tfrc_lh_calc_i_mean(lh);
+
+	return lh->i_mean < old_i_mean;
+}
+
+/* Determine if `new_loss' does begin a new loss interval [RFC 4342, 10.2] */
+static inline u8 tfrc_lh_is_new_loss(struct tfrc_loss_interval *cur,
+				     struct tfrc_rx_hist_entry *new_loss)
+{
+	return	dccp_delta_seqno(cur->li_seqno, new_loss->tfrchrx_seqno) > 0 &&
+		(cur->li_is_closed || SUB16(new_loss->tfrchrx_ccval, cur->li_ccval) > 4);
+}
+
+/**
+ * tfrc_lh_interval_add  -  Insert new record into the Loss Interval database
+ * @lh:		   Loss Interval database
+ * @rh:		   Receive history containing a fresh loss event
+ * @calc_first_li: Caller-dependent routine to compute length of first interval
+ * @sk:		   Used by @calc_first_li in caller-specific way (subtyping)
+ *
+ * Updates I_mean and returns 1 if a new interval has in fact been added to @lh.
+ */
+int tfrc_lh_interval_add(struct tfrc_loss_hist *lh, struct tfrc_rx_hist *rh,
+			 u32 (*calc_first_li)(struct sock *), struct sock *sk)
+{
+	struct tfrc_loss_interval *cur = tfrc_lh_peek(lh), *new;
+
+	if (cur != NULL && !tfrc_lh_is_new_loss(cur, tfrc_rx_hist_loss_prev(rh)))
+		return 0;
+
+	new = tfrc_lh_demand_next(lh);
+	if (unlikely(new == NULL)) {
+		DCCP_CRIT("Cannot allocate/add loss record.");
+		return 0;
+	}
+
+	new->li_seqno	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_seqno;
+	new->li_ccval	  = tfrc_rx_hist_loss_prev(rh)->tfrchrx_ccval;
+	new->li_is_closed = 0;
+
+	if (++lh->counter == 1)
+		lh->i_mean = new->li_length = (*calc_first_li)(sk);
+	else {
+		cur->li_length = dccp_delta_seqno(cur->li_seqno, new->li_seqno);
+		new->li_length = dccp_delta_seqno(new->li_seqno,
+				  tfrc_rx_hist_last_rcv(rh)->tfrchrx_seqno) + 1;
+		if (lh->counter > (2*LIH_SIZE))
+			lh->counter -= LIH_SIZE;
+
+		tfrc_lh_calc_i_mean(lh);
+	}
+	return 1;
+}
+
+int __init tfrc_li_init(void)
+{
+	tfrc_lh_slab = kmem_cache_create("tfrc_li_hist",
+					 sizeof(struct tfrc_loss_interval), 0,
+					 SLAB_HWCACHE_ALIGN, NULL);
+	return tfrc_lh_slab == NULL ? -ENOBUFS : 0;
+}
+
+void tfrc_li_exit(void)
+{
+	if (tfrc_lh_slab != NULL) {
+		kmem_cache_destroy(tfrc_lh_slab);
+		tfrc_lh_slab = NULL;
+	}
+}
diff --git a/net/dccp/ccids/lib/loss_interval.h b/net/dccp/ccids/lib/loss_interval.h
new file mode 100644
index 000000000..c3d95f85e
--- /dev/null
+++ b/net/dccp/ccids/lib/loss_interval.h
@@ -0,0 +1,69 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _DCCP_LI_HIST_
+#define _DCCP_LI_HIST_
+/*
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2005-7 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+#include <linux/ktime.h>
+#include <linux/list.h>
+#include <linux/slab.h>
+
+/*
+ * Number of loss intervals (RFC 4342, 8.6.1). The history size is one more than
+ * NINTERVAL, since the `open' interval I_0 is always stored as the first entry.
+ */
+#define NINTERVAL	8
+#define LIH_SIZE	(NINTERVAL + 1)
+
+/**
+ *  tfrc_loss_interval  -  Loss history record for TFRC-based protocols
+ *  @li_seqno:		Highest received seqno before the start of loss
+ *  @li_ccval:		The CCVal belonging to @li_seqno
+ *  @li_is_closed:	Whether @li_seqno is older than 1 RTT
+ *  @li_length:		Loss interval sequence length
+ */
+struct tfrc_loss_interval {
+	u64		 li_seqno:48,
+			 li_ccval:4,
+			 li_is_closed:1;
+	u32		 li_length;
+};
+
+/**
+ *  tfrc_loss_hist  -  Loss record database
+ *  @ring:	Circular queue managed in LIFO manner
+ *  @counter:	Current count of entries (can be more than %LIH_SIZE)
+ *  @i_mean:	Current Average Loss Interval [RFC 3448, 5.4]
+ */
+struct tfrc_loss_hist {
+	struct tfrc_loss_interval	*ring[LIH_SIZE];
+	u8				counter;
+	u32				i_mean;
+};
+
+static inline void tfrc_lh_init(struct tfrc_loss_hist *lh)
+{
+	memset(lh, 0, sizeof(struct tfrc_loss_hist));
+}
+
+static inline u8 tfrc_lh_is_initialised(struct tfrc_loss_hist *lh)
+{
+	return lh->counter > 0;
+}
+
+static inline u8 tfrc_lh_length(struct tfrc_loss_hist *lh)
+{
+	return min(lh->counter, (u8)LIH_SIZE);
+}
+
+struct tfrc_rx_hist;
+
+int tfrc_lh_interval_add(struct tfrc_loss_hist *, struct tfrc_rx_hist *,
+			 u32 (*first_li)(struct sock *), struct sock *);
+u8 tfrc_lh_update_i_mean(struct tfrc_loss_hist *lh, struct sk_buff *);
+void tfrc_lh_cleanup(struct tfrc_loss_hist *lh);
+
+#endif /* _DCCP_LI_HIST_ */
diff --git a/net/dccp/ccids/lib/packet_history.c b/net/dccp/ccids/lib/packet_history.c
new file mode 100644
index 000000000..af08e2df7
--- /dev/null
+++ b/net/dccp/ccids/lib/packet_history.c
@@ -0,0 +1,436 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-7 The University of Waikato, Hamilton, New Zealand.
+ *
+ *  An implementation of the DCCP protocol
+ *
+ *  This code has been developed by the University of Waikato WAND
+ *  research group. For further information please see https://www.wand.net.nz/
+ *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
+ *
+ *  This code also uses code from Lulea University, rereleased as GPL by its
+ *  authors:
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ *
+ *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
+ *  and to make it work as a loadable module in the DCCP stack written by
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
+ *
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/string.h>
+#include <linux/slab.h>
+#include "packet_history.h"
+#include "../../dccp.h"
+
+/*
+ * Transmitter History Routines
+ */
+static struct kmem_cache *tfrc_tx_hist_slab;
+
+int __init tfrc_tx_packet_history_init(void)
+{
+	tfrc_tx_hist_slab = kmem_cache_create("tfrc_tx_hist",
+					      sizeof(struct tfrc_tx_hist_entry),
+					      0, SLAB_HWCACHE_ALIGN, NULL);
+	return tfrc_tx_hist_slab == NULL ? -ENOBUFS : 0;
+}
+
+void tfrc_tx_packet_history_exit(void)
+{
+	if (tfrc_tx_hist_slab != NULL) {
+		kmem_cache_destroy(tfrc_tx_hist_slab);
+		tfrc_tx_hist_slab = NULL;
+	}
+}
+
+int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno)
+{
+	struct tfrc_tx_hist_entry *entry = kmem_cache_alloc(tfrc_tx_hist_slab, gfp_any());
+
+	if (entry == NULL)
+		return -ENOBUFS;
+	entry->seqno = seqno;
+	entry->stamp = ktime_get_real();
+	entry->next  = *headp;
+	*headp	     = entry;
+	return 0;
+}
+
+void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp)
+{
+	struct tfrc_tx_hist_entry *head = *headp;
+
+	while (head != NULL) {
+		struct tfrc_tx_hist_entry *next = head->next;
+
+		kmem_cache_free(tfrc_tx_hist_slab, head);
+		head = next;
+	}
+
+	*headp = NULL;
+}
+
+/*
+ *	Receiver History Routines
+ */
+static struct kmem_cache *tfrc_rx_hist_slab;
+
+int __init tfrc_rx_packet_history_init(void)
+{
+	tfrc_rx_hist_slab = kmem_cache_create("tfrc_rxh_cache",
+					      sizeof(struct tfrc_rx_hist_entry),
+					      0, SLAB_HWCACHE_ALIGN, NULL);
+	return tfrc_rx_hist_slab == NULL ? -ENOBUFS : 0;
+}
+
+void tfrc_rx_packet_history_exit(void)
+{
+	if (tfrc_rx_hist_slab != NULL) {
+		kmem_cache_destroy(tfrc_rx_hist_slab);
+		tfrc_rx_hist_slab = NULL;
+	}
+}
+
+static inline void tfrc_rx_hist_entry_from_skb(struct tfrc_rx_hist_entry *entry,
+					       const struct sk_buff *skb,
+					       const u64 ndp)
+{
+	const struct dccp_hdr *dh = dccp_hdr(skb);
+
+	entry->tfrchrx_seqno = DCCP_SKB_CB(skb)->dccpd_seq;
+	entry->tfrchrx_ccval = dh->dccph_ccval;
+	entry->tfrchrx_type  = dh->dccph_type;
+	entry->tfrchrx_ndp   = ndp;
+	entry->tfrchrx_tstamp = ktime_get_real();
+}
+
+void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h,
+			     const struct sk_buff *skb,
+			     const u64 ndp)
+{
+	struct tfrc_rx_hist_entry *entry = tfrc_rx_hist_last_rcv(h);
+
+	tfrc_rx_hist_entry_from_skb(entry, skb, ndp);
+}
+
+/* has the packet contained in skb been seen before? */
+int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb)
+{
+	const u64 seq = DCCP_SKB_CB(skb)->dccpd_seq;
+	int i;
+
+	if (dccp_delta_seqno(tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno, seq) <= 0)
+		return 1;
+
+	for (i = 1; i <= h->loss_count; i++)
+		if (tfrc_rx_hist_entry(h, i)->tfrchrx_seqno == seq)
+			return 1;
+
+	return 0;
+}
+
+static void tfrc_rx_hist_swap(struct tfrc_rx_hist *h, const u8 a, const u8 b)
+{
+	const u8 idx_a = tfrc_rx_hist_index(h, a),
+		 idx_b = tfrc_rx_hist_index(h, b);
+
+	swap(h->ring[idx_a], h->ring[idx_b]);
+}
+
+/*
+ * Private helper functions for loss detection.
+ *
+ * In the descriptions, `Si' refers to the sequence number of entry number i,
+ * whose NDP count is `Ni' (lower case is used for variables).
+ * Note: All __xxx_loss functions expect that a test against duplicates has been
+ *       performed already: the seqno of the skb must not be less than the seqno
+ *       of loss_prev; and it must not equal that of any valid history entry.
+ */
+static void __do_track_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u64 n1)
+{
+	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
+	    s1 = DCCP_SKB_CB(skb)->dccpd_seq;
+
+	if (!dccp_loss_free(s0, s1, n1)) {	/* gap between S0 and S1 */
+		h->loss_count = 1;
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n1);
+	}
+}
+
+static void __one_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n2)
+{
+	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
+	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+	    s2 = DCCP_SKB_CB(skb)->dccpd_seq;
+
+	if (likely(dccp_delta_seqno(s1, s2) > 0)) {	/* S1  <  S2 */
+		h->loss_count = 2;
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n2);
+		return;
+	}
+
+	/* S0  <  S2  <  S1 */
+
+	if (dccp_loss_free(s0, s2, n2)) {
+		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;
+
+		if (dccp_loss_free(s2, s1, n1)) {
+			/* hole is filled: S0, S2, and S1 are consecutive */
+			h->loss_count = 0;
+			h->loss_start = tfrc_rx_hist_index(h, 1);
+		} else
+			/* gap between S2 and S1: just update loss_prev */
+			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n2);
+
+	} else {	/* gap between S0 and S2 */
+		/*
+		 * Reorder history to insert S2 between S0 and S1
+		 */
+		tfrc_rx_hist_swap(h, 0, 3);
+		h->loss_start = tfrc_rx_hist_index(h, 3);
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n2);
+		h->loss_count = 2;
+	}
+}
+
+/* return 1 if a new loss event has been identified */
+static int __two_after_loss(struct tfrc_rx_hist *h, struct sk_buff *skb, u32 n3)
+{
+	u64 s0 = tfrc_rx_hist_loss_prev(h)->tfrchrx_seqno,
+	    s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
+	    s3 = DCCP_SKB_CB(skb)->dccpd_seq;
+
+	if (likely(dccp_delta_seqno(s2, s3) > 0)) {	/* S2  <  S3 */
+		h->loss_count = 3;
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 3), skb, n3);
+		return 1;
+	}
+
+	/* S3  <  S2 */
+
+	if (dccp_delta_seqno(s1, s3) > 0) {		/* S1  <  S3  <  S2 */
+		/*
+		 * Reorder history to insert S3 between S1 and S2
+		 */
+		tfrc_rx_hist_swap(h, 2, 3);
+		tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 2), skb, n3);
+		h->loss_count = 3;
+		return 1;
+	}
+
+	/* S0  <  S3  <  S1 */
+
+	if (dccp_loss_free(s0, s3, n3)) {
+		u64 n1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_ndp;
+
+		if (dccp_loss_free(s3, s1, n1)) {
+			/* hole between S0 and S1 filled by S3 */
+			u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp;
+
+			if (dccp_loss_free(s1, s2, n2)) {
+				/* entire hole filled by S0, S3, S1, S2 */
+				h->loss_start = tfrc_rx_hist_index(h, 2);
+				h->loss_count = 0;
+			} else {
+				/* gap remains between S1 and S2 */
+				h->loss_start = tfrc_rx_hist_index(h, 1);
+				h->loss_count = 1;
+			}
+
+		} else /* gap exists between S3 and S1, loss_count stays at 2 */
+			tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_loss_prev(h), skb, n3);
+
+		return 0;
+	}
+
+	/*
+	 * The remaining case:  S0  <  S3  <  S1  <  S2;  gap between S0 and S3
+	 * Reorder history to insert S3 between S0 and S1.
+	 */
+	tfrc_rx_hist_swap(h, 0, 3);
+	h->loss_start = tfrc_rx_hist_index(h, 3);
+	tfrc_rx_hist_entry_from_skb(tfrc_rx_hist_entry(h, 1), skb, n3);
+	h->loss_count = 3;
+
+	return 1;
+}
+
+/* recycle RX history records to continue loss detection if necessary */
+static void __three_after_loss(struct tfrc_rx_hist *h)
+{
+	/*
+	 * At this stage we know already that there is a gap between S0 and S1
+	 * (since S0 was the highest sequence number received before detecting
+	 * the loss). To recycle the loss record, it is	thus only necessary to
+	 * check for other possible gaps between S1/S2 and between S2/S3.
+	 */
+	u64 s1 = tfrc_rx_hist_entry(h, 1)->tfrchrx_seqno,
+	    s2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_seqno,
+	    s3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_seqno;
+	u64 n2 = tfrc_rx_hist_entry(h, 2)->tfrchrx_ndp,
+	    n3 = tfrc_rx_hist_entry(h, 3)->tfrchrx_ndp;
+
+	if (dccp_loss_free(s1, s2, n2)) {
+
+		if (dccp_loss_free(s2, s3, n3)) {
+			/* no gap between S2 and S3: entire hole is filled */
+			h->loss_start = tfrc_rx_hist_index(h, 3);
+			h->loss_count = 0;
+		} else {
+			/* gap between S2 and S3 */
+			h->loss_start = tfrc_rx_hist_index(h, 2);
+			h->loss_count = 1;
+		}
+
+	} else {	/* gap between S1 and S2 */
+		h->loss_start = tfrc_rx_hist_index(h, 1);
+		h->loss_count = 2;
+	}
+}
+
+/**
+ *  tfrc_rx_handle_loss  -  Loss detection and further processing
+ *  @h:		    The non-empty RX history object
+ *  @lh:	    Loss Intervals database to update
+ *  @skb:	    Currently received packet
+ *  @ndp:	    The NDP count belonging to @skb
+ *  @calc_first_li: Caller-dependent computation of first loss interval in @lh
+ *  @sk:	    Used by @calc_first_li (see tfrc_lh_interval_add)
+ *
+ *  Chooses action according to pending loss, updates LI database when a new
+ *  loss was detected, and does required post-processing. Returns 1 when caller
+ *  should send feedback, 0 otherwise.
+ *  Since it also takes care of reordering during loss detection and updates the
+ *  records accordingly, the caller should not perform any more RX history
+ *  operations when loss_count is greater than 0 after calling this function.
+ */
+int tfrc_rx_handle_loss(struct tfrc_rx_hist *h,
+			struct tfrc_loss_hist *lh,
+			struct sk_buff *skb, const u64 ndp,
+			u32 (*calc_first_li)(struct sock *), struct sock *sk)
+{
+	int is_new_loss = 0;
+
+	if (h->loss_count == 0) {
+		__do_track_loss(h, skb, ndp);
+	} else if (h->loss_count == 1) {
+		__one_after_loss(h, skb, ndp);
+	} else if (h->loss_count != 2) {
+		DCCP_BUG("invalid loss_count %d", h->loss_count);
+	} else if (__two_after_loss(h, skb, ndp)) {
+		/*
+		 * Update Loss Interval database and recycle RX records
+		 */
+		is_new_loss = tfrc_lh_interval_add(lh, h, calc_first_li, sk);
+		__three_after_loss(h);
+	}
+	return is_new_loss;
+}
+
+int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h)
+{
+	int i;
+
+	for (i = 0; i <= TFRC_NDUPACK; i++) {
+		h->ring[i] = kmem_cache_alloc(tfrc_rx_hist_slab, GFP_ATOMIC);
+		if (h->ring[i] == NULL)
+			goto out_free;
+	}
+
+	h->loss_count = h->loss_start = 0;
+	return 0;
+
+out_free:
+	while (i-- != 0) {
+		kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
+		h->ring[i] = NULL;
+	}
+	return -ENOBUFS;
+}
+
+void tfrc_rx_hist_purge(struct tfrc_rx_hist *h)
+{
+	int i;
+
+	for (i = 0; i <= TFRC_NDUPACK; ++i)
+		if (h->ring[i] != NULL) {
+			kmem_cache_free(tfrc_rx_hist_slab, h->ring[i]);
+			h->ring[i] = NULL;
+		}
+}
+
+/**
+ * tfrc_rx_hist_rtt_last_s - reference entry to compute RTT samples against
+ * @h:	The non-empty RX history object
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_rtt_last_s(const struct tfrc_rx_hist *h)
+{
+	return h->ring[0];
+}
+
+/**
+ * tfrc_rx_hist_rtt_prev_s - previously suitable (wrt rtt_last_s) RTT-sampling entry
+ * @h:	The non-empty RX history object
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_rtt_prev_s(const struct tfrc_rx_hist *h)
+{
+	return h->ring[h->rtt_sample_prev];
+}
+
+/**
+ * tfrc_rx_hist_sample_rtt  -  Sample RTT from timestamp / CCVal
+ * Based on ideas presented in RFC 4342, 8.1. Returns 0 if it was not able
+ * to compute a sample with given data - calling function should check this.
+ */
+u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb)
+{
+	u32 sample = 0,
+	    delta_v = SUB16(dccp_hdr(skb)->dccph_ccval,
+			    tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+
+	if (delta_v < 1 || delta_v > 4) {	/* unsuitable CCVal delta */
+		if (h->rtt_sample_prev == 2) {	/* previous candidate stored */
+			sample = SUB16(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
+				       tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+			if (sample)
+				sample = 4 / sample *
+				         ktime_us_delta(tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_tstamp,
+							tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp);
+			else    /*
+				 * FIXME: This condition is in principle not
+				 * possible but occurs when CCID is used for
+				 * two-way data traffic. I have tried to trace
+				 * it, but the cause does not seem to be here.
+				 */
+				DCCP_BUG("please report to dccp@vger.kernel.org"
+					 " => prev = %u, last = %u",
+					 tfrc_rx_hist_rtt_prev_s(h)->tfrchrx_ccval,
+					 tfrc_rx_hist_rtt_last_s(h)->tfrchrx_ccval);
+		} else if (delta_v < 1) {
+			h->rtt_sample_prev = 1;
+			goto keep_ref_for_next_time;
+		}
+
+	} else if (delta_v == 4) /* optimal match */
+		sample = ktime_to_us(net_timedelta(tfrc_rx_hist_rtt_last_s(h)->tfrchrx_tstamp));
+	else {			 /* suboptimal match */
+		h->rtt_sample_prev = 2;
+		goto keep_ref_for_next_time;
+	}
+
+	if (unlikely(sample > DCCP_SANE_RTT_MAX)) {
+		DCCP_WARN("RTT sample %u too large, using max\n", sample);
+		sample = DCCP_SANE_RTT_MAX;
+	}
+
+	h->rtt_sample_prev = 0;	       /* use current entry as next reference */
+keep_ref_for_next_time:
+
+	return sample;
+}
diff --git a/net/dccp/ccids/lib/packet_history.h b/net/dccp/ccids/lib/packet_history.h
new file mode 100644
index 000000000..159cc9326
--- /dev/null
+++ b/net/dccp/ccids/lib/packet_history.h
@@ -0,0 +1,142 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+/*
+ *  Packet RX/TX history data structures and routines for TFRC-based protocols.
+ *
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
+ *
+ *  This code has been developed by the University of Waikato WAND
+ *  research group. For further information please see https://www.wand.net.nz/
+ *  or e-mail Ian McDonald - ian.mcdonald@jandi.co.nz
+ *
+ *  This code also uses code from Lulea University, rereleased as GPL by its
+ *  authors:
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ *
+ *  Changes to meet Linux coding standards, to make it meet latest ccid3 draft
+ *  and to make it work as a loadable module in the DCCP stack written by
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>.
+ *
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#ifndef _DCCP_PKT_HIST_
+#define _DCCP_PKT_HIST_
+
+#include <linux/list.h>
+#include <linux/slab.h>
+#include "tfrc.h"
+
+/**
+ *  tfrc_tx_hist_entry  -  Simple singly-linked TX history list
+ *  @next:  next oldest entry (LIFO order)
+ *  @seqno: sequence number of this entry
+ *  @stamp: send time of packet with sequence number @seqno
+ */
+struct tfrc_tx_hist_entry {
+	struct tfrc_tx_hist_entry *next;
+	u64			  seqno;
+	ktime_t			  stamp;
+};
+
+static inline struct tfrc_tx_hist_entry *
+	tfrc_tx_hist_find_entry(struct tfrc_tx_hist_entry *head, u64 seqno)
+{
+	while (head != NULL && head->seqno != seqno)
+		head = head->next;
+	return head;
+}
+
+int tfrc_tx_hist_add(struct tfrc_tx_hist_entry **headp, u64 seqno);
+void tfrc_tx_hist_purge(struct tfrc_tx_hist_entry **headp);
+
+/* Subtraction a-b modulo-16, respects circular wrap-around */
+#define SUB16(a, b) (((a) + 16 - (b)) & 0xF)
+
+/* Number of packets to wait after a missing packet (RFC 4342, 6.1) */
+#define TFRC_NDUPACK 3
+
+/**
+ * tfrc_rx_hist_entry - Store information about a single received packet
+ * @tfrchrx_seqno:	DCCP packet sequence number
+ * @tfrchrx_ccval:	window counter value of packet (RFC 4342, 8.1)
+ * @tfrchrx_ndp:	the NDP count (if any) of the packet
+ * @tfrchrx_tstamp:	actual receive time of packet
+ */
+struct tfrc_rx_hist_entry {
+	u64		 tfrchrx_seqno:48,
+			 tfrchrx_ccval:4,
+			 tfrchrx_type:4;
+	u64		 tfrchrx_ndp:48;
+	ktime_t		 tfrchrx_tstamp;
+};
+
+/**
+ * tfrc_rx_hist  -  RX history structure for TFRC-based protocols
+ * @ring:		Packet history for RTT sampling and loss detection
+ * @loss_count:		Number of entries in circular history
+ * @loss_start:		Movable index (for loss detection)
+ * @rtt_sample_prev:	Used during RTT sampling, points to candidate entry
+ */
+struct tfrc_rx_hist {
+	struct tfrc_rx_hist_entry *ring[TFRC_NDUPACK + 1];
+	u8			  loss_count:2,
+				  loss_start:2;
+#define rtt_sample_prev		  loss_start
+};
+
+/**
+ * tfrc_rx_hist_index - index to reach n-th entry after loss_start
+ */
+static inline u8 tfrc_rx_hist_index(const struct tfrc_rx_hist *h, const u8 n)
+{
+	return (h->loss_start + n) & TFRC_NDUPACK;
+}
+
+/**
+ * tfrc_rx_hist_last_rcv - entry with highest-received-seqno so far
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_last_rcv(const struct tfrc_rx_hist *h)
+{
+	return h->ring[tfrc_rx_hist_index(h, h->loss_count)];
+}
+
+/**
+ * tfrc_rx_hist_entry - return the n-th history entry after loss_start
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_entry(const struct tfrc_rx_hist *h, const u8 n)
+{
+	return h->ring[tfrc_rx_hist_index(h, n)];
+}
+
+/**
+ * tfrc_rx_hist_loss_prev - entry with highest-received-seqno before loss was detected
+ */
+static inline struct tfrc_rx_hist_entry *
+			tfrc_rx_hist_loss_prev(const struct tfrc_rx_hist *h)
+{
+	return h->ring[h->loss_start];
+}
+
+/* indicate whether previously a packet was detected missing */
+static inline bool tfrc_rx_hist_loss_pending(const struct tfrc_rx_hist *h)
+{
+	return h->loss_count > 0;
+}
+
+void tfrc_rx_hist_add_packet(struct tfrc_rx_hist *h, const struct sk_buff *skb,
+			     const u64 ndp);
+
+int tfrc_rx_hist_duplicate(struct tfrc_rx_hist *h, struct sk_buff *skb);
+
+struct tfrc_loss_hist;
+int tfrc_rx_handle_loss(struct tfrc_rx_hist *h, struct tfrc_loss_hist *lh,
+			struct sk_buff *skb, const u64 ndp,
+			u32 (*first_li)(struct sock *sk), struct sock *sk);
+u32 tfrc_rx_hist_sample_rtt(struct tfrc_rx_hist *h, const struct sk_buff *skb);
+int tfrc_rx_hist_alloc(struct tfrc_rx_hist *h);
+void tfrc_rx_hist_purge(struct tfrc_rx_hist *h);
+
+#endif /* _DCCP_PKT_HIST_ */
diff --git a/net/dccp/ccids/lib/tfrc.c b/net/dccp/ccids/lib/tfrc.c
new file mode 100644
index 000000000..d7f265e1f
--- /dev/null
+++ b/net/dccp/ccids/lib/tfrc.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * TFRC library initialisation
+ *
+ * Copyright (c) 2007 The University of Aberdeen, Scotland, UK
+ * Copyright (c) 2007 Arnaldo Carvalho de Melo <acme@redhat.com>
+ */
+#include <linux/moduleparam.h>
+#include "tfrc.h"
+
+#ifdef CONFIG_IP_DCCP_TFRC_DEBUG
+bool tfrc_debug;
+module_param(tfrc_debug, bool, 0644);
+MODULE_PARM_DESC(tfrc_debug, "Enable TFRC debug messages");
+#endif
+
+int __init tfrc_lib_init(void)
+{
+	int rc = tfrc_li_init();
+
+	if (rc)
+		goto out;
+
+	rc = tfrc_tx_packet_history_init();
+	if (rc)
+		goto out_free_loss_intervals;
+
+	rc = tfrc_rx_packet_history_init();
+	if (rc)
+		goto out_free_tx_history;
+	return 0;
+
+out_free_tx_history:
+	tfrc_tx_packet_history_exit();
+out_free_loss_intervals:
+	tfrc_li_exit();
+out:
+	return rc;
+}
+
+void tfrc_lib_exit(void)
+{
+	tfrc_rx_packet_history_exit();
+	tfrc_tx_packet_history_exit();
+	tfrc_li_exit();
+}
diff --git a/net/dccp/ccids/lib/tfrc.h b/net/dccp/ccids/lib/tfrc.h
new file mode 100644
index 000000000..0a63e8750
--- /dev/null
+++ b/net/dccp/ccids/lib/tfrc.h
@@ -0,0 +1,73 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _TFRC_H_
+#define _TFRC_H_
+/*
+ *  Copyright (c) 2007   The University of Aberdeen, Scotland, UK
+ *  Copyright (c) 2005-6 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2005-6 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ *  Copyright (c) 2005   Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *  Copyright (c) 2003   Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ */
+#include <linux/types.h>
+#include <linux/math64.h>
+#include "../../dccp.h"
+
+/* internal includes that this library exports: */
+#include "loss_interval.h"
+#include "packet_history.h"
+
+#ifdef CONFIG_IP_DCCP_TFRC_DEBUG
+extern bool tfrc_debug;
+#define tfrc_pr_debug(format, a...)	DCCP_PR_DEBUG(tfrc_debug, format, ##a)
+#else
+#define tfrc_pr_debug(format, a...)
+#endif
+
+/* integer-arithmetic divisions of type (a * 1000000)/b */
+static inline u64 scaled_div(u64 a, u64 b)
+{
+	BUG_ON(b == 0);
+	return div64_u64(a * 1000000, b);
+}
+
+static inline u32 scaled_div32(u64 a, u64 b)
+{
+	u64 result = scaled_div(a, b);
+
+	if (result > UINT_MAX) {
+		DCCP_CRIT("Overflow: %llu/%llu > UINT_MAX",
+			  (unsigned long long)a, (unsigned long long)b);
+		return UINT_MAX;
+	}
+	return result;
+}
+
+/**
+ * tfrc_ewma  -  Exponentially weighted moving average
+ * @weight: Weight to be used as damping factor, in units of 1/10
+ */
+static inline u32 tfrc_ewma(const u32 avg, const u32 newval, const u8 weight)
+{
+	return avg ? (weight * avg + (10 - weight) * newval) / 10 : newval;
+}
+
+u32 tfrc_calc_x(u16 s, u32 R, u32 p);
+u32 tfrc_calc_x_reverse_lookup(u32 fvalue);
+u32 tfrc_invert_loss_event_rate(u32 loss_event_rate);
+
+int tfrc_tx_packet_history_init(void);
+void tfrc_tx_packet_history_exit(void);
+int tfrc_rx_packet_history_init(void);
+void tfrc_rx_packet_history_exit(void);
+
+int tfrc_li_init(void);
+void tfrc_li_exit(void);
+
+#ifdef CONFIG_IP_DCCP_TFRC_LIB
+int tfrc_lib_init(void);
+void tfrc_lib_exit(void);
+#else
+#define tfrc_lib_init() (0)
+#define tfrc_lib_exit()
+#endif
+#endif /* _TFRC_H_ */
diff --git a/net/dccp/ccids/lib/tfrc_equation.c b/net/dccp/ccids/lib/tfrc_equation.c
new file mode 100644
index 000000000..e2a337fa9
--- /dev/null
+++ b/net/dccp/ccids/lib/tfrc_equation.c
@@ -0,0 +1,701 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2005 The University of Waikato, Hamilton, New Zealand.
+ *  Copyright (c) 2005 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *  Copyright (c) 2003 Nils-Erik Mattsson, Joacim Haggmark, Magnus Erixzon
+ */
+
+#include <linux/module.h>
+#include "../../dccp.h"
+#include "tfrc.h"
+
+#define TFRC_CALC_X_ARRSIZE 500
+#define TFRC_CALC_X_SPLIT   50000	/* 0.05 * 1000000, details below */
+#define TFRC_SMALLEST_P	    (TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE)
+
+/*
+  TFRC TCP Reno Throughput Equation Lookup Table for f(p)
+
+  The following two-column lookup table implements a part of the TCP throughput
+  equation from [RFC 3448, sec. 3.1]:
+
+				     s
+  X_calc  =  --------------------------------------------------------------
+	     R * sqrt(2*b*p/3) + (3 * t_RTO * sqrt(3*b*p/8) * (p + 32*p^3))
+
+  Where:
+	X      is the transmit rate in bytes/second
+	s      is the packet size in bytes
+	R      is the round trip time in seconds
+	p      is the loss event rate, between 0 and 1.0, of the number of loss
+		      events as a fraction of the number of packets transmitted
+	t_RTO  is the TCP retransmission timeout value in seconds
+	b      is the number of packets acknowledged by a single TCP ACK
+
+  We can assume that b = 1 and t_RTO is 4 * R. The equation now becomes:
+
+				     s
+  X_calc  =  -------------------------------------------------------
+	     R * sqrt(p*2/3) + (12 * R * sqrt(p*3/8) * (p + 32*p^3))
+
+  which we can break down into:
+
+		      s
+	X_calc  =  ---------
+		    R * f(p)
+
+  where f(p) is given for 0 < p <= 1 by:
+
+	f(p)  =  sqrt(2*p/3) + 12 * sqrt(3*p/8) *  (p + 32*p^3)
+
+  Since this is kernel code, floating-point arithmetic is avoided in favour of
+  integer arithmetic. This means that nearly all fractional parameters are
+  scaled by 1000000:
+    * the parameters p and R
+    * the return result f(p)
+  The lookup table therefore actually tabulates the following function g(q):
+
+	g(q)  =  1000000 * f(q/1000000)
+
+  Hence, when p <= 1, q must be less than or equal to 1000000. To achieve finer
+  granularity for the practically more relevant case of small values of p (up to
+  5%), the second column is used; the first one ranges up to 100%.  This split
+  corresponds to the value of q = TFRC_CALC_X_SPLIT. At the same time this also
+  determines the smallest resolution possible with this lookup table:
+
+    TFRC_SMALLEST_P   =  TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE
+
+  The entire table is generated by:
+    for(i=0; i < TFRC_CALC_X_ARRSIZE; i++) {
+	lookup[i][0]  =  g((i+1) * 1000000/TFRC_CALC_X_ARRSIZE);
+	lookup[i][1]  =  g((i+1) * TFRC_CALC_X_SPLIT/TFRC_CALC_X_ARRSIZE);
+    }
+
+  With the given configuration, we have, with M = TFRC_CALC_X_ARRSIZE-1,
+    lookup[0][0]  =  g(1000000/(M+1))		= 1000000 * f(0.2%)
+    lookup[M][0]  =  g(1000000)			= 1000000 * f(100%)
+    lookup[0][1]  =  g(TFRC_SMALLEST_P)		= 1000000 * f(0.01%)
+    lookup[M][1]  =  g(TFRC_CALC_X_SPLIT)	= 1000000 * f(5%)
+
+  In summary, the two columns represent f(p) for the following ranges:
+    * The first column is for   0.002  <= p <= 1.0
+    * The second column is for  0.0001 <= p <= 0.05
+  Where the columns overlap, the second (finer-grained) is given preference,
+  i.e. the first column is used only for p >= 0.05.
+ */
+static const u32 tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE][2] = {
+	{     37172,   8172 },
+	{     53499,  11567 },
+	{     66664,  14180 },
+	{     78298,  16388 },
+	{     89021,  18339 },
+	{     99147,  20108 },
+	{    108858,  21738 },
+	{    118273,  23260 },
+	{    127474,  24693 },
+	{    136520,  26052 },
+	{    145456,  27348 },
+	{    154316,  28589 },
+	{    163130,  29783 },
+	{    171919,  30935 },
+	{    180704,  32049 },
+	{    189502,  33130 },
+	{    198328,  34180 },
+	{    207194,  35202 },
+	{    216114,  36198 },
+	{    225097,  37172 },
+	{    234153,  38123 },
+	{    243294,  39055 },
+	{    252527,  39968 },
+	{    261861,  40864 },
+	{    271305,  41743 },
+	{    280866,  42607 },
+	{    290553,  43457 },
+	{    300372,  44293 },
+	{    310333,  45117 },
+	{    320441,  45929 },
+	{    330705,  46729 },
+	{    341131,  47518 },
+	{    351728,  48297 },
+	{    362501,  49066 },
+	{    373460,  49826 },
+	{    384609,  50577 },
+	{    395958,  51320 },
+	{    407513,  52054 },
+	{    419281,  52780 },
+	{    431270,  53499 },
+	{    443487,  54211 },
+	{    455940,  54916 },
+	{    468635,  55614 },
+	{    481581,  56306 },
+	{    494785,  56991 },
+	{    508254,  57671 },
+	{    521996,  58345 },
+	{    536019,  59014 },
+	{    550331,  59677 },
+	{    564939,  60335 },
+	{    579851,  60988 },
+	{    595075,  61636 },
+	{    610619,  62279 },
+	{    626491,  62918 },
+	{    642700,  63553 },
+	{    659253,  64183 },
+	{    676158,  64809 },
+	{    693424,  65431 },
+	{    711060,  66050 },
+	{    729073,  66664 },
+	{    747472,  67275 },
+	{    766266,  67882 },
+	{    785464,  68486 },
+	{    805073,  69087 },
+	{    825103,  69684 },
+	{    845562,  70278 },
+	{    866460,  70868 },
+	{    887805,  71456 },
+	{    909606,  72041 },
+	{    931873,  72623 },
+	{    954614,  73202 },
+	{    977839,  73778 },
+	{   1001557,  74352 },
+	{   1025777,  74923 },
+	{   1050508,  75492 },
+	{   1075761,  76058 },
+	{   1101544,  76621 },
+	{   1127867,  77183 },
+	{   1154739,  77741 },
+	{   1182172,  78298 },
+	{   1210173,  78852 },
+	{   1238753,  79405 },
+	{   1267922,  79955 },
+	{   1297689,  80503 },
+	{   1328066,  81049 },
+	{   1359060,  81593 },
+	{   1390684,  82135 },
+	{   1422947,  82675 },
+	{   1455859,  83213 },
+	{   1489430,  83750 },
+	{   1523671,  84284 },
+	{   1558593,  84817 },
+	{   1594205,  85348 },
+	{   1630518,  85878 },
+	{   1667543,  86406 },
+	{   1705290,  86932 },
+	{   1743770,  87457 },
+	{   1782994,  87980 },
+	{   1822973,  88501 },
+	{   1863717,  89021 },
+	{   1905237,  89540 },
+	{   1947545,  90057 },
+	{   1990650,  90573 },
+	{   2034566,  91087 },
+	{   2079301,  91600 },
+	{   2124869,  92111 },
+	{   2171279,  92622 },
+	{   2218543,  93131 },
+	{   2266673,  93639 },
+	{   2315680,  94145 },
+	{   2365575,  94650 },
+	{   2416371,  95154 },
+	{   2468077,  95657 },
+	{   2520707,  96159 },
+	{   2574271,  96660 },
+	{   2628782,  97159 },
+	{   2684250,  97658 },
+	{   2740689,  98155 },
+	{   2798110,  98651 },
+	{   2856524,  99147 },
+	{   2915944,  99641 },
+	{   2976382, 100134 },
+	{   3037850, 100626 },
+	{   3100360, 101117 },
+	{   3163924, 101608 },
+	{   3228554, 102097 },
+	{   3294263, 102586 },
+	{   3361063, 103073 },
+	{   3428966, 103560 },
+	{   3497984, 104045 },
+	{   3568131, 104530 },
+	{   3639419, 105014 },
+	{   3711860, 105498 },
+	{   3785467, 105980 },
+	{   3860253, 106462 },
+	{   3936229, 106942 },
+	{   4013410, 107422 },
+	{   4091808, 107902 },
+	{   4171435, 108380 },
+	{   4252306, 108858 },
+	{   4334431, 109335 },
+	{   4417825, 109811 },
+	{   4502501, 110287 },
+	{   4588472, 110762 },
+	{   4675750, 111236 },
+	{   4764349, 111709 },
+	{   4854283, 112182 },
+	{   4945564, 112654 },
+	{   5038206, 113126 },
+	{   5132223, 113597 },
+	{   5227627, 114067 },
+	{   5324432, 114537 },
+	{   5422652, 115006 },
+	{   5522299, 115474 },
+	{   5623389, 115942 },
+	{   5725934, 116409 },
+	{   5829948, 116876 },
+	{   5935446, 117342 },
+	{   6042439, 117808 },
+	{   6150943, 118273 },
+	{   6260972, 118738 },
+	{   6372538, 119202 },
+	{   6485657, 119665 },
+	{   6600342, 120128 },
+	{   6716607, 120591 },
+	{   6834467, 121053 },
+	{   6953935, 121514 },
+	{   7075025, 121976 },
+	{   7197752, 122436 },
+	{   7322131, 122896 },
+	{   7448175, 123356 },
+	{   7575898, 123815 },
+	{   7705316, 124274 },
+	{   7836442, 124733 },
+	{   7969291, 125191 },
+	{   8103877, 125648 },
+	{   8240216, 126105 },
+	{   8378321, 126562 },
+	{   8518208, 127018 },
+	{   8659890, 127474 },
+	{   8803384, 127930 },
+	{   8948702, 128385 },
+	{   9095861, 128840 },
+	{   9244875, 129294 },
+	{   9395760, 129748 },
+	{   9548529, 130202 },
+	{   9703198, 130655 },
+	{   9859782, 131108 },
+	{  10018296, 131561 },
+	{  10178755, 132014 },
+	{  10341174, 132466 },
+	{  10505569, 132917 },
+	{  10671954, 133369 },
+	{  10840345, 133820 },
+	{  11010757, 134271 },
+	{  11183206, 134721 },
+	{  11357706, 135171 },
+	{  11534274, 135621 },
+	{  11712924, 136071 },
+	{  11893673, 136520 },
+	{  12076536, 136969 },
+	{  12261527, 137418 },
+	{  12448664, 137867 },
+	{  12637961, 138315 },
+	{  12829435, 138763 },
+	{  13023101, 139211 },
+	{  13218974, 139658 },
+	{  13417071, 140106 },
+	{  13617407, 140553 },
+	{  13819999, 140999 },
+	{  14024862, 141446 },
+	{  14232012, 141892 },
+	{  14441465, 142339 },
+	{  14653238, 142785 },
+	{  14867346, 143230 },
+	{  15083805, 143676 },
+	{  15302632, 144121 },
+	{  15523842, 144566 },
+	{  15747453, 145011 },
+	{  15973479, 145456 },
+	{  16201939, 145900 },
+	{  16432847, 146345 },
+	{  16666221, 146789 },
+	{  16902076, 147233 },
+	{  17140429, 147677 },
+	{  17381297, 148121 },
+	{  17624696, 148564 },
+	{  17870643, 149007 },
+	{  18119154, 149451 },
+	{  18370247, 149894 },
+	{  18623936, 150336 },
+	{  18880241, 150779 },
+	{  19139176, 151222 },
+	{  19400759, 151664 },
+	{  19665007, 152107 },
+	{  19931936, 152549 },
+	{  20201564, 152991 },
+	{  20473907, 153433 },
+	{  20748982, 153875 },
+	{  21026807, 154316 },
+	{  21307399, 154758 },
+	{  21590773, 155199 },
+	{  21876949, 155641 },
+	{  22165941, 156082 },
+	{  22457769, 156523 },
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+	{  28916423, 165328 },
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+	{  29630428, 166208 },
+	{  29992281, 166647 },
+	{  30357392, 167087 },
+	{  30725779, 167526 },
+	{  31097459, 167965 },
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+	{  33792976, 171041 },
+	{  34191663, 171480 },
+	{  34593807, 171919 },
+	{  34999428, 172358 },
+	{  35408544, 172797 },
+	{  35821174, 173237 },
+	{  36237335, 173676 },
+	{  36657047, 174115 },
+	{  37080329, 174554 },
+	{  37507197, 174993 },
+	{  37937673, 175433 },
+	{  38371773, 175872 },
+	{  38809517, 176311 },
+	{  39250924, 176750 },
+	{  39696012, 177190 },
+	{  40144800, 177629 },
+	{  40597308, 178068 },
+	{  41053553, 178507 },
+	{  41513554, 178947 },
+	{  41977332, 179386 },
+	{  42444904, 179825 },
+	{  42916290, 180265 },
+	{  43391509, 180704 },
+	{  43870579, 181144 },
+	{  44353520, 181583 },
+	{  44840352, 182023 },
+	{  45331092, 182462 },
+	{  45825761, 182902 },
+	{  46324378, 183342 },
+	{  46826961, 183781 },
+	{  47333531, 184221 },
+	{  47844106, 184661 },
+	{  48358706, 185101 },
+	{  48877350, 185541 },
+	{  49400058, 185981 },
+	{  49926849, 186421 },
+	{  50457743, 186861 },
+	{  50992759, 187301 },
+	{  51531916, 187741 },
+	{  52075235, 188181 },
+	{  52622735, 188622 },
+	{  53174435, 189062 },
+	{  53730355, 189502 },
+	{  54290515, 189943 },
+	{  54854935, 190383 },
+	{  55423634, 190824 },
+	{  55996633, 191265 },
+	{  56573950, 191706 },
+	{  57155606, 192146 },
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+	{  61967446, 195677 },
+	{  62589050, 196118 },
+	{  63215194, 196560 },
+	{  63845897, 197002 },
+	{  64481179, 197444 },
+	{  65121061, 197886 },
+	{  65765563, 198328 },
+	{  66414705, 198770 },
+	{  67068508, 199213 },
+	{  67726992, 199655 },
+	{  68390177, 200098 },
+	{  69058085, 200540 },
+	{  69730735, 200983 },
+	{  70408147, 201426 },
+	{  71090343, 201869 },
+	{  71777343, 202312 },
+	{  72469168, 202755 },
+	{  73165837, 203199 },
+	{  73867373, 203642 },
+	{  74573795, 204086 },
+	{  75285124, 204529 },
+	{  76001380, 204973 },
+	{  76722586, 205417 },
+	{  77448761, 205861 },
+	{  78179926, 206306 },
+	{  78916102, 206750 },
+	{  79657310, 207194 },
+	{  80403571, 207639 },
+	{  81154906, 208084 },
+	{  81911335, 208529 },
+	{  82672880, 208974 },
+	{  83439562, 209419 },
+	{  84211402, 209864 },
+	{  84988421, 210309 },
+	{  85770640, 210755 },
+	{  86558080, 211201 },
+	{  87350762, 211647 },
+	{  88148708, 212093 },
+	{  88951938, 212539 },
+	{  89760475, 212985 },
+	{  90574339, 213432 },
+	{  91393551, 213878 },
+	{  92218133, 214325 },
+	{  93048107, 214772 },
+	{  93883493, 215219 },
+	{  94724314, 215666 },
+	{  95570590, 216114 },
+	{  96422343, 216561 },
+	{  97279594, 217009 },
+	{  98142366, 217457 },
+	{  99010679, 217905 },
+	{  99884556, 218353 },
+	{ 100764018, 218801 },
+	{ 101649086, 219250 },
+	{ 102539782, 219698 },
+	{ 103436128, 220147 },
+	{ 104338146, 220596 },
+	{ 105245857, 221046 },
+	{ 106159284, 221495 },
+	{ 107078448, 221945 },
+	{ 108003370, 222394 },
+	{ 108934074, 222844 },
+	{ 109870580, 223294 },
+	{ 110812910, 223745 },
+	{ 111761087, 224195 },
+	{ 112715133, 224646 },
+	{ 113675069, 225097 },
+	{ 114640918, 225548 },
+	{ 115612702, 225999 },
+	{ 116590442, 226450 },
+	{ 117574162, 226902 },
+	{ 118563882, 227353 },
+	{ 119559626, 227805 },
+	{ 120561415, 228258 },
+	{ 121569272, 228710 },
+	{ 122583219, 229162 },
+	{ 123603278, 229615 },
+	{ 124629471, 230068 },
+	{ 125661822, 230521 },
+	{ 126700352, 230974 },
+	{ 127745083, 231428 },
+	{ 128796039, 231882 },
+	{ 129853241, 232336 },
+	{ 130916713, 232790 },
+	{ 131986475, 233244 },
+	{ 133062553, 233699 },
+	{ 134144966, 234153 },
+	{ 135233739, 234608 },
+	{ 136328894, 235064 },
+	{ 137430453, 235519 },
+	{ 138538440, 235975 },
+	{ 139652876, 236430 },
+	{ 140773786, 236886 },
+	{ 141901190, 237343 },
+	{ 143035113, 237799 },
+	{ 144175576, 238256 },
+	{ 145322604, 238713 },
+	{ 146476218, 239170 },
+	{ 147636442, 239627 },
+	{ 148803298, 240085 },
+	{ 149976809, 240542 },
+	{ 151156999, 241000 },
+	{ 152343890, 241459 },
+	{ 153537506, 241917 },
+	{ 154737869, 242376 },
+	{ 155945002, 242835 },
+	{ 157158929, 243294 },
+	{ 158379673, 243753 },
+	{ 159607257, 244213 },
+	{ 160841704, 244673 },
+	{ 162083037, 245133 },
+	{ 163331279, 245593 },
+	{ 164586455, 246054 },
+	{ 165848586, 246514 },
+	{ 167117696, 246975 },
+	{ 168393810, 247437 },
+	{ 169676949, 247898 },
+	{ 170967138, 248360 },
+	{ 172264399, 248822 },
+	{ 173568757, 249284 },
+	{ 174880235, 249747 },
+	{ 176198856, 250209 },
+	{ 177524643, 250672 },
+	{ 178857621, 251136 },
+	{ 180197813, 251599 },
+	{ 181545242, 252063 },
+	{ 182899933, 252527 },
+	{ 184261908, 252991 },
+	{ 185631191, 253456 },
+	{ 187007807, 253920 },
+	{ 188391778, 254385 },
+	{ 189783129, 254851 },
+	{ 191181884, 255316 },
+	{ 192588065, 255782 },
+	{ 194001698, 256248 },
+	{ 195422805, 256714 },
+	{ 196851411, 257181 },
+	{ 198287540, 257648 },
+	{ 199731215, 258115 },
+	{ 201182461, 258582 },
+	{ 202641302, 259050 },
+	{ 204107760, 259518 },
+	{ 205581862, 259986 },
+	{ 207063630, 260454 },
+	{ 208553088, 260923 },
+	{ 210050262, 261392 },
+	{ 211555174, 261861 },
+	{ 213067849, 262331 },
+	{ 214588312, 262800 },
+	{ 216116586, 263270 },
+	{ 217652696, 263741 },
+	{ 219196666, 264211 },
+	{ 220748520, 264682 },
+	{ 222308282, 265153 },
+	{ 223875978, 265625 },
+	{ 225451630, 266097 },
+	{ 227035265, 266569 },
+	{ 228626905, 267041 },
+	{ 230226576, 267514 },
+	{ 231834302, 267986 },
+	{ 233450107, 268460 },
+	{ 235074016, 268933 },
+	{ 236706054, 269407 },
+	{ 238346244, 269881 },
+	{ 239994613, 270355 },
+	{ 241651183, 270830 },
+	{ 243315981, 271305 }
+};
+
+/* return largest index i such that fval <= lookup[i][small] */
+static inline u32 tfrc_binsearch(u32 fval, u8 small)
+{
+	u32 try, low = 0, high = TFRC_CALC_X_ARRSIZE - 1;
+
+	while (low < high) {
+		try = (low + high) / 2;
+		if (fval <= tfrc_calc_x_lookup[try][small])
+			high = try;
+		else
+			low  = try + 1;
+	}
+	return high;
+}
+
+/**
+ * tfrc_calc_x - Calculate the send rate as per section 3.1 of RFC3448
+ * @s: packet size          in bytes
+ * @R: RTT                  scaled by 1000000   (i.e., microseconds)
+ * @p: loss ratio estimate  scaled by 1000000
+ *
+ * Returns X_calc           in bytes per second (not scaled).
+ */
+u32 tfrc_calc_x(u16 s, u32 R, u32 p)
+{
+	u16 index;
+	u32 f;
+	u64 result;
+
+	/* check against invalid parameters and divide-by-zero   */
+	BUG_ON(p >  1000000);		/* p must not exceed 100%   */
+	BUG_ON(p == 0);			/* f(0) = 0, divide by zero */
+	if (R == 0) {			/* possible  divide by zero */
+		DCCP_CRIT("WARNING: RTT is 0, returning maximum X_calc.");
+		return ~0U;
+	}
+
+	if (p <= TFRC_CALC_X_SPLIT)		{     /* 0.0000 < p <= 0.05   */
+		if (p < TFRC_SMALLEST_P) {	      /* 0.0000 < p <  0.0001 */
+			DCCP_WARN("Value of p (%d) below resolution. "
+				  "Substituting %d\n", p, TFRC_SMALLEST_P);
+			index = 0;
+		} else				      /* 0.0001 <= p <= 0.05  */
+			index =  p/TFRC_SMALLEST_P - 1;
+
+		f = tfrc_calc_x_lookup[index][1];
+
+	} else {				      /* 0.05   <  p <= 1.00  */
+		index = p/(1000000/TFRC_CALC_X_ARRSIZE) - 1;
+
+		f = tfrc_calc_x_lookup[index][0];
+	}
+
+	/*
+	 * Compute X = s/(R*f(p)) in bytes per second.
+	 * Since f(p) and R are both scaled by 1000000, we need to multiply by
+	 * 1000000^2. To avoid overflow, the result is computed in two stages.
+	 * This works under almost all reasonable operational conditions, for a
+	 * wide range of parameters. Yet, should some strange combination of
+	 * parameters result in overflow, the use of scaled_div32 will catch
+	 * this and return UINT_MAX - which is a logically adequate consequence.
+	 */
+	result = scaled_div(s, R);
+	return scaled_div32(result, f);
+}
+
+/**
+ *  tfrc_calc_x_reverse_lookup  -  try to find p given f(p)
+ *  @fvalue: function value to match, scaled by 1000000
+ *
+ *  Returns closest match for p, also scaled by 1000000
+ */
+u32 tfrc_calc_x_reverse_lookup(u32 fvalue)
+{
+	int index;
+
+	if (fvalue == 0)	/* f(p) = 0  whenever  p = 0 */
+		return 0;
+
+	/* Error cases. */
+	if (fvalue < tfrc_calc_x_lookup[0][1]) {
+		DCCP_WARN("fvalue %u smaller than resolution\n", fvalue);
+		return TFRC_SMALLEST_P;
+	}
+	if (fvalue > tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][0]) {
+		DCCP_WARN("fvalue %u exceeds bounds!\n", fvalue);
+		return 1000000;
+	}
+
+	if (fvalue <= tfrc_calc_x_lookup[TFRC_CALC_X_ARRSIZE - 1][1]) {
+		index = tfrc_binsearch(fvalue, 1);
+		return (index + 1) * TFRC_CALC_X_SPLIT / TFRC_CALC_X_ARRSIZE;
+	}
+
+	/* else ... it must be in the coarse-grained column */
+	index = tfrc_binsearch(fvalue, 0);
+	return (index + 1) * 1000000 / TFRC_CALC_X_ARRSIZE;
+}
+
+/**
+ * tfrc_invert_loss_event_rate  -  Compute p so that 10^6 corresponds to 100%
+ * When @loss_event_rate is large, there is a chance that p is truncated to 0.
+ * To avoid re-entering slow-start in that case, we set p = TFRC_SMALLEST_P > 0.
+ */
+u32 tfrc_invert_loss_event_rate(u32 loss_event_rate)
+{
+	if (loss_event_rate == UINT_MAX)		/* see RFC 4342, 8.5 */
+		return 0;
+	if (unlikely(loss_event_rate == 0))		/* map 1/0 into 100% */
+		return 1000000;
+	return max_t(u32, scaled_div(1, loss_event_rate), TFRC_SMALLEST_P);
+}
diff --git a/net/dccp/dccp.h b/net/dccp/dccp.h
new file mode 100644
index 000000000..0218eb169
--- /dev/null
+++ b/net/dccp/dccp.h
@@ -0,0 +1,488 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DCCP_H
+#define _DCCP_H
+/*
+ *  net/dccp/dccp.h
+ *
+ *  An implementation of the DCCP protocol
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ *  Copyright (c) 2005-6 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ */
+
+#include <linux/dccp.h>
+#include <linux/ktime.h>
+#include <net/snmp.h>
+#include <net/sock.h>
+#include <net/tcp.h>
+#include "ackvec.h"
+
+/*
+ * 	DCCP - specific warning and debugging macros.
+ */
+#define DCCP_WARN(fmt, ...)						\
+	net_warn_ratelimited("%s: " fmt, __func__, ##__VA_ARGS__)
+#define DCCP_CRIT(fmt, a...) printk(KERN_CRIT fmt " at %s:%d/%s()\n", ##a, \
+					 __FILE__, __LINE__, __func__)
+#define DCCP_BUG(a...)       do { DCCP_CRIT("BUG: " a); dump_stack(); } while(0)
+#define DCCP_BUG_ON(cond)    do { if (unlikely((cond) != 0))		   \
+				     DCCP_BUG("\"%s\" holds (exception!)", \
+					      __stringify(cond));          \
+			     } while (0)
+
+#define DCCP_PRINTK(enable, fmt, args...)	do { if (enable)	     \
+							printk(fmt, ##args); \
+						} while(0)
+#define DCCP_PR_DEBUG(enable, fmt, a...)	DCCP_PRINTK(enable, KERN_DEBUG \
+						  "%s: " fmt, __func__, ##a)
+
+#ifdef CONFIG_IP_DCCP_DEBUG
+extern bool dccp_debug;
+#define dccp_pr_debug(format, a...)	  DCCP_PR_DEBUG(dccp_debug, format, ##a)
+#define dccp_pr_debug_cat(format, a...)   DCCP_PRINTK(dccp_debug, format, ##a)
+#define dccp_debug(fmt, a...)		  dccp_pr_debug_cat(KERN_DEBUG fmt, ##a)
+#else
+#define dccp_pr_debug(format, a...)	  do {} while (0)
+#define dccp_pr_debug_cat(format, a...)	  do {} while (0)
+#define dccp_debug(format, a...)	  do {} while (0)
+#endif
+
+extern struct inet_hashinfo dccp_hashinfo;
+
+DECLARE_PER_CPU(unsigned int, dccp_orphan_count);
+
+void dccp_time_wait(struct sock *sk, int state, int timeo);
+
+/*
+ *  Set safe upper bounds for header and option length. Since Data Offset is 8
+ *  bits (RFC 4340, sec. 5.1), the total header length can never be more than
+ *  4 * 255 = 1020 bytes. The largest possible header length is 28 bytes (X=1):
+ *    - DCCP-Response with ACK Subheader and 4 bytes of Service code      OR
+ *    - DCCP-Reset    with ACK Subheader and 4 bytes of Reset Code fields
+ *  Hence a safe upper bound for the maximum option length is 1020-28 = 992
+ */
+#define MAX_DCCP_SPECIFIC_HEADER (255 * sizeof(uint32_t))
+#define DCCP_MAX_PACKET_HDR 28
+#define DCCP_MAX_OPT_LEN (MAX_DCCP_SPECIFIC_HEADER - DCCP_MAX_PACKET_HDR)
+#define MAX_DCCP_HEADER (MAX_DCCP_SPECIFIC_HEADER + MAX_HEADER)
+
+/* Upper bound for initial feature-negotiation overhead (padded to 32 bits) */
+#define DCCP_FEATNEG_OVERHEAD	 (32 * sizeof(uint32_t))
+
+#define DCCP_TIMEWAIT_LEN (60 * HZ) /* how long to wait to destroy TIME-WAIT
+				     * state, about 60 seconds */
+
+/* RFC 1122, 4.2.3.1 initial RTO value */
+#define DCCP_TIMEOUT_INIT ((unsigned int)(3 * HZ))
+
+/*
+ * The maximum back-off value for retransmissions. This is needed for
+ *  - retransmitting client-Requests (sec. 8.1.1),
+ *  - retransmitting Close/CloseReq when closing (sec. 8.3),
+ *  - feature-negotiation retransmission (sec. 6.6.3),
+ *  - Acks in client-PARTOPEN state (sec. 8.1.5).
+ */
+#define DCCP_RTO_MAX ((unsigned int)(64 * HZ))
+
+/*
+ * RTT sampling: sanity bounds and fallback RTT value from RFC 4340, section 3.4
+ */
+#define DCCP_SANE_RTT_MIN	100
+#define DCCP_FALLBACK_RTT	(USEC_PER_SEC / 5)
+#define DCCP_SANE_RTT_MAX	(3 * USEC_PER_SEC)
+
+/* sysctl variables for DCCP */
+extern int  sysctl_dccp_request_retries;
+extern int  sysctl_dccp_retries1;
+extern int  sysctl_dccp_retries2;
+extern int  sysctl_dccp_tx_qlen;
+extern int  sysctl_dccp_sync_ratelimit;
+
+/*
+ *	48-bit sequence number arithmetic (signed and unsigned)
+ */
+#define INT48_MIN	  0x800000000000LL		/* 2^47	    */
+#define UINT48_MAX	  0xFFFFFFFFFFFFLL		/* 2^48 - 1 */
+#define COMPLEMENT48(x)	 (0x1000000000000LL - (x))	/* 2^48 - x */
+#define TO_SIGNED48(x)	 (((x) < INT48_MIN)? (x) : -COMPLEMENT48( (x)))
+#define TO_UNSIGNED48(x) (((x) >= 0)?	     (x) :  COMPLEMENT48(-(x)))
+#define ADD48(a, b)	 (((a) + (b)) & UINT48_MAX)
+#define SUB48(a, b)	 ADD48((a), COMPLEMENT48(b))
+
+static inline void dccp_inc_seqno(u64 *seqno)
+{
+	*seqno = ADD48(*seqno, 1);
+}
+
+/* signed mod-2^48 distance: pos. if seqno1 < seqno2, neg. if seqno1 > seqno2 */
+static inline s64 dccp_delta_seqno(const u64 seqno1, const u64 seqno2)
+{
+	u64 delta = SUB48(seqno2, seqno1);
+
+	return TO_SIGNED48(delta);
+}
+
+/* is seq1 < seq2 ? */
+static inline int before48(const u64 seq1, const u64 seq2)
+{
+	return (s64)((seq2 << 16) - (seq1 << 16)) > 0;
+}
+
+/* is seq1 > seq2 ? */
+#define after48(seq1, seq2)	before48(seq2, seq1)
+
+/* is seq2 <= seq1 <= seq3 ? */
+static inline int between48(const u64 seq1, const u64 seq2, const u64 seq3)
+{
+	return (seq3 << 16) - (seq2 << 16) >= (seq1 << 16) - (seq2 << 16);
+}
+
+static inline u64 max48(const u64 seq1, const u64 seq2)
+{
+	return after48(seq1, seq2) ? seq1 : seq2;
+}
+
+/**
+ * dccp_loss_count - Approximate the number of lost data packets in a burst loss
+ * @s1:  last known sequence number before the loss ('hole')
+ * @s2:  first sequence number seen after the 'hole'
+ * @ndp: NDP count on packet with sequence number @s2
+ */
+static inline u64 dccp_loss_count(const u64 s1, const u64 s2, const u64 ndp)
+{
+	s64 delta = dccp_delta_seqno(s1, s2);
+
+	WARN_ON(delta < 0);
+	delta -= ndp + 1;
+
+	return delta > 0 ? delta : 0;
+}
+
+/**
+ * dccp_loss_free - Evaluate condition for data loss from RFC 4340, 7.7.1
+ */
+static inline bool dccp_loss_free(const u64 s1, const u64 s2, const u64 ndp)
+{
+	return dccp_loss_count(s1, s2, ndp) == 0;
+}
+
+enum {
+	DCCP_MIB_NUM = 0,
+	DCCP_MIB_ACTIVEOPENS,			/* ActiveOpens */
+	DCCP_MIB_ESTABRESETS,			/* EstabResets */
+	DCCP_MIB_CURRESTAB,			/* CurrEstab */
+	DCCP_MIB_OUTSEGS,			/* OutSegs */
+	DCCP_MIB_OUTRSTS,
+	DCCP_MIB_ABORTONTIMEOUT,
+	DCCP_MIB_TIMEOUTS,
+	DCCP_MIB_ABORTFAILED,
+	DCCP_MIB_PASSIVEOPENS,
+	DCCP_MIB_ATTEMPTFAILS,
+	DCCP_MIB_OUTDATAGRAMS,
+	DCCP_MIB_INERRS,
+	DCCP_MIB_OPTMANDATORYERROR,
+	DCCP_MIB_INVALIDOPT,
+	__DCCP_MIB_MAX
+};
+
+#define DCCP_MIB_MAX	__DCCP_MIB_MAX
+struct dccp_mib {
+	unsigned long	mibs[DCCP_MIB_MAX];
+};
+
+DECLARE_SNMP_STAT(struct dccp_mib, dccp_statistics);
+#define DCCP_INC_STATS(field)	SNMP_INC_STATS(dccp_statistics, field)
+#define __DCCP_INC_STATS(field)	__SNMP_INC_STATS(dccp_statistics, field)
+#define DCCP_DEC_STATS(field)	SNMP_DEC_STATS(dccp_statistics, field)
+
+/*
+ * 	Checksumming routines
+ */
+static inline unsigned int dccp_csum_coverage(const struct sk_buff *skb)
+{
+	const struct dccp_hdr* dh = dccp_hdr(skb);
+
+	if (dh->dccph_cscov == 0)
+		return skb->len;
+	return (dh->dccph_doff + dh->dccph_cscov - 1) * sizeof(u32);
+}
+
+static inline void dccp_csum_outgoing(struct sk_buff *skb)
+{
+	unsigned int cov = dccp_csum_coverage(skb);
+
+	if (cov >= skb->len)
+		dccp_hdr(skb)->dccph_cscov = 0;
+
+	skb->csum = skb_checksum(skb, 0, (cov > skb->len)? skb->len : cov, 0);
+}
+
+void dccp_v4_send_check(struct sock *sk, struct sk_buff *skb);
+
+int dccp_retransmit_skb(struct sock *sk);
+
+void dccp_send_ack(struct sock *sk);
+void dccp_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
+			 struct request_sock *rsk);
+
+void dccp_send_sync(struct sock *sk, const u64 seq,
+		    const enum dccp_pkt_type pkt_type);
+
+/*
+ * TX Packet Dequeueing Interface
+ */
+void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb);
+bool dccp_qpolicy_full(struct sock *sk);
+void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb);
+struct sk_buff *dccp_qpolicy_top(struct sock *sk);
+struct sk_buff *dccp_qpolicy_pop(struct sock *sk);
+bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param);
+
+/*
+ * TX Packet Output and TX Timers
+ */
+void dccp_write_xmit(struct sock *sk);
+void dccp_write_space(struct sock *sk);
+void dccp_flush_write_queue(struct sock *sk, long *time_budget);
+
+void dccp_init_xmit_timers(struct sock *sk);
+static inline void dccp_clear_xmit_timers(struct sock *sk)
+{
+	inet_csk_clear_xmit_timers(sk);
+}
+
+unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu);
+
+const char *dccp_packet_name(const int type);
+
+void dccp_set_state(struct sock *sk, const int state);
+void dccp_done(struct sock *sk);
+
+int dccp_reqsk_init(struct request_sock *rq, struct dccp_sock const *dp,
+		    struct sk_buff const *skb);
+
+int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb);
+
+struct sock *dccp_create_openreq_child(const struct sock *sk,
+				       const struct request_sock *req,
+				       const struct sk_buff *skb);
+
+int dccp_v4_do_rcv(struct sock *sk, struct sk_buff *skb);
+
+struct sock *dccp_v4_request_recv_sock(const struct sock *sk, struct sk_buff *skb,
+				       struct request_sock *req,
+				       struct dst_entry *dst,
+				       struct request_sock *req_unhash,
+				       bool *own_req);
+struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
+			    struct request_sock *req);
+
+int dccp_child_process(struct sock *parent, struct sock *child,
+		       struct sk_buff *skb);
+int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
+			   struct dccp_hdr *dh, unsigned int len);
+int dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
+			 const struct dccp_hdr *dh, const unsigned int len);
+
+void dccp_destruct_common(struct sock *sk);
+int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized);
+void dccp_destroy_sock(struct sock *sk);
+
+void dccp_close(struct sock *sk, long timeout);
+struct sk_buff *dccp_make_response(const struct sock *sk, struct dst_entry *dst,
+				   struct request_sock *req);
+
+int dccp_connect(struct sock *sk);
+int dccp_disconnect(struct sock *sk, int flags);
+int dccp_getsockopt(struct sock *sk, int level, int optname,
+		    char __user *optval, int __user *optlen);
+int dccp_setsockopt(struct sock *sk, int level, int optname,
+		    sockptr_t optval, unsigned int optlen);
+int dccp_ioctl(struct sock *sk, int cmd, unsigned long arg);
+int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size);
+int dccp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
+		 int flags, int *addr_len);
+void dccp_shutdown(struct sock *sk, int how);
+int inet_dccp_listen(struct socket *sock, int backlog);
+__poll_t dccp_poll(struct file *file, struct socket *sock,
+		       poll_table *wait);
+int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len);
+void dccp_req_err(struct sock *sk, u64 seq);
+
+struct sk_buff *dccp_ctl_make_reset(struct sock *sk, struct sk_buff *skb);
+int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code);
+void dccp_send_close(struct sock *sk, const int active);
+int dccp_invalid_packet(struct sk_buff *skb);
+u32 dccp_sample_rtt(struct sock *sk, long delta);
+
+static inline bool dccp_bad_service_code(const struct sock *sk,
+					const __be32 service)
+{
+	const struct dccp_sock *dp = dccp_sk(sk);
+
+	if (dp->dccps_service == service)
+		return false;
+	return !dccp_list_has_service(dp->dccps_service_list, service);
+}
+
+/**
+ * dccp_skb_cb  -  DCCP per-packet control information
+ * @dccpd_type: one of %dccp_pkt_type (or unknown)
+ * @dccpd_ccval: CCVal field (5.1), see e.g. RFC 4342, 8.1
+ * @dccpd_reset_code: one of %dccp_reset_codes
+ * @dccpd_reset_data: Data1..3 fields (depend on @dccpd_reset_code)
+ * @dccpd_opt_len: total length of all options (5.8) in the packet
+ * @dccpd_seq: sequence number
+ * @dccpd_ack_seq: acknowledgment number subheader field value
+ *
+ * This is used for transmission as well as for reception.
+ */
+struct dccp_skb_cb {
+	union {
+		struct inet_skb_parm	h4;
+#if IS_ENABLED(CONFIG_IPV6)
+		struct inet6_skb_parm	h6;
+#endif
+	} header;
+	__u8  dccpd_type:4;
+	__u8  dccpd_ccval:4;
+	__u8  dccpd_reset_code,
+	      dccpd_reset_data[3];
+	__u16 dccpd_opt_len;
+	__u64 dccpd_seq;
+	__u64 dccpd_ack_seq;
+};
+
+#define DCCP_SKB_CB(__skb) ((struct dccp_skb_cb *)&((__skb)->cb[0]))
+
+/* RFC 4340, sec. 7.7 */
+static inline int dccp_non_data_packet(const struct sk_buff *skb)
+{
+	const __u8 type = DCCP_SKB_CB(skb)->dccpd_type;
+
+	return type == DCCP_PKT_ACK	 ||
+	       type == DCCP_PKT_CLOSE	 ||
+	       type == DCCP_PKT_CLOSEREQ ||
+	       type == DCCP_PKT_RESET	 ||
+	       type == DCCP_PKT_SYNC	 ||
+	       type == DCCP_PKT_SYNCACK;
+}
+
+/* RFC 4340, sec. 7.7 */
+static inline int dccp_data_packet(const struct sk_buff *skb)
+{
+	const __u8 type = DCCP_SKB_CB(skb)->dccpd_type;
+
+	return type == DCCP_PKT_DATA	 ||
+	       type == DCCP_PKT_DATAACK  ||
+	       type == DCCP_PKT_REQUEST  ||
+	       type == DCCP_PKT_RESPONSE;
+}
+
+static inline int dccp_packet_without_ack(const struct sk_buff *skb)
+{
+	const __u8 type = DCCP_SKB_CB(skb)->dccpd_type;
+
+	return type == DCCP_PKT_DATA || type == DCCP_PKT_REQUEST;
+}
+
+#define DCCP_PKT_WITHOUT_ACK_SEQ (UINT48_MAX << 2)
+
+static inline void dccp_hdr_set_seq(struct dccp_hdr *dh, const u64 gss)
+{
+	struct dccp_hdr_ext *dhx = (struct dccp_hdr_ext *)((void *)dh +
+							   sizeof(*dh));
+	dh->dccph_seq2 = 0;
+	dh->dccph_seq = htons((gss >> 32) & 0xfffff);
+	dhx->dccph_seq_low = htonl(gss & 0xffffffff);
+}
+
+static inline void dccp_hdr_set_ack(struct dccp_hdr_ack_bits *dhack,
+				    const u64 gsr)
+{
+	dhack->dccph_reserved1 = 0;
+	dhack->dccph_ack_nr_high = htons(gsr >> 32);
+	dhack->dccph_ack_nr_low  = htonl(gsr & 0xffffffff);
+}
+
+static inline void dccp_update_gsr(struct sock *sk, u64 seq)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	if (after48(seq, dp->dccps_gsr))
+		dp->dccps_gsr = seq;
+	/* Sequence validity window depends on remote Sequence Window (7.5.1) */
+	dp->dccps_swl = SUB48(ADD48(dp->dccps_gsr, 1), dp->dccps_r_seq_win / 4);
+	/*
+	 * Adjust SWL so that it is not below ISR. In contrast to RFC 4340,
+	 * 7.5.1 we perform this check beyond the initial handshake: W/W' are
+	 * always > 32, so for the first W/W' packets in the lifetime of a
+	 * connection we always have to adjust SWL.
+	 * A second reason why we are doing this is that the window depends on
+	 * the feature-remote value of Sequence Window: nothing stops the peer
+	 * from updating this value while we are busy adjusting SWL for the
+	 * first W packets (we would have to count from scratch again then).
+	 * Therefore it is safer to always make sure that the Sequence Window
+	 * is not artificially extended by a peer who grows SWL downwards by
+	 * continually updating the feature-remote Sequence-Window.
+	 * If sequence numbers wrap it is bad luck. But that will take a while
+	 * (48 bit), and this measure prevents Sequence-number attacks.
+	 */
+	if (before48(dp->dccps_swl, dp->dccps_isr))
+		dp->dccps_swl = dp->dccps_isr;
+	dp->dccps_swh = ADD48(dp->dccps_gsr, (3 * dp->dccps_r_seq_win) / 4);
+}
+
+static inline void dccp_update_gss(struct sock *sk, u64 seq)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	dp->dccps_gss = seq;
+	/* Ack validity window depends on local Sequence Window value (7.5.1) */
+	dp->dccps_awl = SUB48(ADD48(dp->dccps_gss, 1), dp->dccps_l_seq_win);
+	/* Adjust AWL so that it is not below ISS - see comment above for SWL */
+	if (before48(dp->dccps_awl, dp->dccps_iss))
+		dp->dccps_awl = dp->dccps_iss;
+	dp->dccps_awh = dp->dccps_gss;
+}
+
+static inline int dccp_ackvec_pending(const struct sock *sk)
+{
+	return dccp_sk(sk)->dccps_hc_rx_ackvec != NULL &&
+	       !dccp_ackvec_is_empty(dccp_sk(sk)->dccps_hc_rx_ackvec);
+}
+
+static inline int dccp_ack_pending(const struct sock *sk)
+{
+	return dccp_ackvec_pending(sk) || inet_csk_ack_scheduled(sk);
+}
+
+int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val);
+int dccp_feat_finalise_settings(struct dccp_sock *dp);
+int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq);
+int dccp_feat_insert_opts(struct dccp_sock*, struct dccp_request_sock*,
+			  struct sk_buff *skb);
+int dccp_feat_activate_values(struct sock *sk, struct list_head *fn);
+void dccp_feat_list_purge(struct list_head *fn_list);
+
+int dccp_insert_options(struct sock *sk, struct sk_buff *skb);
+int dccp_insert_options_rsk(struct dccp_request_sock *, struct sk_buff *);
+u32 dccp_timestamp(void);
+void dccp_timestamping_init(void);
+int dccp_insert_option(struct sk_buff *skb, unsigned char option,
+		       const void *value, unsigned char len);
+
+#ifdef CONFIG_SYSCTL
+int dccp_sysctl_init(void);
+void dccp_sysctl_exit(void);
+#else
+static inline int dccp_sysctl_init(void)
+{
+	return 0;
+}
+
+static inline void dccp_sysctl_exit(void)
+{
+}
+#endif
+
+#endif /* _DCCP_H */
diff --git a/net/dccp/diag.c b/net/dccp/diag.c
new file mode 100644
index 000000000..8a82c5a2c
--- /dev/null
+++ b/net/dccp/diag.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/diag.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@mandriva.com>
+ */
+
+
+#include <linux/module.h>
+#include <linux/inet_diag.h>
+
+#include "ccid.h"
+#include "dccp.h"
+
+static void dccp_get_info(struct sock *sk, struct tcp_info *info)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+
+	memset(info, 0, sizeof(*info));
+
+	info->tcpi_state	= sk->sk_state;
+	info->tcpi_retransmits	= icsk->icsk_retransmits;
+	info->tcpi_probes	= icsk->icsk_probes_out;
+	info->tcpi_backoff	= icsk->icsk_backoff;
+	info->tcpi_pmtu		= icsk->icsk_pmtu_cookie;
+
+	if (dp->dccps_hc_rx_ackvec != NULL)
+		info->tcpi_options |= TCPI_OPT_SACK;
+
+	if (dp->dccps_hc_rx_ccid != NULL)
+		ccid_hc_rx_get_info(dp->dccps_hc_rx_ccid, sk, info);
+
+	if (dp->dccps_hc_tx_ccid != NULL)
+		ccid_hc_tx_get_info(dp->dccps_hc_tx_ccid, sk, info);
+}
+
+static void dccp_diag_get_info(struct sock *sk, struct inet_diag_msg *r,
+			       void *_info)
+{
+	r->idiag_rqueue = r->idiag_wqueue = 0;
+
+	if (_info != NULL)
+		dccp_get_info(sk, _info);
+}
+
+static void dccp_diag_dump(struct sk_buff *skb, struct netlink_callback *cb,
+			   const struct inet_diag_req_v2 *r)
+{
+	inet_diag_dump_icsk(&dccp_hashinfo, skb, cb, r);
+}
+
+static int dccp_diag_dump_one(struct netlink_callback *cb,
+			      const struct inet_diag_req_v2 *req)
+{
+	return inet_diag_dump_one_icsk(&dccp_hashinfo, cb, req);
+}
+
+static const struct inet_diag_handler dccp_diag_handler = {
+	.dump		 = dccp_diag_dump,
+	.dump_one	 = dccp_diag_dump_one,
+	.idiag_get_info	 = dccp_diag_get_info,
+	.idiag_type	 = IPPROTO_DCCP,
+	.idiag_info_size = sizeof(struct tcp_info),
+};
+
+static int __init dccp_diag_init(void)
+{
+	return inet_diag_register(&dccp_diag_handler);
+}
+
+static void __exit dccp_diag_fini(void)
+{
+	inet_diag_unregister(&dccp_diag_handler);
+}
+
+module_init(dccp_diag_init);
+module_exit(dccp_diag_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
+MODULE_DESCRIPTION("DCCP inet_diag handler");
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_NETLINK, NETLINK_SOCK_DIAG, 2-33 /* AF_INET - IPPROTO_DCCP */);
diff --git a/net/dccp/feat.c b/net/dccp/feat.c
new file mode 100644
index 000000000..788dd629c
--- /dev/null
+++ b/net/dccp/feat.c
@@ -0,0 +1,1571 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/feat.c
+ *
+ *  Feature negotiation for the DCCP protocol (RFC 4340, section 6)
+ *
+ *  Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
+ *  Rewrote from scratch, some bits from earlier code by
+ *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
+ *
+ *  ASSUMPTIONS
+ *  -----------
+ *  o Feature negotiation is coordinated with connection setup (as in TCP), wild
+ *    changes of parameters of an established connection are not supported.
+ *  o Changing non-negotiable (NN) values is supported in state OPEN/PARTOPEN.
+ *  o All currently known SP features have 1-byte quantities. If in the future
+ *    extensions of RFCs 4340..42 define features with item lengths larger than
+ *    one byte, a feature-specific extension of the code will be required.
+ */
+#include <linux/module.h>
+#include <linux/slab.h>
+#include "ccid.h"
+#include "feat.h"
+
+/* feature-specific sysctls - initialised to the defaults from RFC 4340, 6.4 */
+unsigned long	sysctl_dccp_sequence_window __read_mostly = 100;
+int		sysctl_dccp_rx_ccid	    __read_mostly = 2,
+		sysctl_dccp_tx_ccid	    __read_mostly = 2;
+
+/*
+ * Feature activation handlers.
+ *
+ * These all use an u64 argument, to provide enough room for NN/SP features. At
+ * this stage the negotiated values have been checked to be within their range.
+ */
+static int dccp_hdlr_ccid(struct sock *sk, u64 ccid, bool rx)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct ccid *new_ccid = ccid_new(ccid, sk, rx);
+
+	if (new_ccid == NULL)
+		return -ENOMEM;
+
+	if (rx) {
+		ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
+		dp->dccps_hc_rx_ccid = new_ccid;
+	} else {
+		ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
+		dp->dccps_hc_tx_ccid = new_ccid;
+	}
+	return 0;
+}
+
+static int dccp_hdlr_seq_win(struct sock *sk, u64 seq_win, bool rx)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	if (rx) {
+		dp->dccps_r_seq_win = seq_win;
+		/* propagate changes to update SWL/SWH */
+		dccp_update_gsr(sk, dp->dccps_gsr);
+	} else {
+		dp->dccps_l_seq_win = seq_win;
+		/* propagate changes to update AWL */
+		dccp_update_gss(sk, dp->dccps_gss);
+	}
+	return 0;
+}
+
+static int dccp_hdlr_ack_ratio(struct sock *sk, u64 ratio, bool rx)
+{
+	if (rx)
+		dccp_sk(sk)->dccps_r_ack_ratio = ratio;
+	else
+		dccp_sk(sk)->dccps_l_ack_ratio = ratio;
+	return 0;
+}
+
+static int dccp_hdlr_ackvec(struct sock *sk, u64 enable, bool rx)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	if (rx) {
+		if (enable && dp->dccps_hc_rx_ackvec == NULL) {
+			dp->dccps_hc_rx_ackvec = dccp_ackvec_alloc(gfp_any());
+			if (dp->dccps_hc_rx_ackvec == NULL)
+				return -ENOMEM;
+		} else if (!enable) {
+			dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
+			dp->dccps_hc_rx_ackvec = NULL;
+		}
+	}
+	return 0;
+}
+
+static int dccp_hdlr_ndp(struct sock *sk, u64 enable, bool rx)
+{
+	if (!rx)
+		dccp_sk(sk)->dccps_send_ndp_count = (enable > 0);
+	return 0;
+}
+
+/*
+ * Minimum Checksum Coverage is located at the RX side (9.2.1). This means that
+ * `rx' holds when the sending peer informs about his partial coverage via a
+ * ChangeR() option. In the other case, we are the sender and the receiver
+ * announces its coverage via ChangeL() options. The policy here is to honour
+ * such communication by enabling the corresponding partial coverage - but only
+ * if it has not been set manually before; the warning here means that all
+ * packets will be dropped.
+ */
+static int dccp_hdlr_min_cscov(struct sock *sk, u64 cscov, bool rx)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	if (rx)
+		dp->dccps_pcrlen = cscov;
+	else {
+		if (dp->dccps_pcslen == 0)
+			dp->dccps_pcslen = cscov;
+		else if (cscov > dp->dccps_pcslen)
+			DCCP_WARN("CsCov %u too small, peer requires >= %u\n",
+				  dp->dccps_pcslen, (u8)cscov);
+	}
+	return 0;
+}
+
+static const struct {
+	u8			feat_num;		/* DCCPF_xxx */
+	enum dccp_feat_type	rxtx;			/* RX or TX  */
+	enum dccp_feat_type	reconciliation;		/* SP or NN  */
+	u8			default_value;		/* as in 6.4 */
+	int (*activation_hdlr)(struct sock *sk, u64 val, bool rx);
+/*
+ *    Lookup table for location and type of features (from RFC 4340/4342)
+ *  +--------------------------+----+-----+----+----+---------+-----------+
+ *  | Feature                  | Location | Reconc. | Initial |  Section  |
+ *  |                          | RX | TX  | SP | NN |  Value  | Reference |
+ *  +--------------------------+----+-----+----+----+---------+-----------+
+ *  | DCCPF_CCID               |    |  X  | X  |    |   2     | 10        |
+ *  | DCCPF_SHORT_SEQNOS       |    |  X  | X  |    |   0     |  7.6.1    |
+ *  | DCCPF_SEQUENCE_WINDOW    |    |  X  |    | X  | 100     |  7.5.2    |
+ *  | DCCPF_ECN_INCAPABLE      | X  |     | X  |    |   0     | 12.1      |
+ *  | DCCPF_ACK_RATIO          |    |  X  |    | X  |   2     | 11.3      |
+ *  | DCCPF_SEND_ACK_VECTOR    | X  |     | X  |    |   0     | 11.5      |
+ *  | DCCPF_SEND_NDP_COUNT     |    |  X  | X  |    |   0     |  7.7.2    |
+ *  | DCCPF_MIN_CSUM_COVER     | X  |     | X  |    |   0     |  9.2.1    |
+ *  | DCCPF_DATA_CHECKSUM      | X  |     | X  |    |   0     |  9.3.1    |
+ *  | DCCPF_SEND_LEV_RATE      | X  |     | X  |    |   0     | 4342/8.4  |
+ *  +--------------------------+----+-----+----+----+---------+-----------+
+ */
+} dccp_feat_table[] = {
+	{ DCCPF_CCID,		 FEAT_AT_TX, FEAT_SP, 2,   dccp_hdlr_ccid     },
+	{ DCCPF_SHORT_SEQNOS,	 FEAT_AT_TX, FEAT_SP, 0,   NULL },
+	{ DCCPF_SEQUENCE_WINDOW, FEAT_AT_TX, FEAT_NN, 100, dccp_hdlr_seq_win  },
+	{ DCCPF_ECN_INCAPABLE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
+	{ DCCPF_ACK_RATIO,	 FEAT_AT_TX, FEAT_NN, 2,   dccp_hdlr_ack_ratio},
+	{ DCCPF_SEND_ACK_VECTOR, FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_ackvec   },
+	{ DCCPF_SEND_NDP_COUNT,  FEAT_AT_TX, FEAT_SP, 0,   dccp_hdlr_ndp      },
+	{ DCCPF_MIN_CSUM_COVER,  FEAT_AT_RX, FEAT_SP, 0,   dccp_hdlr_min_cscov},
+	{ DCCPF_DATA_CHECKSUM,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
+	{ DCCPF_SEND_LEV_RATE,	 FEAT_AT_RX, FEAT_SP, 0,   NULL },
+};
+#define DCCP_FEAT_SUPPORTED_MAX		ARRAY_SIZE(dccp_feat_table)
+
+/**
+ * dccp_feat_index  -  Hash function to map feature number into array position
+ * @feat_num: feature to hash, one of %dccp_feature_numbers
+ *
+ * Returns consecutive array index or -1 if the feature is not understood.
+ */
+static int dccp_feat_index(u8 feat_num)
+{
+	/* The first 9 entries are occupied by the types from RFC 4340, 6.4 */
+	if (feat_num > DCCPF_RESERVED && feat_num <= DCCPF_DATA_CHECKSUM)
+		return feat_num - 1;
+
+	/*
+	 * Other features: add cases for new feature types here after adding
+	 * them to the above table.
+	 */
+	switch (feat_num) {
+	case DCCPF_SEND_LEV_RATE:
+			return DCCP_FEAT_SUPPORTED_MAX - 1;
+	}
+	return -1;
+}
+
+static u8 dccp_feat_type(u8 feat_num)
+{
+	int idx = dccp_feat_index(feat_num);
+
+	if (idx < 0)
+		return FEAT_UNKNOWN;
+	return dccp_feat_table[idx].reconciliation;
+}
+
+static int dccp_feat_default_value(u8 feat_num)
+{
+	int idx = dccp_feat_index(feat_num);
+	/*
+	 * There are no default values for unknown features, so encountering a
+	 * negative index here indicates a serious problem somewhere else.
+	 */
+	DCCP_BUG_ON(idx < 0);
+
+	return idx < 0 ? 0 : dccp_feat_table[idx].default_value;
+}
+
+/*
+ *	Debugging and verbose-printing section
+ */
+static const char *dccp_feat_fname(const u8 feat)
+{
+	static const char *const feature_names[] = {
+		[DCCPF_RESERVED]	= "Reserved",
+		[DCCPF_CCID]		= "CCID",
+		[DCCPF_SHORT_SEQNOS]	= "Allow Short Seqnos",
+		[DCCPF_SEQUENCE_WINDOW]	= "Sequence Window",
+		[DCCPF_ECN_INCAPABLE]	= "ECN Incapable",
+		[DCCPF_ACK_RATIO]	= "Ack Ratio",
+		[DCCPF_SEND_ACK_VECTOR]	= "Send ACK Vector",
+		[DCCPF_SEND_NDP_COUNT]	= "Send NDP Count",
+		[DCCPF_MIN_CSUM_COVER]	= "Min. Csum Coverage",
+		[DCCPF_DATA_CHECKSUM]	= "Send Data Checksum",
+	};
+	if (feat > DCCPF_DATA_CHECKSUM && feat < DCCPF_MIN_CCID_SPECIFIC)
+		return feature_names[DCCPF_RESERVED];
+
+	if (feat ==  DCCPF_SEND_LEV_RATE)
+		return "Send Loss Event Rate";
+	if (feat >= DCCPF_MIN_CCID_SPECIFIC)
+		return "CCID-specific";
+
+	return feature_names[feat];
+}
+
+static const char *const dccp_feat_sname[] = {
+	"DEFAULT", "INITIALISING", "CHANGING", "UNSTABLE", "STABLE",
+};
+
+#ifdef CONFIG_IP_DCCP_DEBUG
+static const char *dccp_feat_oname(const u8 opt)
+{
+	switch (opt) {
+	case DCCPO_CHANGE_L:  return "Change_L";
+	case DCCPO_CONFIRM_L: return "Confirm_L";
+	case DCCPO_CHANGE_R:  return "Change_R";
+	case DCCPO_CONFIRM_R: return "Confirm_R";
+	}
+	return NULL;
+}
+
+static void dccp_feat_printval(u8 feat_num, dccp_feat_val const *val)
+{
+	u8 i, type = dccp_feat_type(feat_num);
+
+	if (val == NULL || (type == FEAT_SP && val->sp.vec == NULL))
+		dccp_pr_debug_cat("(NULL)");
+	else if (type == FEAT_SP)
+		for (i = 0; i < val->sp.len; i++)
+			dccp_pr_debug_cat("%s%u", i ? " " : "", val->sp.vec[i]);
+	else if (type == FEAT_NN)
+		dccp_pr_debug_cat("%llu", (unsigned long long)val->nn);
+	else
+		dccp_pr_debug_cat("unknown type %u", type);
+}
+
+static void dccp_feat_printvals(u8 feat_num, u8 *list, u8 len)
+{
+	u8 type = dccp_feat_type(feat_num);
+	dccp_feat_val fval = { .sp.vec = list, .sp.len = len };
+
+	if (type == FEAT_NN)
+		fval.nn = dccp_decode_value_var(list, len);
+	dccp_feat_printval(feat_num, &fval);
+}
+
+static void dccp_feat_print_entry(struct dccp_feat_entry const *entry)
+{
+	dccp_debug("   * %s %s = ", entry->is_local ? "local" : "remote",
+				    dccp_feat_fname(entry->feat_num));
+	dccp_feat_printval(entry->feat_num, &entry->val);
+	dccp_pr_debug_cat(", state=%s %s\n", dccp_feat_sname[entry->state],
+			  entry->needs_confirm ? "(Confirm pending)" : "");
+}
+
+#define dccp_feat_print_opt(opt, feat, val, len, mandatory)	do {	      \
+	dccp_pr_debug("%s(%s, ", dccp_feat_oname(opt), dccp_feat_fname(feat));\
+	dccp_feat_printvals(feat, val, len);				      \
+	dccp_pr_debug_cat(") %s\n", mandatory ? "!" : "");	} while (0)
+
+#define dccp_feat_print_fnlist(fn_list)  {		\
+	const struct dccp_feat_entry *___entry;		\
+							\
+	dccp_pr_debug("List Dump:\n");			\
+	list_for_each_entry(___entry, fn_list, node)	\
+		dccp_feat_print_entry(___entry);	\
+}
+#else	/* ! CONFIG_IP_DCCP_DEBUG */
+#define dccp_feat_print_opt(opt, feat, val, len, mandatory)
+#define dccp_feat_print_fnlist(fn_list)
+#endif
+
+static int __dccp_feat_activate(struct sock *sk, const int idx,
+				const bool is_local, dccp_feat_val const *fval)
+{
+	bool rx;
+	u64 val;
+
+	if (idx < 0 || idx >= DCCP_FEAT_SUPPORTED_MAX)
+		return -1;
+	if (dccp_feat_table[idx].activation_hdlr == NULL)
+		return 0;
+
+	if (fval == NULL) {
+		val = dccp_feat_table[idx].default_value;
+	} else if (dccp_feat_table[idx].reconciliation == FEAT_SP) {
+		if (fval->sp.vec == NULL) {
+			/*
+			 * This can happen when an empty Confirm is sent
+			 * for an SP (i.e. known) feature. In this case
+			 * we would be using the default anyway.
+			 */
+			DCCP_CRIT("Feature #%d undefined: using default", idx);
+			val = dccp_feat_table[idx].default_value;
+		} else {
+			val = fval->sp.vec[0];
+		}
+	} else {
+		val = fval->nn;
+	}
+
+	/* Location is RX if this is a local-RX or remote-TX feature */
+	rx = (is_local == (dccp_feat_table[idx].rxtx == FEAT_AT_RX));
+
+	dccp_debug("   -> activating %s %s, %sval=%llu\n", rx ? "RX" : "TX",
+		   dccp_feat_fname(dccp_feat_table[idx].feat_num),
+		   fval ? "" : "default ",  (unsigned long long)val);
+
+	return dccp_feat_table[idx].activation_hdlr(sk, val, rx);
+}
+
+/**
+ * dccp_feat_activate  -  Activate feature value on socket
+ * @sk: fully connected DCCP socket (after handshake is complete)
+ * @feat_num: feature to activate, one of %dccp_feature_numbers
+ * @local: whether local (1) or remote (0) @feat_num is meant
+ * @fval: the value (SP or NN) to activate, or NULL to use the default value
+ *
+ * For general use this function is preferable over __dccp_feat_activate().
+ */
+static int dccp_feat_activate(struct sock *sk, u8 feat_num, bool local,
+			      dccp_feat_val const *fval)
+{
+	return __dccp_feat_activate(sk, dccp_feat_index(feat_num), local, fval);
+}
+
+/* Test for "Req'd" feature (RFC 4340, 6.4) */
+static inline int dccp_feat_must_be_understood(u8 feat_num)
+{
+	return	feat_num == DCCPF_CCID || feat_num == DCCPF_SHORT_SEQNOS ||
+		feat_num == DCCPF_SEQUENCE_WINDOW;
+}
+
+/* copy constructor, fval must not already contain allocated memory */
+static int dccp_feat_clone_sp_val(dccp_feat_val *fval, u8 const *val, u8 len)
+{
+	fval->sp.len = len;
+	if (fval->sp.len > 0) {
+		fval->sp.vec = kmemdup(val, len, gfp_any());
+		if (fval->sp.vec == NULL) {
+			fval->sp.len = 0;
+			return -ENOBUFS;
+		}
+	}
+	return 0;
+}
+
+static void dccp_feat_val_destructor(u8 feat_num, dccp_feat_val *val)
+{
+	if (unlikely(val == NULL))
+		return;
+	if (dccp_feat_type(feat_num) == FEAT_SP)
+		kfree(val->sp.vec);
+	memset(val, 0, sizeof(*val));
+}
+
+static struct dccp_feat_entry *
+	      dccp_feat_clone_entry(struct dccp_feat_entry const *original)
+{
+	struct dccp_feat_entry *new;
+	u8 type = dccp_feat_type(original->feat_num);
+
+	if (type == FEAT_UNKNOWN)
+		return NULL;
+
+	new = kmemdup(original, sizeof(struct dccp_feat_entry), gfp_any());
+	if (new == NULL)
+		return NULL;
+
+	if (type == FEAT_SP && dccp_feat_clone_sp_val(&new->val,
+						      original->val.sp.vec,
+						      original->val.sp.len)) {
+		kfree(new);
+		return NULL;
+	}
+	return new;
+}
+
+static void dccp_feat_entry_destructor(struct dccp_feat_entry *entry)
+{
+	if (entry != NULL) {
+		dccp_feat_val_destructor(entry->feat_num, &entry->val);
+		kfree(entry);
+	}
+}
+
+/*
+ * List management functions
+ *
+ * Feature negotiation lists rely on and maintain the following invariants:
+ * - each feat_num in the list is known, i.e. we know its type and default value
+ * - each feat_num/is_local combination is unique (old entries are overwritten)
+ * - SP values are always freshly allocated
+ * - list is sorted in increasing order of feature number (faster lookup)
+ */
+static struct dccp_feat_entry *dccp_feat_list_lookup(struct list_head *fn_list,
+						     u8 feat_num, bool is_local)
+{
+	struct dccp_feat_entry *entry;
+
+	list_for_each_entry(entry, fn_list, node) {
+		if (entry->feat_num == feat_num && entry->is_local == is_local)
+			return entry;
+		else if (entry->feat_num > feat_num)
+			break;
+	}
+	return NULL;
+}
+
+/**
+ * dccp_feat_entry_new  -  Central list update routine (called by all others)
+ * @head:  list to add to
+ * @feat:  feature number
+ * @local: whether the local (1) or remote feature with number @feat is meant
+ *
+ * This is the only constructor and serves to ensure the above invariants.
+ */
+static struct dccp_feat_entry *
+	      dccp_feat_entry_new(struct list_head *head, u8 feat, bool local)
+{
+	struct dccp_feat_entry *entry;
+
+	list_for_each_entry(entry, head, node)
+		if (entry->feat_num == feat && entry->is_local == local) {
+			dccp_feat_val_destructor(entry->feat_num, &entry->val);
+			return entry;
+		} else if (entry->feat_num > feat) {
+			head = &entry->node;
+			break;
+		}
+
+	entry = kmalloc(sizeof(*entry), gfp_any());
+	if (entry != NULL) {
+		entry->feat_num = feat;
+		entry->is_local = local;
+		list_add_tail(&entry->node, head);
+	}
+	return entry;
+}
+
+/**
+ * dccp_feat_push_change  -  Add/overwrite a Change option in the list
+ * @fn_list: feature-negotiation list to update
+ * @feat: one of %dccp_feature_numbers
+ * @local: whether local (1) or remote (0) @feat_num is meant
+ * @mandatory: whether to use Mandatory feature negotiation options
+ * @fval: pointer to NN/SP value to be inserted (will be copied)
+ */
+static int dccp_feat_push_change(struct list_head *fn_list, u8 feat, u8 local,
+				 u8 mandatory, dccp_feat_val *fval)
+{
+	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
+
+	if (new == NULL)
+		return -ENOMEM;
+
+	new->feat_num	     = feat;
+	new->is_local	     = local;
+	new->state	     = FEAT_INITIALISING;
+	new->needs_confirm   = false;
+	new->empty_confirm   = false;
+	new->val	     = *fval;
+	new->needs_mandatory = mandatory;
+
+	return 0;
+}
+
+/**
+ * dccp_feat_push_confirm  -  Add a Confirm entry to the FN list
+ * @fn_list: feature-negotiation list to add to
+ * @feat: one of %dccp_feature_numbers
+ * @local: whether local (1) or remote (0) @feat_num is being confirmed
+ * @fval: pointer to NN/SP value to be inserted or NULL
+ *
+ * Returns 0 on success, a Reset code for further processing otherwise.
+ */
+static int dccp_feat_push_confirm(struct list_head *fn_list, u8 feat, u8 local,
+				  dccp_feat_val *fval)
+{
+	struct dccp_feat_entry *new = dccp_feat_entry_new(fn_list, feat, local);
+
+	if (new == NULL)
+		return DCCP_RESET_CODE_TOO_BUSY;
+
+	new->feat_num	     = feat;
+	new->is_local	     = local;
+	new->state	     = FEAT_STABLE;	/* transition in 6.6.2 */
+	new->needs_confirm   = true;
+	new->empty_confirm   = (fval == NULL);
+	new->val.nn	     = 0;		/* zeroes the whole structure */
+	if (!new->empty_confirm)
+		new->val     = *fval;
+	new->needs_mandatory = false;
+
+	return 0;
+}
+
+static int dccp_push_empty_confirm(struct list_head *fn_list, u8 feat, u8 local)
+{
+	return dccp_feat_push_confirm(fn_list, feat, local, NULL);
+}
+
+static inline void dccp_feat_list_pop(struct dccp_feat_entry *entry)
+{
+	list_del(&entry->node);
+	dccp_feat_entry_destructor(entry);
+}
+
+void dccp_feat_list_purge(struct list_head *fn_list)
+{
+	struct dccp_feat_entry *entry, *next;
+
+	list_for_each_entry_safe(entry, next, fn_list, node)
+		dccp_feat_entry_destructor(entry);
+	INIT_LIST_HEAD(fn_list);
+}
+EXPORT_SYMBOL_GPL(dccp_feat_list_purge);
+
+/* generate @to as full clone of @from - @to must not contain any nodes */
+int dccp_feat_clone_list(struct list_head const *from, struct list_head *to)
+{
+	struct dccp_feat_entry *entry, *new;
+
+	INIT_LIST_HEAD(to);
+	list_for_each_entry(entry, from, node) {
+		new = dccp_feat_clone_entry(entry);
+		if (new == NULL)
+			goto cloning_failed;
+		list_add_tail(&new->node, to);
+	}
+	return 0;
+
+cloning_failed:
+	dccp_feat_list_purge(to);
+	return -ENOMEM;
+}
+
+/**
+ * dccp_feat_valid_nn_length  -  Enforce length constraints on NN options
+ * @feat_num: feature to return length of, one of %dccp_feature_numbers
+ *
+ * Length is between 0 and %DCCP_OPTVAL_MAXLEN. Used for outgoing packets only,
+ * incoming options are accepted as long as their values are valid.
+ */
+static u8 dccp_feat_valid_nn_length(u8 feat_num)
+{
+	if (feat_num == DCCPF_ACK_RATIO)	/* RFC 4340, 11.3 and 6.6.8 */
+		return 2;
+	if (feat_num == DCCPF_SEQUENCE_WINDOW)	/* RFC 4340, 7.5.2 and 6.5  */
+		return 6;
+	return 0;
+}
+
+static u8 dccp_feat_is_valid_nn_val(u8 feat_num, u64 val)
+{
+	switch (feat_num) {
+	case DCCPF_ACK_RATIO:
+		return val <= DCCPF_ACK_RATIO_MAX;
+	case DCCPF_SEQUENCE_WINDOW:
+		return val >= DCCPF_SEQ_WMIN && val <= DCCPF_SEQ_WMAX;
+	}
+	return 0;	/* feature unknown - so we can't tell */
+}
+
+/* check that SP values are within the ranges defined in RFC 4340 */
+static u8 dccp_feat_is_valid_sp_val(u8 feat_num, u8 val)
+{
+	switch (feat_num) {
+	case DCCPF_CCID:
+		return val == DCCPC_CCID2 || val == DCCPC_CCID3;
+	/* Type-check Boolean feature values: */
+	case DCCPF_SHORT_SEQNOS:
+	case DCCPF_ECN_INCAPABLE:
+	case DCCPF_SEND_ACK_VECTOR:
+	case DCCPF_SEND_NDP_COUNT:
+	case DCCPF_DATA_CHECKSUM:
+	case DCCPF_SEND_LEV_RATE:
+		return val < 2;
+	case DCCPF_MIN_CSUM_COVER:
+		return val < 16;
+	}
+	return 0;			/* feature unknown */
+}
+
+static u8 dccp_feat_sp_list_ok(u8 feat_num, u8 const *sp_list, u8 sp_len)
+{
+	if (sp_list == NULL || sp_len < 1)
+		return 0;
+	while (sp_len--)
+		if (!dccp_feat_is_valid_sp_val(feat_num, *sp_list++))
+			return 0;
+	return 1;
+}
+
+/**
+ * dccp_feat_insert_opts  -  Generate FN options from current list state
+ * @skb: next sk_buff to be sent to the peer
+ * @dp: for client during handshake and general negotiation
+ * @dreq: used by the server only (all Changes/Confirms in LISTEN/RESPOND)
+ */
+int dccp_feat_insert_opts(struct dccp_sock *dp, struct dccp_request_sock *dreq,
+			  struct sk_buff *skb)
+{
+	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
+	struct dccp_feat_entry *pos, *next;
+	u8 opt, type, len, *ptr, nn_in_nbo[DCCP_OPTVAL_MAXLEN];
+	bool rpt;
+
+	/* put entries into @skb in the order they appear in the list */
+	list_for_each_entry_safe_reverse(pos, next, fn, node) {
+		opt  = dccp_feat_genopt(pos);
+		type = dccp_feat_type(pos->feat_num);
+		rpt  = false;
+
+		if (pos->empty_confirm) {
+			len = 0;
+			ptr = NULL;
+		} else {
+			if (type == FEAT_SP) {
+				len = pos->val.sp.len;
+				ptr = pos->val.sp.vec;
+				rpt = pos->needs_confirm;
+			} else if (type == FEAT_NN) {
+				len = dccp_feat_valid_nn_length(pos->feat_num);
+				ptr = nn_in_nbo;
+				dccp_encode_value_var(pos->val.nn, ptr, len);
+			} else {
+				DCCP_BUG("unknown feature %u", pos->feat_num);
+				return -1;
+			}
+		}
+		dccp_feat_print_opt(opt, pos->feat_num, ptr, len, 0);
+
+		if (dccp_insert_fn_opt(skb, opt, pos->feat_num, ptr, len, rpt))
+			return -1;
+		if (pos->needs_mandatory && dccp_insert_option_mandatory(skb))
+			return -1;
+
+		if (skb->sk->sk_state == DCCP_OPEN &&
+		    (opt == DCCPO_CONFIRM_R || opt == DCCPO_CONFIRM_L)) {
+			/*
+			 * Confirms don't get retransmitted (6.6.3) once the
+			 * connection is in state OPEN
+			 */
+			dccp_feat_list_pop(pos);
+		} else {
+			/*
+			 * Enter CHANGING after transmitting the Change
+			 * option (6.6.2).
+			 */
+			if (pos->state == FEAT_INITIALISING)
+				pos->state = FEAT_CHANGING;
+		}
+	}
+	return 0;
+}
+
+/**
+ * __feat_register_nn  -  Register new NN value on socket
+ * @fn: feature-negotiation list to register with
+ * @feat: an NN feature from %dccp_feature_numbers
+ * @mandatory: use Mandatory option if 1
+ * @nn_val: value to register (restricted to 4 bytes)
+ *
+ * Note that NN features are local by definition (RFC 4340, 6.3.2).
+ */
+static int __feat_register_nn(struct list_head *fn, u8 feat,
+			      u8 mandatory, u64 nn_val)
+{
+	dccp_feat_val fval = { .nn = nn_val };
+
+	if (dccp_feat_type(feat) != FEAT_NN ||
+	    !dccp_feat_is_valid_nn_val(feat, nn_val))
+		return -EINVAL;
+
+	/* Don't bother with default values, they will be activated anyway. */
+	if (nn_val - (u64)dccp_feat_default_value(feat) == 0)
+		return 0;
+
+	return dccp_feat_push_change(fn, feat, 1, mandatory, &fval);
+}
+
+/**
+ * __feat_register_sp  -  Register new SP value/list on socket
+ * @fn: feature-negotiation list to register with
+ * @feat: an SP feature from %dccp_feature_numbers
+ * @is_local: whether the local (1) or the remote (0) @feat is meant
+ * @mandatory: use Mandatory option if 1
+ * @sp_val: SP value followed by optional preference list
+ * @sp_len: length of @sp_val in bytes
+ */
+static int __feat_register_sp(struct list_head *fn, u8 feat, u8 is_local,
+			      u8 mandatory, u8 const *sp_val, u8 sp_len)
+{
+	dccp_feat_val fval;
+
+	if (dccp_feat_type(feat) != FEAT_SP ||
+	    !dccp_feat_sp_list_ok(feat, sp_val, sp_len))
+		return -EINVAL;
+
+	/* Avoid negotiating alien CCIDs by only advertising supported ones */
+	if (feat == DCCPF_CCID && !ccid_support_check(sp_val, sp_len))
+		return -EOPNOTSUPP;
+
+	if (dccp_feat_clone_sp_val(&fval, sp_val, sp_len))
+		return -ENOMEM;
+
+	if (dccp_feat_push_change(fn, feat, is_local, mandatory, &fval)) {
+		kfree(fval.sp.vec);
+		return -ENOMEM;
+	}
+
+	return 0;
+}
+
+/**
+ * dccp_feat_register_sp  -  Register requests to change SP feature values
+ * @sk: client or listening socket
+ * @feat: one of %dccp_feature_numbers
+ * @is_local: whether the local (1) or remote (0) @feat is meant
+ * @list: array of preferred values, in descending order of preference
+ * @len: length of @list in bytes
+ */
+int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
+			  u8 const *list, u8 len)
+{	 /* any changes must be registered before establishing the connection */
+	if (sk->sk_state != DCCP_CLOSED)
+		return -EISCONN;
+	if (dccp_feat_type(feat) != FEAT_SP)
+		return -EINVAL;
+	return __feat_register_sp(&dccp_sk(sk)->dccps_featneg, feat, is_local,
+				  0, list, len);
+}
+
+/**
+ * dccp_feat_nn_get  -  Query current/pending value of NN feature
+ * @sk: DCCP socket of an established connection
+ * @feat: NN feature number from %dccp_feature_numbers
+ *
+ * For a known NN feature, returns value currently being negotiated, or
+ * current (confirmed) value if no negotiation is going on.
+ */
+u64 dccp_feat_nn_get(struct sock *sk, u8 feat)
+{
+	if (dccp_feat_type(feat) == FEAT_NN) {
+		struct dccp_sock *dp = dccp_sk(sk);
+		struct dccp_feat_entry *entry;
+
+		entry = dccp_feat_list_lookup(&dp->dccps_featneg, feat, 1);
+		if (entry != NULL)
+			return entry->val.nn;
+
+		switch (feat) {
+		case DCCPF_ACK_RATIO:
+			return dp->dccps_l_ack_ratio;
+		case DCCPF_SEQUENCE_WINDOW:
+			return dp->dccps_l_seq_win;
+		}
+	}
+	DCCP_BUG("attempt to look up unsupported feature %u", feat);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dccp_feat_nn_get);
+
+/**
+ * dccp_feat_signal_nn_change  -  Update NN values for an established connection
+ * @sk: DCCP socket of an established connection
+ * @feat: NN feature number from %dccp_feature_numbers
+ * @nn_val: the new value to use
+ *
+ * This function is used to communicate NN updates out-of-band.
+ */
+int dccp_feat_signal_nn_change(struct sock *sk, u8 feat, u64 nn_val)
+{
+	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
+	dccp_feat_val fval = { .nn = nn_val };
+	struct dccp_feat_entry *entry;
+
+	if (sk->sk_state != DCCP_OPEN && sk->sk_state != DCCP_PARTOPEN)
+		return 0;
+
+	if (dccp_feat_type(feat) != FEAT_NN ||
+	    !dccp_feat_is_valid_nn_val(feat, nn_val))
+		return -EINVAL;
+
+	if (nn_val == dccp_feat_nn_get(sk, feat))
+		return 0;	/* already set or negotiation under way */
+
+	entry = dccp_feat_list_lookup(fn, feat, 1);
+	if (entry != NULL) {
+		dccp_pr_debug("Clobbering existing NN entry %llu -> %llu\n",
+			      (unsigned long long)entry->val.nn,
+			      (unsigned long long)nn_val);
+		dccp_feat_list_pop(entry);
+	}
+
+	inet_csk_schedule_ack(sk);
+	return dccp_feat_push_change(fn, feat, 1, 0, &fval);
+}
+EXPORT_SYMBOL_GPL(dccp_feat_signal_nn_change);
+
+/*
+ *	Tracking features whose value depend on the choice of CCID
+ *
+ * This is designed with an extension in mind so that a list walk could be done
+ * before activating any features. However, the existing framework was found to
+ * work satisfactorily up until now, the automatic verification is left open.
+ * When adding new CCIDs, add a corresponding dependency table here.
+ */
+static const struct ccid_dependency *dccp_feat_ccid_deps(u8 ccid, bool is_local)
+{
+	static const struct ccid_dependency ccid2_dependencies[2][2] = {
+		/*
+		 * CCID2 mandates Ack Vectors (RFC 4341, 4.): as CCID is a TX
+		 * feature and Send Ack Vector is an RX feature, `is_local'
+		 * needs to be reversed.
+		 */
+		{	/* Dependencies of the receiver-side (remote) CCID2 */
+			{
+				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
+				.is_local	= true,
+				.is_mandatory	= true,
+				.val		= 1
+			},
+			{ 0, 0, 0, 0 }
+		},
+		{	/* Dependencies of the sender-side (local) CCID2 */
+			{
+				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
+				.is_local	= false,
+				.is_mandatory	= true,
+				.val		= 1
+			},
+			{ 0, 0, 0, 0 }
+		}
+	};
+	static const struct ccid_dependency ccid3_dependencies[2][5] = {
+		{	/*
+			 * Dependencies of the receiver-side CCID3
+			 */
+			{	/* locally disable Ack Vectors */
+				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
+				.is_local	= true,
+				.is_mandatory	= false,
+				.val		= 0
+			},
+			{	/* see below why Send Loss Event Rate is on */
+				.dependent_feat	= DCCPF_SEND_LEV_RATE,
+				.is_local	= true,
+				.is_mandatory	= true,
+				.val		= 1
+			},
+			{	/* NDP Count is needed as per RFC 4342, 6.1.1 */
+				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
+				.is_local	= false,
+				.is_mandatory	= true,
+				.val		= 1
+			},
+			{ 0, 0, 0, 0 },
+		},
+		{	/*
+			 * CCID3 at the TX side: we request that the HC-receiver
+			 * will not send Ack Vectors (they will be ignored, so
+			 * Mandatory is not set); we enable Send Loss Event Rate
+			 * (Mandatory since the implementation does not support
+			 * the Loss Intervals option of RFC 4342, 8.6).
+			 * The last two options are for peer's information only.
+			*/
+			{
+				.dependent_feat	= DCCPF_SEND_ACK_VECTOR,
+				.is_local	= false,
+				.is_mandatory	= false,
+				.val		= 0
+			},
+			{
+				.dependent_feat	= DCCPF_SEND_LEV_RATE,
+				.is_local	= false,
+				.is_mandatory	= true,
+				.val		= 1
+			},
+			{	/* this CCID does not support Ack Ratio */
+				.dependent_feat	= DCCPF_ACK_RATIO,
+				.is_local	= true,
+				.is_mandatory	= false,
+				.val		= 0
+			},
+			{	/* tell receiver we are sending NDP counts */
+				.dependent_feat	= DCCPF_SEND_NDP_COUNT,
+				.is_local	= true,
+				.is_mandatory	= false,
+				.val		= 1
+			},
+			{ 0, 0, 0, 0 }
+		}
+	};
+	switch (ccid) {
+	case DCCPC_CCID2:
+		return ccid2_dependencies[is_local];
+	case DCCPC_CCID3:
+		return ccid3_dependencies[is_local];
+	default:
+		return NULL;
+	}
+}
+
+/**
+ * dccp_feat_propagate_ccid - Resolve dependencies of features on choice of CCID
+ * @fn: feature-negotiation list to update
+ * @id: CCID number to track
+ * @is_local: whether TX CCID (1) or RX CCID (0) is meant
+ *
+ * This function needs to be called after registering all other features.
+ */
+static int dccp_feat_propagate_ccid(struct list_head *fn, u8 id, bool is_local)
+{
+	const struct ccid_dependency *table = dccp_feat_ccid_deps(id, is_local);
+	int i, rc = (table == NULL);
+
+	for (i = 0; rc == 0 && table[i].dependent_feat != DCCPF_RESERVED; i++)
+		if (dccp_feat_type(table[i].dependent_feat) == FEAT_SP)
+			rc = __feat_register_sp(fn, table[i].dependent_feat,
+						    table[i].is_local,
+						    table[i].is_mandatory,
+						    &table[i].val, 1);
+		else
+			rc = __feat_register_nn(fn, table[i].dependent_feat,
+						    table[i].is_mandatory,
+						    table[i].val);
+	return rc;
+}
+
+/**
+ * dccp_feat_finalise_settings  -  Finalise settings before starting negotiation
+ * @dp: client or listening socket (settings will be inherited)
+ *
+ * This is called after all registrations (socket initialisation, sysctls, and
+ * sockopt calls), and before sending the first packet containing Change options
+ * (ie. client-Request or server-Response), to ensure internal consistency.
+ */
+int dccp_feat_finalise_settings(struct dccp_sock *dp)
+{
+	struct list_head *fn = &dp->dccps_featneg;
+	struct dccp_feat_entry *entry;
+	int i = 2, ccids[2] = { -1, -1 };
+
+	/*
+	 * Propagating CCIDs:
+	 * 1) not useful to propagate CCID settings if this host advertises more
+	 *    than one CCID: the choice of CCID  may still change - if this is
+	 *    the client, or if this is the server and the client sends
+	 *    singleton CCID values.
+	 * 2) since is that propagate_ccid changes the list, we defer changing
+	 *    the sorted list until after the traversal.
+	 */
+	list_for_each_entry(entry, fn, node)
+		if (entry->feat_num == DCCPF_CCID && entry->val.sp.len == 1)
+			ccids[entry->is_local] = entry->val.sp.vec[0];
+	while (i--)
+		if (ccids[i] > 0 && dccp_feat_propagate_ccid(fn, ccids[i], i))
+			return -1;
+	dccp_feat_print_fnlist(fn);
+	return 0;
+}
+
+/**
+ * dccp_feat_server_ccid_dependencies  -  Resolve CCID-dependent features
+ * It is the server which resolves the dependencies once the CCID has been
+ * fully negotiated. If no CCID has been negotiated, it uses the default CCID.
+ */
+int dccp_feat_server_ccid_dependencies(struct dccp_request_sock *dreq)
+{
+	struct list_head *fn = &dreq->dreq_featneg;
+	struct dccp_feat_entry *entry;
+	u8 is_local, ccid;
+
+	for (is_local = 0; is_local <= 1; is_local++) {
+		entry = dccp_feat_list_lookup(fn, DCCPF_CCID, is_local);
+
+		if (entry != NULL && !entry->empty_confirm)
+			ccid = entry->val.sp.vec[0];
+		else
+			ccid = dccp_feat_default_value(DCCPF_CCID);
+
+		if (dccp_feat_propagate_ccid(fn, ccid, is_local))
+			return -1;
+	}
+	return 0;
+}
+
+/* Select the first entry in @servlist that also occurs in @clilist (6.3.1) */
+static int dccp_feat_preflist_match(u8 *servlist, u8 slen, u8 *clilist, u8 clen)
+{
+	u8 c, s;
+
+	for (s = 0; s < slen; s++)
+		for (c = 0; c < clen; c++)
+			if (servlist[s] == clilist[c])
+				return servlist[s];
+	return -1;
+}
+
+/**
+ * dccp_feat_prefer  -  Move preferred entry to the start of array
+ * Reorder the @array_len elements in @array so that @preferred_value comes
+ * first. Returns >0 to indicate that @preferred_value does occur in @array.
+ */
+static u8 dccp_feat_prefer(u8 preferred_value, u8 *array, u8 array_len)
+{
+	u8 i, does_occur = 0;
+
+	if (array != NULL) {
+		for (i = 0; i < array_len; i++)
+			if (array[i] == preferred_value) {
+				array[i] = array[0];
+				does_occur++;
+			}
+		if (does_occur)
+			array[0] = preferred_value;
+	}
+	return does_occur;
+}
+
+/**
+ * dccp_feat_reconcile  -  Reconcile SP preference lists
+ *  @fv: SP list to reconcile into
+ *  @arr: received SP preference list
+ *  @len: length of @arr in bytes
+ *  @is_server: whether this side is the server (and @fv is the server's list)
+ *  @reorder: whether to reorder the list in @fv after reconciling with @arr
+ * When successful, > 0 is returned and the reconciled list is in @fval.
+ * A value of 0 means that negotiation failed (no shared entry).
+ */
+static int dccp_feat_reconcile(dccp_feat_val *fv, u8 *arr, u8 len,
+			       bool is_server, bool reorder)
+{
+	int rc;
+
+	if (!fv->sp.vec || !arr) {
+		DCCP_CRIT("NULL feature value or array");
+		return 0;
+	}
+
+	if (is_server)
+		rc = dccp_feat_preflist_match(fv->sp.vec, fv->sp.len, arr, len);
+	else
+		rc = dccp_feat_preflist_match(arr, len, fv->sp.vec, fv->sp.len);
+
+	if (!reorder)
+		return rc;
+	if (rc < 0)
+		return 0;
+
+	/*
+	 * Reorder list: used for activating features and in dccp_insert_fn_opt.
+	 */
+	return dccp_feat_prefer(rc, fv->sp.vec, fv->sp.len);
+}
+
+/**
+ * dccp_feat_change_recv  -  Process incoming ChangeL/R options
+ * @fn: feature-negotiation list to update
+ * @is_mandatory: whether the Change was preceded by a Mandatory option
+ * @opt: %DCCPO_CHANGE_L or %DCCPO_CHANGE_R
+ * @feat: one of %dccp_feature_numbers
+ * @val: NN value or SP value/preference list
+ * @len: length of @val in bytes
+ * @server: whether this node is the server (1) or the client (0)
+ */
+static u8 dccp_feat_change_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
+				u8 feat, u8 *val, u8 len, const bool server)
+{
+	u8 defval, type = dccp_feat_type(feat);
+	const bool local = (opt == DCCPO_CHANGE_R);
+	struct dccp_feat_entry *entry;
+	dccp_feat_val fval;
+
+	if (len == 0 || type == FEAT_UNKNOWN)		/* 6.1 and 6.6.8 */
+		goto unknown_feature_or_value;
+
+	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
+
+	/*
+	 *	Negotiation of NN features: Change R is invalid, so there is no
+	 *	simultaneous negotiation; hence we do not look up in the list.
+	 */
+	if (type == FEAT_NN) {
+		if (local || len > sizeof(fval.nn))
+			goto unknown_feature_or_value;
+
+		/* 6.3.2: "The feature remote MUST accept any valid value..." */
+		fval.nn = dccp_decode_value_var(val, len);
+		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
+			goto unknown_feature_or_value;
+
+		return dccp_feat_push_confirm(fn, feat, local, &fval);
+	}
+
+	/*
+	 *	Unidirectional/simultaneous negotiation of SP features (6.3.1)
+	 */
+	entry = dccp_feat_list_lookup(fn, feat, local);
+	if (entry == NULL) {
+		/*
+		 * No particular preferences have been registered. We deal with
+		 * this situation by assuming that all valid values are equally
+		 * acceptable, and apply the following checks:
+		 * - if the peer's list is a singleton, we accept a valid value;
+		 * - if we are the server, we first try to see if the peer (the
+		 *   client) advertises the default value. If yes, we use it,
+		 *   otherwise we accept the preferred value;
+		 * - else if we are the client, we use the first list element.
+		 */
+		if (dccp_feat_clone_sp_val(&fval, val, 1))
+			return DCCP_RESET_CODE_TOO_BUSY;
+
+		if (len > 1 && server) {
+			defval = dccp_feat_default_value(feat);
+			if (dccp_feat_preflist_match(&defval, 1, val, len) > -1)
+				fval.sp.vec[0] = defval;
+		} else if (!dccp_feat_is_valid_sp_val(feat, fval.sp.vec[0])) {
+			kfree(fval.sp.vec);
+			goto unknown_feature_or_value;
+		}
+
+		/* Treat unsupported CCIDs like invalid values */
+		if (feat == DCCPF_CCID && !ccid_support_check(fval.sp.vec, 1)) {
+			kfree(fval.sp.vec);
+			goto not_valid_or_not_known;
+		}
+
+		return dccp_feat_push_confirm(fn, feat, local, &fval);
+
+	} else if (entry->state == FEAT_UNSTABLE) {	/* 6.6.2 */
+		return 0;
+	}
+
+	if (dccp_feat_reconcile(&entry->val, val, len, server, true)) {
+		entry->empty_confirm = false;
+	} else if (is_mandatory) {
+		return DCCP_RESET_CODE_MANDATORY_ERROR;
+	} else if (entry->state == FEAT_INITIALISING) {
+		/*
+		 * Failed simultaneous negotiation (server only): try to `save'
+		 * the connection by checking whether entry contains the default
+		 * value for @feat. If yes, send an empty Confirm to signal that
+		 * the received Change was not understood - which implies using
+		 * the default value.
+		 * If this also fails, we use Reset as the last resort.
+		 */
+		WARN_ON(!server);
+		defval = dccp_feat_default_value(feat);
+		if (!dccp_feat_reconcile(&entry->val, &defval, 1, server, true))
+			return DCCP_RESET_CODE_OPTION_ERROR;
+		entry->empty_confirm = true;
+	}
+	entry->needs_confirm   = true;
+	entry->needs_mandatory = false;
+	entry->state	       = FEAT_STABLE;
+	return 0;
+
+unknown_feature_or_value:
+	if (!is_mandatory)
+		return dccp_push_empty_confirm(fn, feat, local);
+
+not_valid_or_not_known:
+	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
+			    : DCCP_RESET_CODE_OPTION_ERROR;
+}
+
+/**
+ * dccp_feat_confirm_recv  -  Process received Confirm options
+ * @fn: feature-negotiation list to update
+ * @is_mandatory: whether @opt was preceded by a Mandatory option
+ * @opt: %DCCPO_CONFIRM_L or %DCCPO_CONFIRM_R
+ * @feat: one of %dccp_feature_numbers
+ * @val: NN value or SP value/preference list
+ * @len: length of @val in bytes
+ * @server: whether this node is server (1) or client (0)
+ */
+static u8 dccp_feat_confirm_recv(struct list_head *fn, u8 is_mandatory, u8 opt,
+				 u8 feat, u8 *val, u8 len, const bool server)
+{
+	u8 *plist, plen, type = dccp_feat_type(feat);
+	const bool local = (opt == DCCPO_CONFIRM_R);
+	struct dccp_feat_entry *entry = dccp_feat_list_lookup(fn, feat, local);
+
+	dccp_feat_print_opt(opt, feat, val, len, is_mandatory);
+
+	if (entry == NULL) {	/* nothing queued: ignore or handle error */
+		if (is_mandatory && type == FEAT_UNKNOWN)
+			return DCCP_RESET_CODE_MANDATORY_ERROR;
+
+		if (!local && type == FEAT_NN)		/* 6.3.2 */
+			goto confirmation_failed;
+		return 0;
+	}
+
+	if (entry->state != FEAT_CHANGING)		/* 6.6.2 */
+		return 0;
+
+	if (len == 0) {
+		if (dccp_feat_must_be_understood(feat))	/* 6.6.7 */
+			goto confirmation_failed;
+		/*
+		 * Empty Confirm during connection setup: this means reverting
+		 * to the `old' value, which in this case is the default. Since
+		 * we handle default values automatically when no other values
+		 * have been set, we revert to the old value by removing this
+		 * entry from the list.
+		 */
+		dccp_feat_list_pop(entry);
+		return 0;
+	}
+
+	if (type == FEAT_NN) {
+		if (len > sizeof(entry->val.nn))
+			goto confirmation_failed;
+
+		if (entry->val.nn == dccp_decode_value_var(val, len))
+			goto confirmation_succeeded;
+
+		DCCP_WARN("Bogus Confirm for non-existing value\n");
+		goto confirmation_failed;
+	}
+
+	/*
+	 * Parsing SP Confirms: the first element of @val is the preferred
+	 * SP value which the peer confirms, the remainder depends on @len.
+	 * Note that only the confirmed value need to be a valid SP value.
+	 */
+	if (!dccp_feat_is_valid_sp_val(feat, *val))
+		goto confirmation_failed;
+
+	if (len == 1) {		/* peer didn't supply a preference list */
+		plist = val;
+		plen  = len;
+	} else {		/* preferred value + preference list */
+		plist = val + 1;
+		plen  = len - 1;
+	}
+
+	/* Check whether the peer got the reconciliation right (6.6.8) */
+	if (dccp_feat_reconcile(&entry->val, plist, plen, server, 0) != *val) {
+		DCCP_WARN("Confirm selected the wrong value %u\n", *val);
+		return DCCP_RESET_CODE_OPTION_ERROR;
+	}
+	entry->val.sp.vec[0] = *val;
+
+confirmation_succeeded:
+	entry->state = FEAT_STABLE;
+	return 0;
+
+confirmation_failed:
+	DCCP_WARN("Confirmation failed\n");
+	return is_mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
+			    : DCCP_RESET_CODE_OPTION_ERROR;
+}
+
+/**
+ * dccp_feat_handle_nn_established  -  Fast-path reception of NN options
+ * @sk:		socket of an established DCCP connection
+ * @mandatory:	whether @opt was preceded by a Mandatory option
+ * @opt:	%DCCPO_CHANGE_L | %DCCPO_CONFIRM_R (NN only)
+ * @feat:	NN number, one of %dccp_feature_numbers
+ * @val:	NN value
+ * @len:	length of @val in bytes
+ *
+ * This function combines the functionality of change_recv/confirm_recv, with
+ * the following differences (reset codes are the same):
+ *    - cleanup after receiving the Confirm;
+ *    - values are directly activated after successful parsing;
+ *    - deliberately restricted to NN features.
+ * The restriction to NN features is essential since SP features can have non-
+ * predictable outcomes (depending on the remote configuration), and are inter-
+ * dependent (CCIDs for instance cause further dependencies).
+ */
+static u8 dccp_feat_handle_nn_established(struct sock *sk, u8 mandatory, u8 opt,
+					  u8 feat, u8 *val, u8 len)
+{
+	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
+	const bool local = (opt == DCCPO_CONFIRM_R);
+	struct dccp_feat_entry *entry;
+	u8 type = dccp_feat_type(feat);
+	dccp_feat_val fval;
+
+	dccp_feat_print_opt(opt, feat, val, len, mandatory);
+
+	/* Ignore non-mandatory unknown and non-NN features */
+	if (type == FEAT_UNKNOWN) {
+		if (local && !mandatory)
+			return 0;
+		goto fast_path_unknown;
+	} else if (type != FEAT_NN) {
+		return 0;
+	}
+
+	/*
+	 * We don't accept empty Confirms, since in fast-path feature
+	 * negotiation the values are enabled immediately after sending
+	 * the Change option.
+	 * Empty Changes on the other hand are invalid (RFC 4340, 6.1).
+	 */
+	if (len == 0 || len > sizeof(fval.nn))
+		goto fast_path_unknown;
+
+	if (opt == DCCPO_CHANGE_L) {
+		fval.nn = dccp_decode_value_var(val, len);
+		if (!dccp_feat_is_valid_nn_val(feat, fval.nn))
+			goto fast_path_unknown;
+
+		if (dccp_feat_push_confirm(fn, feat, local, &fval) ||
+		    dccp_feat_activate(sk, feat, local, &fval))
+			return DCCP_RESET_CODE_TOO_BUSY;
+
+		/* set the `Ack Pending' flag to piggyback a Confirm */
+		inet_csk_schedule_ack(sk);
+
+	} else if (opt == DCCPO_CONFIRM_R) {
+		entry = dccp_feat_list_lookup(fn, feat, local);
+		if (entry == NULL || entry->state != FEAT_CHANGING)
+			return 0;
+
+		fval.nn = dccp_decode_value_var(val, len);
+		/*
+		 * Just ignore a value that doesn't match our current value.
+		 * If the option changes twice within two RTTs, then at least
+		 * one CONFIRM will be received for the old value after a
+		 * new CHANGE was sent.
+		 */
+		if (fval.nn != entry->val.nn)
+			return 0;
+
+		/* Only activate after receiving the Confirm option (6.6.1). */
+		dccp_feat_activate(sk, feat, local, &fval);
+
+		/* It has been confirmed - so remove the entry */
+		dccp_feat_list_pop(entry);
+
+	} else {
+		DCCP_WARN("Received illegal option %u\n", opt);
+		goto fast_path_failed;
+	}
+	return 0;
+
+fast_path_unknown:
+	if (!mandatory)
+		return dccp_push_empty_confirm(fn, feat, local);
+
+fast_path_failed:
+	return mandatory ? DCCP_RESET_CODE_MANDATORY_ERROR
+			 : DCCP_RESET_CODE_OPTION_ERROR;
+}
+
+/**
+ * dccp_feat_parse_options  -  Process Feature-Negotiation Options
+ * @sk: for general use and used by the client during connection setup
+ * @dreq: used by the server during connection setup
+ * @mandatory: whether @opt was preceded by a Mandatory option
+ * @opt: %DCCPO_CHANGE_L | %DCCPO_CHANGE_R | %DCCPO_CONFIRM_L | %DCCPO_CONFIRM_R
+ * @feat: one of %dccp_feature_numbers
+ * @val: value contents of @opt
+ * @len: length of @val in bytes
+ *
+ * Returns 0 on success, a Reset code for ending the connection otherwise.
+ */
+int dccp_feat_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
+			    u8 mandatory, u8 opt, u8 feat, u8 *val, u8 len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct list_head *fn = dreq ? &dreq->dreq_featneg : &dp->dccps_featneg;
+	bool server = false;
+
+	switch (sk->sk_state) {
+	/*
+	 *	Negotiation during connection setup
+	 */
+	case DCCP_LISTEN:
+		server = true;
+		fallthrough;
+	case DCCP_REQUESTING:
+		switch (opt) {
+		case DCCPO_CHANGE_L:
+		case DCCPO_CHANGE_R:
+			return dccp_feat_change_recv(fn, mandatory, opt, feat,
+						     val, len, server);
+		case DCCPO_CONFIRM_R:
+		case DCCPO_CONFIRM_L:
+			return dccp_feat_confirm_recv(fn, mandatory, opt, feat,
+						      val, len, server);
+		}
+		break;
+	/*
+	 *	Support for exchanging NN options on an established connection.
+	 */
+	case DCCP_OPEN:
+	case DCCP_PARTOPEN:
+		return dccp_feat_handle_nn_established(sk, mandatory, opt, feat,
+						       val, len);
+	}
+	return 0;	/* ignore FN options in all other states */
+}
+
+/**
+ * dccp_feat_init  -  Seed feature negotiation with host-specific defaults
+ * @sk: Socket to initialize.
+ *
+ * This initialises global defaults, depending on the value of the sysctls.
+ * These can later be overridden by registering changes via setsockopt calls.
+ * The last link in the chain is finalise_settings, to make sure that between
+ * here and the start of actual feature negotiation no inconsistencies enter.
+ *
+ * All features not appearing below use either defaults or are otherwise
+ * later adjusted through dccp_feat_finalise_settings().
+ */
+int dccp_feat_init(struct sock *sk)
+{
+	struct list_head *fn = &dccp_sk(sk)->dccps_featneg;
+	u8 on = 1, off = 0;
+	int rc;
+	struct {
+		u8 *val;
+		u8 len;
+	} tx, rx;
+
+	/* Non-negotiable (NN) features */
+	rc = __feat_register_nn(fn, DCCPF_SEQUENCE_WINDOW, 0,
+				    sysctl_dccp_sequence_window);
+	if (rc)
+		return rc;
+
+	/* Server-priority (SP) features */
+
+	/* Advertise that short seqnos are not supported (7.6.1) */
+	rc = __feat_register_sp(fn, DCCPF_SHORT_SEQNOS, true, true, &off, 1);
+	if (rc)
+		return rc;
+
+	/* RFC 4340 12.1: "If a DCCP is not ECN capable, ..." */
+	rc = __feat_register_sp(fn, DCCPF_ECN_INCAPABLE, true, true, &on, 1);
+	if (rc)
+		return rc;
+
+	/*
+	 * We advertise the available list of CCIDs and reorder according to
+	 * preferences, to avoid failure resulting from negotiating different
+	 * singleton values (which always leads to failure).
+	 * These settings can still (later) be overridden via sockopts.
+	 */
+	if (ccid_get_builtin_ccids(&tx.val, &tx.len))
+		return -ENOBUFS;
+	if (ccid_get_builtin_ccids(&rx.val, &rx.len)) {
+		kfree(tx.val);
+		return -ENOBUFS;
+	}
+
+	if (!dccp_feat_prefer(sysctl_dccp_tx_ccid, tx.val, tx.len) ||
+	    !dccp_feat_prefer(sysctl_dccp_rx_ccid, rx.val, rx.len))
+		goto free_ccid_lists;
+
+	rc = __feat_register_sp(fn, DCCPF_CCID, true, false, tx.val, tx.len);
+	if (rc)
+		goto free_ccid_lists;
+
+	rc = __feat_register_sp(fn, DCCPF_CCID, false, false, rx.val, rx.len);
+
+free_ccid_lists:
+	kfree(tx.val);
+	kfree(rx.val);
+	return rc;
+}
+
+int dccp_feat_activate_values(struct sock *sk, struct list_head *fn_list)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct dccp_feat_entry *cur, *next;
+	int idx;
+	dccp_feat_val *fvals[DCCP_FEAT_SUPPORTED_MAX][2] = {
+		 [0 ... DCCP_FEAT_SUPPORTED_MAX-1] = { NULL, NULL }
+	};
+
+	list_for_each_entry(cur, fn_list, node) {
+		/*
+		 * An empty Confirm means that either an unknown feature type
+		 * or an invalid value was present. In the first case there is
+		 * nothing to activate, in the other the default value is used.
+		 */
+		if (cur->empty_confirm)
+			continue;
+
+		idx = dccp_feat_index(cur->feat_num);
+		if (idx < 0) {
+			DCCP_BUG("Unknown feature %u", cur->feat_num);
+			goto activation_failed;
+		}
+		if (cur->state != FEAT_STABLE) {
+			DCCP_CRIT("Negotiation of %s %s failed in state %s",
+				  cur->is_local ? "local" : "remote",
+				  dccp_feat_fname(cur->feat_num),
+				  dccp_feat_sname[cur->state]);
+			goto activation_failed;
+		}
+		fvals[idx][cur->is_local] = &cur->val;
+	}
+
+	/*
+	 * Activate in decreasing order of index, so that the CCIDs are always
+	 * activated as the last feature. This avoids the case where a CCID
+	 * relies on the initialisation of one or more features that it depends
+	 * on (e.g. Send NDP Count, Send Ack Vector, and Ack Ratio features).
+	 */
+	for (idx = DCCP_FEAT_SUPPORTED_MAX; --idx >= 0;)
+		if (__dccp_feat_activate(sk, idx, 0, fvals[idx][0]) ||
+		    __dccp_feat_activate(sk, idx, 1, fvals[idx][1])) {
+			DCCP_CRIT("Could not activate %d", idx);
+			goto activation_failed;
+		}
+
+	/* Clean up Change options which have been confirmed already */
+	list_for_each_entry_safe(cur, next, fn_list, node)
+		if (!cur->needs_confirm)
+			dccp_feat_list_pop(cur);
+
+	dccp_pr_debug("Activation OK\n");
+	return 0;
+
+activation_failed:
+	/*
+	 * We clean up everything that may have been allocated, since
+	 * it is difficult to track at which stage negotiation failed.
+	 * This is ok, since all allocation functions below are robust
+	 * against NULL arguments.
+	 */
+	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
+	ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
+	dp->dccps_hc_rx_ccid = dp->dccps_hc_tx_ccid = NULL;
+	dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
+	dp->dccps_hc_rx_ackvec = NULL;
+	return -1;
+}
diff --git a/net/dccp/feat.h b/net/dccp/feat.h
new file mode 100644
index 000000000..d76c9be5b
--- /dev/null
+++ b/net/dccp/feat.h
@@ -0,0 +1,134 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DCCP_FEAT_H
+#define _DCCP_FEAT_H
+/*
+ *  net/dccp/feat.h
+ *
+ *  Feature negotiation for the DCCP protocol (RFC 4340, section 6)
+ *  Copyright (c) 2008 Gerrit Renker <gerrit@erg.abdn.ac.uk>
+ *  Copyright (c) 2005 Andrea Bittau <a.bittau@cs.ucl.ac.uk>
+ */
+#include <linux/types.h>
+#include "dccp.h"
+
+/*
+ * Known limit values
+ */
+/* Ack Ratio takes 2-byte integer values (11.3) */
+#define DCCPF_ACK_RATIO_MAX	0xFFFF
+/* Wmin=32 and Wmax=2^46-1 from 7.5.2 */
+#define DCCPF_SEQ_WMIN		32
+#define DCCPF_SEQ_WMAX		0x3FFFFFFFFFFFull
+/* Maximum number of SP values that fit in a single (Confirm) option */
+#define DCCP_FEAT_MAX_SP_VALS	(DCCP_SINGLE_OPT_MAXLEN - 2)
+
+enum dccp_feat_type {
+	FEAT_AT_RX   = 1,	/* located at RX side of half-connection  */
+	FEAT_AT_TX   = 2,	/* located at TX side of half-connection  */
+	FEAT_SP      = 4,	/* server-priority reconciliation (6.3.1) */
+	FEAT_NN	     = 8,	/* non-negotiable reconciliation (6.3.2)  */
+	FEAT_UNKNOWN = 0xFF	/* not understood or invalid feature	  */
+};
+
+enum dccp_feat_state {
+	FEAT_DEFAULT = 0,	/* using default values from 6.4 */
+	FEAT_INITIALISING,	/* feature is being initialised  */
+	FEAT_CHANGING,		/* Change sent but not confirmed yet */
+	FEAT_UNSTABLE,		/* local modification in state CHANGING */
+	FEAT_STABLE		/* both ends (think they) agree */
+};
+
+/**
+ * dccp_feat_val  -  Container for SP or NN feature values
+ * @nn:     single NN value
+ * @sp.vec: single SP value plus optional preference list
+ * @sp.len: length of @sp.vec in bytes
+ */
+typedef union {
+	u64 nn;
+	struct {
+		u8	*vec;
+		u8	len;
+	}   sp;
+} dccp_feat_val;
+
+/**
+ * struct feat_entry  -  Data structure to perform feature negotiation
+ * @val: feature's current value (SP features may have preference list)
+ * @state: feature's current state
+ * @feat_num: one of %dccp_feature_numbers
+ * @needs_mandatory: whether Mandatory options should be sent
+ * @needs_confirm: whether to send a Confirm instead of a Change
+ * @empty_confirm: whether to send an empty Confirm (depends on @needs_confirm)
+ * @is_local: feature location (1) or feature-remote (0)
+ * @node: list pointers, entries arranged in FIFO order
+ */
+struct dccp_feat_entry {
+	dccp_feat_val           val;
+	enum dccp_feat_state    state:8;
+	u8                      feat_num;
+
+	bool			needs_mandatory,
+				needs_confirm,
+				empty_confirm,
+				is_local;
+
+	struct list_head	node;
+};
+
+static inline u8 dccp_feat_genopt(struct dccp_feat_entry *entry)
+{
+	if (entry->needs_confirm)
+		return entry->is_local ? DCCPO_CONFIRM_L : DCCPO_CONFIRM_R;
+	return entry->is_local ? DCCPO_CHANGE_L : DCCPO_CHANGE_R;
+}
+
+/**
+ * struct ccid_dependency  -  Track changes resulting from choosing a CCID
+ * @dependent_feat: one of %dccp_feature_numbers
+ * @is_local: local (1) or remote (0) @dependent_feat
+ * @is_mandatory: whether presence of @dependent_feat is mission-critical or not
+ * @val: corresponding default value for @dependent_feat (u8 is sufficient here)
+ */
+struct ccid_dependency {
+	u8	dependent_feat;
+	bool	is_local:1,
+		is_mandatory:1;
+	u8	val;
+};
+
+/*
+ * Sysctls to seed defaults for feature negotiation
+ */
+extern unsigned long sysctl_dccp_sequence_window;
+extern int	     sysctl_dccp_rx_ccid;
+extern int	     sysctl_dccp_tx_ccid;
+
+int dccp_feat_init(struct sock *sk);
+void dccp_feat_initialise_sysctls(void);
+int dccp_feat_register_sp(struct sock *sk, u8 feat, u8 is_local,
+			  u8 const *list, u8 len);
+int dccp_feat_parse_options(struct sock *, struct dccp_request_sock *,
+			    u8 mand, u8 opt, u8 feat, u8 *val, u8 len);
+int dccp_feat_clone_list(struct list_head const *, struct list_head *);
+
+/*
+ * Encoding variable-length options and their maximum length.
+ *
+ * This affects NN options (SP options are all u8) and other variable-length
+ * options (see table 3 in RFC 4340). The limit is currently given the Sequence
+ * Window NN value (sec. 7.5.2) and the NDP count (sec. 7.7) option, all other
+ * options consume less than 6 bytes (timestamps are 4 bytes).
+ * When updating this constant (e.g. due to new internet drafts / RFCs), make
+ * sure that you also update all code which refers to it.
+ */
+#define DCCP_OPTVAL_MAXLEN	6
+
+void dccp_encode_value_var(const u64 value, u8 *to, const u8 len);
+u64 dccp_decode_value_var(const u8 *bf, const u8 len);
+u64 dccp_feat_nn_get(struct sock *sk, u8 feat);
+
+int dccp_insert_option_mandatory(struct sk_buff *skb);
+int dccp_insert_fn_opt(struct sk_buff *skb, u8 type, u8 feat, u8 *val, u8 len,
+		       bool repeat_first);
+#endif /* _DCCP_FEAT_H */
diff --git a/net/dccp/input.c b/net/dccp/input.c
new file mode 100644
index 000000000..2cbb757a8
--- /dev/null
+++ b/net/dccp/input.c
@@ -0,0 +1,739 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/input.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+
+#include <net/sock.h>
+
+#include "ackvec.h"
+#include "ccid.h"
+#include "dccp.h"
+
+/* rate-limit for syncs in reply to sequence-invalid packets; RFC 4340, 7.5.4 */
+int sysctl_dccp_sync_ratelimit	__read_mostly = HZ / 8;
+
+static void dccp_enqueue_skb(struct sock *sk, struct sk_buff *skb)
+{
+	__skb_pull(skb, dccp_hdr(skb)->dccph_doff * 4);
+	__skb_queue_tail(&sk->sk_receive_queue, skb);
+	skb_set_owner_r(skb, sk);
+	sk->sk_data_ready(sk);
+}
+
+static void dccp_fin(struct sock *sk, struct sk_buff *skb)
+{
+	/*
+	 * On receiving Close/CloseReq, both RD/WR shutdown are performed.
+	 * RFC 4340, 8.3 says that we MAY send further Data/DataAcks after
+	 * receiving the closing segment, but there is no guarantee that such
+	 * data will be processed at all.
+	 */
+	sk->sk_shutdown = SHUTDOWN_MASK;
+	sock_set_flag(sk, SOCK_DONE);
+	dccp_enqueue_skb(sk, skb);
+}
+
+static int dccp_rcv_close(struct sock *sk, struct sk_buff *skb)
+{
+	int queued = 0;
+
+	switch (sk->sk_state) {
+	/*
+	 * We ignore Close when received in one of the following states:
+	 *  - CLOSED		(may be a late or duplicate packet)
+	 *  - PASSIVE_CLOSEREQ	(the peer has sent a CloseReq earlier)
+	 *  - RESPOND		(already handled by dccp_check_req)
+	 */
+	case DCCP_CLOSING:
+		/*
+		 * Simultaneous-close: receiving a Close after sending one. This
+		 * can happen if both client and server perform active-close and
+		 * will result in an endless ping-pong of crossing and retrans-
+		 * mitted Close packets, which only terminates when one of the
+		 * nodes times out (min. 64 seconds). Quicker convergence can be
+		 * achieved when one of the nodes acts as tie-breaker.
+		 * This is ok as both ends are done with data transfer and each
+		 * end is just waiting for the other to acknowledge termination.
+		 */
+		if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT)
+			break;
+		fallthrough;
+	case DCCP_REQUESTING:
+	case DCCP_ACTIVE_CLOSEREQ:
+		dccp_send_reset(sk, DCCP_RESET_CODE_CLOSED);
+		dccp_done(sk);
+		break;
+	case DCCP_OPEN:
+	case DCCP_PARTOPEN:
+		/* Give waiting application a chance to read pending data */
+		queued = 1;
+		dccp_fin(sk, skb);
+		dccp_set_state(sk, DCCP_PASSIVE_CLOSE);
+		fallthrough;
+	case DCCP_PASSIVE_CLOSE:
+		/*
+		 * Retransmitted Close: we have already enqueued the first one.
+		 */
+		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
+	}
+	return queued;
+}
+
+static int dccp_rcv_closereq(struct sock *sk, struct sk_buff *skb)
+{
+	int queued = 0;
+
+	/*
+	 *   Step 7: Check for unexpected packet types
+	 *      If (S.is_server and P.type == CloseReq)
+	 *	  Send Sync packet acknowledging P.seqno
+	 *	  Drop packet and return
+	 */
+	if (dccp_sk(sk)->dccps_role != DCCP_ROLE_CLIENT) {
+		dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq, DCCP_PKT_SYNC);
+		return queued;
+	}
+
+	/* Step 13: process relevant Client states < CLOSEREQ */
+	switch (sk->sk_state) {
+	case DCCP_REQUESTING:
+		dccp_send_close(sk, 0);
+		dccp_set_state(sk, DCCP_CLOSING);
+		break;
+	case DCCP_OPEN:
+	case DCCP_PARTOPEN:
+		/* Give waiting application a chance to read pending data */
+		queued = 1;
+		dccp_fin(sk, skb);
+		dccp_set_state(sk, DCCP_PASSIVE_CLOSEREQ);
+		fallthrough;
+	case DCCP_PASSIVE_CLOSEREQ:
+		sk_wake_async(sk, SOCK_WAKE_WAITD, POLL_HUP);
+	}
+	return queued;
+}
+
+static u16 dccp_reset_code_convert(const u8 code)
+{
+	static const u16 error_code[] = {
+	[DCCP_RESET_CODE_CLOSED]	     = 0,	/* normal termination */
+	[DCCP_RESET_CODE_UNSPECIFIED]	     = 0,	/* nothing known */
+	[DCCP_RESET_CODE_ABORTED]	     = ECONNRESET,
+
+	[DCCP_RESET_CODE_NO_CONNECTION]	     = ECONNREFUSED,
+	[DCCP_RESET_CODE_CONNECTION_REFUSED] = ECONNREFUSED,
+	[DCCP_RESET_CODE_TOO_BUSY]	     = EUSERS,
+	[DCCP_RESET_CODE_AGGRESSION_PENALTY] = EDQUOT,
+
+	[DCCP_RESET_CODE_PACKET_ERROR]	     = ENOMSG,
+	[DCCP_RESET_CODE_BAD_INIT_COOKIE]    = EBADR,
+	[DCCP_RESET_CODE_BAD_SERVICE_CODE]   = EBADRQC,
+	[DCCP_RESET_CODE_OPTION_ERROR]	     = EILSEQ,
+	[DCCP_RESET_CODE_MANDATORY_ERROR]    = EOPNOTSUPP,
+	};
+
+	return code >= DCCP_MAX_RESET_CODES ? 0 : error_code[code];
+}
+
+static void dccp_rcv_reset(struct sock *sk, struct sk_buff *skb)
+{
+	u16 err = dccp_reset_code_convert(dccp_hdr_reset(skb)->dccph_reset_code);
+
+	sk->sk_err = err;
+
+	/* Queue the equivalent of TCP fin so that dccp_recvmsg exits the loop */
+	dccp_fin(sk, skb);
+
+	if (err && !sock_flag(sk, SOCK_DEAD))
+		sk_wake_async(sk, SOCK_WAKE_IO, POLL_ERR);
+	dccp_time_wait(sk, DCCP_TIME_WAIT, 0);
+}
+
+static void dccp_handle_ackvec_processing(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_ackvec *av = dccp_sk(sk)->dccps_hc_rx_ackvec;
+
+	if (av == NULL)
+		return;
+	if (DCCP_SKB_CB(skb)->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
+		dccp_ackvec_clear_state(av, DCCP_SKB_CB(skb)->dccpd_ack_seq);
+	dccp_ackvec_input(av, skb);
+}
+
+static void dccp_deliver_input_to_ccids(struct sock *sk, struct sk_buff *skb)
+{
+	const struct dccp_sock *dp = dccp_sk(sk);
+
+	/* Don't deliver to RX CCID when node has shut down read end. */
+	if (!(sk->sk_shutdown & RCV_SHUTDOWN))
+		ccid_hc_rx_packet_recv(dp->dccps_hc_rx_ccid, sk, skb);
+	/*
+	 * Until the TX queue has been drained, we can not honour SHUT_WR, since
+	 * we need received feedback as input to adjust congestion control.
+	 */
+	if (sk->sk_write_queue.qlen > 0 || !(sk->sk_shutdown & SEND_SHUTDOWN))
+		ccid_hc_tx_packet_recv(dp->dccps_hc_tx_ccid, sk, skb);
+}
+
+static int dccp_check_seqno(struct sock *sk, struct sk_buff *skb)
+{
+	const struct dccp_hdr *dh = dccp_hdr(skb);
+	struct dccp_sock *dp = dccp_sk(sk);
+	u64 lswl, lawl, seqno = DCCP_SKB_CB(skb)->dccpd_seq,
+			ackno = DCCP_SKB_CB(skb)->dccpd_ack_seq;
+
+	/*
+	 *   Step 5: Prepare sequence numbers for Sync
+	 *     If P.type == Sync or P.type == SyncAck,
+	 *	  If S.AWL <= P.ackno <= S.AWH and P.seqno >= S.SWL,
+	 *	     / * P is valid, so update sequence number variables
+	 *		 accordingly.  After this update, P will pass the tests
+	 *		 in Step 6.  A SyncAck is generated if necessary in
+	 *		 Step 15 * /
+	 *	     Update S.GSR, S.SWL, S.SWH
+	 *	  Otherwise,
+	 *	     Drop packet and return
+	 */
+	if (dh->dccph_type == DCCP_PKT_SYNC ||
+	    dh->dccph_type == DCCP_PKT_SYNCACK) {
+		if (between48(ackno, dp->dccps_awl, dp->dccps_awh) &&
+		    dccp_delta_seqno(dp->dccps_swl, seqno) >= 0)
+			dccp_update_gsr(sk, seqno);
+		else
+			return -1;
+	}
+
+	/*
+	 *   Step 6: Check sequence numbers
+	 *      Let LSWL = S.SWL and LAWL = S.AWL
+	 *      If P.type == CloseReq or P.type == Close or P.type == Reset,
+	 *	  LSWL := S.GSR + 1, LAWL := S.GAR
+	 *      If LSWL <= P.seqno <= S.SWH
+	 *	     and (P.ackno does not exist or LAWL <= P.ackno <= S.AWH),
+	 *	  Update S.GSR, S.SWL, S.SWH
+	 *	  If P.type != Sync,
+	 *	     Update S.GAR
+	 */
+	lswl = dp->dccps_swl;
+	lawl = dp->dccps_awl;
+
+	if (dh->dccph_type == DCCP_PKT_CLOSEREQ ||
+	    dh->dccph_type == DCCP_PKT_CLOSE ||
+	    dh->dccph_type == DCCP_PKT_RESET) {
+		lswl = ADD48(dp->dccps_gsr, 1);
+		lawl = dp->dccps_gar;
+	}
+
+	if (between48(seqno, lswl, dp->dccps_swh) &&
+	    (ackno == DCCP_PKT_WITHOUT_ACK_SEQ ||
+	     between48(ackno, lawl, dp->dccps_awh))) {
+		dccp_update_gsr(sk, seqno);
+
+		if (dh->dccph_type != DCCP_PKT_SYNC &&
+		    ackno != DCCP_PKT_WITHOUT_ACK_SEQ &&
+		    after48(ackno, dp->dccps_gar))
+			dp->dccps_gar = ackno;
+	} else {
+		unsigned long now = jiffies;
+		/*
+		 *   Step 6: Check sequence numbers
+		 *      Otherwise,
+		 *         If P.type == Reset,
+		 *            Send Sync packet acknowledging S.GSR
+		 *         Otherwise,
+		 *            Send Sync packet acknowledging P.seqno
+		 *      Drop packet and return
+		 *
+		 *   These Syncs are rate-limited as per RFC 4340, 7.5.4:
+		 *   at most 1 / (dccp_sync_rate_limit * HZ) Syncs per second.
+		 */
+		if (time_before(now, (dp->dccps_rate_last +
+				      sysctl_dccp_sync_ratelimit)))
+			return -1;
+
+		DCCP_WARN("Step 6 failed for %s packet, "
+			  "(LSWL(%llu) <= P.seqno(%llu) <= S.SWH(%llu)) and "
+			  "(P.ackno %s or LAWL(%llu) <= P.ackno(%llu) <= S.AWH(%llu), "
+			  "sending SYNC...\n",  dccp_packet_name(dh->dccph_type),
+			  (unsigned long long) lswl, (unsigned long long) seqno,
+			  (unsigned long long) dp->dccps_swh,
+			  (ackno == DCCP_PKT_WITHOUT_ACK_SEQ) ? "doesn't exist"
+							      : "exists",
+			  (unsigned long long) lawl, (unsigned long long) ackno,
+			  (unsigned long long) dp->dccps_awh);
+
+		dp->dccps_rate_last = now;
+
+		if (dh->dccph_type == DCCP_PKT_RESET)
+			seqno = dp->dccps_gsr;
+		dccp_send_sync(sk, seqno, DCCP_PKT_SYNC);
+		return -1;
+	}
+
+	return 0;
+}
+
+static int __dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
+				  const struct dccp_hdr *dh, const unsigned int len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	switch (dccp_hdr(skb)->dccph_type) {
+	case DCCP_PKT_DATAACK:
+	case DCCP_PKT_DATA:
+		/*
+		 * FIXME: schedule DATA_DROPPED (RFC 4340, 11.7.2) if and when
+		 * - sk_shutdown == RCV_SHUTDOWN, use Code 1, "Not Listening"
+		 * - sk_receive_queue is full, use Code 2, "Receive Buffer"
+		 */
+		dccp_enqueue_skb(sk, skb);
+		return 0;
+	case DCCP_PKT_ACK:
+		goto discard;
+	case DCCP_PKT_RESET:
+		/*
+		 *  Step 9: Process Reset
+		 *	If P.type == Reset,
+		 *		Tear down connection
+		 *		S.state := TIMEWAIT
+		 *		Set TIMEWAIT timer
+		 *		Drop packet and return
+		 */
+		dccp_rcv_reset(sk, skb);
+		return 0;
+	case DCCP_PKT_CLOSEREQ:
+		if (dccp_rcv_closereq(sk, skb))
+			return 0;
+		goto discard;
+	case DCCP_PKT_CLOSE:
+		if (dccp_rcv_close(sk, skb))
+			return 0;
+		goto discard;
+	case DCCP_PKT_REQUEST:
+		/* Step 7
+		 *   or (S.is_server and P.type == Response)
+		 *   or (S.is_client and P.type == Request)
+		 *   or (S.state >= OPEN and P.type == Request
+		 *	and P.seqno >= S.OSR)
+		 *    or (S.state >= OPEN and P.type == Response
+		 *	and P.seqno >= S.OSR)
+		 *    or (S.state == RESPOND and P.type == Data),
+		 *  Send Sync packet acknowledging P.seqno
+		 *  Drop packet and return
+		 */
+		if (dp->dccps_role != DCCP_ROLE_LISTEN)
+			goto send_sync;
+		goto check_seq;
+	case DCCP_PKT_RESPONSE:
+		if (dp->dccps_role != DCCP_ROLE_CLIENT)
+			goto send_sync;
+check_seq:
+		if (dccp_delta_seqno(dp->dccps_osr,
+				     DCCP_SKB_CB(skb)->dccpd_seq) >= 0) {
+send_sync:
+			dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
+				       DCCP_PKT_SYNC);
+		}
+		break;
+	case DCCP_PKT_SYNC:
+		dccp_send_sync(sk, DCCP_SKB_CB(skb)->dccpd_seq,
+			       DCCP_PKT_SYNCACK);
+		/*
+		 * From RFC 4340, sec. 5.7
+		 *
+		 * As with DCCP-Ack packets, DCCP-Sync and DCCP-SyncAck packets
+		 * MAY have non-zero-length application data areas, whose
+		 * contents receivers MUST ignore.
+		 */
+		goto discard;
+	}
+
+	DCCP_INC_STATS(DCCP_MIB_INERRS);
+discard:
+	__kfree_skb(skb);
+	return 0;
+}
+
+int dccp_rcv_established(struct sock *sk, struct sk_buff *skb,
+			 const struct dccp_hdr *dh, const unsigned int len)
+{
+	if (dccp_check_seqno(sk, skb))
+		goto discard;
+
+	if (dccp_parse_options(sk, NULL, skb))
+		return 1;
+
+	dccp_handle_ackvec_processing(sk, skb);
+	dccp_deliver_input_to_ccids(sk, skb);
+
+	return __dccp_rcv_established(sk, skb, dh, len);
+discard:
+	__kfree_skb(skb);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_rcv_established);
+
+static int dccp_rcv_request_sent_state_process(struct sock *sk,
+					       struct sk_buff *skb,
+					       const struct dccp_hdr *dh,
+					       const unsigned int len)
+{
+	/*
+	 *  Step 4: Prepare sequence numbers in REQUEST
+	 *     If S.state == REQUEST,
+	 *	  If (P.type == Response or P.type == Reset)
+	 *		and S.AWL <= P.ackno <= S.AWH,
+	 *	     / * Set sequence number variables corresponding to the
+	 *		other endpoint, so P will pass the tests in Step 6 * /
+	 *	     Set S.GSR, S.ISR, S.SWL, S.SWH
+	 *	     / * Response processing continues in Step 10; Reset
+	 *		processing continues in Step 9 * /
+	*/
+	if (dh->dccph_type == DCCP_PKT_RESPONSE) {
+		const struct inet_connection_sock *icsk = inet_csk(sk);
+		struct dccp_sock *dp = dccp_sk(sk);
+		long tstamp = dccp_timestamp();
+
+		if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
+			       dp->dccps_awl, dp->dccps_awh)) {
+			dccp_pr_debug("invalid ackno: S.AWL=%llu, "
+				      "P.ackno=%llu, S.AWH=%llu\n",
+				      (unsigned long long)dp->dccps_awl,
+			   (unsigned long long)DCCP_SKB_CB(skb)->dccpd_ack_seq,
+				      (unsigned long long)dp->dccps_awh);
+			goto out_invalid_packet;
+		}
+
+		/*
+		 * If option processing (Step 8) failed, return 1 here so that
+		 * dccp_v4_do_rcv() sends a Reset. The Reset code depends on
+		 * the option type and is set in dccp_parse_options().
+		 */
+		if (dccp_parse_options(sk, NULL, skb))
+			return 1;
+
+		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */
+		if (likely(dp->dccps_options_received.dccpor_timestamp_echo))
+			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * (tstamp -
+			    dp->dccps_options_received.dccpor_timestamp_echo));
+
+		/* Stop the REQUEST timer */
+		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);
+		WARN_ON(sk->sk_send_head == NULL);
+		kfree_skb(sk->sk_send_head);
+		sk->sk_send_head = NULL;
+
+		/*
+		 * Set ISR, GSR from packet. ISS was set in dccp_v{4,6}_connect
+		 * and GSS in dccp_transmit_skb(). Setting AWL/AWH and SWL/SWH
+		 * is done as part of activating the feature values below, since
+		 * these settings depend on the local/remote Sequence Window
+		 * features, which were undefined or not confirmed until now.
+		 */
+		dp->dccps_gsr = dp->dccps_isr = DCCP_SKB_CB(skb)->dccpd_seq;
+
+		dccp_sync_mss(sk, icsk->icsk_pmtu_cookie);
+
+		/*
+		 *    Step 10: Process REQUEST state (second part)
+		 *       If S.state == REQUEST,
+		 *	  / * If we get here, P is a valid Response from the
+		 *	      server (see Step 4), and we should move to
+		 *	      PARTOPEN state. PARTOPEN means send an Ack,
+		 *	      don't send Data packets, retransmit Acks
+		 *	      periodically, and always include any Init Cookie
+		 *	      from the Response * /
+		 *	  S.state := PARTOPEN
+		 *	  Set PARTOPEN timer
+		 *	  Continue with S.state == PARTOPEN
+		 *	  / * Step 12 will send the Ack completing the
+		 *	      three-way handshake * /
+		 */
+		dccp_set_state(sk, DCCP_PARTOPEN);
+
+		/*
+		 * If feature negotiation was successful, activate features now;
+		 * an activation failure means that this host could not activate
+		 * one ore more features (e.g. insufficient memory), which would
+		 * leave at least one feature in an undefined state.
+		 */
+		if (dccp_feat_activate_values(sk, &dp->dccps_featneg))
+			goto unable_to_proceed;
+
+		/* Make sure socket is routed, for correct metrics. */
+		icsk->icsk_af_ops->rebuild_header(sk);
+
+		if (!sock_flag(sk, SOCK_DEAD)) {
+			sk->sk_state_change(sk);
+			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
+		}
+
+		if (sk->sk_write_pending || inet_csk_in_pingpong_mode(sk) ||
+		    icsk->icsk_accept_queue.rskq_defer_accept) {
+			/* Save one ACK. Data will be ready after
+			 * several ticks, if write_pending is set.
+			 *
+			 * It may be deleted, but with this feature tcpdumps
+			 * look so _wonderfully_ clever, that I was not able
+			 * to stand against the temptation 8)     --ANK
+			 */
+			/*
+			 * OK, in DCCP we can as well do a similar trick, its
+			 * even in the draft, but there is no need for us to
+			 * schedule an ack here, as dccp_sendmsg does this for
+			 * us, also stated in the draft. -acme
+			 */
+			__kfree_skb(skb);
+			return 0;
+		}
+		dccp_send_ack(sk);
+		return -1;
+	}
+
+out_invalid_packet:
+	/* dccp_v4_do_rcv will send a reset */
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;
+	return 1;
+
+unable_to_proceed:
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_ABORTED;
+	/*
+	 * We mark this socket as no longer usable, so that the loop in
+	 * dccp_sendmsg() terminates and the application gets notified.
+	 */
+	dccp_set_state(sk, DCCP_CLOSED);
+	sk->sk_err = ECOMM;
+	return 1;
+}
+
+static int dccp_rcv_respond_partopen_state_process(struct sock *sk,
+						   struct sk_buff *skb,
+						   const struct dccp_hdr *dh,
+						   const unsigned int len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	u32 sample = dp->dccps_options_received.dccpor_timestamp_echo;
+	int queued = 0;
+
+	switch (dh->dccph_type) {
+	case DCCP_PKT_RESET:
+		inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
+		break;
+	case DCCP_PKT_DATA:
+		if (sk->sk_state == DCCP_RESPOND)
+			break;
+		fallthrough;
+	case DCCP_PKT_DATAACK:
+	case DCCP_PKT_ACK:
+		/*
+		 * FIXME: we should be resetting the PARTOPEN (DELACK) timer
+		 * here but only if we haven't used the DELACK timer for
+		 * something else, like sending a delayed ack for a TIMESTAMP
+		 * echo, etc, for now were not clearing it, sending an extra
+		 * ACK when there is nothing else to do in DELACK is not a big
+		 * deal after all.
+		 */
+
+		/* Stop the PARTOPEN timer */
+		if (sk->sk_state == DCCP_PARTOPEN)
+			inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
+
+		/* Obtain usec RTT sample from SYN exchange (used by TFRC). */
+		if (likely(sample)) {
+			long delta = dccp_timestamp() - sample;
+
+			dp->dccps_syn_rtt = dccp_sample_rtt(sk, 10 * delta);
+		}
+
+		dp->dccps_osr = DCCP_SKB_CB(skb)->dccpd_seq;
+		dccp_set_state(sk, DCCP_OPEN);
+
+		if (dh->dccph_type == DCCP_PKT_DATAACK ||
+		    dh->dccph_type == DCCP_PKT_DATA) {
+			__dccp_rcv_established(sk, skb, dh, len);
+			queued = 1; /* packet was queued
+				       (by __dccp_rcv_established) */
+		}
+		break;
+	}
+
+	return queued;
+}
+
+int dccp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
+			   struct dccp_hdr *dh, unsigned int len)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+	const int old_state = sk->sk_state;
+	bool acceptable;
+	int queued = 0;
+
+	/*
+	 *  Step 3: Process LISTEN state
+	 *
+	 *     If S.state == LISTEN,
+	 *	 If P.type == Request or P contains a valid Init Cookie option,
+	 *	      (* Must scan the packet's options to check for Init
+	 *		 Cookies.  Only Init Cookies are processed here,
+	 *		 however; other options are processed in Step 8.  This
+	 *		 scan need only be performed if the endpoint uses Init
+	 *		 Cookies *)
+	 *	      (* Generate a new socket and switch to that socket *)
+	 *	      Set S := new socket for this port pair
+	 *	      S.state = RESPOND
+	 *	      Choose S.ISS (initial seqno) or set from Init Cookies
+	 *	      Initialize S.GAR := S.ISS
+	 *	      Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init
+	 *	      Cookies Continue with S.state == RESPOND
+	 *	      (* A Response packet will be generated in Step 11 *)
+	 *	 Otherwise,
+	 *	      Generate Reset(No Connection) unless P.type == Reset
+	 *	      Drop packet and return
+	 */
+	if (sk->sk_state == DCCP_LISTEN) {
+		if (dh->dccph_type == DCCP_PKT_REQUEST) {
+			/* It is possible that we process SYN packets from backlog,
+			 * so we need to make sure to disable BH and RCU right there.
+			 */
+			rcu_read_lock();
+			local_bh_disable();
+			acceptable = inet_csk(sk)->icsk_af_ops->conn_request(sk, skb) >= 0;
+			local_bh_enable();
+			rcu_read_unlock();
+			if (!acceptable)
+				return 1;
+			consume_skb(skb);
+			return 0;
+		}
+		if (dh->dccph_type == DCCP_PKT_RESET)
+			goto discard;
+
+		/* Caller (dccp_v4_do_rcv) will send Reset */
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;
+		return 1;
+	} else if (sk->sk_state == DCCP_CLOSED) {
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_NO_CONNECTION;
+		return 1;
+	}
+
+	/* Step 6: Check sequence numbers (omitted in LISTEN/REQUEST state) */
+	if (sk->sk_state != DCCP_REQUESTING && dccp_check_seqno(sk, skb))
+		goto discard;
+
+	/*
+	 *   Step 7: Check for unexpected packet types
+	 *      If (S.is_server and P.type == Response)
+	 *	    or (S.is_client and P.type == Request)
+	 *	    or (S.state == RESPOND and P.type == Data),
+	 *	  Send Sync packet acknowledging P.seqno
+	 *	  Drop packet and return
+	 */
+	if ((dp->dccps_role != DCCP_ROLE_CLIENT &&
+	     dh->dccph_type == DCCP_PKT_RESPONSE) ||
+	    (dp->dccps_role == DCCP_ROLE_CLIENT &&
+	     dh->dccph_type == DCCP_PKT_REQUEST) ||
+	    (sk->sk_state == DCCP_RESPOND && dh->dccph_type == DCCP_PKT_DATA)) {
+		dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNC);
+		goto discard;
+	}
+
+	/*  Step 8: Process options */
+	if (dccp_parse_options(sk, NULL, skb))
+		return 1;
+
+	/*
+	 *  Step 9: Process Reset
+	 *	If P.type == Reset,
+	 *		Tear down connection
+	 *		S.state := TIMEWAIT
+	 *		Set TIMEWAIT timer
+	 *		Drop packet and return
+	 */
+	if (dh->dccph_type == DCCP_PKT_RESET) {
+		dccp_rcv_reset(sk, skb);
+		return 0;
+	} else if (dh->dccph_type == DCCP_PKT_CLOSEREQ) {	/* Step 13 */
+		if (dccp_rcv_closereq(sk, skb))
+			return 0;
+		goto discard;
+	} else if (dh->dccph_type == DCCP_PKT_CLOSE) {		/* Step 14 */
+		if (dccp_rcv_close(sk, skb))
+			return 0;
+		goto discard;
+	}
+
+	switch (sk->sk_state) {
+	case DCCP_REQUESTING:
+		queued = dccp_rcv_request_sent_state_process(sk, skb, dh, len);
+		if (queued >= 0)
+			return queued;
+
+		__kfree_skb(skb);
+		return 0;
+
+	case DCCP_PARTOPEN:
+		/* Step 8: if using Ack Vectors, mark packet acknowledgeable */
+		dccp_handle_ackvec_processing(sk, skb);
+		dccp_deliver_input_to_ccids(sk, skb);
+		fallthrough;
+	case DCCP_RESPOND:
+		queued = dccp_rcv_respond_partopen_state_process(sk, skb,
+								 dh, len);
+		break;
+	}
+
+	if (dh->dccph_type == DCCP_PKT_ACK ||
+	    dh->dccph_type == DCCP_PKT_DATAACK) {
+		switch (old_state) {
+		case DCCP_PARTOPEN:
+			sk->sk_state_change(sk);
+			sk_wake_async(sk, SOCK_WAKE_IO, POLL_OUT);
+			break;
+		}
+	} else if (unlikely(dh->dccph_type == DCCP_PKT_SYNC)) {
+		dccp_send_sync(sk, dcb->dccpd_seq, DCCP_PKT_SYNCACK);
+		goto discard;
+	}
+
+	if (!queued) {
+discard:
+		__kfree_skb(skb);
+	}
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_rcv_state_process);
+
+/**
+ *  dccp_sample_rtt  -  Validate and finalise computation of RTT sample
+ *  @sk:	socket structure
+ *  @delta:	number of microseconds between packet and acknowledgment
+ *
+ *  The routine is kept generic to work in different contexts. It should be
+ *  called immediately when the ACK used for the RTT sample arrives.
+ */
+u32 dccp_sample_rtt(struct sock *sk, long delta)
+{
+	/* dccpor_elapsed_time is either zeroed out or set and > 0 */
+	delta -= dccp_sk(sk)->dccps_options_received.dccpor_elapsed_time * 10;
+
+	if (unlikely(delta <= 0)) {
+		DCCP_WARN("unusable RTT sample %ld, using min\n", delta);
+		return DCCP_SANE_RTT_MIN;
+	}
+	if (unlikely(delta > DCCP_SANE_RTT_MAX)) {
+		DCCP_WARN("RTT sample %ld too large, using max\n", delta);
+		return DCCP_SANE_RTT_MAX;
+	}
+
+	return delta;
+}
diff --git a/net/dccp/ipv4.c b/net/dccp/ipv4.c
new file mode 100644
index 000000000..2c7c1bdd3
--- /dev/null
+++ b/net/dccp/ipv4.c
@@ -0,0 +1,1080 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/ipv4.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/icmp.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/skbuff.h>
+#include <linux/random.h>
+
+#include <net/icmp.h>
+#include <net/inet_common.h>
+#include <net/inet_hashtables.h>
+#include <net/inet_sock.h>
+#include <net/protocol.h>
+#include <net/sock.h>
+#include <net/timewait_sock.h>
+#include <net/tcp_states.h>
+#include <net/xfrm.h>
+#include <net/secure_seq.h>
+
+#include "ackvec.h"
+#include "ccid.h"
+#include "dccp.h"
+#include "feat.h"
+
+/*
+ * The per-net dccp.v4_ctl_sk socket is used for responding to
+ * the Out-of-the-blue (OOTB) packets. A control sock will be created
+ * for this socket at the initialization time.
+ */
+
+int dccp_v4_connect(struct sock *sk, struct sockaddr *uaddr, int addr_len)
+{
+	const struct sockaddr_in *usin = (struct sockaddr_in *)uaddr;
+	struct inet_sock *inet = inet_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	__be16 orig_sport, orig_dport;
+	__be32 daddr, nexthop;
+	struct flowi4 *fl4;
+	struct rtable *rt;
+	int err;
+	struct ip_options_rcu *inet_opt;
+
+	dp->dccps_role = DCCP_ROLE_CLIENT;
+
+	if (addr_len < sizeof(struct sockaddr_in))
+		return -EINVAL;
+
+	if (usin->sin_family != AF_INET)
+		return -EAFNOSUPPORT;
+
+	nexthop = daddr = usin->sin_addr.s_addr;
+
+	inet_opt = rcu_dereference_protected(inet->inet_opt,
+					     lockdep_sock_is_held(sk));
+	if (inet_opt != NULL && inet_opt->opt.srr) {
+		if (daddr == 0)
+			return -EINVAL;
+		nexthop = inet_opt->opt.faddr;
+	}
+
+	orig_sport = inet->inet_sport;
+	orig_dport = usin->sin_port;
+	fl4 = &inet->cork.fl.u.ip4;
+	rt = ip_route_connect(fl4, nexthop, inet->inet_saddr,
+			      RT_CONN_FLAGS(sk), sk->sk_bound_dev_if,
+			      IPPROTO_DCCP,
+			      orig_sport, orig_dport, sk);
+	if (IS_ERR(rt))
+		return PTR_ERR(rt);
+
+	if (rt->rt_flags & (RTCF_MULTICAST | RTCF_BROADCAST)) {
+		ip_rt_put(rt);
+		return -ENETUNREACH;
+	}
+
+	if (inet_opt == NULL || !inet_opt->opt.srr)
+		daddr = fl4->daddr;
+
+	if (inet->inet_saddr == 0)
+		inet->inet_saddr = fl4->saddr;
+	sk_rcv_saddr_set(sk, inet->inet_saddr);
+	inet->inet_dport = usin->sin_port;
+	sk_daddr_set(sk, daddr);
+
+	inet_csk(sk)->icsk_ext_hdr_len = 0;
+	if (inet_opt)
+		inet_csk(sk)->icsk_ext_hdr_len = inet_opt->opt.optlen;
+	/*
+	 * Socket identity is still unknown (sport may be zero).
+	 * However we set state to DCCP_REQUESTING and not releasing socket
+	 * lock select source port, enter ourselves into the hash tables and
+	 * complete initialization after this.
+	 */
+	dccp_set_state(sk, DCCP_REQUESTING);
+	err = inet_hash_connect(&dccp_death_row, sk);
+	if (err != 0)
+		goto failure;
+
+	rt = ip_route_newports(fl4, rt, orig_sport, orig_dport,
+			       inet->inet_sport, inet->inet_dport, sk);
+	if (IS_ERR(rt)) {
+		err = PTR_ERR(rt);
+		rt = NULL;
+		goto failure;
+	}
+	/* OK, now commit destination to socket.  */
+	sk_setup_caps(sk, &rt->dst);
+
+	dp->dccps_iss = secure_dccp_sequence_number(inet->inet_saddr,
+						    inet->inet_daddr,
+						    inet->inet_sport,
+						    inet->inet_dport);
+	inet->inet_id = prandom_u32();
+
+	err = dccp_connect(sk);
+	rt = NULL;
+	if (err != 0)
+		goto failure;
+out:
+	return err;
+failure:
+	/*
+	 * This unhashes the socket and releases the local port, if necessary.
+	 */
+	dccp_set_state(sk, DCCP_CLOSED);
+	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
+		inet_reset_saddr(sk);
+	ip_rt_put(rt);
+	sk->sk_route_caps = 0;
+	inet->inet_dport = 0;
+	goto out;
+}
+EXPORT_SYMBOL_GPL(dccp_v4_connect);
+
+/*
+ * This routine does path mtu discovery as defined in RFC1191.
+ */
+static inline void dccp_do_pmtu_discovery(struct sock *sk,
+					  const struct iphdr *iph,
+					  u32 mtu)
+{
+	struct dst_entry *dst;
+	const struct inet_sock *inet = inet_sk(sk);
+	const struct dccp_sock *dp = dccp_sk(sk);
+
+	/* We are not interested in DCCP_LISTEN and request_socks (RESPONSEs
+	 * send out by Linux are always < 576bytes so they should go through
+	 * unfragmented).
+	 */
+	if (sk->sk_state == DCCP_LISTEN)
+		return;
+
+	dst = inet_csk_update_pmtu(sk, mtu);
+	if (!dst)
+		return;
+
+	/* Something is about to be wrong... Remember soft error
+	 * for the case, if this connection will not able to recover.
+	 */
+	if (mtu < dst_mtu(dst) && ip_dont_fragment(sk, dst))
+		sk->sk_err_soft = EMSGSIZE;
+
+	mtu = dst_mtu(dst);
+
+	if (inet->pmtudisc != IP_PMTUDISC_DONT &&
+	    ip_sk_accept_pmtu(sk) &&
+	    inet_csk(sk)->icsk_pmtu_cookie > mtu) {
+		dccp_sync_mss(sk, mtu);
+
+		/*
+		 * From RFC 4340, sec. 14.1:
+		 *
+		 *	DCCP-Sync packets are the best choice for upward
+		 *	probing, since DCCP-Sync probes do not risk application
+		 *	data loss.
+		 */
+		dccp_send_sync(sk, dp->dccps_gsr, DCCP_PKT_SYNC);
+	} /* else let the usual retransmit timer handle it */
+}
+
+static void dccp_do_redirect(struct sk_buff *skb, struct sock *sk)
+{
+	struct dst_entry *dst = __sk_dst_check(sk, 0);
+
+	if (dst)
+		dst->ops->redirect(dst, sk, skb);
+}
+
+void dccp_req_err(struct sock *sk, u64 seq)
+	{
+	struct request_sock *req = inet_reqsk(sk);
+	struct net *net = sock_net(sk);
+
+	/*
+	 * ICMPs are not backlogged, hence we cannot get an established
+	 * socket here.
+	 */
+	if (!between48(seq, dccp_rsk(req)->dreq_iss, dccp_rsk(req)->dreq_gss)) {
+		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);
+	} else {
+		/*
+		 * Still in RESPOND, just remove it silently.
+		 * There is no good way to pass the error to the newly
+		 * created socket, and POSIX does not want network
+		 * errors returned from accept().
+		 */
+		inet_csk_reqsk_queue_drop(req->rsk_listener, req);
+	}
+	reqsk_put(req);
+}
+EXPORT_SYMBOL(dccp_req_err);
+
+/*
+ * This routine is called by the ICMP module when it gets some sort of error
+ * condition. If err < 0 then the socket should be closed and the error
+ * returned to the user. If err > 0 it's just the icmp type << 8 | icmp code.
+ * After adjustment header points to the first 8 bytes of the tcp header. We
+ * need to find the appropriate port.
+ *
+ * The locking strategy used here is very "optimistic". When someone else
+ * accesses the socket the ICMP is just dropped and for some paths there is no
+ * check at all. A more general error queue to queue errors for later handling
+ * is probably better.
+ */
+static int dccp_v4_err(struct sk_buff *skb, u32 info)
+{
+	const struct iphdr *iph = (struct iphdr *)skb->data;
+	const u8 offset = iph->ihl << 2;
+	const struct dccp_hdr *dh;
+	struct dccp_sock *dp;
+	struct inet_sock *inet;
+	const int type = icmp_hdr(skb)->type;
+	const int code = icmp_hdr(skb)->code;
+	struct sock *sk;
+	__u64 seq;
+	int err;
+	struct net *net = dev_net(skb->dev);
+
+	if (!pskb_may_pull(skb, offset + sizeof(*dh)))
+		return -EINVAL;
+	dh = (struct dccp_hdr *)(skb->data + offset);
+	if (!pskb_may_pull(skb, offset + __dccp_basic_hdr_len(dh)))
+		return -EINVAL;
+	iph = (struct iphdr *)skb->data;
+	dh = (struct dccp_hdr *)(skb->data + offset);
+
+	sk = __inet_lookup_established(net, &dccp_hashinfo,
+				       iph->daddr, dh->dccph_dport,
+				       iph->saddr, ntohs(dh->dccph_sport),
+				       inet_iif(skb), 0);
+	if (!sk) {
+		__ICMP_INC_STATS(net, ICMP_MIB_INERRORS);
+		return -ENOENT;
+	}
+
+	if (sk->sk_state == DCCP_TIME_WAIT) {
+		inet_twsk_put(inet_twsk(sk));
+		return 0;
+	}
+	seq = dccp_hdr_seq(dh);
+	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
+		dccp_req_err(sk, seq);
+		return 0;
+	}
+
+	bh_lock_sock(sk);
+	/* If too many ICMPs get dropped on busy
+	 * servers this needs to be solved differently.
+	 */
+	if (sock_owned_by_user(sk))
+		__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);
+
+	if (sk->sk_state == DCCP_CLOSED)
+		goto out;
+
+	dp = dccp_sk(sk);
+	if ((1 << sk->sk_state) & ~(DCCPF_REQUESTING | DCCPF_LISTEN) &&
+	    !between48(seq, dp->dccps_awl, dp->dccps_awh)) {
+		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);
+		goto out;
+	}
+
+	switch (type) {
+	case ICMP_REDIRECT:
+		if (!sock_owned_by_user(sk))
+			dccp_do_redirect(skb, sk);
+		goto out;
+	case ICMP_SOURCE_QUENCH:
+		/* Just silently ignore these. */
+		goto out;
+	case ICMP_PARAMETERPROB:
+		err = EPROTO;
+		break;
+	case ICMP_DEST_UNREACH:
+		if (code > NR_ICMP_UNREACH)
+			goto out;
+
+		if (code == ICMP_FRAG_NEEDED) { /* PMTU discovery (RFC1191) */
+			if (!sock_owned_by_user(sk))
+				dccp_do_pmtu_discovery(sk, iph, info);
+			goto out;
+		}
+
+		err = icmp_err_convert[code].errno;
+		break;
+	case ICMP_TIME_EXCEEDED:
+		err = EHOSTUNREACH;
+		break;
+	default:
+		goto out;
+	}
+
+	switch (sk->sk_state) {
+	case DCCP_REQUESTING:
+	case DCCP_RESPOND:
+		if (!sock_owned_by_user(sk)) {
+			__DCCP_INC_STATS(DCCP_MIB_ATTEMPTFAILS);
+			sk->sk_err = err;
+
+			sk->sk_error_report(sk);
+
+			dccp_done(sk);
+		} else
+			sk->sk_err_soft = err;
+		goto out;
+	}
+
+	/* If we've already connected we will keep trying
+	 * until we time out, or the user gives up.
+	 *
+	 * rfc1122 4.2.3.9 allows to consider as hard errors
+	 * only PROTO_UNREACH and PORT_UNREACH (well, FRAG_FAILED too,
+	 * but it is obsoleted by pmtu discovery).
+	 *
+	 * Note, that in modern internet, where routing is unreliable
+	 * and in each dark corner broken firewalls sit, sending random
+	 * errors ordered by their masters even this two messages finally lose
+	 * their original sense (even Linux sends invalid PORT_UNREACHs)
+	 *
+	 * Now we are in compliance with RFCs.
+	 *							--ANK (980905)
+	 */
+
+	inet = inet_sk(sk);
+	if (!sock_owned_by_user(sk) && inet->recverr) {
+		sk->sk_err = err;
+		sk->sk_error_report(sk);
+	} else /* Only an error on timeout */
+		sk->sk_err_soft = err;
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+	return 0;
+}
+
+static inline __sum16 dccp_v4_csum_finish(struct sk_buff *skb,
+				      __be32 src, __be32 dst)
+{
+	return csum_tcpudp_magic(src, dst, skb->len, IPPROTO_DCCP, skb->csum);
+}
+
+void dccp_v4_send_check(struct sock *sk, struct sk_buff *skb)
+{
+	const struct inet_sock *inet = inet_sk(sk);
+	struct dccp_hdr *dh = dccp_hdr(skb);
+
+	dccp_csum_outgoing(skb);
+	dh->dccph_checksum = dccp_v4_csum_finish(skb,
+						 inet->inet_saddr,
+						 inet->inet_daddr);
+}
+EXPORT_SYMBOL_GPL(dccp_v4_send_check);
+
+static inline u64 dccp_v4_init_sequence(const struct sk_buff *skb)
+{
+	return secure_dccp_sequence_number(ip_hdr(skb)->daddr,
+					   ip_hdr(skb)->saddr,
+					   dccp_hdr(skb)->dccph_dport,
+					   dccp_hdr(skb)->dccph_sport);
+}
+
+/*
+ * The three way handshake has completed - we got a valid ACK or DATAACK -
+ * now create the new socket.
+ *
+ * This is the equivalent of TCP's tcp_v4_syn_recv_sock
+ */
+struct sock *dccp_v4_request_recv_sock(const struct sock *sk,
+				       struct sk_buff *skb,
+				       struct request_sock *req,
+				       struct dst_entry *dst,
+				       struct request_sock *req_unhash,
+				       bool *own_req)
+{
+	struct inet_request_sock *ireq;
+	struct inet_sock *newinet;
+	struct sock *newsk;
+
+	if (sk_acceptq_is_full(sk))
+		goto exit_overflow;
+
+	newsk = dccp_create_openreq_child(sk, req, skb);
+	if (newsk == NULL)
+		goto exit_nonewsk;
+
+	newinet		   = inet_sk(newsk);
+	ireq		   = inet_rsk(req);
+	sk_daddr_set(newsk, ireq->ir_rmt_addr);
+	sk_rcv_saddr_set(newsk, ireq->ir_loc_addr);
+	newinet->inet_saddr	= ireq->ir_loc_addr;
+	RCU_INIT_POINTER(newinet->inet_opt, rcu_dereference(ireq->ireq_opt));
+	newinet->mc_index  = inet_iif(skb);
+	newinet->mc_ttl	   = ip_hdr(skb)->ttl;
+	newinet->inet_id   = prandom_u32();
+
+	if (dst == NULL && (dst = inet_csk_route_child_sock(sk, newsk, req)) == NULL)
+		goto put_and_exit;
+
+	sk_setup_caps(newsk, dst);
+
+	dccp_sync_mss(newsk, dst_mtu(dst));
+
+	if (__inet_inherit_port(sk, newsk) < 0)
+		goto put_and_exit;
+	*own_req = inet_ehash_nolisten(newsk, req_to_sk(req_unhash), NULL);
+	if (*own_req)
+		ireq->ireq_opt = NULL;
+	else
+		newinet->inet_opt = NULL;
+	return newsk;
+
+exit_overflow:
+	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+exit_nonewsk:
+	dst_release(dst);
+exit:
+	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENDROPS);
+	return NULL;
+put_and_exit:
+	newinet->inet_opt = NULL;
+	inet_csk_prepare_forced_close(newsk);
+	dccp_done(newsk);
+	goto exit;
+}
+EXPORT_SYMBOL_GPL(dccp_v4_request_recv_sock);
+
+static struct dst_entry* dccp_v4_route_skb(struct net *net, struct sock *sk,
+					   struct sk_buff *skb)
+{
+	struct rtable *rt;
+	const struct iphdr *iph = ip_hdr(skb);
+	struct flowi4 fl4 = {
+		.flowi4_oif = inet_iif(skb),
+		.daddr = iph->saddr,
+		.saddr = iph->daddr,
+		.flowi4_tos = RT_CONN_FLAGS(sk),
+		.flowi4_proto = sk->sk_protocol,
+		.fl4_sport = dccp_hdr(skb)->dccph_dport,
+		.fl4_dport = dccp_hdr(skb)->dccph_sport,
+	};
+
+	security_skb_classify_flow(skb, flowi4_to_flowi_common(&fl4));
+	rt = ip_route_output_flow(net, &fl4, sk);
+	if (IS_ERR(rt)) {
+		IP_INC_STATS(net, IPSTATS_MIB_OUTNOROUTES);
+		return NULL;
+	}
+
+	return &rt->dst;
+}
+
+static int dccp_v4_send_response(const struct sock *sk, struct request_sock *req)
+{
+	int err = -1;
+	struct sk_buff *skb;
+	struct dst_entry *dst;
+	struct flowi4 fl4;
+
+	dst = inet_csk_route_req(sk, &fl4, req);
+	if (dst == NULL)
+		goto out;
+
+	skb = dccp_make_response(sk, dst, req);
+	if (skb != NULL) {
+		const struct inet_request_sock *ireq = inet_rsk(req);
+		struct dccp_hdr *dh = dccp_hdr(skb);
+
+		dh->dccph_checksum = dccp_v4_csum_finish(skb, ireq->ir_loc_addr,
+							      ireq->ir_rmt_addr);
+		rcu_read_lock();
+		err = ip_build_and_send_pkt(skb, sk, ireq->ir_loc_addr,
+					    ireq->ir_rmt_addr,
+					    rcu_dereference(ireq->ireq_opt),
+					    inet_sk(sk)->tos);
+		rcu_read_unlock();
+		err = net_xmit_eval(err);
+	}
+
+out:
+	dst_release(dst);
+	return err;
+}
+
+static void dccp_v4_ctl_send_reset(const struct sock *sk, struct sk_buff *rxskb)
+{
+	int err;
+	const struct iphdr *rxiph;
+	struct sk_buff *skb;
+	struct dst_entry *dst;
+	struct net *net = dev_net(skb_dst(rxskb)->dev);
+	struct sock *ctl_sk = net->dccp.v4_ctl_sk;
+
+	/* Never send a reset in response to a reset. */
+	if (dccp_hdr(rxskb)->dccph_type == DCCP_PKT_RESET)
+		return;
+
+	if (skb_rtable(rxskb)->rt_type != RTN_LOCAL)
+		return;
+
+	dst = dccp_v4_route_skb(net, ctl_sk, rxskb);
+	if (dst == NULL)
+		return;
+
+	skb = dccp_ctl_make_reset(ctl_sk, rxskb);
+	if (skb == NULL)
+		goto out;
+
+	rxiph = ip_hdr(rxskb);
+	dccp_hdr(skb)->dccph_checksum = dccp_v4_csum_finish(skb, rxiph->saddr,
+								 rxiph->daddr);
+	skb_dst_set(skb, dst_clone(dst));
+
+	local_bh_disable();
+	bh_lock_sock(ctl_sk);
+	err = ip_build_and_send_pkt(skb, ctl_sk,
+				    rxiph->daddr, rxiph->saddr, NULL,
+				    inet_sk(ctl_sk)->tos);
+	bh_unlock_sock(ctl_sk);
+
+	if (net_xmit_eval(err) == 0) {
+		__DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+		__DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
+	}
+	local_bh_enable();
+out:
+	dst_release(dst);
+}
+
+static void dccp_v4_reqsk_destructor(struct request_sock *req)
+{
+	dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg);
+	kfree(rcu_dereference_protected(inet_rsk(req)->ireq_opt, 1));
+}
+
+void dccp_syn_ack_timeout(const struct request_sock *req)
+{
+}
+EXPORT_SYMBOL(dccp_syn_ack_timeout);
+
+static struct request_sock_ops dccp_request_sock_ops __read_mostly = {
+	.family		= PF_INET,
+	.obj_size	= sizeof(struct dccp_request_sock),
+	.rtx_syn_ack	= dccp_v4_send_response,
+	.send_ack	= dccp_reqsk_send_ack,
+	.destructor	= dccp_v4_reqsk_destructor,
+	.send_reset	= dccp_v4_ctl_send_reset,
+	.syn_ack_timeout = dccp_syn_ack_timeout,
+};
+
+int dccp_v4_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+	struct inet_request_sock *ireq;
+	struct request_sock *req;
+	struct dccp_request_sock *dreq;
+	const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
+	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+
+	/* Never answer to DCCP_PKT_REQUESTs send to broadcast or multicast */
+	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
+		return 0;	/* discard, don't send a reset here */
+
+	if (dccp_bad_service_code(sk, service)) {
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
+		goto drop;
+	}
+	/*
+	 * TW buckets are converted to open requests without
+	 * limitations, they conserve resources and peer is
+	 * evidently real one.
+	 */
+	dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
+	if (inet_csk_reqsk_queue_is_full(sk))
+		goto drop;
+
+	if (sk_acceptq_is_full(sk))
+		goto drop;
+
+	req = inet_reqsk_alloc(&dccp_request_sock_ops, sk, true);
+	if (req == NULL)
+		goto drop;
+
+	if (dccp_reqsk_init(req, dccp_sk(sk), skb))
+		goto drop_and_free;
+
+	dreq = dccp_rsk(req);
+	if (dccp_parse_options(sk, dreq, skb))
+		goto drop_and_free;
+
+	ireq = inet_rsk(req);
+	sk_rcv_saddr_set(req_to_sk(req), ip_hdr(skb)->daddr);
+	sk_daddr_set(req_to_sk(req), ip_hdr(skb)->saddr);
+	ireq->ir_mark = inet_request_mark(sk, skb);
+	ireq->ireq_family = AF_INET;
+	ireq->ir_iif = sk->sk_bound_dev_if;
+
+	if (security_inet_conn_request(sk, skb, req))
+		goto drop_and_free;
+
+	/*
+	 * Step 3: Process LISTEN state
+	 *
+	 * Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
+	 *
+	 * Setting S.SWL/S.SWH to is deferred to dccp_create_openreq_child().
+	 */
+	dreq->dreq_isr	   = dcb->dccpd_seq;
+	dreq->dreq_gsr	   = dreq->dreq_isr;
+	dreq->dreq_iss	   = dccp_v4_init_sequence(skb);
+	dreq->dreq_gss     = dreq->dreq_iss;
+	dreq->dreq_service = service;
+
+	if (dccp_v4_send_response(sk, req))
+		goto drop_and_free;
+
+	inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT);
+	reqsk_put(req);
+	return 0;
+
+drop_and_free:
+	reqsk_free(req);
+drop:
+	__DCCP_INC_STATS(DCCP_MIB_ATTEMPTFAILS);
+	return -1;
+}
+EXPORT_SYMBOL_GPL(dccp_v4_conn_request);
+
+int dccp_v4_do_rcv(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_hdr *dh = dccp_hdr(skb);
+
+	if (sk->sk_state == DCCP_OPEN) { /* Fast path */
+		if (dccp_rcv_established(sk, skb, dh, skb->len))
+			goto reset;
+		return 0;
+	}
+
+	/*
+	 *  Step 3: Process LISTEN state
+	 *	 If P.type == Request or P contains a valid Init Cookie option,
+	 *	      (* Must scan the packet's options to check for Init
+	 *		 Cookies.  Only Init Cookies are processed here,
+	 *		 however; other options are processed in Step 8.  This
+	 *		 scan need only be performed if the endpoint uses Init
+	 *		 Cookies *)
+	 *	      (* Generate a new socket and switch to that socket *)
+	 *	      Set S := new socket for this port pair
+	 *	      S.state = RESPOND
+	 *	      Choose S.ISS (initial seqno) or set from Init Cookies
+	 *	      Initialize S.GAR := S.ISS
+	 *	      Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookies
+	 *	      Continue with S.state == RESPOND
+	 *	      (* A Response packet will be generated in Step 11 *)
+	 *	 Otherwise,
+	 *	      Generate Reset(No Connection) unless P.type == Reset
+	 *	      Drop packet and return
+	 *
+	 * NOTE: the check for the packet types is done in
+	 *	 dccp_rcv_state_process
+	 */
+
+	if (dccp_rcv_state_process(sk, skb, dh, skb->len))
+		goto reset;
+	return 0;
+
+reset:
+	dccp_v4_ctl_send_reset(sk, skb);
+	kfree_skb(skb);
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dccp_v4_do_rcv);
+
+/**
+ *	dccp_invalid_packet  -  check for malformed packets
+ *	@skb: Packet to validate
+ *
+ *	Implements RFC 4340, 8.5:  Step 1: Check header basics
+ *	Packets that fail these checks are ignored and do not receive Resets.
+ */
+int dccp_invalid_packet(struct sk_buff *skb)
+{
+	const struct dccp_hdr *dh;
+	unsigned int cscov;
+	u8 dccph_doff;
+
+	if (skb->pkt_type != PACKET_HOST)
+		return 1;
+
+	/* If the packet is shorter than 12 bytes, drop packet and return */
+	if (!pskb_may_pull(skb, sizeof(struct dccp_hdr))) {
+		DCCP_WARN("pskb_may_pull failed\n");
+		return 1;
+	}
+
+	dh = dccp_hdr(skb);
+
+	/* If P.type is not understood, drop packet and return */
+	if (dh->dccph_type >= DCCP_PKT_INVALID) {
+		DCCP_WARN("invalid packet type\n");
+		return 1;
+	}
+
+	/*
+	 * If P.Data Offset is too small for packet type, drop packet and return
+	 */
+	dccph_doff = dh->dccph_doff;
+	if (dccph_doff < dccp_hdr_len(skb) / sizeof(u32)) {
+		DCCP_WARN("P.Data Offset(%u) too small\n", dccph_doff);
+		return 1;
+	}
+	/*
+	 * If P.Data Offset is too large for packet, drop packet and return
+	 */
+	if (!pskb_may_pull(skb, dccph_doff * sizeof(u32))) {
+		DCCP_WARN("P.Data Offset(%u) too large\n", dccph_doff);
+		return 1;
+	}
+	dh = dccp_hdr(skb);
+	/*
+	 * If P.type is not Data, Ack, or DataAck and P.X == 0 (the packet
+	 * has short sequence numbers), drop packet and return
+	 */
+	if ((dh->dccph_type < DCCP_PKT_DATA    ||
+	    dh->dccph_type > DCCP_PKT_DATAACK) && dh->dccph_x == 0)  {
+		DCCP_WARN("P.type (%s) not Data || [Data]Ack, while P.X == 0\n",
+			  dccp_packet_name(dh->dccph_type));
+		return 1;
+	}
+
+	/*
+	 * If P.CsCov is too large for the packet size, drop packet and return.
+	 * This must come _before_ checksumming (not as RFC 4340 suggests).
+	 */
+	cscov = dccp_csum_coverage(skb);
+	if (cscov > skb->len) {
+		DCCP_WARN("P.CsCov %u exceeds packet length %d\n",
+			  dh->dccph_cscov, skb->len);
+		return 1;
+	}
+
+	/* If header checksum is incorrect, drop packet and return.
+	 * (This step is completed in the AF-dependent functions.) */
+	skb->csum = skb_checksum(skb, 0, cscov, 0);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(dccp_invalid_packet);
+
+/* this is called when real data arrives */
+static int dccp_v4_rcv(struct sk_buff *skb)
+{
+	const struct dccp_hdr *dh;
+	const struct iphdr *iph;
+	bool refcounted;
+	struct sock *sk;
+	int min_cov;
+
+	/* Step 1: Check header basics */
+
+	if (dccp_invalid_packet(skb))
+		goto discard_it;
+
+	iph = ip_hdr(skb);
+	/* Step 1: If header checksum is incorrect, drop packet and return */
+	if (dccp_v4_csum_finish(skb, iph->saddr, iph->daddr)) {
+		DCCP_WARN("dropped packet with invalid checksum\n");
+		goto discard_it;
+	}
+
+	dh = dccp_hdr(skb);
+
+	DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(dh);
+	DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;
+
+	dccp_pr_debug("%8.8s src=%pI4@%-5d dst=%pI4@%-5d seq=%llu",
+		      dccp_packet_name(dh->dccph_type),
+		      &iph->saddr, ntohs(dh->dccph_sport),
+		      &iph->daddr, ntohs(dh->dccph_dport),
+		      (unsigned long long) DCCP_SKB_CB(skb)->dccpd_seq);
+
+	if (dccp_packet_without_ack(skb)) {
+		DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
+		dccp_pr_debug_cat("\n");
+	} else {
+		DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);
+		dccp_pr_debug_cat(", ack=%llu\n", (unsigned long long)
+				  DCCP_SKB_CB(skb)->dccpd_ack_seq);
+	}
+
+lookup:
+	sk = __inet_lookup_skb(&dccp_hashinfo, skb, __dccp_hdr_len(dh),
+			       dh->dccph_sport, dh->dccph_dport, 0, &refcounted);
+	if (!sk) {
+		dccp_pr_debug("failed to look up flow ID in table and "
+			      "get corresponding socket\n");
+		goto no_dccp_socket;
+	}
+
+	/*
+	 * Step 2:
+	 *	... or S.state == TIMEWAIT,
+	 *		Generate Reset(No Connection) unless P.type == Reset
+	 *		Drop packet and return
+	 */
+	if (sk->sk_state == DCCP_TIME_WAIT) {
+		dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: do_time_wait\n");
+		inet_twsk_put(inet_twsk(sk));
+		goto no_dccp_socket;
+	}
+
+	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
+		struct request_sock *req = inet_reqsk(sk);
+		struct sock *nsk;
+
+		sk = req->rsk_listener;
+		if (unlikely(sk->sk_state != DCCP_LISTEN)) {
+			inet_csk_reqsk_queue_drop_and_put(sk, req);
+			goto lookup;
+		}
+		sock_hold(sk);
+		refcounted = true;
+		nsk = dccp_check_req(sk, skb, req);
+		if (!nsk) {
+			reqsk_put(req);
+			goto discard_and_relse;
+		}
+		if (nsk == sk) {
+			reqsk_put(req);
+		} else if (dccp_child_process(sk, nsk, skb)) {
+			dccp_v4_ctl_send_reset(sk, skb);
+			goto discard_and_relse;
+		} else {
+			sock_put(sk);
+			return 0;
+		}
+	}
+	/*
+	 * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
+	 *	o if MinCsCov = 0, only packets with CsCov = 0 are accepted
+	 *	o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
+	 */
+	min_cov = dccp_sk(sk)->dccps_pcrlen;
+	if (dh->dccph_cscov && (min_cov == 0 || dh->dccph_cscov < min_cov))  {
+		dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
+			      dh->dccph_cscov, min_cov);
+		/* FIXME: "Such packets SHOULD be reported using Data Dropped
+		 *         options (Section 11.7) with Drop Code 0, Protocol
+		 *         Constraints."                                     */
+		goto discard_and_relse;
+	}
+
+	if (!xfrm4_policy_check(sk, XFRM_POLICY_IN, skb))
+		goto discard_and_relse;
+	nf_reset_ct(skb);
+
+	return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4, refcounted);
+
+no_dccp_socket:
+	if (!xfrm4_policy_check(NULL, XFRM_POLICY_IN, skb))
+		goto discard_it;
+	/*
+	 * Step 2:
+	 *	If no socket ...
+	 *		Generate Reset(No Connection) unless P.type == Reset
+	 *		Drop packet and return
+	 */
+	if (dh->dccph_type != DCCP_PKT_RESET) {
+		DCCP_SKB_CB(skb)->dccpd_reset_code =
+					DCCP_RESET_CODE_NO_CONNECTION;
+		dccp_v4_ctl_send_reset(sk, skb);
+	}
+
+discard_it:
+	kfree_skb(skb);
+	return 0;
+
+discard_and_relse:
+	if (refcounted)
+		sock_put(sk);
+	goto discard_it;
+}
+
+static const struct inet_connection_sock_af_ops dccp_ipv4_af_ops = {
+	.queue_xmit	   = ip_queue_xmit,
+	.send_check	   = dccp_v4_send_check,
+	.rebuild_header	   = inet_sk_rebuild_header,
+	.conn_request	   = dccp_v4_conn_request,
+	.syn_recv_sock	   = dccp_v4_request_recv_sock,
+	.net_header_len	   = sizeof(struct iphdr),
+	.setsockopt	   = ip_setsockopt,
+	.getsockopt	   = ip_getsockopt,
+	.addr2sockaddr	   = inet_csk_addr2sockaddr,
+	.sockaddr_len	   = sizeof(struct sockaddr_in),
+};
+
+static int dccp_v4_init_sock(struct sock *sk)
+{
+	static __u8 dccp_v4_ctl_sock_initialized;
+	int err = dccp_init_sock(sk, dccp_v4_ctl_sock_initialized);
+
+	if (err == 0) {
+		if (unlikely(!dccp_v4_ctl_sock_initialized))
+			dccp_v4_ctl_sock_initialized = 1;
+		inet_csk(sk)->icsk_af_ops = &dccp_ipv4_af_ops;
+	}
+
+	return err;
+}
+
+static struct timewait_sock_ops dccp_timewait_sock_ops = {
+	.twsk_obj_size	= sizeof(struct inet_timewait_sock),
+};
+
+static struct proto dccp_v4_prot = {
+	.name			= "DCCP",
+	.owner			= THIS_MODULE,
+	.close			= dccp_close,
+	.connect		= dccp_v4_connect,
+	.disconnect		= dccp_disconnect,
+	.ioctl			= dccp_ioctl,
+	.init			= dccp_v4_init_sock,
+	.setsockopt		= dccp_setsockopt,
+	.getsockopt		= dccp_getsockopt,
+	.sendmsg		= dccp_sendmsg,
+	.recvmsg		= dccp_recvmsg,
+	.backlog_rcv		= dccp_v4_do_rcv,
+	.hash			= inet_hash,
+	.unhash			= inet_unhash,
+	.accept			= inet_csk_accept,
+	.get_port		= inet_csk_get_port,
+	.shutdown		= dccp_shutdown,
+	.destroy		= dccp_destroy_sock,
+	.orphan_count		= &dccp_orphan_count,
+	.max_header		= MAX_DCCP_HEADER,
+	.obj_size		= sizeof(struct dccp_sock),
+	.slab_flags		= SLAB_TYPESAFE_BY_RCU,
+	.rsk_prot		= &dccp_request_sock_ops,
+	.twsk_prot		= &dccp_timewait_sock_ops,
+	.h.hashinfo		= &dccp_hashinfo,
+};
+
+static const struct net_protocol dccp_v4_protocol = {
+	.handler	= dccp_v4_rcv,
+	.err_handler	= dccp_v4_err,
+	.no_policy	= 1,
+	.netns_ok	= 1,
+	.icmp_strict_tag_validation = 1,
+};
+
+static const struct proto_ops inet_dccp_ops = {
+	.family		   = PF_INET,
+	.owner		   = THIS_MODULE,
+	.release	   = inet_release,
+	.bind		   = inet_bind,
+	.connect	   = inet_stream_connect,
+	.socketpair	   = sock_no_socketpair,
+	.accept		   = inet_accept,
+	.getname	   = inet_getname,
+	/* FIXME: work on tcp_poll to rename it to inet_csk_poll */
+	.poll		   = dccp_poll,
+	.ioctl		   = inet_ioctl,
+	.gettstamp	   = sock_gettstamp,
+	/* FIXME: work on inet_listen to rename it to sock_common_listen */
+	.listen		   = inet_dccp_listen,
+	.shutdown	   = inet_shutdown,
+	.setsockopt	   = sock_common_setsockopt,
+	.getsockopt	   = sock_common_getsockopt,
+	.sendmsg	   = inet_sendmsg,
+	.recvmsg	   = sock_common_recvmsg,
+	.mmap		   = sock_no_mmap,
+	.sendpage	   = sock_no_sendpage,
+};
+
+static struct inet_protosw dccp_v4_protosw = {
+	.type		= SOCK_DCCP,
+	.protocol	= IPPROTO_DCCP,
+	.prot		= &dccp_v4_prot,
+	.ops		= &inet_dccp_ops,
+	.flags		= INET_PROTOSW_ICSK,
+};
+
+static int __net_init dccp_v4_init_net(struct net *net)
+{
+	if (dccp_hashinfo.bhash == NULL)
+		return -ESOCKTNOSUPPORT;
+
+	return inet_ctl_sock_create(&net->dccp.v4_ctl_sk, PF_INET,
+				    SOCK_DCCP, IPPROTO_DCCP, net);
+}
+
+static void __net_exit dccp_v4_exit_net(struct net *net)
+{
+	inet_ctl_sock_destroy(net->dccp.v4_ctl_sk);
+}
+
+static void __net_exit dccp_v4_exit_batch(struct list_head *net_exit_list)
+{
+	inet_twsk_purge(&dccp_hashinfo, AF_INET);
+}
+
+static struct pernet_operations dccp_v4_ops = {
+	.init	= dccp_v4_init_net,
+	.exit	= dccp_v4_exit_net,
+	.exit_batch = dccp_v4_exit_batch,
+};
+
+static int __init dccp_v4_init(void)
+{
+	int err = proto_register(&dccp_v4_prot, 1);
+
+	if (err)
+		goto out;
+
+	inet_register_protosw(&dccp_v4_protosw);
+
+	err = register_pernet_subsys(&dccp_v4_ops);
+	if (err)
+		goto out_destroy_ctl_sock;
+
+	err = inet_add_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
+	if (err)
+		goto out_proto_unregister;
+
+out:
+	return err;
+out_proto_unregister:
+	unregister_pernet_subsys(&dccp_v4_ops);
+out_destroy_ctl_sock:
+	inet_unregister_protosw(&dccp_v4_protosw);
+	proto_unregister(&dccp_v4_prot);
+	goto out;
+}
+
+static void __exit dccp_v4_exit(void)
+{
+	inet_del_protocol(&dccp_v4_protocol, IPPROTO_DCCP);
+	unregister_pernet_subsys(&dccp_v4_ops);
+	inet_unregister_protosw(&dccp_v4_protosw);
+	proto_unregister(&dccp_v4_prot);
+}
+
+module_init(dccp_v4_init);
+module_exit(dccp_v4_exit);
+
+/*
+ * __stringify doesn't likes enums, so use SOCK_DCCP (6) and IPPROTO_DCCP (33)
+ * values directly, Also cover the case where the protocol is not specified,
+ * i.e. net-pf-PF_INET-proto-0-type-SOCK_DCCP
+ */
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 33, 6);
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 0, 6);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
+MODULE_DESCRIPTION("DCCP - Datagram Congestion Controlled Protocol");
diff --git a/net/dccp/ipv6.c b/net/dccp/ipv6.c
new file mode 100644
index 000000000..991ca2dc2
--- /dev/null
+++ b/net/dccp/ipv6.c
@@ -0,0 +1,1162 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *	DCCP over IPv6
+ *	Linux INET6 implementation
+ *
+ *	Based on net/dccp6/ipv6.c
+ *
+ *	Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
+ */
+
+#include <linux/module.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/xfrm.h>
+#include <linux/string.h>
+
+#include <net/addrconf.h>
+#include <net/inet_common.h>
+#include <net/inet_hashtables.h>
+#include <net/inet_sock.h>
+#include <net/inet6_connection_sock.h>
+#include <net/inet6_hashtables.h>
+#include <net/ip6_route.h>
+#include <net/ipv6.h>
+#include <net/protocol.h>
+#include <net/transp_v6.h>
+#include <net/ip6_checksum.h>
+#include <net/xfrm.h>
+#include <net/secure_seq.h>
+#include <net/sock.h>
+
+#include "dccp.h"
+#include "ipv6.h"
+#include "feat.h"
+
+/* The per-net dccp.v6_ctl_sk is used for sending RSTs and ACKs */
+
+static const struct inet_connection_sock_af_ops dccp_ipv6_mapped;
+static const struct inet_connection_sock_af_ops dccp_ipv6_af_ops;
+
+/* add pseudo-header to DCCP checksum stored in skb->csum */
+static inline __sum16 dccp_v6_csum_finish(struct sk_buff *skb,
+				      const struct in6_addr *saddr,
+				      const struct in6_addr *daddr)
+{
+	return csum_ipv6_magic(saddr, daddr, skb->len, IPPROTO_DCCP, skb->csum);
+}
+
+static inline void dccp_v6_send_check(struct sock *sk, struct sk_buff *skb)
+{
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct dccp_hdr *dh = dccp_hdr(skb);
+
+	dccp_csum_outgoing(skb);
+	dh->dccph_checksum = dccp_v6_csum_finish(skb, &np->saddr, &sk->sk_v6_daddr);
+}
+
+static inline __u64 dccp_v6_init_sequence(struct sk_buff *skb)
+{
+	return secure_dccpv6_sequence_number(ipv6_hdr(skb)->daddr.s6_addr32,
+					     ipv6_hdr(skb)->saddr.s6_addr32,
+					     dccp_hdr(skb)->dccph_dport,
+					     dccp_hdr(skb)->dccph_sport     );
+
+}
+
+static int dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
+			u8 type, u8 code, int offset, __be32 info)
+{
+	const struct ipv6hdr *hdr;
+	const struct dccp_hdr *dh;
+	struct dccp_sock *dp;
+	struct ipv6_pinfo *np;
+	struct sock *sk;
+	int err;
+	__u64 seq;
+	struct net *net = dev_net(skb->dev);
+
+	if (!pskb_may_pull(skb, offset + sizeof(*dh)))
+		return -EINVAL;
+	dh = (struct dccp_hdr *)(skb->data + offset);
+	if (!pskb_may_pull(skb, offset + __dccp_basic_hdr_len(dh)))
+		return -EINVAL;
+	hdr = (const struct ipv6hdr *)skb->data;
+	dh = (struct dccp_hdr *)(skb->data + offset);
+
+	sk = __inet6_lookup_established(net, &dccp_hashinfo,
+					&hdr->daddr, dh->dccph_dport,
+					&hdr->saddr, ntohs(dh->dccph_sport),
+					inet6_iif(skb), 0);
+
+	if (!sk) {
+		__ICMP6_INC_STATS(net, __in6_dev_get(skb->dev),
+				  ICMP6_MIB_INERRORS);
+		return -ENOENT;
+	}
+
+	if (sk->sk_state == DCCP_TIME_WAIT) {
+		inet_twsk_put(inet_twsk(sk));
+		return 0;
+	}
+	seq = dccp_hdr_seq(dh);
+	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
+		dccp_req_err(sk, seq);
+		return 0;
+	}
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk))
+		__NET_INC_STATS(net, LINUX_MIB_LOCKDROPPEDICMPS);
+
+	if (sk->sk_state == DCCP_CLOSED)
+		goto out;
+
+	dp = dccp_sk(sk);
+	if ((1 << sk->sk_state) & ~(DCCPF_REQUESTING | DCCPF_LISTEN) &&
+	    !between48(seq, dp->dccps_awl, dp->dccps_awh)) {
+		__NET_INC_STATS(net, LINUX_MIB_OUTOFWINDOWICMPS);
+		goto out;
+	}
+
+	np = inet6_sk(sk);
+
+	if (type == NDISC_REDIRECT) {
+		if (!sock_owned_by_user(sk)) {
+			struct dst_entry *dst = __sk_dst_check(sk, np->dst_cookie);
+
+			if (dst)
+				dst->ops->redirect(dst, sk, skb);
+		}
+		goto out;
+	}
+
+	if (type == ICMPV6_PKT_TOOBIG) {
+		struct dst_entry *dst = NULL;
+
+		if (!ip6_sk_accept_pmtu(sk))
+			goto out;
+
+		if (sock_owned_by_user(sk))
+			goto out;
+		if ((1 << sk->sk_state) & (DCCPF_LISTEN | DCCPF_CLOSED))
+			goto out;
+
+		dst = inet6_csk_update_pmtu(sk, ntohl(info));
+		if (!dst)
+			goto out;
+
+		if (inet_csk(sk)->icsk_pmtu_cookie > dst_mtu(dst))
+			dccp_sync_mss(sk, dst_mtu(dst));
+		goto out;
+	}
+
+	icmpv6_err_convert(type, code, &err);
+
+	/* Might be for an request_sock */
+	switch (sk->sk_state) {
+	case DCCP_REQUESTING:
+	case DCCP_RESPOND:  /* Cannot happen.
+			       It can, it SYNs are crossed. --ANK */
+		if (!sock_owned_by_user(sk)) {
+			__DCCP_INC_STATS(DCCP_MIB_ATTEMPTFAILS);
+			sk->sk_err = err;
+			/*
+			 * Wake people up to see the error
+			 * (see connect in sock.c)
+			 */
+			sk->sk_error_report(sk);
+			dccp_done(sk);
+		} else
+			sk->sk_err_soft = err;
+		goto out;
+	}
+
+	if (!sock_owned_by_user(sk) && np->recverr) {
+		sk->sk_err = err;
+		sk->sk_error_report(sk);
+	} else
+		sk->sk_err_soft = err;
+
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+	return 0;
+}
+
+
+static int dccp_v6_send_response(const struct sock *sk, struct request_sock *req)
+{
+	struct inet_request_sock *ireq = inet_rsk(req);
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct sk_buff *skb;
+	struct in6_addr *final_p, final;
+	struct flowi6 fl6;
+	int err = -1;
+	struct dst_entry *dst;
+
+	memset(&fl6, 0, sizeof(fl6));
+	fl6.flowi6_proto = IPPROTO_DCCP;
+	fl6.daddr = ireq->ir_v6_rmt_addr;
+	fl6.saddr = ireq->ir_v6_loc_addr;
+	fl6.flowlabel = 0;
+	fl6.flowi6_oif = ireq->ir_iif;
+	fl6.fl6_dport = ireq->ir_rmt_port;
+	fl6.fl6_sport = htons(ireq->ir_num);
+	security_req_classify_flow(req, flowi6_to_flowi_common(&fl6));
+
+
+	rcu_read_lock();
+	final_p = fl6_update_dst(&fl6, rcu_dereference(np->opt), &final);
+	rcu_read_unlock();
+
+	dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
+	if (IS_ERR(dst)) {
+		err = PTR_ERR(dst);
+		dst = NULL;
+		goto done;
+	}
+
+	skb = dccp_make_response(sk, dst, req);
+	if (skb != NULL) {
+		struct dccp_hdr *dh = dccp_hdr(skb);
+		struct ipv6_txoptions *opt;
+
+		dh->dccph_checksum = dccp_v6_csum_finish(skb,
+							 &ireq->ir_v6_loc_addr,
+							 &ireq->ir_v6_rmt_addr);
+		fl6.daddr = ireq->ir_v6_rmt_addr;
+		rcu_read_lock();
+		opt = ireq->ipv6_opt;
+		if (!opt)
+			opt = rcu_dereference(np->opt);
+		err = ip6_xmit(sk, skb, &fl6, sk->sk_mark, opt, np->tclass,
+			       sk->sk_priority);
+		rcu_read_unlock();
+		err = net_xmit_eval(err);
+	}
+
+done:
+	dst_release(dst);
+	return err;
+}
+
+static void dccp_v6_reqsk_destructor(struct request_sock *req)
+{
+	dccp_feat_list_purge(&dccp_rsk(req)->dreq_featneg);
+	kfree(inet_rsk(req)->ipv6_opt);
+	kfree_skb(inet_rsk(req)->pktopts);
+}
+
+static void dccp_v6_ctl_send_reset(const struct sock *sk, struct sk_buff *rxskb)
+{
+	const struct ipv6hdr *rxip6h;
+	struct sk_buff *skb;
+	struct flowi6 fl6;
+	struct net *net = dev_net(skb_dst(rxskb)->dev);
+	struct sock *ctl_sk = net->dccp.v6_ctl_sk;
+	struct dst_entry *dst;
+
+	if (dccp_hdr(rxskb)->dccph_type == DCCP_PKT_RESET)
+		return;
+
+	if (!ipv6_unicast_destination(rxskb))
+		return;
+
+	skb = dccp_ctl_make_reset(ctl_sk, rxskb);
+	if (skb == NULL)
+		return;
+
+	rxip6h = ipv6_hdr(rxskb);
+	dccp_hdr(skb)->dccph_checksum = dccp_v6_csum_finish(skb, &rxip6h->saddr,
+							    &rxip6h->daddr);
+
+	memset(&fl6, 0, sizeof(fl6));
+	fl6.daddr = rxip6h->saddr;
+	fl6.saddr = rxip6h->daddr;
+
+	fl6.flowi6_proto = IPPROTO_DCCP;
+	fl6.flowi6_oif = inet6_iif(rxskb);
+	fl6.fl6_dport = dccp_hdr(skb)->dccph_dport;
+	fl6.fl6_sport = dccp_hdr(skb)->dccph_sport;
+	security_skb_classify_flow(rxskb, flowi6_to_flowi_common(&fl6));
+
+	/* sk = NULL, but it is safe for now. RST socket required. */
+	dst = ip6_dst_lookup_flow(sock_net(ctl_sk), ctl_sk, &fl6, NULL);
+	if (!IS_ERR(dst)) {
+		skb_dst_set(skb, dst);
+		ip6_xmit(ctl_sk, skb, &fl6, 0, NULL, 0, 0);
+		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+		DCCP_INC_STATS(DCCP_MIB_OUTRSTS);
+		return;
+	}
+
+	kfree_skb(skb);
+}
+
+static struct request_sock_ops dccp6_request_sock_ops = {
+	.family		= AF_INET6,
+	.obj_size	= sizeof(struct dccp6_request_sock),
+	.rtx_syn_ack	= dccp_v6_send_response,
+	.send_ack	= dccp_reqsk_send_ack,
+	.destructor	= dccp_v6_reqsk_destructor,
+	.send_reset	= dccp_v6_ctl_send_reset,
+	.syn_ack_timeout = dccp_syn_ack_timeout,
+};
+
+static int dccp_v6_conn_request(struct sock *sk, struct sk_buff *skb)
+{
+	struct request_sock *req;
+	struct dccp_request_sock *dreq;
+	struct inet_request_sock *ireq;
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	const __be32 service = dccp_hdr_request(skb)->dccph_req_service;
+	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+
+	if (skb->protocol == htons(ETH_P_IP))
+		return dccp_v4_conn_request(sk, skb);
+
+	if (!ipv6_unicast_destination(skb))
+		return 0;	/* discard, don't send a reset here */
+
+	if (ipv6_addr_v4mapped(&ipv6_hdr(skb)->saddr)) {
+		__IP6_INC_STATS(sock_net(sk), NULL, IPSTATS_MIB_INHDRERRORS);
+		return 0;
+	}
+
+	if (dccp_bad_service_code(sk, service)) {
+		dcb->dccpd_reset_code = DCCP_RESET_CODE_BAD_SERVICE_CODE;
+		goto drop;
+	}
+	/*
+	 * There are no SYN attacks on IPv6, yet...
+	 */
+	dcb->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
+	if (inet_csk_reqsk_queue_is_full(sk))
+		goto drop;
+
+	if (sk_acceptq_is_full(sk))
+		goto drop;
+
+	req = inet_reqsk_alloc(&dccp6_request_sock_ops, sk, true);
+	if (req == NULL)
+		goto drop;
+
+	if (dccp_reqsk_init(req, dccp_sk(sk), skb))
+		goto drop_and_free;
+
+	dreq = dccp_rsk(req);
+	if (dccp_parse_options(sk, dreq, skb))
+		goto drop_and_free;
+
+	ireq = inet_rsk(req);
+	ireq->ir_v6_rmt_addr = ipv6_hdr(skb)->saddr;
+	ireq->ir_v6_loc_addr = ipv6_hdr(skb)->daddr;
+	ireq->ireq_family = AF_INET6;
+	ireq->ir_mark = inet_request_mark(sk, skb);
+
+	if (security_inet_conn_request(sk, skb, req))
+		goto drop_and_free;
+
+	if (ipv6_opt_accepted(sk, skb, IP6CB(skb)) ||
+	    np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo ||
+	    np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim) {
+		refcount_inc(&skb->users);
+		ireq->pktopts = skb;
+	}
+	ireq->ir_iif = sk->sk_bound_dev_if;
+
+	/* So that link locals have meaning */
+	if (!sk->sk_bound_dev_if &&
+	    ipv6_addr_type(&ireq->ir_v6_rmt_addr) & IPV6_ADDR_LINKLOCAL)
+		ireq->ir_iif = inet6_iif(skb);
+
+	/*
+	 * Step 3: Process LISTEN state
+	 *
+	 *   Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookie
+	 *
+	 * Setting S.SWL/S.SWH to is deferred to dccp_create_openreq_child().
+	 */
+	dreq->dreq_isr	   = dcb->dccpd_seq;
+	dreq->dreq_gsr     = dreq->dreq_isr;
+	dreq->dreq_iss	   = dccp_v6_init_sequence(skb);
+	dreq->dreq_gss     = dreq->dreq_iss;
+	dreq->dreq_service = service;
+
+	if (dccp_v6_send_response(sk, req))
+		goto drop_and_free;
+
+	inet_csk_reqsk_queue_hash_add(sk, req, DCCP_TIMEOUT_INIT);
+	reqsk_put(req);
+	return 0;
+
+drop_and_free:
+	reqsk_free(req);
+drop:
+	__DCCP_INC_STATS(DCCP_MIB_ATTEMPTFAILS);
+	return -1;
+}
+
+static struct sock *dccp_v6_request_recv_sock(const struct sock *sk,
+					      struct sk_buff *skb,
+					      struct request_sock *req,
+					      struct dst_entry *dst,
+					      struct request_sock *req_unhash,
+					      bool *own_req)
+{
+	struct inet_request_sock *ireq = inet_rsk(req);
+	struct ipv6_pinfo *newnp;
+	const struct ipv6_pinfo *np = inet6_sk(sk);
+	struct ipv6_txoptions *opt;
+	struct inet_sock *newinet;
+	struct dccp6_sock *newdp6;
+	struct sock *newsk;
+
+	if (skb->protocol == htons(ETH_P_IP)) {
+		/*
+		 *	v6 mapped
+		 */
+		newsk = dccp_v4_request_recv_sock(sk, skb, req, dst,
+						  req_unhash, own_req);
+		if (newsk == NULL)
+			return NULL;
+
+		newdp6 = (struct dccp6_sock *)newsk;
+		newinet = inet_sk(newsk);
+		newinet->pinet6 = &newdp6->inet6;
+		newnp = inet6_sk(newsk);
+
+		memcpy(newnp, np, sizeof(struct ipv6_pinfo));
+
+		newnp->saddr = newsk->sk_v6_rcv_saddr;
+
+		inet_csk(newsk)->icsk_af_ops = &dccp_ipv6_mapped;
+		newsk->sk_backlog_rcv = dccp_v4_do_rcv;
+		newnp->pktoptions  = NULL;
+		newnp->opt	   = NULL;
+		newnp->ipv6_mc_list = NULL;
+		newnp->ipv6_ac_list = NULL;
+		newnp->ipv6_fl_list = NULL;
+		newnp->mcast_oif   = inet_iif(skb);
+		newnp->mcast_hops  = ip_hdr(skb)->ttl;
+
+		/*
+		 * No need to charge this sock to the relevant IPv6 refcnt debug socks count
+		 * here, dccp_create_openreq_child now does this for us, see the comment in
+		 * that function for the gory details. -acme
+		 */
+
+		/* It is tricky place. Until this moment IPv4 tcp
+		   worked with IPv6 icsk.icsk_af_ops.
+		   Sync it now.
+		 */
+		dccp_sync_mss(newsk, inet_csk(newsk)->icsk_pmtu_cookie);
+
+		return newsk;
+	}
+
+
+	if (sk_acceptq_is_full(sk))
+		goto out_overflow;
+
+	if (!dst) {
+		struct flowi6 fl6;
+
+		dst = inet6_csk_route_req(sk, &fl6, req, IPPROTO_DCCP);
+		if (!dst)
+			goto out;
+	}
+
+	newsk = dccp_create_openreq_child(sk, req, skb);
+	if (newsk == NULL)
+		goto out_nonewsk;
+
+	/*
+	 * No need to charge this sock to the relevant IPv6 refcnt debug socks
+	 * count here, dccp_create_openreq_child now does this for us, see the
+	 * comment in that function for the gory details. -acme
+	 */
+
+	ip6_dst_store(newsk, dst, NULL, NULL);
+	newsk->sk_route_caps = dst->dev->features & ~(NETIF_F_IP_CSUM |
+						      NETIF_F_TSO);
+	newdp6 = (struct dccp6_sock *)newsk;
+	newinet = inet_sk(newsk);
+	newinet->pinet6 = &newdp6->inet6;
+	newnp = inet6_sk(newsk);
+
+	memcpy(newnp, np, sizeof(struct ipv6_pinfo));
+
+	newsk->sk_v6_daddr	= ireq->ir_v6_rmt_addr;
+	newnp->saddr		= ireq->ir_v6_loc_addr;
+	newsk->sk_v6_rcv_saddr	= ireq->ir_v6_loc_addr;
+	newsk->sk_bound_dev_if	= ireq->ir_iif;
+
+	/* Now IPv6 options...
+
+	   First: no IPv4 options.
+	 */
+	newinet->inet_opt = NULL;
+
+	/* Clone RX bits */
+	newnp->rxopt.all = np->rxopt.all;
+
+	newnp->ipv6_mc_list = NULL;
+	newnp->ipv6_ac_list = NULL;
+	newnp->ipv6_fl_list = NULL;
+	newnp->pktoptions = NULL;
+	newnp->opt	  = NULL;
+	newnp->mcast_oif  = inet6_iif(skb);
+	newnp->mcast_hops = ipv6_hdr(skb)->hop_limit;
+
+	/*
+	 * Clone native IPv6 options from listening socket (if any)
+	 *
+	 * Yes, keeping reference count would be much more clever, but we make
+	 * one more one thing there: reattach optmem to newsk.
+	 */
+	opt = ireq->ipv6_opt;
+	if (!opt)
+		opt = rcu_dereference(np->opt);
+	if (opt) {
+		opt = ipv6_dup_options(newsk, opt);
+		RCU_INIT_POINTER(newnp->opt, opt);
+	}
+	inet_csk(newsk)->icsk_ext_hdr_len = 0;
+	if (opt)
+		inet_csk(newsk)->icsk_ext_hdr_len = opt->opt_nflen +
+						    opt->opt_flen;
+
+	dccp_sync_mss(newsk, dst_mtu(dst));
+
+	newinet->inet_daddr = newinet->inet_saddr = LOOPBACK4_IPV6;
+	newinet->inet_rcv_saddr = LOOPBACK4_IPV6;
+
+	if (__inet_inherit_port(sk, newsk) < 0) {
+		inet_csk_prepare_forced_close(newsk);
+		dccp_done(newsk);
+		goto out;
+	}
+	*own_req = inet_ehash_nolisten(newsk, req_to_sk(req_unhash), NULL);
+	/* Clone pktoptions received with SYN, if we own the req */
+	if (*own_req && ireq->pktopts) {
+		newnp->pktoptions = skb_clone_and_charge_r(ireq->pktopts, newsk);
+		consume_skb(ireq->pktopts);
+		ireq->pktopts = NULL;
+	}
+
+	return newsk;
+
+out_overflow:
+	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENOVERFLOWS);
+out_nonewsk:
+	dst_release(dst);
+out:
+	__NET_INC_STATS(sock_net(sk), LINUX_MIB_LISTENDROPS);
+	return NULL;
+}
+
+/* The socket must have it's spinlock held when we get
+ * here.
+ *
+ * We have a potential double-lock case here, so even when
+ * doing backlog processing we use the BH locking scheme.
+ * This is because we cannot sleep with the original spinlock
+ * held.
+ */
+static int dccp_v6_do_rcv(struct sock *sk, struct sk_buff *skb)
+{
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct sk_buff *opt_skb = NULL;
+
+	/* Imagine: socket is IPv6. IPv4 packet arrives,
+	   goes to IPv4 receive handler and backlogged.
+	   From backlog it always goes here. Kerboom...
+	   Fortunately, dccp_rcv_established and rcv_established
+	   handle them correctly, but it is not case with
+	   dccp_v6_hnd_req and dccp_v6_ctl_send_reset().   --ANK
+	 */
+
+	if (skb->protocol == htons(ETH_P_IP))
+		return dccp_v4_do_rcv(sk, skb);
+
+	if (sk_filter(sk, skb))
+		goto discard;
+
+	/*
+	 * socket locking is here for SMP purposes as backlog rcv is currently
+	 * called with bh processing disabled.
+	 */
+
+	/* Do Stevens' IPV6_PKTOPTIONS.
+
+	   Yes, guys, it is the only place in our code, where we
+	   may make it not affecting IPv4.
+	   The rest of code is protocol independent,
+	   and I do not like idea to uglify IPv4.
+
+	   Actually, all the idea behind IPV6_PKTOPTIONS
+	   looks not very well thought. For now we latch
+	   options, received in the last packet, enqueued
+	   by tcp. Feel free to propose better solution.
+					       --ANK (980728)
+	 */
+	if (np->rxopt.all)
+		opt_skb = skb_clone_and_charge_r(skb, sk);
+
+	if (sk->sk_state == DCCP_OPEN) { /* Fast path */
+		if (dccp_rcv_established(sk, skb, dccp_hdr(skb), skb->len))
+			goto reset;
+		if (opt_skb)
+			goto ipv6_pktoptions;
+		return 0;
+	}
+
+	/*
+	 *  Step 3: Process LISTEN state
+	 *     If S.state == LISTEN,
+	 *	 If P.type == Request or P contains a valid Init Cookie option,
+	 *	      (* Must scan the packet's options to check for Init
+	 *		 Cookies.  Only Init Cookies are processed here,
+	 *		 however; other options are processed in Step 8.  This
+	 *		 scan need only be performed if the endpoint uses Init
+	 *		 Cookies *)
+	 *	      (* Generate a new socket and switch to that socket *)
+	 *	      Set S := new socket for this port pair
+	 *	      S.state = RESPOND
+	 *	      Choose S.ISS (initial seqno) or set from Init Cookies
+	 *	      Initialize S.GAR := S.ISS
+	 *	      Set S.ISR, S.GSR, S.SWL, S.SWH from packet or Init Cookies
+	 *	      Continue with S.state == RESPOND
+	 *	      (* A Response packet will be generated in Step 11 *)
+	 *	 Otherwise,
+	 *	      Generate Reset(No Connection) unless P.type == Reset
+	 *	      Drop packet and return
+	 *
+	 * NOTE: the check for the packet types is done in
+	 *	 dccp_rcv_state_process
+	 */
+
+	if (dccp_rcv_state_process(sk, skb, dccp_hdr(skb), skb->len))
+		goto reset;
+	if (opt_skb)
+		goto ipv6_pktoptions;
+	return 0;
+
+reset:
+	dccp_v6_ctl_send_reset(sk, skb);
+discard:
+	if (opt_skb != NULL)
+		__kfree_skb(opt_skb);
+	kfree_skb(skb);
+	return 0;
+
+/* Handling IPV6_PKTOPTIONS skb the similar
+ * way it's done for net/ipv6/tcp_ipv6.c
+ */
+ipv6_pktoptions:
+	if (!((1 << sk->sk_state) & (DCCPF_CLOSED | DCCPF_LISTEN))) {
+		if (np->rxopt.bits.rxinfo || np->rxopt.bits.rxoinfo)
+			np->mcast_oif = inet6_iif(opt_skb);
+		if (np->rxopt.bits.rxhlim || np->rxopt.bits.rxohlim)
+			np->mcast_hops = ipv6_hdr(opt_skb)->hop_limit;
+		if (np->rxopt.bits.rxflow || np->rxopt.bits.rxtclass)
+			np->rcv_flowinfo = ip6_flowinfo(ipv6_hdr(opt_skb));
+		if (np->repflow)
+			np->flow_label = ip6_flowlabel(ipv6_hdr(opt_skb));
+		if (ipv6_opt_accepted(sk, opt_skb,
+				      &DCCP_SKB_CB(opt_skb)->header.h6)) {
+			memmove(IP6CB(opt_skb),
+				&DCCP_SKB_CB(opt_skb)->header.h6,
+				sizeof(struct inet6_skb_parm));
+			opt_skb = xchg(&np->pktoptions, opt_skb);
+		} else {
+			__kfree_skb(opt_skb);
+			opt_skb = xchg(&np->pktoptions, NULL);
+		}
+	}
+
+	kfree_skb(opt_skb);
+	return 0;
+}
+
+static int dccp_v6_rcv(struct sk_buff *skb)
+{
+	const struct dccp_hdr *dh;
+	bool refcounted;
+	struct sock *sk;
+	int min_cov;
+
+	/* Step 1: Check header basics */
+
+	if (dccp_invalid_packet(skb))
+		goto discard_it;
+
+	/* Step 1: If header checksum is incorrect, drop packet and return. */
+	if (dccp_v6_csum_finish(skb, &ipv6_hdr(skb)->saddr,
+				     &ipv6_hdr(skb)->daddr)) {
+		DCCP_WARN("dropped packet with invalid checksum\n");
+		goto discard_it;
+	}
+
+	dh = dccp_hdr(skb);
+
+	DCCP_SKB_CB(skb)->dccpd_seq  = dccp_hdr_seq(dh);
+	DCCP_SKB_CB(skb)->dccpd_type = dh->dccph_type;
+
+	if (dccp_packet_without_ack(skb))
+		DCCP_SKB_CB(skb)->dccpd_ack_seq = DCCP_PKT_WITHOUT_ACK_SEQ;
+	else
+		DCCP_SKB_CB(skb)->dccpd_ack_seq = dccp_hdr_ack_seq(skb);
+
+lookup:
+	sk = __inet6_lookup_skb(&dccp_hashinfo, skb, __dccp_hdr_len(dh),
+			        dh->dccph_sport, dh->dccph_dport,
+				inet6_iif(skb), 0, &refcounted);
+	if (!sk) {
+		dccp_pr_debug("failed to look up flow ID in table and "
+			      "get corresponding socket\n");
+		goto no_dccp_socket;
+	}
+
+	/*
+	 * Step 2:
+	 *	... or S.state == TIMEWAIT,
+	 *		Generate Reset(No Connection) unless P.type == Reset
+	 *		Drop packet and return
+	 */
+	if (sk->sk_state == DCCP_TIME_WAIT) {
+		dccp_pr_debug("sk->sk_state == DCCP_TIME_WAIT: do_time_wait\n");
+		inet_twsk_put(inet_twsk(sk));
+		goto no_dccp_socket;
+	}
+
+	if (sk->sk_state == DCCP_NEW_SYN_RECV) {
+		struct request_sock *req = inet_reqsk(sk);
+		struct sock *nsk;
+
+		sk = req->rsk_listener;
+		if (unlikely(sk->sk_state != DCCP_LISTEN)) {
+			inet_csk_reqsk_queue_drop_and_put(sk, req);
+			goto lookup;
+		}
+		sock_hold(sk);
+		refcounted = true;
+		nsk = dccp_check_req(sk, skb, req);
+		if (!nsk) {
+			reqsk_put(req);
+			goto discard_and_relse;
+		}
+		if (nsk == sk) {
+			reqsk_put(req);
+		} else if (dccp_child_process(sk, nsk, skb)) {
+			dccp_v6_ctl_send_reset(sk, skb);
+			goto discard_and_relse;
+		} else {
+			sock_put(sk);
+			return 0;
+		}
+	}
+	/*
+	 * RFC 4340, sec. 9.2.1: Minimum Checksum Coverage
+	 *	o if MinCsCov = 0, only packets with CsCov = 0 are accepted
+	 *	o if MinCsCov > 0, also accept packets with CsCov >= MinCsCov
+	 */
+	min_cov = dccp_sk(sk)->dccps_pcrlen;
+	if (dh->dccph_cscov  &&  (min_cov == 0 || dh->dccph_cscov < min_cov))  {
+		dccp_pr_debug("Packet CsCov %d does not satisfy MinCsCov %d\n",
+			      dh->dccph_cscov, min_cov);
+		/* FIXME: send Data Dropped option (see also dccp_v4_rcv) */
+		goto discard_and_relse;
+	}
+
+	if (!xfrm6_policy_check(sk, XFRM_POLICY_IN, skb))
+		goto discard_and_relse;
+
+	return __sk_receive_skb(sk, skb, 1, dh->dccph_doff * 4,
+				refcounted) ? -1 : 0;
+
+no_dccp_socket:
+	if (!xfrm6_policy_check(NULL, XFRM_POLICY_IN, skb))
+		goto discard_it;
+	/*
+	 * Step 2:
+	 *	If no socket ...
+	 *		Generate Reset(No Connection) unless P.type == Reset
+	 *		Drop packet and return
+	 */
+	if (dh->dccph_type != DCCP_PKT_RESET) {
+		DCCP_SKB_CB(skb)->dccpd_reset_code =
+					DCCP_RESET_CODE_NO_CONNECTION;
+		dccp_v6_ctl_send_reset(sk, skb);
+	}
+
+discard_it:
+	kfree_skb(skb);
+	return 0;
+
+discard_and_relse:
+	if (refcounted)
+		sock_put(sk);
+	goto discard_it;
+}
+
+static int dccp_v6_connect(struct sock *sk, struct sockaddr *uaddr,
+			   int addr_len)
+{
+	struct sockaddr_in6 *usin = (struct sockaddr_in6 *)uaddr;
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct inet_sock *inet = inet_sk(sk);
+	struct ipv6_pinfo *np = inet6_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct in6_addr *saddr = NULL, *final_p, final;
+	struct ipv6_txoptions *opt;
+	struct flowi6 fl6;
+	struct dst_entry *dst;
+	int addr_type;
+	int err;
+
+	dp->dccps_role = DCCP_ROLE_CLIENT;
+
+	if (addr_len < SIN6_LEN_RFC2133)
+		return -EINVAL;
+
+	if (usin->sin6_family != AF_INET6)
+		return -EAFNOSUPPORT;
+
+	memset(&fl6, 0, sizeof(fl6));
+
+	if (np->sndflow) {
+		fl6.flowlabel = usin->sin6_flowinfo & IPV6_FLOWINFO_MASK;
+		IP6_ECN_flow_init(fl6.flowlabel);
+		if (fl6.flowlabel & IPV6_FLOWLABEL_MASK) {
+			struct ip6_flowlabel *flowlabel;
+			flowlabel = fl6_sock_lookup(sk, fl6.flowlabel);
+			if (IS_ERR(flowlabel))
+				return -EINVAL;
+			fl6_sock_release(flowlabel);
+		}
+	}
+	/*
+	 * connect() to INADDR_ANY means loopback (BSD'ism).
+	 */
+	if (ipv6_addr_any(&usin->sin6_addr))
+		usin->sin6_addr.s6_addr[15] = 1;
+
+	addr_type = ipv6_addr_type(&usin->sin6_addr);
+
+	if (addr_type & IPV6_ADDR_MULTICAST)
+		return -ENETUNREACH;
+
+	if (addr_type & IPV6_ADDR_LINKLOCAL) {
+		if (addr_len >= sizeof(struct sockaddr_in6) &&
+		    usin->sin6_scope_id) {
+			/* If interface is set while binding, indices
+			 * must coincide.
+			 */
+			if (sk->sk_bound_dev_if &&
+			    sk->sk_bound_dev_if != usin->sin6_scope_id)
+				return -EINVAL;
+
+			sk->sk_bound_dev_if = usin->sin6_scope_id;
+		}
+
+		/* Connect to link-local address requires an interface */
+		if (!sk->sk_bound_dev_if)
+			return -EINVAL;
+	}
+
+	sk->sk_v6_daddr = usin->sin6_addr;
+	np->flow_label = fl6.flowlabel;
+
+	/*
+	 * DCCP over IPv4
+	 */
+	if (addr_type == IPV6_ADDR_MAPPED) {
+		u32 exthdrlen = icsk->icsk_ext_hdr_len;
+		struct sockaddr_in sin;
+
+		SOCK_DEBUG(sk, "connect: ipv4 mapped\n");
+
+		if (__ipv6_only_sock(sk))
+			return -ENETUNREACH;
+
+		sin.sin_family = AF_INET;
+		sin.sin_port = usin->sin6_port;
+		sin.sin_addr.s_addr = usin->sin6_addr.s6_addr32[3];
+
+		icsk->icsk_af_ops = &dccp_ipv6_mapped;
+		sk->sk_backlog_rcv = dccp_v4_do_rcv;
+
+		err = dccp_v4_connect(sk, (struct sockaddr *)&sin, sizeof(sin));
+		if (err) {
+			icsk->icsk_ext_hdr_len = exthdrlen;
+			icsk->icsk_af_ops = &dccp_ipv6_af_ops;
+			sk->sk_backlog_rcv = dccp_v6_do_rcv;
+			goto failure;
+		}
+		np->saddr = sk->sk_v6_rcv_saddr;
+		return err;
+	}
+
+	if (!ipv6_addr_any(&sk->sk_v6_rcv_saddr))
+		saddr = &sk->sk_v6_rcv_saddr;
+
+	fl6.flowi6_proto = IPPROTO_DCCP;
+	fl6.daddr = sk->sk_v6_daddr;
+	fl6.saddr = saddr ? *saddr : np->saddr;
+	fl6.flowi6_oif = sk->sk_bound_dev_if;
+	fl6.fl6_dport = usin->sin6_port;
+	fl6.fl6_sport = inet->inet_sport;
+	security_sk_classify_flow(sk, flowi6_to_flowi_common(&fl6));
+
+	opt = rcu_dereference_protected(np->opt, lockdep_sock_is_held(sk));
+	final_p = fl6_update_dst(&fl6, opt, &final);
+
+	dst = ip6_dst_lookup_flow(sock_net(sk), sk, &fl6, final_p);
+	if (IS_ERR(dst)) {
+		err = PTR_ERR(dst);
+		goto failure;
+	}
+
+	if (saddr == NULL) {
+		saddr = &fl6.saddr;
+		sk->sk_v6_rcv_saddr = *saddr;
+	}
+
+	/* set the source address */
+	np->saddr = *saddr;
+	inet->inet_rcv_saddr = LOOPBACK4_IPV6;
+
+	ip6_dst_store(sk, dst, NULL, NULL);
+
+	icsk->icsk_ext_hdr_len = 0;
+	if (opt)
+		icsk->icsk_ext_hdr_len = opt->opt_flen + opt->opt_nflen;
+
+	inet->inet_dport = usin->sin6_port;
+
+	dccp_set_state(sk, DCCP_REQUESTING);
+	err = inet6_hash_connect(&dccp_death_row, sk);
+	if (err)
+		goto late_failure;
+
+	dp->dccps_iss = secure_dccpv6_sequence_number(np->saddr.s6_addr32,
+						      sk->sk_v6_daddr.s6_addr32,
+						      inet->inet_sport,
+						      inet->inet_dport);
+	err = dccp_connect(sk);
+	if (err)
+		goto late_failure;
+
+	return 0;
+
+late_failure:
+	dccp_set_state(sk, DCCP_CLOSED);
+	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
+		inet_reset_saddr(sk);
+	__sk_dst_reset(sk);
+failure:
+	inet->inet_dport = 0;
+	sk->sk_route_caps = 0;
+	return err;
+}
+
+static const struct inet_connection_sock_af_ops dccp_ipv6_af_ops = {
+	.queue_xmit	   = inet6_csk_xmit,
+	.send_check	   = dccp_v6_send_check,
+	.rebuild_header	   = inet6_sk_rebuild_header,
+	.conn_request	   = dccp_v6_conn_request,
+	.syn_recv_sock	   = dccp_v6_request_recv_sock,
+	.net_header_len	   = sizeof(struct ipv6hdr),
+	.setsockopt	   = ipv6_setsockopt,
+	.getsockopt	   = ipv6_getsockopt,
+	.addr2sockaddr	   = inet6_csk_addr2sockaddr,
+	.sockaddr_len	   = sizeof(struct sockaddr_in6),
+};
+
+/*
+ *	DCCP over IPv4 via INET6 API
+ */
+static const struct inet_connection_sock_af_ops dccp_ipv6_mapped = {
+	.queue_xmit	   = ip_queue_xmit,
+	.send_check	   = dccp_v4_send_check,
+	.rebuild_header	   = inet_sk_rebuild_header,
+	.conn_request	   = dccp_v6_conn_request,
+	.syn_recv_sock	   = dccp_v6_request_recv_sock,
+	.net_header_len	   = sizeof(struct iphdr),
+	.setsockopt	   = ipv6_setsockopt,
+	.getsockopt	   = ipv6_getsockopt,
+	.addr2sockaddr	   = inet6_csk_addr2sockaddr,
+	.sockaddr_len	   = sizeof(struct sockaddr_in6),
+};
+
+static void dccp_v6_sk_destruct(struct sock *sk)
+{
+	dccp_destruct_common(sk);
+	inet6_sock_destruct(sk);
+}
+
+/* NOTE: A lot of things set to zero explicitly by call to
+ *       sk_alloc() so need not be done here.
+ */
+static int dccp_v6_init_sock(struct sock *sk)
+{
+	static __u8 dccp_v6_ctl_sock_initialized;
+	int err = dccp_init_sock(sk, dccp_v6_ctl_sock_initialized);
+
+	if (err == 0) {
+		if (unlikely(!dccp_v6_ctl_sock_initialized))
+			dccp_v6_ctl_sock_initialized = 1;
+		inet_csk(sk)->icsk_af_ops = &dccp_ipv6_af_ops;
+		sk->sk_destruct = dccp_v6_sk_destruct;
+	}
+
+	return err;
+}
+
+static struct timewait_sock_ops dccp6_timewait_sock_ops = {
+	.twsk_obj_size	= sizeof(struct dccp6_timewait_sock),
+};
+
+static struct proto dccp_v6_prot = {
+	.name		   = "DCCPv6",
+	.owner		   = THIS_MODULE,
+	.close		   = dccp_close,
+	.connect	   = dccp_v6_connect,
+	.disconnect	   = dccp_disconnect,
+	.ioctl		   = dccp_ioctl,
+	.init		   = dccp_v6_init_sock,
+	.setsockopt	   = dccp_setsockopt,
+	.getsockopt	   = dccp_getsockopt,
+	.sendmsg	   = dccp_sendmsg,
+	.recvmsg	   = dccp_recvmsg,
+	.backlog_rcv	   = dccp_v6_do_rcv,
+	.hash		   = inet6_hash,
+	.unhash		   = inet_unhash,
+	.accept		   = inet_csk_accept,
+	.get_port	   = inet_csk_get_port,
+	.shutdown	   = dccp_shutdown,
+	.destroy	   = dccp_destroy_sock,
+	.orphan_count	   = &dccp_orphan_count,
+	.max_header	   = MAX_DCCP_HEADER,
+	.obj_size	   = sizeof(struct dccp6_sock),
+	.slab_flags	   = SLAB_TYPESAFE_BY_RCU,
+	.rsk_prot	   = &dccp6_request_sock_ops,
+	.twsk_prot	   = &dccp6_timewait_sock_ops,
+	.h.hashinfo	   = &dccp_hashinfo,
+};
+
+static const struct inet6_protocol dccp_v6_protocol = {
+	.handler	= dccp_v6_rcv,
+	.err_handler	= dccp_v6_err,
+	.flags		= INET6_PROTO_NOPOLICY | INET6_PROTO_FINAL,
+};
+
+static const struct proto_ops inet6_dccp_ops = {
+	.family		   = PF_INET6,
+	.owner		   = THIS_MODULE,
+	.release	   = inet6_release,
+	.bind		   = inet6_bind,
+	.connect	   = inet_stream_connect,
+	.socketpair	   = sock_no_socketpair,
+	.accept		   = inet_accept,
+	.getname	   = inet6_getname,
+	.poll		   = dccp_poll,
+	.ioctl		   = inet6_ioctl,
+	.gettstamp	   = sock_gettstamp,
+	.listen		   = inet_dccp_listen,
+	.shutdown	   = inet_shutdown,
+	.setsockopt	   = sock_common_setsockopt,
+	.getsockopt	   = sock_common_getsockopt,
+	.sendmsg	   = inet_sendmsg,
+	.recvmsg	   = sock_common_recvmsg,
+	.mmap		   = sock_no_mmap,
+	.sendpage	   = sock_no_sendpage,
+#ifdef CONFIG_COMPAT
+	.compat_ioctl	   = inet6_compat_ioctl,
+#endif
+};
+
+static struct inet_protosw dccp_v6_protosw = {
+	.type		= SOCK_DCCP,
+	.protocol	= IPPROTO_DCCP,
+	.prot		= &dccp_v6_prot,
+	.ops		= &inet6_dccp_ops,
+	.flags		= INET_PROTOSW_ICSK,
+};
+
+static int __net_init dccp_v6_init_net(struct net *net)
+{
+	if (dccp_hashinfo.bhash == NULL)
+		return -ESOCKTNOSUPPORT;
+
+	return inet_ctl_sock_create(&net->dccp.v6_ctl_sk, PF_INET6,
+				    SOCK_DCCP, IPPROTO_DCCP, net);
+}
+
+static void __net_exit dccp_v6_exit_net(struct net *net)
+{
+	inet_ctl_sock_destroy(net->dccp.v6_ctl_sk);
+}
+
+static void __net_exit dccp_v6_exit_batch(struct list_head *net_exit_list)
+{
+	inet_twsk_purge(&dccp_hashinfo, AF_INET6);
+}
+
+static struct pernet_operations dccp_v6_ops = {
+	.init   = dccp_v6_init_net,
+	.exit   = dccp_v6_exit_net,
+	.exit_batch = dccp_v6_exit_batch,
+};
+
+static int __init dccp_v6_init(void)
+{
+	int err = proto_register(&dccp_v6_prot, 1);
+
+	if (err)
+		goto out;
+
+	inet6_register_protosw(&dccp_v6_protosw);
+
+	err = register_pernet_subsys(&dccp_v6_ops);
+	if (err)
+		goto out_destroy_ctl_sock;
+
+	err = inet6_add_protocol(&dccp_v6_protocol, IPPROTO_DCCP);
+	if (err)
+		goto out_unregister_proto;
+
+out:
+	return err;
+out_unregister_proto:
+	unregister_pernet_subsys(&dccp_v6_ops);
+out_destroy_ctl_sock:
+	inet6_unregister_protosw(&dccp_v6_protosw);
+	proto_unregister(&dccp_v6_prot);
+	goto out;
+}
+
+static void __exit dccp_v6_exit(void)
+{
+	inet6_del_protocol(&dccp_v6_protocol, IPPROTO_DCCP);
+	unregister_pernet_subsys(&dccp_v6_ops);
+	inet6_unregister_protosw(&dccp_v6_protosw);
+	proto_unregister(&dccp_v6_prot);
+}
+
+module_init(dccp_v6_init);
+module_exit(dccp_v6_exit);
+
+/*
+ * __stringify doesn't likes enums, so use SOCK_DCCP (6) and IPPROTO_DCCP (33)
+ * values directly, Also cover the case where the protocol is not specified,
+ * i.e. net-pf-PF_INET6-proto-0-type-SOCK_DCCP
+ */
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET6, 33, 6);
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET6, 0, 6);
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@mandriva.com>");
+MODULE_DESCRIPTION("DCCPv6 - Datagram Congestion Controlled Protocol");
diff --git a/net/dccp/ipv6.h b/net/dccp/ipv6.h
new file mode 100644
index 000000000..7e4c2a3b3
--- /dev/null
+++ b/net/dccp/ipv6.h
@@ -0,0 +1,31 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+#ifndef _DCCP_IPV6_H
+#define _DCCP_IPV6_H
+/*
+ *  net/dccp/ipv6.h
+ *
+ *  An implementation of the DCCP protocol
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
+ */
+
+#include <linux/dccp.h>
+#include <linux/ipv6.h>
+
+struct dccp6_sock {
+	struct dccp_sock  dccp;
+	/*
+	 * ipv6_pinfo has to be the last member of dccp6_sock,
+	 * see inet6_sk_generic.
+	 */
+	struct ipv6_pinfo inet6;
+};
+
+struct dccp6_request_sock {
+	struct dccp_request_sock  dccp;
+};
+
+struct dccp6_timewait_sock {
+	struct inet_timewait_sock   inet;
+};
+
+#endif /* _DCCP_IPV6_H */
diff --git a/net/dccp/minisocks.c b/net/dccp/minisocks.c
new file mode 100644
index 000000000..91e7a2202
--- /dev/null
+++ b/net/dccp/minisocks.c
@@ -0,0 +1,271 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/minisocks.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/gfp.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/timer.h>
+
+#include <net/sock.h>
+#include <net/xfrm.h>
+#include <net/inet_timewait_sock.h>
+
+#include "ackvec.h"
+#include "ccid.h"
+#include "dccp.h"
+#include "feat.h"
+
+struct inet_timewait_death_row dccp_death_row = {
+	.sysctl_max_tw_buckets = NR_FILE * 2,
+	.hashinfo	= &dccp_hashinfo,
+};
+
+EXPORT_SYMBOL_GPL(dccp_death_row);
+
+void dccp_time_wait(struct sock *sk, int state, int timeo)
+{
+	struct inet_timewait_sock *tw;
+
+	tw = inet_twsk_alloc(sk, &dccp_death_row, state);
+
+	if (tw != NULL) {
+		const struct inet_connection_sock *icsk = inet_csk(sk);
+		const int rto = (icsk->icsk_rto << 2) - (icsk->icsk_rto >> 1);
+#if IS_ENABLED(CONFIG_IPV6)
+		if (tw->tw_family == PF_INET6) {
+			tw->tw_v6_daddr = sk->sk_v6_daddr;
+			tw->tw_v6_rcv_saddr = sk->sk_v6_rcv_saddr;
+			tw->tw_ipv6only = sk->sk_ipv6only;
+		}
+#endif
+
+		/* Get the TIME_WAIT timeout firing. */
+		if (timeo < rto)
+			timeo = rto;
+
+		if (state == DCCP_TIME_WAIT)
+			timeo = DCCP_TIMEWAIT_LEN;
+
+		/* tw_timer is pinned, so we need to make sure BH are disabled
+		 * in following section, otherwise timer handler could run before
+		 * we complete the initialization.
+		 */
+		local_bh_disable();
+		inet_twsk_schedule(tw, timeo);
+		/* Linkage updates.
+		 * Note that access to tw after this point is illegal.
+		 */
+		inet_twsk_hashdance(tw, sk, &dccp_hashinfo);
+		local_bh_enable();
+	} else {
+		/* Sorry, if we're out of memory, just CLOSE this
+		 * socket up.  We've got bigger problems than
+		 * non-graceful socket closings.
+		 */
+		DCCP_WARN("time wait bucket table overflow\n");
+	}
+
+	dccp_done(sk);
+}
+
+struct sock *dccp_create_openreq_child(const struct sock *sk,
+				       const struct request_sock *req,
+				       const struct sk_buff *skb)
+{
+	/*
+	 * Step 3: Process LISTEN state
+	 *
+	 *   (* Generate a new socket and switch to that socket *)
+	 *   Set S := new socket for this port pair
+	 */
+	struct sock *newsk = inet_csk_clone_lock(sk, req, GFP_ATOMIC);
+
+	if (newsk != NULL) {
+		struct dccp_request_sock *dreq = dccp_rsk(req);
+		struct inet_connection_sock *newicsk = inet_csk(newsk);
+		struct dccp_sock *newdp = dccp_sk(newsk);
+
+		newdp->dccps_role	    = DCCP_ROLE_SERVER;
+		newdp->dccps_hc_rx_ackvec   = NULL;
+		newdp->dccps_service_list   = NULL;
+		newdp->dccps_hc_rx_ccid     = NULL;
+		newdp->dccps_hc_tx_ccid     = NULL;
+		newdp->dccps_service	    = dreq->dreq_service;
+		newdp->dccps_timestamp_echo = dreq->dreq_timestamp_echo;
+		newdp->dccps_timestamp_time = dreq->dreq_timestamp_time;
+		newicsk->icsk_rto	    = DCCP_TIMEOUT_INIT;
+
+		INIT_LIST_HEAD(&newdp->dccps_featneg);
+		/*
+		 * Step 3: Process LISTEN state
+		 *
+		 *    Choose S.ISS (initial seqno) or set from Init Cookies
+		 *    Initialize S.GAR := S.ISS
+		 *    Set S.ISR, S.GSR from packet (or Init Cookies)
+		 *
+		 *    Setting AWL/AWH and SWL/SWH happens as part of the feature
+		 *    activation below, as these windows all depend on the local
+		 *    and remote Sequence Window feature values (7.5.2).
+		 */
+		newdp->dccps_iss = dreq->dreq_iss;
+		newdp->dccps_gss = dreq->dreq_gss;
+		newdp->dccps_gar = newdp->dccps_iss;
+		newdp->dccps_isr = dreq->dreq_isr;
+		newdp->dccps_gsr = dreq->dreq_gsr;
+
+		/*
+		 * Activate features: initialise CCIDs, sequence windows etc.
+		 */
+		if (dccp_feat_activate_values(newsk, &dreq->dreq_featneg)) {
+			sk_free_unlock_clone(newsk);
+			return NULL;
+		}
+		dccp_init_xmit_timers(newsk);
+
+		__DCCP_INC_STATS(DCCP_MIB_PASSIVEOPENS);
+	}
+	return newsk;
+}
+
+EXPORT_SYMBOL_GPL(dccp_create_openreq_child);
+
+/*
+ * Process an incoming packet for RESPOND sockets represented
+ * as an request_sock.
+ */
+struct sock *dccp_check_req(struct sock *sk, struct sk_buff *skb,
+			    struct request_sock *req)
+{
+	struct sock *child = NULL;
+	struct dccp_request_sock *dreq = dccp_rsk(req);
+	bool own_req;
+
+	/* TCP/DCCP listeners became lockless.
+	 * DCCP stores complex state in its request_sock, so we need
+	 * a protection for them, now this code runs without being protected
+	 * by the parent (listener) lock.
+	 */
+	spin_lock_bh(&dreq->dreq_lock);
+
+	/* Check for retransmitted REQUEST */
+	if (dccp_hdr(skb)->dccph_type == DCCP_PKT_REQUEST) {
+
+		if (after48(DCCP_SKB_CB(skb)->dccpd_seq, dreq->dreq_gsr)) {
+			dccp_pr_debug("Retransmitted REQUEST\n");
+			dreq->dreq_gsr = DCCP_SKB_CB(skb)->dccpd_seq;
+			/*
+			 * Send another RESPONSE packet
+			 * To protect against Request floods, increment retrans
+			 * counter (backoff, monitored by dccp_response_timer).
+			 */
+			inet_rtx_syn_ack(sk, req);
+		}
+		/* Network Duplicate, discard packet */
+		goto out;
+	}
+
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_PACKET_ERROR;
+
+	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_ACK &&
+	    dccp_hdr(skb)->dccph_type != DCCP_PKT_DATAACK)
+		goto drop;
+
+	/* Invalid ACK */
+	if (!between48(DCCP_SKB_CB(skb)->dccpd_ack_seq,
+				dreq->dreq_iss, dreq->dreq_gss)) {
+		dccp_pr_debug("Invalid ACK number: ack_seq=%llu, "
+			      "dreq_iss=%llu, dreq_gss=%llu\n",
+			      (unsigned long long)
+			      DCCP_SKB_CB(skb)->dccpd_ack_seq,
+			      (unsigned long long) dreq->dreq_iss,
+			      (unsigned long long) dreq->dreq_gss);
+		goto drop;
+	}
+
+	if (dccp_parse_options(sk, dreq, skb))
+		 goto drop;
+
+	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
+							 req, &own_req);
+	if (child) {
+		child = inet_csk_complete_hashdance(sk, child, req, own_req);
+		goto out;
+	}
+
+	DCCP_SKB_CB(skb)->dccpd_reset_code = DCCP_RESET_CODE_TOO_BUSY;
+drop:
+	if (dccp_hdr(skb)->dccph_type != DCCP_PKT_RESET)
+		req->rsk_ops->send_reset(sk, skb);
+
+	inet_csk_reqsk_queue_drop(sk, req);
+out:
+	spin_unlock_bh(&dreq->dreq_lock);
+	return child;
+}
+
+EXPORT_SYMBOL_GPL(dccp_check_req);
+
+/*
+ *  Queue segment on the new socket if the new socket is active,
+ *  otherwise we just shortcircuit this and continue with
+ *  the new socket.
+ */
+int dccp_child_process(struct sock *parent, struct sock *child,
+		       struct sk_buff *skb)
+	__releases(child)
+{
+	int ret = 0;
+	const int state = child->sk_state;
+
+	if (!sock_owned_by_user(child)) {
+		ret = dccp_rcv_state_process(child, skb, dccp_hdr(skb),
+					     skb->len);
+
+		/* Wakeup parent, send SIGIO */
+		if (state == DCCP_RESPOND && child->sk_state != state)
+			parent->sk_data_ready(parent);
+	} else {
+		/* Alas, it is possible again, because we do lookup
+		 * in main socket hash table and lock on listening
+		 * socket does not protect us more.
+		 */
+		__sk_add_backlog(child, skb);
+	}
+
+	bh_unlock_sock(child);
+	sock_put(child);
+	return ret;
+}
+
+EXPORT_SYMBOL_GPL(dccp_child_process);
+
+void dccp_reqsk_send_ack(const struct sock *sk, struct sk_buff *skb,
+			 struct request_sock *rsk)
+{
+	DCCP_BUG("DCCP-ACK packets are never sent in LISTEN/RESPOND state");
+}
+
+EXPORT_SYMBOL_GPL(dccp_reqsk_send_ack);
+
+int dccp_reqsk_init(struct request_sock *req,
+		    struct dccp_sock const *dp, struct sk_buff const *skb)
+{
+	struct dccp_request_sock *dreq = dccp_rsk(req);
+
+	spin_lock_init(&dreq->dreq_lock);
+	inet_rsk(req)->ir_rmt_port = dccp_hdr(skb)->dccph_sport;
+	inet_rsk(req)->ir_num	   = ntohs(dccp_hdr(skb)->dccph_dport);
+	inet_rsk(req)->acked	   = 0;
+	dreq->dreq_timestamp_echo  = 0;
+
+	/* inherit feature negotiation options from listening socket */
+	return dccp_feat_clone_list(&dp->dccps_featneg, &dreq->dreq_featneg);
+}
+
+EXPORT_SYMBOL_GPL(dccp_reqsk_init);
diff --git a/net/dccp/options.c b/net/dccp/options.c
new file mode 100644
index 000000000..d24cad050
--- /dev/null
+++ b/net/dccp/options.c
@@ -0,0 +1,609 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/options.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Copyright (c) 2005 Aristeu Sergio Rozanski Filho <aris@cathedrallabs.org>
+ *  Copyright (c) 2005 Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
+ *  Copyright (c) 2005 Ian McDonald <ian.mcdonald@jandi.co.nz>
+ */
+#include <linux/dccp.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <asm/unaligned.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+
+#include "ackvec.h"
+#include "ccid.h"
+#include "dccp.h"
+#include "feat.h"
+
+u64 dccp_decode_value_var(const u8 *bf, const u8 len)
+{
+	u64 value = 0;
+
+	if (len >= DCCP_OPTVAL_MAXLEN)
+		value += ((u64)*bf++) << 40;
+	if (len > 4)
+		value += ((u64)*bf++) << 32;
+	if (len > 3)
+		value += ((u64)*bf++) << 24;
+	if (len > 2)
+		value += ((u64)*bf++) << 16;
+	if (len > 1)
+		value += ((u64)*bf++) << 8;
+	if (len > 0)
+		value += *bf;
+
+	return value;
+}
+
+/**
+ * dccp_parse_options  -  Parse DCCP options present in @skb
+ * @sk: client|server|listening dccp socket (when @dreq != NULL)
+ * @dreq: request socket to use during connection setup, or NULL
+ * @skb: frame to parse
+ */
+int dccp_parse_options(struct sock *sk, struct dccp_request_sock *dreq,
+		       struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	const struct dccp_hdr *dh = dccp_hdr(skb);
+	const u8 pkt_type = DCCP_SKB_CB(skb)->dccpd_type;
+	unsigned char *options = (unsigned char *)dh + dccp_hdr_len(skb);
+	unsigned char *opt_ptr = options;
+	const unsigned char *opt_end = (unsigned char *)dh +
+					(dh->dccph_doff * 4);
+	struct dccp_options_received *opt_recv = &dp->dccps_options_received;
+	unsigned char opt, len;
+	unsigned char *value;
+	u32 elapsed_time;
+	__be32 opt_val;
+	int rc;
+	int mandatory = 0;
+
+	memset(opt_recv, 0, sizeof(*opt_recv));
+
+	opt = len = 0;
+	while (opt_ptr != opt_end) {
+		opt   = *opt_ptr++;
+		len   = 0;
+		value = NULL;
+
+		/* Check if this isn't a single byte option */
+		if (opt > DCCPO_MAX_RESERVED) {
+			if (opt_ptr == opt_end)
+				goto out_nonsensical_length;
+
+			len = *opt_ptr++;
+			if (len < 2)
+				goto out_nonsensical_length;
+			/*
+			 * Remove the type and len fields, leaving
+			 * just the value size
+			 */
+			len	-= 2;
+			value	= opt_ptr;
+			opt_ptr += len;
+
+			if (opt_ptr > opt_end)
+				goto out_nonsensical_length;
+		}
+
+		/*
+		 * CCID-specific options are ignored during connection setup, as
+		 * negotiation may still be in progress (see RFC 4340, 10.3).
+		 * The same applies to Ack Vectors, as these depend on the CCID.
+		 */
+		if (dreq != NULL && (opt >= DCCPO_MIN_RX_CCID_SPECIFIC ||
+		    opt == DCCPO_ACK_VECTOR_0 || opt == DCCPO_ACK_VECTOR_1))
+			goto ignore_option;
+
+		switch (opt) {
+		case DCCPO_PADDING:
+			break;
+		case DCCPO_MANDATORY:
+			if (mandatory)
+				goto out_invalid_option;
+			if (pkt_type != DCCP_PKT_DATA)
+				mandatory = 1;
+			break;
+		case DCCPO_NDP_COUNT:
+			if (len > 6)
+				goto out_invalid_option;
+
+			opt_recv->dccpor_ndp = dccp_decode_value_var(value, len);
+			dccp_pr_debug("%s opt: NDP count=%llu\n", dccp_role(sk),
+				      (unsigned long long)opt_recv->dccpor_ndp);
+			break;
+		case DCCPO_CHANGE_L ... DCCPO_CONFIRM_R:
+			if (pkt_type == DCCP_PKT_DATA)      /* RFC 4340, 6 */
+				break;
+			if (len == 0)
+				goto out_invalid_option;
+			rc = dccp_feat_parse_options(sk, dreq, mandatory, opt,
+						    *value, value + 1, len - 1);
+			if (rc)
+				goto out_featneg_failed;
+			break;
+		case DCCPO_TIMESTAMP:
+			if (len != 4)
+				goto out_invalid_option;
+			/*
+			 * RFC 4340 13.1: "The precise time corresponding to
+			 * Timestamp Value zero is not specified". We use
+			 * zero to indicate absence of a meaningful timestamp.
+			 */
+			opt_val = get_unaligned((__be32 *)value);
+			if (unlikely(opt_val == 0)) {
+				DCCP_WARN("Timestamp with zero value\n");
+				break;
+			}
+
+			if (dreq != NULL) {
+				dreq->dreq_timestamp_echo = ntohl(opt_val);
+				dreq->dreq_timestamp_time = dccp_timestamp();
+			} else {
+				opt_recv->dccpor_timestamp =
+					dp->dccps_timestamp_echo = ntohl(opt_val);
+				dp->dccps_timestamp_time = dccp_timestamp();
+			}
+			dccp_pr_debug("%s rx opt: TIMESTAMP=%u, ackno=%llu\n",
+				      dccp_role(sk), ntohl(opt_val),
+				      (unsigned long long)
+				      DCCP_SKB_CB(skb)->dccpd_ack_seq);
+			/* schedule an Ack in case this sender is quiescent */
+			inet_csk_schedule_ack(sk);
+			break;
+		case DCCPO_TIMESTAMP_ECHO:
+			if (len != 4 && len != 6 && len != 8)
+				goto out_invalid_option;
+
+			opt_val = get_unaligned((__be32 *)value);
+			opt_recv->dccpor_timestamp_echo = ntohl(opt_val);
+
+			dccp_pr_debug("%s rx opt: TIMESTAMP_ECHO=%u, len=%d, "
+				      "ackno=%llu", dccp_role(sk),
+				      opt_recv->dccpor_timestamp_echo,
+				      len + 2,
+				      (unsigned long long)
+				      DCCP_SKB_CB(skb)->dccpd_ack_seq);
+
+			value += 4;
+
+			if (len == 4) {		/* no elapsed time included */
+				dccp_pr_debug_cat("\n");
+				break;
+			}
+
+			if (len == 6) {		/* 2-byte elapsed time */
+				__be16 opt_val2 = get_unaligned((__be16 *)value);
+				elapsed_time = ntohs(opt_val2);
+			} else {		/* 4-byte elapsed time */
+				opt_val = get_unaligned((__be32 *)value);
+				elapsed_time = ntohl(opt_val);
+			}
+
+			dccp_pr_debug_cat(", ELAPSED_TIME=%u\n", elapsed_time);
+
+			/* Give precedence to the biggest ELAPSED_TIME */
+			if (elapsed_time > opt_recv->dccpor_elapsed_time)
+				opt_recv->dccpor_elapsed_time = elapsed_time;
+			break;
+		case DCCPO_ELAPSED_TIME:
+			if (dccp_packet_without_ack(skb))   /* RFC 4340, 13.2 */
+				break;
+
+			if (len == 2) {
+				__be16 opt_val2 = get_unaligned((__be16 *)value);
+				elapsed_time = ntohs(opt_val2);
+			} else if (len == 4) {
+				opt_val = get_unaligned((__be32 *)value);
+				elapsed_time = ntohl(opt_val);
+			} else {
+				goto out_invalid_option;
+			}
+
+			if (elapsed_time > opt_recv->dccpor_elapsed_time)
+				opt_recv->dccpor_elapsed_time = elapsed_time;
+
+			dccp_pr_debug("%s rx opt: ELAPSED_TIME=%d\n",
+				      dccp_role(sk), elapsed_time);
+			break;
+		case DCCPO_MIN_RX_CCID_SPECIFIC ... DCCPO_MAX_RX_CCID_SPECIFIC:
+			if (ccid_hc_rx_parse_options(dp->dccps_hc_rx_ccid, sk,
+						     pkt_type, opt, value, len))
+				goto out_invalid_option;
+			break;
+		case DCCPO_ACK_VECTOR_0:
+		case DCCPO_ACK_VECTOR_1:
+			if (dccp_packet_without_ack(skb))   /* RFC 4340, 11.4 */
+				break;
+			/*
+			 * Ack vectors are processed by the TX CCID if it is
+			 * interested. The RX CCID need not parse Ack Vectors,
+			 * since it is only interested in clearing old state.
+			 */
+			fallthrough;
+		case DCCPO_MIN_TX_CCID_SPECIFIC ... DCCPO_MAX_TX_CCID_SPECIFIC:
+			if (ccid_hc_tx_parse_options(dp->dccps_hc_tx_ccid, sk,
+						     pkt_type, opt, value, len))
+				goto out_invalid_option;
+			break;
+		default:
+			DCCP_CRIT("DCCP(%p): option %d(len=%d) not "
+				  "implemented, ignoring", sk, opt, len);
+			break;
+		}
+ignore_option:
+		if (opt != DCCPO_MANDATORY)
+			mandatory = 0;
+	}
+
+	/* mandatory was the last byte in option list -> reset connection */
+	if (mandatory)
+		goto out_invalid_option;
+
+out_nonsensical_length:
+	/* RFC 4340, 5.8: ignore option and all remaining option space */
+	return 0;
+
+out_invalid_option:
+	DCCP_INC_STATS(DCCP_MIB_INVALIDOPT);
+	rc = DCCP_RESET_CODE_OPTION_ERROR;
+out_featneg_failed:
+	DCCP_WARN("DCCP(%p): Option %d (len=%d) error=%u\n", sk, opt, len, rc);
+	DCCP_SKB_CB(skb)->dccpd_reset_code = rc;
+	DCCP_SKB_CB(skb)->dccpd_reset_data[0] = opt;
+	DCCP_SKB_CB(skb)->dccpd_reset_data[1] = len > 0 ? value[0] : 0;
+	DCCP_SKB_CB(skb)->dccpd_reset_data[2] = len > 1 ? value[1] : 0;
+	return -1;
+}
+
+EXPORT_SYMBOL_GPL(dccp_parse_options);
+
+void dccp_encode_value_var(const u64 value, u8 *to, const u8 len)
+{
+	if (len >= DCCP_OPTVAL_MAXLEN)
+		*to++ = (value & 0xFF0000000000ull) >> 40;
+	if (len > 4)
+		*to++ = (value & 0xFF00000000ull) >> 32;
+	if (len > 3)
+		*to++ = (value & 0xFF000000) >> 24;
+	if (len > 2)
+		*to++ = (value & 0xFF0000) >> 16;
+	if (len > 1)
+		*to++ = (value & 0xFF00) >> 8;
+	if (len > 0)
+		*to++ = (value & 0xFF);
+}
+
+static inline u8 dccp_ndp_len(const u64 ndp)
+{
+	if (likely(ndp <= 0xFF))
+		return 1;
+	return likely(ndp <= USHRT_MAX) ? 2 : (ndp <= UINT_MAX ? 4 : 6);
+}
+
+int dccp_insert_option(struct sk_buff *skb, const unsigned char option,
+		       const void *value, const unsigned char len)
+{
+	unsigned char *to;
+
+	if (DCCP_SKB_CB(skb)->dccpd_opt_len + len + 2 > DCCP_MAX_OPT_LEN)
+		return -1;
+
+	DCCP_SKB_CB(skb)->dccpd_opt_len += len + 2;
+
+	to    = skb_push(skb, len + 2);
+	*to++ = option;
+	*to++ = len + 2;
+
+	memcpy(to, value, len);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_insert_option);
+
+static int dccp_insert_option_ndp(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	u64 ndp = dp->dccps_ndp_count;
+
+	if (dccp_non_data_packet(skb))
+		++dp->dccps_ndp_count;
+	else
+		dp->dccps_ndp_count = 0;
+
+	if (ndp > 0) {
+		unsigned char *ptr;
+		const int ndp_len = dccp_ndp_len(ndp);
+		const int len = ndp_len + 2;
+
+		if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
+			return -1;
+
+		DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+		ptr = skb_push(skb, len);
+		*ptr++ = DCCPO_NDP_COUNT;
+		*ptr++ = len;
+		dccp_encode_value_var(ndp, ptr, ndp_len);
+	}
+
+	return 0;
+}
+
+static inline int dccp_elapsed_time_len(const u32 elapsed_time)
+{
+	return elapsed_time == 0 ? 0 : elapsed_time <= 0xFFFF ? 2 : 4;
+}
+
+static int dccp_insert_option_timestamp(struct sk_buff *skb)
+{
+	__be32 now = htonl(dccp_timestamp());
+	/* yes this will overflow but that is the point as we want a
+	 * 10 usec 32 bit timer which mean it wraps every 11.9 hours */
+
+	return dccp_insert_option(skb, DCCPO_TIMESTAMP, &now, sizeof(now));
+}
+
+static int dccp_insert_option_timestamp_echo(struct dccp_sock *dp,
+					     struct dccp_request_sock *dreq,
+					     struct sk_buff *skb)
+{
+	__be32 tstamp_echo;
+	unsigned char *to;
+	u32 elapsed_time, elapsed_time_len, len;
+
+	if (dreq != NULL) {
+		elapsed_time = dccp_timestamp() - dreq->dreq_timestamp_time;
+		tstamp_echo  = htonl(dreq->dreq_timestamp_echo);
+		dreq->dreq_timestamp_echo = 0;
+	} else {
+		elapsed_time = dccp_timestamp() - dp->dccps_timestamp_time;
+		tstamp_echo  = htonl(dp->dccps_timestamp_echo);
+		dp->dccps_timestamp_echo = 0;
+	}
+
+	elapsed_time_len = dccp_elapsed_time_len(elapsed_time);
+	len = 6 + elapsed_time_len;
+
+	if (DCCP_SKB_CB(skb)->dccpd_opt_len + len > DCCP_MAX_OPT_LEN)
+		return -1;
+
+	DCCP_SKB_CB(skb)->dccpd_opt_len += len;
+
+	to    = skb_push(skb, len);
+	*to++ = DCCPO_TIMESTAMP_ECHO;
+	*to++ = len;
+
+	memcpy(to, &tstamp_echo, 4);
+	to += 4;
+
+	if (elapsed_time_len == 2) {
+		const __be16 var16 = htons((u16)elapsed_time);
+		memcpy(to, &var16, 2);
+	} else if (elapsed_time_len == 4) {
+		const __be32 var32 = htonl(elapsed_time);
+		memcpy(to, &var32, 4);
+	}
+
+	return 0;
+}
+
+static int dccp_insert_option_ackvec(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct dccp_ackvec *av = dp->dccps_hc_rx_ackvec;
+	struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+	const u16 buflen = dccp_ackvec_buflen(av);
+	/* Figure out how many options do we need to represent the ackvec */
+	const u8 nr_opts = DIV_ROUND_UP(buflen, DCCP_SINGLE_OPT_MAXLEN);
+	u16 len = buflen + 2 * nr_opts;
+	u8 i, nonce = 0;
+	const unsigned char *tail, *from;
+	unsigned char *to;
+
+	if (dcb->dccpd_opt_len + len > DCCP_MAX_OPT_LEN) {
+		DCCP_WARN("Lacking space for %u bytes on %s packet\n", len,
+			  dccp_packet_name(dcb->dccpd_type));
+		return -1;
+	}
+	/*
+	 * Since Ack Vectors are variable-length, we can not always predict
+	 * their size. To catch exception cases where the space is running out
+	 * on the skb, a separate Sync is scheduled to carry the Ack Vector.
+	 */
+	if (len > DCCPAV_MIN_OPTLEN &&
+	    len + dcb->dccpd_opt_len + skb->len > dp->dccps_mss_cache) {
+		DCCP_WARN("No space left for Ack Vector (%u) on skb (%u+%u), "
+			  "MPS=%u ==> reduce payload size?\n", len, skb->len,
+			  dcb->dccpd_opt_len, dp->dccps_mss_cache);
+		dp->dccps_sync_scheduled = 1;
+		return 0;
+	}
+	dcb->dccpd_opt_len += len;
+
+	to   = skb_push(skb, len);
+	len  = buflen;
+	from = av->av_buf + av->av_buf_head;
+	tail = av->av_buf + DCCPAV_MAX_ACKVEC_LEN;
+
+	for (i = 0; i < nr_opts; ++i) {
+		int copylen = len;
+
+		if (len > DCCP_SINGLE_OPT_MAXLEN)
+			copylen = DCCP_SINGLE_OPT_MAXLEN;
+
+		/*
+		 * RFC 4340, 12.2: Encode the Nonce Echo for this Ack Vector via
+		 * its type; ack_nonce is the sum of all individual buf_nonce's.
+		 */
+		nonce ^= av->av_buf_nonce[i];
+
+		*to++ = DCCPO_ACK_VECTOR_0 + av->av_buf_nonce[i];
+		*to++ = copylen + 2;
+
+		/* Check if buf_head wraps */
+		if (from + copylen > tail) {
+			const u16 tailsize = tail - from;
+
+			memcpy(to, from, tailsize);
+			to	+= tailsize;
+			len	-= tailsize;
+			copylen	-= tailsize;
+			from	= av->av_buf;
+		}
+
+		memcpy(to, from, copylen);
+		from += copylen;
+		to   += copylen;
+		len  -= copylen;
+	}
+	/*
+	 * Each sent Ack Vector is recorded in the list, as per A.2 of RFC 4340.
+	 */
+	if (dccp_ackvec_update_records(av, dcb->dccpd_seq, nonce))
+		return -ENOBUFS;
+	return 0;
+}
+
+/**
+ * dccp_insert_option_mandatory  -  Mandatory option (5.8.2)
+ * @skb: frame into which to insert option
+ *
+ * Note that since we are using skb_push, this function needs to be called
+ * _after_ inserting the option it is supposed to influence (stack order).
+ */
+int dccp_insert_option_mandatory(struct sk_buff *skb)
+{
+	if (DCCP_SKB_CB(skb)->dccpd_opt_len >= DCCP_MAX_OPT_LEN)
+		return -1;
+
+	DCCP_SKB_CB(skb)->dccpd_opt_len++;
+	*(u8 *)skb_push(skb, 1) = DCCPO_MANDATORY;
+	return 0;
+}
+
+/**
+ * dccp_insert_fn_opt  -  Insert single Feature-Negotiation option into @skb
+ * @skb: frame to insert feature negotiation option into
+ * @type: %DCCPO_CHANGE_L, %DCCPO_CHANGE_R, %DCCPO_CONFIRM_L, %DCCPO_CONFIRM_R
+ * @feat: one out of %dccp_feature_numbers
+ * @val: NN value or SP array (preferred element first) to copy
+ * @len: true length of @val in bytes (excluding first element repetition)
+ * @repeat_first: whether to copy the first element of @val twice
+ *
+ * The last argument is used to construct Confirm options, where the preferred
+ * value and the preference list appear separately (RFC 4340, 6.3.1). Preference
+ * lists are kept such that the preferred entry is always first, so we only need
+ * to copy twice, and avoid the overhead of cloning into a bigger array.
+ */
+int dccp_insert_fn_opt(struct sk_buff *skb, u8 type, u8 feat,
+		       u8 *val, u8 len, bool repeat_first)
+{
+	u8 tot_len, *to;
+
+	/* take the `Feature' field and possible repetition into account */
+	if (len > (DCCP_SINGLE_OPT_MAXLEN - 2)) {
+		DCCP_WARN("length %u for feature %u too large\n", len, feat);
+		return -1;
+	}
+
+	if (unlikely(val == NULL || len == 0))
+		len = repeat_first = false;
+	tot_len = 3 + repeat_first + len;
+
+	if (DCCP_SKB_CB(skb)->dccpd_opt_len + tot_len > DCCP_MAX_OPT_LEN) {
+		DCCP_WARN("packet too small for feature %d option!\n", feat);
+		return -1;
+	}
+	DCCP_SKB_CB(skb)->dccpd_opt_len += tot_len;
+
+	to    = skb_push(skb, tot_len);
+	*to++ = type;
+	*to++ = tot_len;
+	*to++ = feat;
+
+	if (repeat_first)
+		*to++ = *val;
+	if (len)
+		memcpy(to, val, len);
+	return 0;
+}
+
+/* The length of all options needs to be a multiple of 4 (5.8) */
+static void dccp_insert_option_padding(struct sk_buff *skb)
+{
+	int padding = DCCP_SKB_CB(skb)->dccpd_opt_len % 4;
+
+	if (padding != 0) {
+		padding = 4 - padding;
+		memset(skb_push(skb, padding), 0, padding);
+		DCCP_SKB_CB(skb)->dccpd_opt_len += padding;
+	}
+}
+
+int dccp_insert_options(struct sock *sk, struct sk_buff *skb)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	DCCP_SKB_CB(skb)->dccpd_opt_len = 0;
+
+	if (dp->dccps_send_ndp_count && dccp_insert_option_ndp(sk, skb))
+		return -1;
+
+	if (DCCP_SKB_CB(skb)->dccpd_type != DCCP_PKT_DATA) {
+
+		/* Feature Negotiation */
+		if (dccp_feat_insert_opts(dp, NULL, skb))
+			return -1;
+
+		if (DCCP_SKB_CB(skb)->dccpd_type == DCCP_PKT_REQUEST) {
+			/*
+			 * Obtain RTT sample from Request/Response exchange.
+			 * This is currently used for TFRC initialisation.
+			 */
+			if (dccp_insert_option_timestamp(skb))
+				return -1;
+
+		} else if (dccp_ackvec_pending(sk) &&
+			   dccp_insert_option_ackvec(sk, skb)) {
+				return -1;
+		}
+	}
+
+	if (dp->dccps_hc_rx_insert_options) {
+		if (ccid_hc_rx_insert_options(dp->dccps_hc_rx_ccid, sk, skb))
+			return -1;
+		dp->dccps_hc_rx_insert_options = 0;
+	}
+
+	if (dp->dccps_timestamp_echo != 0 &&
+	    dccp_insert_option_timestamp_echo(dp, NULL, skb))
+		return -1;
+
+	dccp_insert_option_padding(skb);
+	return 0;
+}
+
+int dccp_insert_options_rsk(struct dccp_request_sock *dreq, struct sk_buff *skb)
+{
+	DCCP_SKB_CB(skb)->dccpd_opt_len = 0;
+
+	if (dccp_feat_insert_opts(NULL, dreq, skb))
+		return -1;
+
+	/* Obtain RTT sample from Response/Ack exchange (used by TFRC). */
+	if (dccp_insert_option_timestamp(skb))
+		return -1;
+
+	if (dreq->dreq_timestamp_echo != 0 &&
+	    dccp_insert_option_timestamp_echo(NULL, dreq, skb))
+		return -1;
+
+	dccp_insert_option_padding(skb);
+	return 0;
+}
diff --git a/net/dccp/output.c b/net/dccp/output.c
new file mode 100644
index 000000000..d679032f0
--- /dev/null
+++ b/net/dccp/output.c
@@ -0,0 +1,700 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/output.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/slab.h>
+#include <linux/sched/signal.h>
+
+#include <net/inet_sock.h>
+#include <net/sock.h>
+
+#include "ackvec.h"
+#include "ccid.h"
+#include "dccp.h"
+
+static inline void dccp_event_ack_sent(struct sock *sk)
+{
+	inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
+}
+
+/* enqueue @skb on sk_send_head for retransmission, return clone to send now */
+static struct sk_buff *dccp_skb_entail(struct sock *sk, struct sk_buff *skb)
+{
+	skb_set_owner_w(skb, sk);
+	WARN_ON(sk->sk_send_head);
+	sk->sk_send_head = skb;
+	return skb_clone(sk->sk_send_head, gfp_any());
+}
+
+/*
+ * All SKB's seen here are completely headerless. It is our
+ * job to build the DCCP header, and pass the packet down to
+ * IP so it can do the same plus pass the packet off to the
+ * device.
+ */
+static int dccp_transmit_skb(struct sock *sk, struct sk_buff *skb)
+{
+	if (likely(skb != NULL)) {
+		struct inet_sock *inet = inet_sk(sk);
+		const struct inet_connection_sock *icsk = inet_csk(sk);
+		struct dccp_sock *dp = dccp_sk(sk);
+		struct dccp_skb_cb *dcb = DCCP_SKB_CB(skb);
+		struct dccp_hdr *dh;
+		/* XXX For now we're using only 48 bits sequence numbers */
+		const u32 dccp_header_size = sizeof(*dh) +
+					     sizeof(struct dccp_hdr_ext) +
+					  dccp_packet_hdr_len(dcb->dccpd_type);
+		int err, set_ack = 1;
+		u64 ackno = dp->dccps_gsr;
+		/*
+		 * Increment GSS here already in case the option code needs it.
+		 * Update GSS for real only if option processing below succeeds.
+		 */
+		dcb->dccpd_seq = ADD48(dp->dccps_gss, 1);
+
+		switch (dcb->dccpd_type) {
+		case DCCP_PKT_DATA:
+			set_ack = 0;
+			fallthrough;
+		case DCCP_PKT_DATAACK:
+		case DCCP_PKT_RESET:
+			break;
+
+		case DCCP_PKT_REQUEST:
+			set_ack = 0;
+			/* Use ISS on the first (non-retransmitted) Request. */
+			if (icsk->icsk_retransmits == 0)
+				dcb->dccpd_seq = dp->dccps_iss;
+			fallthrough;
+
+		case DCCP_PKT_SYNC:
+		case DCCP_PKT_SYNCACK:
+			ackno = dcb->dccpd_ack_seq;
+			fallthrough;
+		default:
+			/*
+			 * Set owner/destructor: some skbs are allocated via
+			 * alloc_skb (e.g. when retransmission may happen).
+			 * Only Data, DataAck, and Reset packets should come
+			 * through here with skb->sk set.
+			 */
+			WARN_ON(skb->sk);
+			skb_set_owner_w(skb, sk);
+			break;
+		}
+
+		if (dccp_insert_options(sk, skb)) {
+			kfree_skb(skb);
+			return -EPROTO;
+		}
+
+
+		/* Build DCCP header and checksum it. */
+		dh = dccp_zeroed_hdr(skb, dccp_header_size);
+		dh->dccph_type	= dcb->dccpd_type;
+		dh->dccph_sport	= inet->inet_sport;
+		dh->dccph_dport	= inet->inet_dport;
+		dh->dccph_doff	= (dccp_header_size + dcb->dccpd_opt_len) / 4;
+		dh->dccph_ccval	= dcb->dccpd_ccval;
+		dh->dccph_cscov = dp->dccps_pcslen;
+		/* XXX For now we're using only 48 bits sequence numbers */
+		dh->dccph_x	= 1;
+
+		dccp_update_gss(sk, dcb->dccpd_seq);
+		dccp_hdr_set_seq(dh, dp->dccps_gss);
+		if (set_ack)
+			dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), ackno);
+
+		switch (dcb->dccpd_type) {
+		case DCCP_PKT_REQUEST:
+			dccp_hdr_request(skb)->dccph_req_service =
+							dp->dccps_service;
+			/*
+			 * Limit Ack window to ISS <= P.ackno <= GSS, so that
+			 * only Responses to Requests we sent are considered.
+			 */
+			dp->dccps_awl = dp->dccps_iss;
+			break;
+		case DCCP_PKT_RESET:
+			dccp_hdr_reset(skb)->dccph_reset_code =
+							dcb->dccpd_reset_code;
+			break;
+		}
+
+		icsk->icsk_af_ops->send_check(sk, skb);
+
+		if (set_ack)
+			dccp_event_ack_sent(sk);
+
+		DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+
+		err = icsk->icsk_af_ops->queue_xmit(sk, skb, &inet->cork.fl);
+		return net_xmit_eval(err);
+	}
+	return -ENOBUFS;
+}
+
+/**
+ * dccp_determine_ccmps  -  Find out about CCID-specific packet-size limits
+ * We only consider the HC-sender CCID for setting the CCMPS (RFC 4340, 14.),
+ * since the RX CCID is restricted to feedback packets (Acks), which are small
+ * in comparison with the data traffic. A value of 0 means "no current CCMPS".
+ */
+static u32 dccp_determine_ccmps(const struct dccp_sock *dp)
+{
+	const struct ccid *tx_ccid = dp->dccps_hc_tx_ccid;
+
+	if (tx_ccid == NULL || tx_ccid->ccid_ops == NULL)
+		return 0;
+	return tx_ccid->ccid_ops->ccid_ccmps;
+}
+
+unsigned int dccp_sync_mss(struct sock *sk, u32 pmtu)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	u32 ccmps = dccp_determine_ccmps(dp);
+	u32 cur_mps = ccmps ? min(pmtu, ccmps) : pmtu;
+
+	/* Account for header lengths and IPv4/v6 option overhead */
+	cur_mps -= (icsk->icsk_af_ops->net_header_len + icsk->icsk_ext_hdr_len +
+		    sizeof(struct dccp_hdr) + sizeof(struct dccp_hdr_ext));
+
+	/*
+	 * Leave enough headroom for common DCCP header options.
+	 * This only considers options which may appear on DCCP-Data packets, as
+	 * per table 3 in RFC 4340, 5.8. When running out of space for other
+	 * options (eg. Ack Vector which can take up to 255 bytes), it is better
+	 * to schedule a separate Ack. Thus we leave headroom for the following:
+	 *  - 1 byte for Slow Receiver (11.6)
+	 *  - 6 bytes for Timestamp (13.1)
+	 *  - 10 bytes for Timestamp Echo (13.3)
+	 *  - 8 bytes for NDP count (7.7, when activated)
+	 *  - 6 bytes for Data Checksum (9.3)
+	 *  - %DCCPAV_MIN_OPTLEN bytes for Ack Vector size (11.4, when enabled)
+	 */
+	cur_mps -= roundup(1 + 6 + 10 + dp->dccps_send_ndp_count * 8 + 6 +
+			   (dp->dccps_hc_rx_ackvec ? DCCPAV_MIN_OPTLEN : 0), 4);
+
+	/* And store cached results */
+	icsk->icsk_pmtu_cookie = pmtu;
+	WRITE_ONCE(dp->dccps_mss_cache, cur_mps);
+
+	return cur_mps;
+}
+
+EXPORT_SYMBOL_GPL(dccp_sync_mss);
+
+void dccp_write_space(struct sock *sk)
+{
+	struct socket_wq *wq;
+
+	rcu_read_lock();
+	wq = rcu_dereference(sk->sk_wq);
+	if (skwq_has_sleeper(wq))
+		wake_up_interruptible(&wq->wait);
+	/* Should agree with poll, otherwise some programs break */
+	if (sock_writeable(sk))
+		sk_wake_async(sk, SOCK_WAKE_SPACE, POLL_OUT);
+
+	rcu_read_unlock();
+}
+
+/**
+ * dccp_wait_for_ccid  -  Await CCID send permission
+ * @sk:    socket to wait for
+ * @delay: timeout in jiffies
+ *
+ * This is used by CCIDs which need to delay the send time in process context.
+ */
+static int dccp_wait_for_ccid(struct sock *sk, unsigned long delay)
+{
+	DEFINE_WAIT(wait);
+	long remaining;
+
+	prepare_to_wait(sk_sleep(sk), &wait, TASK_INTERRUPTIBLE);
+	sk->sk_write_pending++;
+	release_sock(sk);
+
+	remaining = schedule_timeout(delay);
+
+	lock_sock(sk);
+	sk->sk_write_pending--;
+	finish_wait(sk_sleep(sk), &wait);
+
+	if (signal_pending(current) || sk->sk_err)
+		return -1;
+	return remaining;
+}
+
+/**
+ * dccp_xmit_packet  -  Send data packet under control of CCID
+ * Transmits next-queued payload and informs CCID to account for the packet.
+ */
+static void dccp_xmit_packet(struct sock *sk)
+{
+	int err, len;
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct sk_buff *skb = dccp_qpolicy_pop(sk);
+
+	if (unlikely(skb == NULL))
+		return;
+	len = skb->len;
+
+	if (sk->sk_state == DCCP_PARTOPEN) {
+		const u32 cur_mps = dp->dccps_mss_cache - DCCP_FEATNEG_OVERHEAD;
+		/*
+		 * See 8.1.5 - Handshake Completion.
+		 *
+		 * For robustness we resend Confirm options until the client has
+		 * entered OPEN. During the initial feature negotiation, the MPS
+		 * is smaller than usual, reduced by the Change/Confirm options.
+		 */
+		if (!list_empty(&dp->dccps_featneg) && len > cur_mps) {
+			DCCP_WARN("Payload too large (%d) for featneg.\n", len);
+			dccp_send_ack(sk);
+			dccp_feat_list_purge(&dp->dccps_featneg);
+		}
+
+		inet_csk_schedule_ack(sk);
+		inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
+					      inet_csk(sk)->icsk_rto,
+					      DCCP_RTO_MAX);
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATAACK;
+	} else if (dccp_ack_pending(sk)) {
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATAACK;
+	} else {
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_DATA;
+	}
+
+	err = dccp_transmit_skb(sk, skb);
+	if (err)
+		dccp_pr_debug("transmit_skb() returned err=%d\n", err);
+	/*
+	 * Register this one as sent even if an error occurred. To the remote
+	 * end a local packet drop is indistinguishable from network loss, i.e.
+	 * any local drop will eventually be reported via receiver feedback.
+	 */
+	ccid_hc_tx_packet_sent(dp->dccps_hc_tx_ccid, sk, len);
+
+	/*
+	 * If the CCID needs to transfer additional header options out-of-band
+	 * (e.g. Ack Vectors or feature-negotiation options), it activates this
+	 * flag to schedule a Sync. The Sync will automatically incorporate all
+	 * currently pending header options, thus clearing the backlog.
+	 */
+	if (dp->dccps_sync_scheduled)
+		dccp_send_sync(sk, dp->dccps_gsr, DCCP_PKT_SYNC);
+}
+
+/**
+ * dccp_flush_write_queue  -  Drain queue at end of connection
+ * Since dccp_sendmsg queues packets without waiting for them to be sent, it may
+ * happen that the TX queue is not empty at the end of a connection. We give the
+ * HC-sender CCID a grace period of up to @time_budget jiffies. If this function
+ * returns with a non-empty write queue, it will be purged later.
+ */
+void dccp_flush_write_queue(struct sock *sk, long *time_budget)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct sk_buff *skb;
+	long delay, rc;
+
+	while (*time_budget > 0 && (skb = skb_peek(&sk->sk_write_queue))) {
+		rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
+
+		switch (ccid_packet_dequeue_eval(rc)) {
+		case CCID_PACKET_WILL_DEQUEUE_LATER:
+			/*
+			 * If the CCID determines when to send, the next sending
+			 * time is unknown or the CCID may not even send again
+			 * (e.g. remote host crashes or lost Ack packets).
+			 */
+			DCCP_WARN("CCID did not manage to send all packets\n");
+			return;
+		case CCID_PACKET_DELAY:
+			delay = msecs_to_jiffies(rc);
+			if (delay > *time_budget)
+				return;
+			rc = dccp_wait_for_ccid(sk, delay);
+			if (rc < 0)
+				return;
+			*time_budget -= (delay - rc);
+			/* check again if we can send now */
+			break;
+		case CCID_PACKET_SEND_AT_ONCE:
+			dccp_xmit_packet(sk);
+			break;
+		case CCID_PACKET_ERR:
+			skb_dequeue(&sk->sk_write_queue);
+			kfree_skb(skb);
+			dccp_pr_debug("packet discarded due to err=%ld\n", rc);
+		}
+	}
+}
+
+void dccp_write_xmit(struct sock *sk)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct sk_buff *skb;
+
+	while ((skb = dccp_qpolicy_top(sk))) {
+		int rc = ccid_hc_tx_send_packet(dp->dccps_hc_tx_ccid, sk, skb);
+
+		switch (ccid_packet_dequeue_eval(rc)) {
+		case CCID_PACKET_WILL_DEQUEUE_LATER:
+			return;
+		case CCID_PACKET_DELAY:
+			sk_reset_timer(sk, &dp->dccps_xmit_timer,
+				       jiffies + msecs_to_jiffies(rc));
+			return;
+		case CCID_PACKET_SEND_AT_ONCE:
+			dccp_xmit_packet(sk);
+			break;
+		case CCID_PACKET_ERR:
+			dccp_qpolicy_drop(sk, skb);
+			dccp_pr_debug("packet discarded due to err=%d\n", rc);
+		}
+	}
+}
+
+/**
+ * dccp_retransmit_skb  -  Retransmit Request, Close, or CloseReq packets
+ * There are only four retransmittable packet types in DCCP:
+ * - Request  in client-REQUEST  state (sec. 8.1.1),
+ * - CloseReq in server-CLOSEREQ state (sec. 8.3),
+ * - Close    in   node-CLOSING  state (sec. 8.3),
+ * - Acks in client-PARTOPEN state (sec. 8.1.5, handled by dccp_delack_timer()).
+ * This function expects sk->sk_send_head to contain the original skb.
+ */
+int dccp_retransmit_skb(struct sock *sk)
+{
+	WARN_ON(sk->sk_send_head == NULL);
+
+	if (inet_csk(sk)->icsk_af_ops->rebuild_header(sk) != 0)
+		return -EHOSTUNREACH; /* Routing failure or similar. */
+
+	/* this count is used to distinguish original and retransmitted skb */
+	inet_csk(sk)->icsk_retransmits++;
+
+	return dccp_transmit_skb(sk, skb_clone(sk->sk_send_head, GFP_ATOMIC));
+}
+
+struct sk_buff *dccp_make_response(const struct sock *sk, struct dst_entry *dst,
+				   struct request_sock *req)
+{
+	struct dccp_hdr *dh;
+	struct dccp_request_sock *dreq;
+	const u32 dccp_header_size = sizeof(struct dccp_hdr) +
+				     sizeof(struct dccp_hdr_ext) +
+				     sizeof(struct dccp_hdr_response);
+	struct sk_buff *skb;
+
+	/* sk is marked const to clearly express we dont hold socket lock.
+	 * sock_wmalloc() will atomically change sk->sk_wmem_alloc,
+	 * it is safe to promote sk to non const.
+	 */
+	skb = sock_wmalloc((struct sock *)sk, MAX_DCCP_HEADER, 1,
+			   GFP_ATOMIC);
+	if (!skb)
+		return NULL;
+
+	skb_reserve(skb, MAX_DCCP_HEADER);
+
+	skb_dst_set(skb, dst_clone(dst));
+
+	dreq = dccp_rsk(req);
+	if (inet_rsk(req)->acked)	/* increase GSS upon retransmission */
+		dccp_inc_seqno(&dreq->dreq_gss);
+	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_RESPONSE;
+	DCCP_SKB_CB(skb)->dccpd_seq  = dreq->dreq_gss;
+
+	/* Resolve feature dependencies resulting from choice of CCID */
+	if (dccp_feat_server_ccid_dependencies(dreq))
+		goto response_failed;
+
+	if (dccp_insert_options_rsk(dreq, skb))
+		goto response_failed;
+
+	/* Build and checksum header */
+	dh = dccp_zeroed_hdr(skb, dccp_header_size);
+
+	dh->dccph_sport	= htons(inet_rsk(req)->ir_num);
+	dh->dccph_dport	= inet_rsk(req)->ir_rmt_port;
+	dh->dccph_doff	= (dccp_header_size +
+			   DCCP_SKB_CB(skb)->dccpd_opt_len) / 4;
+	dh->dccph_type	= DCCP_PKT_RESPONSE;
+	dh->dccph_x	= 1;
+	dccp_hdr_set_seq(dh, dreq->dreq_gss);
+	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dreq->dreq_gsr);
+	dccp_hdr_response(skb)->dccph_resp_service = dreq->dreq_service;
+
+	dccp_csum_outgoing(skb);
+
+	/* We use `acked' to remember that a Response was already sent. */
+	inet_rsk(req)->acked = 1;
+	DCCP_INC_STATS(DCCP_MIB_OUTSEGS);
+	return skb;
+response_failed:
+	kfree_skb(skb);
+	return NULL;
+}
+
+EXPORT_SYMBOL_GPL(dccp_make_response);
+
+/* answer offending packet in @rcv_skb with Reset from control socket @ctl */
+struct sk_buff *dccp_ctl_make_reset(struct sock *sk, struct sk_buff *rcv_skb)
+{
+	struct dccp_hdr *rxdh = dccp_hdr(rcv_skb), *dh;
+	struct dccp_skb_cb *dcb = DCCP_SKB_CB(rcv_skb);
+	const u32 dccp_hdr_reset_len = sizeof(struct dccp_hdr) +
+				       sizeof(struct dccp_hdr_ext) +
+				       sizeof(struct dccp_hdr_reset);
+	struct dccp_hdr_reset *dhr;
+	struct sk_buff *skb;
+
+	skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);
+	if (skb == NULL)
+		return NULL;
+
+	skb_reserve(skb, sk->sk_prot->max_header);
+
+	/* Swap the send and the receive. */
+	dh = dccp_zeroed_hdr(skb, dccp_hdr_reset_len);
+	dh->dccph_type	= DCCP_PKT_RESET;
+	dh->dccph_sport	= rxdh->dccph_dport;
+	dh->dccph_dport	= rxdh->dccph_sport;
+	dh->dccph_doff	= dccp_hdr_reset_len / 4;
+	dh->dccph_x	= 1;
+
+	dhr = dccp_hdr_reset(skb);
+	dhr->dccph_reset_code = dcb->dccpd_reset_code;
+
+	switch (dcb->dccpd_reset_code) {
+	case DCCP_RESET_CODE_PACKET_ERROR:
+		dhr->dccph_reset_data[0] = rxdh->dccph_type;
+		break;
+	case DCCP_RESET_CODE_OPTION_ERROR:
+	case DCCP_RESET_CODE_MANDATORY_ERROR:
+		memcpy(dhr->dccph_reset_data, dcb->dccpd_reset_data, 3);
+		break;
+	}
+	/*
+	 * From RFC 4340, 8.3.1:
+	 *   If P.ackno exists, set R.seqno := P.ackno + 1.
+	 *   Else set R.seqno := 0.
+	 */
+	if (dcb->dccpd_ack_seq != DCCP_PKT_WITHOUT_ACK_SEQ)
+		dccp_hdr_set_seq(dh, ADD48(dcb->dccpd_ack_seq, 1));
+	dccp_hdr_set_ack(dccp_hdr_ack_bits(skb), dcb->dccpd_seq);
+
+	dccp_csum_outgoing(skb);
+	return skb;
+}
+
+EXPORT_SYMBOL_GPL(dccp_ctl_make_reset);
+
+/* send Reset on established socket, to close or abort the connection */
+int dccp_send_reset(struct sock *sk, enum dccp_reset_codes code)
+{
+	struct sk_buff *skb;
+	/*
+	 * FIXME: what if rebuild_header fails?
+	 * Should we be doing a rebuild_header here?
+	 */
+	int err = inet_csk(sk)->icsk_af_ops->rebuild_header(sk);
+
+	if (err != 0)
+		return err;
+
+	skb = sock_wmalloc(sk, sk->sk_prot->max_header, 1, GFP_ATOMIC);
+	if (skb == NULL)
+		return -ENOBUFS;
+
+	/* Reserve space for headers and prepare control bits. */
+	skb_reserve(skb, sk->sk_prot->max_header);
+	DCCP_SKB_CB(skb)->dccpd_type	   = DCCP_PKT_RESET;
+	DCCP_SKB_CB(skb)->dccpd_reset_code = code;
+
+	return dccp_transmit_skb(sk, skb);
+}
+
+/*
+ * Do all connect socket setups that can be done AF independent.
+ */
+int dccp_connect(struct sock *sk)
+{
+	struct sk_buff *skb;
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct dst_entry *dst = __sk_dst_get(sk);
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	sk->sk_err = 0;
+	sock_reset_flag(sk, SOCK_DONE);
+
+	dccp_sync_mss(sk, dst_mtu(dst));
+
+	/* do not connect if feature negotiation setup fails */
+	if (dccp_feat_finalise_settings(dccp_sk(sk)))
+		return -EPROTO;
+
+	/* Initialise GAR as per 8.5; AWL/AWH are set in dccp_transmit_skb() */
+	dp->dccps_gar = dp->dccps_iss;
+
+	skb = alloc_skb(sk->sk_prot->max_header, sk->sk_allocation);
+	if (unlikely(skb == NULL))
+		return -ENOBUFS;
+
+	/* Reserve space for headers. */
+	skb_reserve(skb, sk->sk_prot->max_header);
+
+	DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_REQUEST;
+
+	dccp_transmit_skb(sk, dccp_skb_entail(sk, skb));
+	DCCP_INC_STATS(DCCP_MIB_ACTIVEOPENS);
+
+	/* Timer for repeating the REQUEST until an answer. */
+	icsk->icsk_retransmits = 0;
+	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+				  icsk->icsk_rto, DCCP_RTO_MAX);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_connect);
+
+void dccp_send_ack(struct sock *sk)
+{
+	/* If we have been reset, we may not send again. */
+	if (sk->sk_state != DCCP_CLOSED) {
+		struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header,
+						GFP_ATOMIC);
+
+		if (skb == NULL) {
+			inet_csk_schedule_ack(sk);
+			inet_csk(sk)->icsk_ack.ato = TCP_ATO_MIN;
+			inet_csk_reset_xmit_timer(sk, ICSK_TIME_DACK,
+						  TCP_DELACK_MAX,
+						  DCCP_RTO_MAX);
+			return;
+		}
+
+		/* Reserve space for headers */
+		skb_reserve(skb, sk->sk_prot->max_header);
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_ACK;
+		dccp_transmit_skb(sk, skb);
+	}
+}
+
+EXPORT_SYMBOL_GPL(dccp_send_ack);
+
+#if 0
+/* FIXME: Is this still necessary (11.3) - currently nowhere used by DCCP. */
+void dccp_send_delayed_ack(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	/*
+	 * FIXME: tune this timer. elapsed time fixes the skew, so no problem
+	 * with using 2s, and active senders also piggyback the ACK into a
+	 * DATAACK packet, so this is really for quiescent senders.
+	 */
+	unsigned long timeout = jiffies + 2 * HZ;
+
+	/* Use new timeout only if there wasn't a older one earlier. */
+	if (icsk->icsk_ack.pending & ICSK_ACK_TIMER) {
+		/* If delack timer was blocked or is about to expire,
+		 * send ACK now.
+		 *
+		 * FIXME: check the "about to expire" part
+		 */
+		if (icsk->icsk_ack.blocked) {
+			dccp_send_ack(sk);
+			return;
+		}
+
+		if (!time_before(timeout, icsk->icsk_ack.timeout))
+			timeout = icsk->icsk_ack.timeout;
+	}
+	icsk->icsk_ack.pending |= ICSK_ACK_SCHED | ICSK_ACK_TIMER;
+	icsk->icsk_ack.timeout = timeout;
+	sk_reset_timer(sk, &icsk->icsk_delack_timer, timeout);
+}
+#endif
+
+void dccp_send_sync(struct sock *sk, const u64 ackno,
+		    const enum dccp_pkt_type pkt_type)
+{
+	/*
+	 * We are not putting this on the write queue, so
+	 * dccp_transmit_skb() will set the ownership to this
+	 * sock.
+	 */
+	struct sk_buff *skb = alloc_skb(sk->sk_prot->max_header, GFP_ATOMIC);
+
+	if (skb == NULL) {
+		/* FIXME: how to make sure the sync is sent? */
+		DCCP_CRIT("could not send %s", dccp_packet_name(pkt_type));
+		return;
+	}
+
+	/* Reserve space for headers and prepare control bits. */
+	skb_reserve(skb, sk->sk_prot->max_header);
+	DCCP_SKB_CB(skb)->dccpd_type = pkt_type;
+	DCCP_SKB_CB(skb)->dccpd_ack_seq = ackno;
+
+	/*
+	 * Clear the flag in case the Sync was scheduled for out-of-band data,
+	 * such as carrying a long Ack Vector.
+	 */
+	dccp_sk(sk)->dccps_sync_scheduled = 0;
+
+	dccp_transmit_skb(sk, skb);
+}
+
+EXPORT_SYMBOL_GPL(dccp_send_sync);
+
+/*
+ * Send a DCCP_PKT_CLOSE/CLOSEREQ. The caller locks the socket for us. This
+ * cannot be allowed to fail queueing a DCCP_PKT_CLOSE/CLOSEREQ frame under
+ * any circumstances.
+ */
+void dccp_send_close(struct sock *sk, const int active)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct sk_buff *skb;
+	const gfp_t prio = active ? GFP_KERNEL : GFP_ATOMIC;
+
+	skb = alloc_skb(sk->sk_prot->max_header, prio);
+	if (skb == NULL)
+		return;
+
+	/* Reserve space for headers and prepare control bits. */
+	skb_reserve(skb, sk->sk_prot->max_header);
+	if (dp->dccps_role == DCCP_ROLE_SERVER && !dp->dccps_server_timewait)
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSEREQ;
+	else
+		DCCP_SKB_CB(skb)->dccpd_type = DCCP_PKT_CLOSE;
+
+	if (active) {
+		skb = dccp_skb_entail(sk, skb);
+		/*
+		 * Retransmission timer for active-close: RFC 4340, 8.3 requires
+		 * to retransmit the Close/CloseReq until the CLOSING/CLOSEREQ
+		 * state can be left. The initial timeout is 2 RTTs.
+		 * Since RTT measurement is done by the CCIDs, there is no easy
+		 * way to get an RTT sample. The fallback RTT from RFC 4340, 3.4
+		 * is too low (200ms); we use a high value to avoid unnecessary
+		 * retransmissions when the link RTT is > 0.2 seconds.
+		 * FIXME: Let main module sample RTTs and use that instead.
+		 */
+		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+					  DCCP_TIMEOUT_INIT, DCCP_RTO_MAX);
+	}
+	dccp_transmit_skb(sk, skb);
+}
diff --git a/net/dccp/proto.c b/net/dccp/proto.c
new file mode 100644
index 000000000..c647035a3
--- /dev/null
+++ b/net/dccp/proto.c
@@ -0,0 +1,1271 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/proto.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/module.h>
+#include <linux/types.h>
+#include <linux/sched.h>
+#include <linux/kernel.h>
+#include <linux/skbuff.h>
+#include <linux/netdevice.h>
+#include <linux/in.h>
+#include <linux/if_arp.h>
+#include <linux/init.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <net/checksum.h>
+
+#include <net/inet_sock.h>
+#include <net/inet_common.h>
+#include <net/sock.h>
+#include <net/xfrm.h>
+
+#include <asm/ioctls.h>
+#include <linux/spinlock.h>
+#include <linux/timer.h>
+#include <linux/delay.h>
+#include <linux/poll.h>
+
+#include "ccid.h"
+#include "dccp.h"
+#include "feat.h"
+
+#define CREATE_TRACE_POINTS
+#include "trace.h"
+
+DEFINE_SNMP_STAT(struct dccp_mib, dccp_statistics) __read_mostly;
+
+EXPORT_SYMBOL_GPL(dccp_statistics);
+
+DEFINE_PER_CPU(unsigned int, dccp_orphan_count);
+EXPORT_PER_CPU_SYMBOL_GPL(dccp_orphan_count);
+
+struct inet_hashinfo dccp_hashinfo;
+EXPORT_SYMBOL_GPL(dccp_hashinfo);
+
+/* the maximum queue length for tx in packets. 0 is no limit */
+int sysctl_dccp_tx_qlen __read_mostly = 5;
+
+#ifdef CONFIG_IP_DCCP_DEBUG
+static const char *dccp_state_name(const int state)
+{
+	static const char *const dccp_state_names[] = {
+	[DCCP_OPEN]		= "OPEN",
+	[DCCP_REQUESTING]	= "REQUESTING",
+	[DCCP_PARTOPEN]		= "PARTOPEN",
+	[DCCP_LISTEN]		= "LISTEN",
+	[DCCP_RESPOND]		= "RESPOND",
+	[DCCP_CLOSING]		= "CLOSING",
+	[DCCP_ACTIVE_CLOSEREQ]	= "CLOSEREQ",
+	[DCCP_PASSIVE_CLOSE]	= "PASSIVE_CLOSE",
+	[DCCP_PASSIVE_CLOSEREQ]	= "PASSIVE_CLOSEREQ",
+	[DCCP_TIME_WAIT]	= "TIME_WAIT",
+	[DCCP_CLOSED]		= "CLOSED",
+	};
+
+	if (state >= DCCP_MAX_STATES)
+		return "INVALID STATE!";
+	else
+		return dccp_state_names[state];
+}
+#endif
+
+void dccp_set_state(struct sock *sk, const int state)
+{
+	const int oldstate = sk->sk_state;
+
+	dccp_pr_debug("%s(%p)  %s  -->  %s\n", dccp_role(sk), sk,
+		      dccp_state_name(oldstate), dccp_state_name(state));
+	WARN_ON(state == oldstate);
+
+	switch (state) {
+	case DCCP_OPEN:
+		if (oldstate != DCCP_OPEN)
+			DCCP_INC_STATS(DCCP_MIB_CURRESTAB);
+		/* Client retransmits all Confirm options until entering OPEN */
+		if (oldstate == DCCP_PARTOPEN)
+			dccp_feat_list_purge(&dccp_sk(sk)->dccps_featneg);
+		break;
+
+	case DCCP_CLOSED:
+		if (oldstate == DCCP_OPEN || oldstate == DCCP_ACTIVE_CLOSEREQ ||
+		    oldstate == DCCP_CLOSING)
+			DCCP_INC_STATS(DCCP_MIB_ESTABRESETS);
+
+		sk->sk_prot->unhash(sk);
+		if (inet_csk(sk)->icsk_bind_hash != NULL &&
+		    !(sk->sk_userlocks & SOCK_BINDPORT_LOCK))
+			inet_put_port(sk);
+		fallthrough;
+	default:
+		if (oldstate == DCCP_OPEN)
+			DCCP_DEC_STATS(DCCP_MIB_CURRESTAB);
+	}
+
+	/* Change state AFTER socket is unhashed to avoid closed
+	 * socket sitting in hash tables.
+	 */
+	inet_sk_set_state(sk, state);
+}
+
+EXPORT_SYMBOL_GPL(dccp_set_state);
+
+static void dccp_finish_passive_close(struct sock *sk)
+{
+	switch (sk->sk_state) {
+	case DCCP_PASSIVE_CLOSE:
+		/* Node (client or server) has received Close packet. */
+		dccp_send_reset(sk, DCCP_RESET_CODE_CLOSED);
+		dccp_set_state(sk, DCCP_CLOSED);
+		break;
+	case DCCP_PASSIVE_CLOSEREQ:
+		/*
+		 * Client received CloseReq. We set the `active' flag so that
+		 * dccp_send_close() retransmits the Close as per RFC 4340, 8.3.
+		 */
+		dccp_send_close(sk, 1);
+		dccp_set_state(sk, DCCP_CLOSING);
+	}
+}
+
+void dccp_done(struct sock *sk)
+{
+	dccp_set_state(sk, DCCP_CLOSED);
+	dccp_clear_xmit_timers(sk);
+
+	sk->sk_shutdown = SHUTDOWN_MASK;
+
+	if (!sock_flag(sk, SOCK_DEAD))
+		sk->sk_state_change(sk);
+	else
+		inet_csk_destroy_sock(sk);
+}
+
+EXPORT_SYMBOL_GPL(dccp_done);
+
+const char *dccp_packet_name(const int type)
+{
+	static const char *const dccp_packet_names[] = {
+		[DCCP_PKT_REQUEST]  = "REQUEST",
+		[DCCP_PKT_RESPONSE] = "RESPONSE",
+		[DCCP_PKT_DATA]	    = "DATA",
+		[DCCP_PKT_ACK]	    = "ACK",
+		[DCCP_PKT_DATAACK]  = "DATAACK",
+		[DCCP_PKT_CLOSEREQ] = "CLOSEREQ",
+		[DCCP_PKT_CLOSE]    = "CLOSE",
+		[DCCP_PKT_RESET]    = "RESET",
+		[DCCP_PKT_SYNC]	    = "SYNC",
+		[DCCP_PKT_SYNCACK]  = "SYNCACK",
+	};
+
+	if (type >= DCCP_NR_PKT_TYPES)
+		return "INVALID";
+	else
+		return dccp_packet_names[type];
+}
+
+EXPORT_SYMBOL_GPL(dccp_packet_name);
+
+void dccp_destruct_common(struct sock *sk)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	ccid_hc_tx_delete(dp->dccps_hc_tx_ccid, sk);
+	dp->dccps_hc_tx_ccid = NULL;
+}
+EXPORT_SYMBOL_GPL(dccp_destruct_common);
+
+static void dccp_sk_destruct(struct sock *sk)
+{
+	dccp_destruct_common(sk);
+	inet_sock_destruct(sk);
+}
+
+int dccp_init_sock(struct sock *sk, const __u8 ctl_sock_initialized)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	icsk->icsk_rto		= DCCP_TIMEOUT_INIT;
+	icsk->icsk_syn_retries	= sysctl_dccp_request_retries;
+	sk->sk_state		= DCCP_CLOSED;
+	sk->sk_write_space	= dccp_write_space;
+	sk->sk_destruct		= dccp_sk_destruct;
+	icsk->icsk_sync_mss	= dccp_sync_mss;
+	dp->dccps_mss_cache	= 536;
+	dp->dccps_rate_last	= jiffies;
+	dp->dccps_role		= DCCP_ROLE_UNDEFINED;
+	dp->dccps_service	= DCCP_SERVICE_CODE_IS_ABSENT;
+	dp->dccps_tx_qlen	= sysctl_dccp_tx_qlen;
+
+	dccp_init_xmit_timers(sk);
+
+	INIT_LIST_HEAD(&dp->dccps_featneg);
+	/* control socket doesn't need feat nego */
+	if (likely(ctl_sock_initialized))
+		return dccp_feat_init(sk);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_init_sock);
+
+void dccp_destroy_sock(struct sock *sk)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	__skb_queue_purge(&sk->sk_write_queue);
+	if (sk->sk_send_head != NULL) {
+		kfree_skb(sk->sk_send_head);
+		sk->sk_send_head = NULL;
+	}
+
+	/* Clean up a referenced DCCP bind bucket. */
+	if (inet_csk(sk)->icsk_bind_hash != NULL)
+		inet_put_port(sk);
+
+	kfree(dp->dccps_service_list);
+	dp->dccps_service_list = NULL;
+
+	if (dp->dccps_hc_rx_ackvec != NULL) {
+		dccp_ackvec_free(dp->dccps_hc_rx_ackvec);
+		dp->dccps_hc_rx_ackvec = NULL;
+	}
+	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
+	dp->dccps_hc_rx_ccid = NULL;
+
+	/* clean up feature negotiation state */
+	dccp_feat_list_purge(&dp->dccps_featneg);
+}
+
+EXPORT_SYMBOL_GPL(dccp_destroy_sock);
+
+static inline int dccp_listen_start(struct sock *sk, int backlog)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	dp->dccps_role = DCCP_ROLE_LISTEN;
+	/* do not start to listen if feature negotiation setup fails */
+	if (dccp_feat_finalise_settings(dp))
+		return -EPROTO;
+	return inet_csk_listen_start(sk, backlog);
+}
+
+static inline int dccp_need_reset(int state)
+{
+	return state != DCCP_CLOSED && state != DCCP_LISTEN &&
+	       state != DCCP_REQUESTING;
+}
+
+int dccp_disconnect(struct sock *sk, int flags)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+	struct inet_sock *inet = inet_sk(sk);
+	struct dccp_sock *dp = dccp_sk(sk);
+	const int old_state = sk->sk_state;
+
+	if (old_state != DCCP_CLOSED)
+		dccp_set_state(sk, DCCP_CLOSED);
+
+	/*
+	 * This corresponds to the ABORT function of RFC793, sec. 3.8
+	 * TCP uses a RST segment, DCCP a Reset packet with Code 2, "Aborted".
+	 */
+	if (old_state == DCCP_LISTEN) {
+		inet_csk_listen_stop(sk);
+	} else if (dccp_need_reset(old_state)) {
+		dccp_send_reset(sk, DCCP_RESET_CODE_ABORTED);
+		sk->sk_err = ECONNRESET;
+	} else if (old_state == DCCP_REQUESTING)
+		sk->sk_err = ECONNRESET;
+
+	dccp_clear_xmit_timers(sk);
+	ccid_hc_rx_delete(dp->dccps_hc_rx_ccid, sk);
+	dp->dccps_hc_rx_ccid = NULL;
+
+	__skb_queue_purge(&sk->sk_receive_queue);
+	__skb_queue_purge(&sk->sk_write_queue);
+	if (sk->sk_send_head != NULL) {
+		__kfree_skb(sk->sk_send_head);
+		sk->sk_send_head = NULL;
+	}
+
+	inet->inet_dport = 0;
+
+	if (!(sk->sk_userlocks & SOCK_BINDADDR_LOCK))
+		inet_reset_saddr(sk);
+
+	sk->sk_shutdown = 0;
+	sock_reset_flag(sk, SOCK_DONE);
+
+	icsk->icsk_backoff = 0;
+	inet_csk_delack_init(sk);
+	__sk_dst_reset(sk);
+
+	WARN_ON(inet->inet_num && !icsk->icsk_bind_hash);
+
+	sk->sk_error_report(sk);
+	return 0;
+}
+
+EXPORT_SYMBOL_GPL(dccp_disconnect);
+
+/*
+ *	Wait for a DCCP event.
+ *
+ *	Note that we don't need to lock the socket, as the upper poll layers
+ *	take care of normal races (between the test and the event) and we don't
+ *	go look at any of the socket buffers directly.
+ */
+__poll_t dccp_poll(struct file *file, struct socket *sock,
+		       poll_table *wait)
+{
+	struct sock *sk = sock->sk;
+	__poll_t mask;
+	u8 shutdown;
+	int state;
+
+	sock_poll_wait(file, sock, wait);
+
+	state = inet_sk_state_load(sk);
+	if (state == DCCP_LISTEN)
+		return inet_csk_listen_poll(sk);
+
+	/* Socket is not locked. We are protected from async events
+	   by poll logic and correct handling of state changes
+	   made by another threads is impossible in any case.
+	 */
+
+	mask = 0;
+	if (READ_ONCE(sk->sk_err))
+		mask = EPOLLERR;
+	shutdown = READ_ONCE(sk->sk_shutdown);
+
+	if (shutdown == SHUTDOWN_MASK || state == DCCP_CLOSED)
+		mask |= EPOLLHUP;
+	if (shutdown & RCV_SHUTDOWN)
+		mask |= EPOLLIN | EPOLLRDNORM | EPOLLRDHUP;
+
+	/* Connected? */
+	if ((1 << state) & ~(DCCPF_REQUESTING | DCCPF_RESPOND)) {
+		if (atomic_read(&sk->sk_rmem_alloc) > 0)
+			mask |= EPOLLIN | EPOLLRDNORM;
+
+		if (!(shutdown & SEND_SHUTDOWN)) {
+			if (sk_stream_is_writeable(sk)) {
+				mask |= EPOLLOUT | EPOLLWRNORM;
+			} else {  /* send SIGIO later */
+				sk_set_bit(SOCKWQ_ASYNC_NOSPACE, sk);
+				set_bit(SOCK_NOSPACE, &sk->sk_socket->flags);
+
+				/* Race breaker. If space is freed after
+				 * wspace test but before the flags are set,
+				 * IO signal will be lost.
+				 */
+				if (sk_stream_is_writeable(sk))
+					mask |= EPOLLOUT | EPOLLWRNORM;
+			}
+		}
+	}
+	return mask;
+}
+EXPORT_SYMBOL_GPL(dccp_poll);
+
+int dccp_ioctl(struct sock *sk, int cmd, unsigned long arg)
+{
+	int rc = -ENOTCONN;
+
+	lock_sock(sk);
+
+	if (sk->sk_state == DCCP_LISTEN)
+		goto out;
+
+	switch (cmd) {
+	case SIOCOUTQ: {
+		int amount = sk_wmem_alloc_get(sk);
+		/* Using sk_wmem_alloc here because sk_wmem_queued is not used by DCCP and
+		 * always 0, comparably to UDP.
+		 */
+
+		rc = put_user(amount, (int __user *)arg);
+	}
+		break;
+	case SIOCINQ: {
+		struct sk_buff *skb;
+		unsigned long amount = 0;
+
+		skb = skb_peek(&sk->sk_receive_queue);
+		if (skb != NULL) {
+			/*
+			 * We will only return the amount of this packet since
+			 * that is all that will be read.
+			 */
+			amount = skb->len;
+		}
+		rc = put_user(amount, (int __user *)arg);
+	}
+		break;
+	default:
+		rc = -ENOIOCTLCMD;
+		break;
+	}
+out:
+	release_sock(sk);
+	return rc;
+}
+
+EXPORT_SYMBOL_GPL(dccp_ioctl);
+
+static int dccp_setsockopt_service(struct sock *sk, const __be32 service,
+				   sockptr_t optval, unsigned int optlen)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct dccp_service_list *sl = NULL;
+
+	if (service == DCCP_SERVICE_INVALID_VALUE ||
+	    optlen > DCCP_SERVICE_LIST_MAX_LEN * sizeof(u32))
+		return -EINVAL;
+
+	if (optlen > sizeof(service)) {
+		sl = kmalloc(optlen, GFP_KERNEL);
+		if (sl == NULL)
+			return -ENOMEM;
+
+		sl->dccpsl_nr = optlen / sizeof(u32) - 1;
+		if (copy_from_sockptr_offset(sl->dccpsl_list, optval,
+				sizeof(service), optlen - sizeof(service)) ||
+		    dccp_list_has_service(sl, DCCP_SERVICE_INVALID_VALUE)) {
+			kfree(sl);
+			return -EFAULT;
+		}
+	}
+
+	lock_sock(sk);
+	dp->dccps_service = service;
+
+	kfree(dp->dccps_service_list);
+
+	dp->dccps_service_list = sl;
+	release_sock(sk);
+	return 0;
+}
+
+static int dccp_setsockopt_cscov(struct sock *sk, int cscov, bool rx)
+{
+	u8 *list, len;
+	int i, rc;
+
+	if (cscov < 0 || cscov > 15)
+		return -EINVAL;
+	/*
+	 * Populate a list of permissible values, in the range cscov...15. This
+	 * is necessary since feature negotiation of single values only works if
+	 * both sides incidentally choose the same value. Since the list starts
+	 * lowest-value first, negotiation will pick the smallest shared value.
+	 */
+	if (cscov == 0)
+		return 0;
+	len = 16 - cscov;
+
+	list = kmalloc(len, GFP_KERNEL);
+	if (list == NULL)
+		return -ENOBUFS;
+
+	for (i = 0; i < len; i++)
+		list[i] = cscov++;
+
+	rc = dccp_feat_register_sp(sk, DCCPF_MIN_CSUM_COVER, rx, list, len);
+
+	if (rc == 0) {
+		if (rx)
+			dccp_sk(sk)->dccps_pcrlen = cscov;
+		else
+			dccp_sk(sk)->dccps_pcslen = cscov;
+	}
+	kfree(list);
+	return rc;
+}
+
+static int dccp_setsockopt_ccid(struct sock *sk, int type,
+				sockptr_t optval, unsigned int optlen)
+{
+	u8 *val;
+	int rc = 0;
+
+	if (optlen < 1 || optlen > DCCP_FEAT_MAX_SP_VALS)
+		return -EINVAL;
+
+	val = memdup_sockptr(optval, optlen);
+	if (IS_ERR(val))
+		return PTR_ERR(val);
+
+	lock_sock(sk);
+	if (type == DCCP_SOCKOPT_TX_CCID || type == DCCP_SOCKOPT_CCID)
+		rc = dccp_feat_register_sp(sk, DCCPF_CCID, 1, val, optlen);
+
+	if (!rc && (type == DCCP_SOCKOPT_RX_CCID || type == DCCP_SOCKOPT_CCID))
+		rc = dccp_feat_register_sp(sk, DCCPF_CCID, 0, val, optlen);
+	release_sock(sk);
+
+	kfree(val);
+	return rc;
+}
+
+static int do_dccp_setsockopt(struct sock *sk, int level, int optname,
+		sockptr_t optval, unsigned int optlen)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	int val, err = 0;
+
+	switch (optname) {
+	case DCCP_SOCKOPT_PACKET_SIZE:
+		DCCP_WARN("sockopt(PACKET_SIZE) is deprecated: fix your app\n");
+		return 0;
+	case DCCP_SOCKOPT_CHANGE_L:
+	case DCCP_SOCKOPT_CHANGE_R:
+		DCCP_WARN("sockopt(CHANGE_L/R) is deprecated: fix your app\n");
+		return 0;
+	case DCCP_SOCKOPT_CCID:
+	case DCCP_SOCKOPT_RX_CCID:
+	case DCCP_SOCKOPT_TX_CCID:
+		return dccp_setsockopt_ccid(sk, optname, optval, optlen);
+	}
+
+	if (optlen < (int)sizeof(int))
+		return -EINVAL;
+
+	if (copy_from_sockptr(&val, optval, sizeof(int)))
+		return -EFAULT;
+
+	if (optname == DCCP_SOCKOPT_SERVICE)
+		return dccp_setsockopt_service(sk, val, optval, optlen);
+
+	lock_sock(sk);
+	switch (optname) {
+	case DCCP_SOCKOPT_SERVER_TIMEWAIT:
+		if (dp->dccps_role != DCCP_ROLE_SERVER)
+			err = -EOPNOTSUPP;
+		else
+			dp->dccps_server_timewait = (val != 0);
+		break;
+	case DCCP_SOCKOPT_SEND_CSCOV:
+		err = dccp_setsockopt_cscov(sk, val, false);
+		break;
+	case DCCP_SOCKOPT_RECV_CSCOV:
+		err = dccp_setsockopt_cscov(sk, val, true);
+		break;
+	case DCCP_SOCKOPT_QPOLICY_ID:
+		if (sk->sk_state != DCCP_CLOSED)
+			err = -EISCONN;
+		else if (val < 0 || val >= DCCPQ_POLICY_MAX)
+			err = -EINVAL;
+		else
+			dp->dccps_qpolicy = val;
+		break;
+	case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+		if (val < 0)
+			err = -EINVAL;
+		else
+			dp->dccps_tx_qlen = val;
+		break;
+	default:
+		err = -ENOPROTOOPT;
+		break;
+	}
+	release_sock(sk);
+
+	return err;
+}
+
+int dccp_setsockopt(struct sock *sk, int level, int optname, sockptr_t optval,
+		    unsigned int optlen)
+{
+	if (level != SOL_DCCP)
+		return inet_csk(sk)->icsk_af_ops->setsockopt(sk, level,
+							     optname, optval,
+							     optlen);
+	return do_dccp_setsockopt(sk, level, optname, optval, optlen);
+}
+
+EXPORT_SYMBOL_GPL(dccp_setsockopt);
+
+static int dccp_getsockopt_service(struct sock *sk, int len,
+				   __be32 __user *optval,
+				   int __user *optlen)
+{
+	const struct dccp_sock *dp = dccp_sk(sk);
+	const struct dccp_service_list *sl;
+	int err = -ENOENT, slen = 0, total_len = sizeof(u32);
+
+	lock_sock(sk);
+	if ((sl = dp->dccps_service_list) != NULL) {
+		slen = sl->dccpsl_nr * sizeof(u32);
+		total_len += slen;
+	}
+
+	err = -EINVAL;
+	if (total_len > len)
+		goto out;
+
+	err = 0;
+	if (put_user(total_len, optlen) ||
+	    put_user(dp->dccps_service, optval) ||
+	    (sl != NULL && copy_to_user(optval + 1, sl->dccpsl_list, slen)))
+		err = -EFAULT;
+out:
+	release_sock(sk);
+	return err;
+}
+
+static int do_dccp_getsockopt(struct sock *sk, int level, int optname,
+		    char __user *optval, int __user *optlen)
+{
+	struct dccp_sock *dp;
+	int val, len;
+
+	if (get_user(len, optlen))
+		return -EFAULT;
+
+	if (len < (int)sizeof(int))
+		return -EINVAL;
+
+	dp = dccp_sk(sk);
+
+	switch (optname) {
+	case DCCP_SOCKOPT_PACKET_SIZE:
+		DCCP_WARN("sockopt(PACKET_SIZE) is deprecated: fix your app\n");
+		return 0;
+	case DCCP_SOCKOPT_SERVICE:
+		return dccp_getsockopt_service(sk, len,
+					       (__be32 __user *)optval, optlen);
+	case DCCP_SOCKOPT_GET_CUR_MPS:
+		val = READ_ONCE(dp->dccps_mss_cache);
+		break;
+	case DCCP_SOCKOPT_AVAILABLE_CCIDS:
+		return ccid_getsockopt_builtin_ccids(sk, len, optval, optlen);
+	case DCCP_SOCKOPT_TX_CCID:
+		val = ccid_get_current_tx_ccid(dp);
+		if (val < 0)
+			return -ENOPROTOOPT;
+		break;
+	case DCCP_SOCKOPT_RX_CCID:
+		val = ccid_get_current_rx_ccid(dp);
+		if (val < 0)
+			return -ENOPROTOOPT;
+		break;
+	case DCCP_SOCKOPT_SERVER_TIMEWAIT:
+		val = dp->dccps_server_timewait;
+		break;
+	case DCCP_SOCKOPT_SEND_CSCOV:
+		val = dp->dccps_pcslen;
+		break;
+	case DCCP_SOCKOPT_RECV_CSCOV:
+		val = dp->dccps_pcrlen;
+		break;
+	case DCCP_SOCKOPT_QPOLICY_ID:
+		val = dp->dccps_qpolicy;
+		break;
+	case DCCP_SOCKOPT_QPOLICY_TXQLEN:
+		val = dp->dccps_tx_qlen;
+		break;
+	case 128 ... 191:
+		return ccid_hc_rx_getsockopt(dp->dccps_hc_rx_ccid, sk, optname,
+					     len, (u32 __user *)optval, optlen);
+	case 192 ... 255:
+		return ccid_hc_tx_getsockopt(dp->dccps_hc_tx_ccid, sk, optname,
+					     len, (u32 __user *)optval, optlen);
+	default:
+		return -ENOPROTOOPT;
+	}
+
+	len = sizeof(val);
+	if (put_user(len, optlen) || copy_to_user(optval, &val, len))
+		return -EFAULT;
+
+	return 0;
+}
+
+int dccp_getsockopt(struct sock *sk, int level, int optname,
+		    char __user *optval, int __user *optlen)
+{
+	if (level != SOL_DCCP)
+		return inet_csk(sk)->icsk_af_ops->getsockopt(sk, level,
+							     optname, optval,
+							     optlen);
+	return do_dccp_getsockopt(sk, level, optname, optval, optlen);
+}
+
+EXPORT_SYMBOL_GPL(dccp_getsockopt);
+
+static int dccp_msghdr_parse(struct msghdr *msg, struct sk_buff *skb)
+{
+	struct cmsghdr *cmsg;
+
+	/*
+	 * Assign an (opaque) qpolicy priority value to skb->priority.
+	 *
+	 * We are overloading this skb field for use with the qpolicy subystem.
+	 * The skb->priority is normally used for the SO_PRIORITY option, which
+	 * is initialised from sk_priority. Since the assignment of sk_priority
+	 * to skb->priority happens later (on layer 3), we overload this field
+	 * for use with queueing priorities as long as the skb is on layer 4.
+	 * The default priority value (if nothing is set) is 0.
+	 */
+	skb->priority = 0;
+
+	for_each_cmsghdr(cmsg, msg) {
+		if (!CMSG_OK(msg, cmsg))
+			return -EINVAL;
+
+		if (cmsg->cmsg_level != SOL_DCCP)
+			continue;
+
+		if (cmsg->cmsg_type <= DCCP_SCM_QPOLICY_MAX &&
+		    !dccp_qpolicy_param_ok(skb->sk, cmsg->cmsg_type))
+			return -EINVAL;
+
+		switch (cmsg->cmsg_type) {
+		case DCCP_SCM_PRIORITY:
+			if (cmsg->cmsg_len != CMSG_LEN(sizeof(__u32)))
+				return -EINVAL;
+			skb->priority = *(__u32 *)CMSG_DATA(cmsg);
+			break;
+		default:
+			return -EINVAL;
+		}
+	}
+	return 0;
+}
+
+int dccp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
+{
+	const struct dccp_sock *dp = dccp_sk(sk);
+	const int flags = msg->msg_flags;
+	const int noblock = flags & MSG_DONTWAIT;
+	struct sk_buff *skb;
+	int rc, size;
+	long timeo;
+
+	trace_dccp_probe(sk, len);
+
+	if (len > READ_ONCE(dp->dccps_mss_cache))
+		return -EMSGSIZE;
+
+	lock_sock(sk);
+
+	timeo = sock_sndtimeo(sk, noblock);
+
+	/*
+	 * We have to use sk_stream_wait_connect here to set sk_write_pending,
+	 * so that the trick in dccp_rcv_request_sent_state_process.
+	 */
+	/* Wait for a connection to finish. */
+	if ((1 << sk->sk_state) & ~(DCCPF_OPEN | DCCPF_PARTOPEN))
+		if ((rc = sk_stream_wait_connect(sk, &timeo)) != 0)
+			goto out_release;
+
+	size = sk->sk_prot->max_header + len;
+	release_sock(sk);
+	skb = sock_alloc_send_skb(sk, size, noblock, &rc);
+	lock_sock(sk);
+	if (skb == NULL)
+		goto out_release;
+
+	if (dccp_qpolicy_full(sk)) {
+		rc = -EAGAIN;
+		goto out_discard;
+	}
+
+	if (sk->sk_state == DCCP_CLOSED) {
+		rc = -ENOTCONN;
+		goto out_discard;
+	}
+
+	/* We need to check dccps_mss_cache after socket is locked. */
+	if (len > dp->dccps_mss_cache) {
+		rc = -EMSGSIZE;
+		goto out_discard;
+	}
+
+	skb_reserve(skb, sk->sk_prot->max_header);
+	rc = memcpy_from_msg(skb_put(skb, len), msg, len);
+	if (rc != 0)
+		goto out_discard;
+
+	rc = dccp_msghdr_parse(msg, skb);
+	if (rc != 0)
+		goto out_discard;
+
+	dccp_qpolicy_push(sk, skb);
+	/*
+	 * The xmit_timer is set if the TX CCID is rate-based and will expire
+	 * when congestion control permits to release further packets into the
+	 * network. Window-based CCIDs do not use this timer.
+	 */
+	if (!timer_pending(&dp->dccps_xmit_timer))
+		dccp_write_xmit(sk);
+out_release:
+	release_sock(sk);
+	return rc ? : len;
+out_discard:
+	kfree_skb(skb);
+	goto out_release;
+}
+
+EXPORT_SYMBOL_GPL(dccp_sendmsg);
+
+int dccp_recvmsg(struct sock *sk, struct msghdr *msg, size_t len, int nonblock,
+		 int flags, int *addr_len)
+{
+	const struct dccp_hdr *dh;
+	long timeo;
+
+	lock_sock(sk);
+
+	if (sk->sk_state == DCCP_LISTEN) {
+		len = -ENOTCONN;
+		goto out;
+	}
+
+	timeo = sock_rcvtimeo(sk, nonblock);
+
+	do {
+		struct sk_buff *skb = skb_peek(&sk->sk_receive_queue);
+
+		if (skb == NULL)
+			goto verify_sock_status;
+
+		dh = dccp_hdr(skb);
+
+		switch (dh->dccph_type) {
+		case DCCP_PKT_DATA:
+		case DCCP_PKT_DATAACK:
+			goto found_ok_skb;
+
+		case DCCP_PKT_CLOSE:
+		case DCCP_PKT_CLOSEREQ:
+			if (!(flags & MSG_PEEK))
+				dccp_finish_passive_close(sk);
+			fallthrough;
+		case DCCP_PKT_RESET:
+			dccp_pr_debug("found fin (%s) ok!\n",
+				      dccp_packet_name(dh->dccph_type));
+			len = 0;
+			goto found_fin_ok;
+		default:
+			dccp_pr_debug("packet_type=%s\n",
+				      dccp_packet_name(dh->dccph_type));
+			sk_eat_skb(sk, skb);
+		}
+verify_sock_status:
+		if (sock_flag(sk, SOCK_DONE)) {
+			len = 0;
+			break;
+		}
+
+		if (sk->sk_err) {
+			len = sock_error(sk);
+			break;
+		}
+
+		if (sk->sk_shutdown & RCV_SHUTDOWN) {
+			len = 0;
+			break;
+		}
+
+		if (sk->sk_state == DCCP_CLOSED) {
+			if (!sock_flag(sk, SOCK_DONE)) {
+				/* This occurs when user tries to read
+				 * from never connected socket.
+				 */
+				len = -ENOTCONN;
+				break;
+			}
+			len = 0;
+			break;
+		}
+
+		if (!timeo) {
+			len = -EAGAIN;
+			break;
+		}
+
+		if (signal_pending(current)) {
+			len = sock_intr_errno(timeo);
+			break;
+		}
+
+		sk_wait_data(sk, &timeo, NULL);
+		continue;
+	found_ok_skb:
+		if (len > skb->len)
+			len = skb->len;
+		else if (len < skb->len)
+			msg->msg_flags |= MSG_TRUNC;
+
+		if (skb_copy_datagram_msg(skb, 0, msg, len)) {
+			/* Exception. Bailout! */
+			len = -EFAULT;
+			break;
+		}
+		if (flags & MSG_TRUNC)
+			len = skb->len;
+	found_fin_ok:
+		if (!(flags & MSG_PEEK))
+			sk_eat_skb(sk, skb);
+		break;
+	} while (1);
+out:
+	release_sock(sk);
+	return len;
+}
+
+EXPORT_SYMBOL_GPL(dccp_recvmsg);
+
+int inet_dccp_listen(struct socket *sock, int backlog)
+{
+	struct sock *sk = sock->sk;
+	unsigned char old_state;
+	int err;
+
+	lock_sock(sk);
+
+	err = -EINVAL;
+	if (sock->state != SS_UNCONNECTED || sock->type != SOCK_DCCP)
+		goto out;
+
+	old_state = sk->sk_state;
+	if (!((1 << old_state) & (DCCPF_CLOSED | DCCPF_LISTEN)))
+		goto out;
+
+	WRITE_ONCE(sk->sk_max_ack_backlog, backlog);
+	/* Really, if the socket is already in listen state
+	 * we can only allow the backlog to be adjusted.
+	 */
+	if (old_state != DCCP_LISTEN) {
+		/*
+		 * FIXME: here it probably should be sk->sk_prot->listen_start
+		 * see tcp_listen_start
+		 */
+		err = dccp_listen_start(sk, backlog);
+		if (err)
+			goto out;
+	}
+	err = 0;
+
+out:
+	release_sock(sk);
+	return err;
+}
+
+EXPORT_SYMBOL_GPL(inet_dccp_listen);
+
+static void dccp_terminate_connection(struct sock *sk)
+{
+	u8 next_state = DCCP_CLOSED;
+
+	switch (sk->sk_state) {
+	case DCCP_PASSIVE_CLOSE:
+	case DCCP_PASSIVE_CLOSEREQ:
+		dccp_finish_passive_close(sk);
+		break;
+	case DCCP_PARTOPEN:
+		dccp_pr_debug("Stop PARTOPEN timer (%p)\n", sk);
+		inet_csk_clear_xmit_timer(sk, ICSK_TIME_DACK);
+		fallthrough;
+	case DCCP_OPEN:
+		dccp_send_close(sk, 1);
+
+		if (dccp_sk(sk)->dccps_role == DCCP_ROLE_SERVER &&
+		    !dccp_sk(sk)->dccps_server_timewait)
+			next_state = DCCP_ACTIVE_CLOSEREQ;
+		else
+			next_state = DCCP_CLOSING;
+		fallthrough;
+	default:
+		dccp_set_state(sk, next_state);
+	}
+}
+
+void dccp_close(struct sock *sk, long timeout)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+	struct sk_buff *skb;
+	u32 data_was_unread = 0;
+	int state;
+
+	lock_sock(sk);
+
+	sk->sk_shutdown = SHUTDOWN_MASK;
+
+	if (sk->sk_state == DCCP_LISTEN) {
+		dccp_set_state(sk, DCCP_CLOSED);
+
+		/* Special case. */
+		inet_csk_listen_stop(sk);
+
+		goto adjudge_to_death;
+	}
+
+	sk_stop_timer(sk, &dp->dccps_xmit_timer);
+
+	/*
+	 * We need to flush the recv. buffs.  We do this only on the
+	 * descriptor close, not protocol-sourced closes, because the
+	  *reader process may not have drained the data yet!
+	 */
+	while ((skb = __skb_dequeue(&sk->sk_receive_queue)) != NULL) {
+		data_was_unread += skb->len;
+		__kfree_skb(skb);
+	}
+
+	/* If socket has been already reset kill it. */
+	if (sk->sk_state == DCCP_CLOSED)
+		goto adjudge_to_death;
+
+	if (data_was_unread) {
+		/* Unread data was tossed, send an appropriate Reset Code */
+		DCCP_WARN("ABORT with %u bytes unread\n", data_was_unread);
+		dccp_send_reset(sk, DCCP_RESET_CODE_ABORTED);
+		dccp_set_state(sk, DCCP_CLOSED);
+	} else if (sock_flag(sk, SOCK_LINGER) && !sk->sk_lingertime) {
+		/* Check zero linger _after_ checking for unread data. */
+		sk->sk_prot->disconnect(sk, 0);
+	} else if (sk->sk_state != DCCP_CLOSED) {
+		/*
+		 * Normal connection termination. May need to wait if there are
+		 * still packets in the TX queue that are delayed by the CCID.
+		 */
+		dccp_flush_write_queue(sk, &timeout);
+		dccp_terminate_connection(sk);
+	}
+
+	/*
+	 * Flush write queue. This may be necessary in several cases:
+	 * - we have been closed by the peer but still have application data;
+	 * - abortive termination (unread data or zero linger time),
+	 * - normal termination but queue could not be flushed within time limit
+	 */
+	__skb_queue_purge(&sk->sk_write_queue);
+
+	sk_stream_wait_close(sk, timeout);
+
+adjudge_to_death:
+	state = sk->sk_state;
+	sock_hold(sk);
+	sock_orphan(sk);
+
+	/*
+	 * It is the last release_sock in its life. It will remove backlog.
+	 */
+	release_sock(sk);
+	/*
+	 * Now socket is owned by kernel and we acquire BH lock
+	 * to finish close. No need to check for user refs.
+	 */
+	local_bh_disable();
+	bh_lock_sock(sk);
+	WARN_ON(sock_owned_by_user(sk));
+
+	this_cpu_inc(dccp_orphan_count);
+
+	/* Have we already been destroyed by a softirq or backlog? */
+	if (state != DCCP_CLOSED && sk->sk_state == DCCP_CLOSED)
+		goto out;
+
+	if (sk->sk_state == DCCP_CLOSED)
+		inet_csk_destroy_sock(sk);
+
+	/* Otherwise, socket is reprieved until protocol close. */
+
+out:
+	bh_unlock_sock(sk);
+	local_bh_enable();
+	sock_put(sk);
+}
+
+EXPORT_SYMBOL_GPL(dccp_close);
+
+void dccp_shutdown(struct sock *sk, int how)
+{
+	dccp_pr_debug("called shutdown(%x)\n", how);
+}
+
+EXPORT_SYMBOL_GPL(dccp_shutdown);
+
+static inline int __init dccp_mib_init(void)
+{
+	dccp_statistics = alloc_percpu(struct dccp_mib);
+	if (!dccp_statistics)
+		return -ENOMEM;
+	return 0;
+}
+
+static inline void dccp_mib_exit(void)
+{
+	free_percpu(dccp_statistics);
+}
+
+static int thash_entries;
+module_param(thash_entries, int, 0444);
+MODULE_PARM_DESC(thash_entries, "Number of ehash buckets");
+
+#ifdef CONFIG_IP_DCCP_DEBUG
+bool dccp_debug;
+module_param(dccp_debug, bool, 0644);
+MODULE_PARM_DESC(dccp_debug, "Enable debug messages");
+
+EXPORT_SYMBOL_GPL(dccp_debug);
+#endif
+
+static int __init dccp_init(void)
+{
+	unsigned long goal;
+	unsigned long nr_pages = totalram_pages();
+	int ehash_order, bhash_order, i;
+	int rc;
+
+	BUILD_BUG_ON(sizeof(struct dccp_skb_cb) >
+		     sizeof_field(struct sk_buff, cb));
+	inet_hashinfo_init(&dccp_hashinfo);
+	rc = inet_hashinfo2_init_mod(&dccp_hashinfo);
+	if (rc)
+		goto out_fail;
+	rc = -ENOBUFS;
+	dccp_hashinfo.bind_bucket_cachep =
+		kmem_cache_create("dccp_bind_bucket",
+				  sizeof(struct inet_bind_bucket), 0,
+				  SLAB_HWCACHE_ALIGN, NULL);
+	if (!dccp_hashinfo.bind_bucket_cachep)
+		goto out_free_hashinfo2;
+
+	/*
+	 * Size and allocate the main established and bind bucket
+	 * hash tables.
+	 *
+	 * The methodology is similar to that of the buffer cache.
+	 */
+	if (nr_pages >= (128 * 1024))
+		goal = nr_pages >> (21 - PAGE_SHIFT);
+	else
+		goal = nr_pages >> (23 - PAGE_SHIFT);
+
+	if (thash_entries)
+		goal = (thash_entries *
+			sizeof(struct inet_ehash_bucket)) >> PAGE_SHIFT;
+	for (ehash_order = 0; (1UL << ehash_order) < goal; ehash_order++)
+		;
+	do {
+		unsigned long hash_size = (1UL << ehash_order) * PAGE_SIZE /
+					sizeof(struct inet_ehash_bucket);
+
+		while (hash_size & (hash_size - 1))
+			hash_size--;
+		dccp_hashinfo.ehash_mask = hash_size - 1;
+		dccp_hashinfo.ehash = (struct inet_ehash_bucket *)
+			__get_free_pages(GFP_ATOMIC|__GFP_NOWARN, ehash_order);
+	} while (!dccp_hashinfo.ehash && --ehash_order > 0);
+
+	if (!dccp_hashinfo.ehash) {
+		DCCP_CRIT("Failed to allocate DCCP established hash table");
+		goto out_free_bind_bucket_cachep;
+	}
+
+	for (i = 0; i <= dccp_hashinfo.ehash_mask; i++)
+		INIT_HLIST_NULLS_HEAD(&dccp_hashinfo.ehash[i].chain, i);
+
+	if (inet_ehash_locks_alloc(&dccp_hashinfo))
+			goto out_free_dccp_ehash;
+
+	bhash_order = ehash_order;
+
+	do {
+		dccp_hashinfo.bhash_size = (1UL << bhash_order) * PAGE_SIZE /
+					sizeof(struct inet_bind_hashbucket);
+		if ((dccp_hashinfo.bhash_size > (64 * 1024)) &&
+		    bhash_order > 0)
+			continue;
+		dccp_hashinfo.bhash = (struct inet_bind_hashbucket *)
+			__get_free_pages(GFP_ATOMIC|__GFP_NOWARN, bhash_order);
+	} while (!dccp_hashinfo.bhash && --bhash_order >= 0);
+
+	if (!dccp_hashinfo.bhash) {
+		DCCP_CRIT("Failed to allocate DCCP bind hash table");
+		goto out_free_dccp_locks;
+	}
+
+	for (i = 0; i < dccp_hashinfo.bhash_size; i++) {
+		spin_lock_init(&dccp_hashinfo.bhash[i].lock);
+		INIT_HLIST_HEAD(&dccp_hashinfo.bhash[i].chain);
+	}
+
+	rc = dccp_mib_init();
+	if (rc)
+		goto out_free_dccp_bhash;
+
+	rc = dccp_ackvec_init();
+	if (rc)
+		goto out_free_dccp_mib;
+
+	rc = dccp_sysctl_init();
+	if (rc)
+		goto out_ackvec_exit;
+
+	rc = ccid_initialize_builtins();
+	if (rc)
+		goto out_sysctl_exit;
+
+	dccp_timestamping_init();
+
+	return 0;
+
+out_sysctl_exit:
+	dccp_sysctl_exit();
+out_ackvec_exit:
+	dccp_ackvec_exit();
+out_free_dccp_mib:
+	dccp_mib_exit();
+out_free_dccp_bhash:
+	free_pages((unsigned long)dccp_hashinfo.bhash, bhash_order);
+out_free_dccp_locks:
+	inet_ehash_locks_free(&dccp_hashinfo);
+out_free_dccp_ehash:
+	free_pages((unsigned long)dccp_hashinfo.ehash, ehash_order);
+out_free_bind_bucket_cachep:
+	kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
+out_free_hashinfo2:
+	inet_hashinfo2_free_mod(&dccp_hashinfo);
+out_fail:
+	dccp_hashinfo.bhash = NULL;
+	dccp_hashinfo.ehash = NULL;
+	dccp_hashinfo.bind_bucket_cachep = NULL;
+	return rc;
+}
+
+static void __exit dccp_fini(void)
+{
+	ccid_cleanup_builtins();
+	dccp_mib_exit();
+	free_pages((unsigned long)dccp_hashinfo.bhash,
+		   get_order(dccp_hashinfo.bhash_size *
+			     sizeof(struct inet_bind_hashbucket)));
+	free_pages((unsigned long)dccp_hashinfo.ehash,
+		   get_order((dccp_hashinfo.ehash_mask + 1) *
+			     sizeof(struct inet_ehash_bucket)));
+	inet_ehash_locks_free(&dccp_hashinfo);
+	kmem_cache_destroy(dccp_hashinfo.bind_bucket_cachep);
+	dccp_ackvec_exit();
+	dccp_sysctl_exit();
+	inet_hashinfo2_free_mod(&dccp_hashinfo);
+}
+
+module_init(dccp_init);
+module_exit(dccp_fini);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Arnaldo Carvalho de Melo <acme@conectiva.com.br>");
+MODULE_DESCRIPTION("DCCP - Datagram Congestion Controlled Protocol");
diff --git a/net/dccp/qpolicy.c b/net/dccp/qpolicy.c
new file mode 100644
index 000000000..db2448c33
--- /dev/null
+++ b/net/dccp/qpolicy.c
@@ -0,0 +1,134 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/qpolicy.c
+ *
+ *  Policy-based packet dequeueing interface for DCCP.
+ *
+ *  Copyright (c) 2008 Tomasz Grobelny <tomasz@grobelny.oswiecenia.net>
+ */
+#include "dccp.h"
+
+/*
+ *	Simple Dequeueing Policy:
+ *	If tx_qlen is different from 0, enqueue up to tx_qlen elements.
+ */
+static void qpolicy_simple_push(struct sock *sk, struct sk_buff *skb)
+{
+	skb_queue_tail(&sk->sk_write_queue, skb);
+}
+
+static bool qpolicy_simple_full(struct sock *sk)
+{
+	return dccp_sk(sk)->dccps_tx_qlen &&
+	       sk->sk_write_queue.qlen >= dccp_sk(sk)->dccps_tx_qlen;
+}
+
+static struct sk_buff *qpolicy_simple_top(struct sock *sk)
+{
+	return skb_peek(&sk->sk_write_queue);
+}
+
+/*
+ *	Priority-based Dequeueing Policy:
+ *	If tx_qlen is different from 0 and the queue has reached its upper bound
+ *	of tx_qlen elements, replace older packets lowest-priority-first.
+ */
+static struct sk_buff *qpolicy_prio_best_skb(struct sock *sk)
+{
+	struct sk_buff *skb, *best = NULL;
+
+	skb_queue_walk(&sk->sk_write_queue, skb)
+		if (best == NULL || skb->priority > best->priority)
+			best = skb;
+	return best;
+}
+
+static struct sk_buff *qpolicy_prio_worst_skb(struct sock *sk)
+{
+	struct sk_buff *skb, *worst = NULL;
+
+	skb_queue_walk(&sk->sk_write_queue, skb)
+		if (worst == NULL || skb->priority < worst->priority)
+			worst = skb;
+	return worst;
+}
+
+static bool qpolicy_prio_full(struct sock *sk)
+{
+	if (qpolicy_simple_full(sk))
+		dccp_qpolicy_drop(sk, qpolicy_prio_worst_skb(sk));
+	return false;
+}
+
+/**
+ * struct dccp_qpolicy_operations  -  TX Packet Dequeueing Interface
+ * @push: add a new @skb to the write queue
+ * @full: indicates that no more packets will be admitted
+ * @top:  peeks at whatever the queueing policy defines as its `top'
+ */
+static struct dccp_qpolicy_operations {
+	void		(*push)	(struct sock *sk, struct sk_buff *skb);
+	bool		(*full) (struct sock *sk);
+	struct sk_buff*	(*top)  (struct sock *sk);
+	__be32		params;
+
+} qpol_table[DCCPQ_POLICY_MAX] = {
+	[DCCPQ_POLICY_SIMPLE] = {
+		.push   = qpolicy_simple_push,
+		.full   = qpolicy_simple_full,
+		.top    = qpolicy_simple_top,
+		.params = 0,
+	},
+	[DCCPQ_POLICY_PRIO] = {
+		.push   = qpolicy_simple_push,
+		.full   = qpolicy_prio_full,
+		.top    = qpolicy_prio_best_skb,
+		.params = DCCP_SCM_PRIORITY,
+	},
+};
+
+/*
+ *	Externally visible interface
+ */
+void dccp_qpolicy_push(struct sock *sk, struct sk_buff *skb)
+{
+	qpol_table[dccp_sk(sk)->dccps_qpolicy].push(sk, skb);
+}
+
+bool dccp_qpolicy_full(struct sock *sk)
+{
+	return qpol_table[dccp_sk(sk)->dccps_qpolicy].full(sk);
+}
+
+void dccp_qpolicy_drop(struct sock *sk, struct sk_buff *skb)
+{
+	if (skb != NULL) {
+		skb_unlink(skb, &sk->sk_write_queue);
+		kfree_skb(skb);
+	}
+}
+
+struct sk_buff *dccp_qpolicy_top(struct sock *sk)
+{
+	return qpol_table[dccp_sk(sk)->dccps_qpolicy].top(sk);
+}
+
+struct sk_buff *dccp_qpolicy_pop(struct sock *sk)
+{
+	struct sk_buff *skb = dccp_qpolicy_top(sk);
+
+	if (skb != NULL) {
+		/* Clear any skb fields that we used internally */
+		skb->priority = 0;
+		skb_unlink(skb, &sk->sk_write_queue);
+	}
+	return skb;
+}
+
+bool dccp_qpolicy_param_ok(struct sock *sk, __be32 param)
+{
+	/* check if exactly one bit is set */
+	if (!param || (param & (param - 1)))
+		return false;
+	return (qpol_table[dccp_sk(sk)->dccps_qpolicy].params & param) == param;
+}
diff --git a/net/dccp/sysctl.c b/net/dccp/sysctl.c
new file mode 100644
index 000000000..ee8d4f5af
--- /dev/null
+++ b/net/dccp/sysctl.c
@@ -0,0 +1,113 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  net/dccp/sysctl.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@mandriva.com>
+ */
+
+#include <linux/mm.h>
+#include <linux/sysctl.h>
+#include "dccp.h"
+#include "feat.h"
+
+#ifndef CONFIG_SYSCTL
+#error This file should not be compiled without CONFIG_SYSCTL defined
+#endif
+
+/* Boundary values */
+static int		u8_max   = 0xFF;
+static unsigned long	seqw_min = DCCPF_SEQ_WMIN,
+			seqw_max = 0xFFFFFFFF;		/* maximum on 32 bit */
+
+static struct ctl_table dccp_default_table[] = {
+	{
+		.procname	= "seq_window",
+		.data		= &sysctl_dccp_sequence_window,
+		.maxlen		= sizeof(sysctl_dccp_sequence_window),
+		.mode		= 0644,
+		.proc_handler	= proc_doulongvec_minmax,
+		.extra1		= &seqw_min,		/* RFC 4340, 7.5.2 */
+		.extra2		= &seqw_max,
+	},
+	{
+		.procname	= "rx_ccid",
+		.data		= &sysctl_dccp_rx_ccid,
+		.maxlen		= sizeof(sysctl_dccp_rx_ccid),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &u8_max,		/* RFC 4340, 10. */
+	},
+	{
+		.procname	= "tx_ccid",
+		.data		= &sysctl_dccp_tx_ccid,
+		.maxlen		= sizeof(sysctl_dccp_tx_ccid),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &u8_max,		/* RFC 4340, 10. */
+	},
+	{
+		.procname	= "request_retries",
+		.data		= &sysctl_dccp_request_retries,
+		.maxlen		= sizeof(sysctl_dccp_request_retries),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ONE,
+		.extra2		= &u8_max,
+	},
+	{
+		.procname	= "retries1",
+		.data		= &sysctl_dccp_retries1,
+		.maxlen		= sizeof(sysctl_dccp_retries1),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &u8_max,
+	},
+	{
+		.procname	= "retries2",
+		.data		= &sysctl_dccp_retries2,
+		.maxlen		= sizeof(sysctl_dccp_retries2),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+		.extra2		= &u8_max,
+	},
+	{
+		.procname	= "tx_qlen",
+		.data		= &sysctl_dccp_tx_qlen,
+		.maxlen		= sizeof(sysctl_dccp_tx_qlen),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ZERO,
+	},
+	{
+		.procname	= "sync_ratelimit",
+		.data		= &sysctl_dccp_sync_ratelimit,
+		.maxlen		= sizeof(sysctl_dccp_sync_ratelimit),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_ms_jiffies,
+	},
+
+	{ }
+};
+
+static struct ctl_table_header *dccp_table_header;
+
+int __init dccp_sysctl_init(void)
+{
+	dccp_table_header = register_net_sysctl(&init_net, "net/dccp/default",
+			dccp_default_table);
+
+	return dccp_table_header != NULL ? 0 : -ENOMEM;
+}
+
+void dccp_sysctl_exit(void)
+{
+	if (dccp_table_header != NULL) {
+		unregister_net_sysctl_table(dccp_table_header);
+		dccp_table_header = NULL;
+	}
+}
diff --git a/net/dccp/timer.c b/net/dccp/timer.c
new file mode 100644
index 000000000..a934d2932
--- /dev/null
+++ b/net/dccp/timer.c
@@ -0,0 +1,272 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  net/dccp/timer.c
+ *
+ *  An implementation of the DCCP protocol
+ *  Arnaldo Carvalho de Melo <acme@conectiva.com.br>
+ */
+
+#include <linux/dccp.h>
+#include <linux/skbuff.h>
+#include <linux/export.h>
+
+#include "dccp.h"
+
+/* sysctl variables governing numbers of retransmission attempts */
+int  sysctl_dccp_request_retries	__read_mostly = TCP_SYN_RETRIES;
+int  sysctl_dccp_retries1		__read_mostly = TCP_RETR1;
+int  sysctl_dccp_retries2		__read_mostly = TCP_RETR2;
+
+static void dccp_write_err(struct sock *sk)
+{
+	sk->sk_err = sk->sk_err_soft ? : ETIMEDOUT;
+	sk->sk_error_report(sk);
+
+	dccp_send_reset(sk, DCCP_RESET_CODE_ABORTED);
+	dccp_done(sk);
+	__DCCP_INC_STATS(DCCP_MIB_ABORTONTIMEOUT);
+}
+
+/* A write timeout has occurred. Process the after effects. */
+static int dccp_write_timeout(struct sock *sk)
+{
+	const struct inet_connection_sock *icsk = inet_csk(sk);
+	int retry_until;
+
+	if (sk->sk_state == DCCP_REQUESTING || sk->sk_state == DCCP_PARTOPEN) {
+		if (icsk->icsk_retransmits != 0)
+			dst_negative_advice(sk);
+		retry_until = icsk->icsk_syn_retries ?
+			    : sysctl_dccp_request_retries;
+	} else {
+		if (icsk->icsk_retransmits >= sysctl_dccp_retries1) {
+			/* NOTE. draft-ietf-tcpimpl-pmtud-01.txt requires pmtu
+			   black hole detection. :-(
+
+			   It is place to make it. It is not made. I do not want
+			   to make it. It is disguisting. It does not work in any
+			   case. Let me to cite the same draft, which requires for
+			   us to implement this:
+
+   "The one security concern raised by this memo is that ICMP black holes
+   are often caused by over-zealous security administrators who block
+   all ICMP messages.  It is vitally important that those who design and
+   deploy security systems understand the impact of strict filtering on
+   upper-layer protocols.  The safest web site in the world is worthless
+   if most TCP implementations cannot transfer data from it.  It would
+   be far nicer to have all of the black holes fixed rather than fixing
+   all of the TCP implementations."
+
+			   Golden words :-).
+		   */
+
+			dst_negative_advice(sk);
+		}
+
+		retry_until = sysctl_dccp_retries2;
+		/*
+		 * FIXME: see tcp_write_timout and tcp_out_of_resources
+		 */
+	}
+
+	if (icsk->icsk_retransmits >= retry_until) {
+		/* Has it gone just too far? */
+		dccp_write_err(sk);
+		return 1;
+	}
+	return 0;
+}
+
+/*
+ *	The DCCP retransmit timer.
+ */
+static void dccp_retransmit_timer(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	/*
+	 * More than 4MSL (8 minutes) has passed, a RESET(aborted) was
+	 * sent, no need to retransmit, this sock is dead.
+	 */
+	if (dccp_write_timeout(sk))
+		return;
+
+	/*
+	 * We want to know the number of packets retransmitted, not the
+	 * total number of retransmissions of clones of original packets.
+	 */
+	if (icsk->icsk_retransmits == 0)
+		__DCCP_INC_STATS(DCCP_MIB_TIMEOUTS);
+
+	if (dccp_retransmit_skb(sk) != 0) {
+		/*
+		 * Retransmission failed because of local congestion,
+		 * do not backoff.
+		 */
+		if (--icsk->icsk_retransmits == 0)
+			icsk->icsk_retransmits = 1;
+		inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
+					  min(icsk->icsk_rto,
+					      TCP_RESOURCE_PROBE_INTERVAL),
+					  DCCP_RTO_MAX);
+		return;
+	}
+
+	icsk->icsk_backoff++;
+
+	icsk->icsk_rto = min(icsk->icsk_rto << 1, DCCP_RTO_MAX);
+	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS, icsk->icsk_rto,
+				  DCCP_RTO_MAX);
+	if (icsk->icsk_retransmits > sysctl_dccp_retries1)
+		__sk_dst_reset(sk);
+}
+
+static void dccp_write_timer(struct timer_list *t)
+{
+	struct inet_connection_sock *icsk =
+			from_timer(icsk, t, icsk_retransmit_timer);
+	struct sock *sk = &icsk->icsk_inet.sk;
+	int event = 0;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later */
+		sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
+			       jiffies + (HZ / 20));
+		goto out;
+	}
+
+	if (sk->sk_state == DCCP_CLOSED || !icsk->icsk_pending)
+		goto out;
+
+	if (time_after(icsk->icsk_timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_retransmit_timer,
+			       icsk->icsk_timeout);
+		goto out;
+	}
+
+	event = icsk->icsk_pending;
+	icsk->icsk_pending = 0;
+
+	switch (event) {
+	case ICSK_TIME_RETRANS:
+		dccp_retransmit_timer(sk);
+		break;
+	}
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+static void dccp_keepalive_timer(struct timer_list *t)
+{
+	struct sock *sk = from_timer(sk, t, sk_timer);
+
+	pr_err("dccp should not use a keepalive timer !\n");
+	sock_put(sk);
+}
+
+/* This is the same as tcp_delack_timer, sans prequeue & mem_reclaim stuff */
+static void dccp_delack_timer(struct timer_list *t)
+{
+	struct inet_connection_sock *icsk =
+			from_timer(icsk, t, icsk_delack_timer);
+	struct sock *sk = &icsk->icsk_inet.sk;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk)) {
+		/* Try again later. */
+		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKLOCKED);
+		sk_reset_timer(sk, &icsk->icsk_delack_timer,
+			       jiffies + TCP_DELACK_MIN);
+		goto out;
+	}
+
+	if (sk->sk_state == DCCP_CLOSED ||
+	    !(icsk->icsk_ack.pending & ICSK_ACK_TIMER))
+		goto out;
+	if (time_after(icsk->icsk_ack.timeout, jiffies)) {
+		sk_reset_timer(sk, &icsk->icsk_delack_timer,
+			       icsk->icsk_ack.timeout);
+		goto out;
+	}
+
+	icsk->icsk_ack.pending &= ~ICSK_ACK_TIMER;
+
+	if (inet_csk_ack_scheduled(sk)) {
+		if (!inet_csk_in_pingpong_mode(sk)) {
+			/* Delayed ACK missed: inflate ATO. */
+			icsk->icsk_ack.ato = min(icsk->icsk_ack.ato << 1,
+						 icsk->icsk_rto);
+		} else {
+			/* Delayed ACK missed: leave pingpong mode and
+			 * deflate ATO.
+			 */
+			inet_csk_exit_pingpong_mode(sk);
+			icsk->icsk_ack.ato = TCP_ATO_MIN;
+		}
+		dccp_send_ack(sk);
+		__NET_INC_STATS(sock_net(sk), LINUX_MIB_DELAYEDACKS);
+	}
+out:
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+/**
+ * dccp_write_xmitlet  -  Workhorse for CCID packet dequeueing interface
+ * @data: Socket to act on
+ *
+ * See the comments above %ccid_dequeueing_decision for supported modes.
+ */
+static void dccp_write_xmitlet(unsigned long data)
+{
+	struct sock *sk = (struct sock *)data;
+
+	bh_lock_sock(sk);
+	if (sock_owned_by_user(sk))
+		sk_reset_timer(sk, &dccp_sk(sk)->dccps_xmit_timer, jiffies + 1);
+	else
+		dccp_write_xmit(sk);
+	bh_unlock_sock(sk);
+	sock_put(sk);
+}
+
+static void dccp_write_xmit_timer(struct timer_list *t)
+{
+	struct dccp_sock *dp = from_timer(dp, t, dccps_xmit_timer);
+	struct sock *sk = &dp->dccps_inet_connection.icsk_inet.sk;
+
+	dccp_write_xmitlet((unsigned long)sk);
+}
+
+void dccp_init_xmit_timers(struct sock *sk)
+{
+	struct dccp_sock *dp = dccp_sk(sk);
+
+	tasklet_init(&dp->dccps_xmitlet, dccp_write_xmitlet, (unsigned long)sk);
+	timer_setup(&dp->dccps_xmit_timer, dccp_write_xmit_timer, 0);
+	inet_csk_init_xmit_timers(sk, &dccp_write_timer, &dccp_delack_timer,
+				  &dccp_keepalive_timer);
+}
+
+static ktime_t dccp_timestamp_seed;
+/**
+ * dccp_timestamp  -  10s of microseconds time source
+ * Returns the number of 10s of microseconds since loading DCCP. This is native
+ * DCCP time difference format (RFC 4340, sec. 13).
+ * Please note: This will wrap around about circa every 11.9 hours.
+ */
+u32 dccp_timestamp(void)
+{
+	u64 delta = (u64)ktime_us_delta(ktime_get_real(), dccp_timestamp_seed);
+
+	do_div(delta, 10);
+	return delta;
+}
+EXPORT_SYMBOL_GPL(dccp_timestamp);
+
+void __init dccp_timestamping_init(void)
+{
+	dccp_timestamp_seed = ktime_get_real();
+}
diff --git a/net/dccp/trace.h b/net/dccp/trace.h
new file mode 100644
index 000000000..5062421be
--- /dev/null
+++ b/net/dccp/trace.h
@@ -0,0 +1,84 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#undef TRACE_SYSTEM
+#define TRACE_SYSTEM dccp
+
+#if !defined(_TRACE_DCCP_H) || defined(TRACE_HEADER_MULTI_READ)
+#define _TRACE_DCCP_H
+
+#include <net/sock.h>
+#include "dccp.h"
+#include "ccids/ccid3.h"
+#include <linux/tracepoint.h>
+#include <trace/events/net_probe_common.h>
+
+TRACE_EVENT(dccp_probe,
+
+	TP_PROTO(struct sock *sk, size_t size),
+
+	TP_ARGS(sk, size),
+
+	TP_STRUCT__entry(
+		/* sockaddr_in6 is always bigger than sockaddr_in */
+		__array(__u8, saddr, sizeof(struct sockaddr_in6))
+		__array(__u8, daddr, sizeof(struct sockaddr_in6))
+		__field(__u16, sport)
+		__field(__u16, dport)
+		__field(__u16, size)
+		__field(__u16, tx_s)
+		__field(__u32, tx_rtt)
+		__field(__u32, tx_p)
+		__field(__u32, tx_x_calc)
+		__field(__u64, tx_x_recv)
+		__field(__u64, tx_x)
+		__field(__u32, tx_t_ipi)
+	),
+
+	TP_fast_assign(
+		const struct inet_sock *inet = inet_sk(sk);
+		struct ccid3_hc_tx_sock *hc = NULL;
+
+		if (ccid_get_current_tx_ccid(dccp_sk(sk)) == DCCPC_CCID3)
+			hc = ccid3_hc_tx_sk(sk);
+
+		memset(__entry->saddr, 0, sizeof(struct sockaddr_in6));
+		memset(__entry->daddr, 0, sizeof(struct sockaddr_in6));
+
+		TP_STORE_ADDR_PORTS(__entry, inet, sk);
+
+		/* For filtering use */
+		__entry->sport = ntohs(inet->inet_sport);
+		__entry->dport = ntohs(inet->inet_dport);
+
+		__entry->size = size;
+		if (hc) {
+			__entry->tx_s = hc->tx_s;
+			__entry->tx_rtt = hc->tx_rtt;
+			__entry->tx_p = hc->tx_p;
+			__entry->tx_x_calc = hc->tx_x_calc;
+			__entry->tx_x_recv = hc->tx_x_recv >> 6;
+			__entry->tx_x = hc->tx_x >> 6;
+			__entry->tx_t_ipi = hc->tx_t_ipi;
+		} else {
+			__entry->tx_s = 0;
+			memset(&__entry->tx_rtt, 0, (void *)&__entry->tx_t_ipi -
+			       (void *)&__entry->tx_rtt +
+			       sizeof(__entry->tx_t_ipi));
+		}
+	),
+
+	TP_printk("src=%pISpc dest=%pISpc size=%d tx_s=%d tx_rtt=%d "
+		  "tx_p=%d tx_x_calc=%u tx_x_recv=%llu tx_x=%llu tx_t_ipi=%d",
+		  __entry->saddr, __entry->daddr, __entry->size,
+		  __entry->tx_s, __entry->tx_rtt, __entry->tx_p,
+		  __entry->tx_x_calc, __entry->tx_x_recv, __entry->tx_x,
+		  __entry->tx_t_ipi)
+);
+
+#endif /* _TRACE_TCP_H */
+
+/* This part must be outside protection */
+#undef TRACE_INCLUDE_PATH
+#define TRACE_INCLUDE_PATH .
+#undef TRACE_INCLUDE_FILE
+#define TRACE_INCLUDE_FILE trace
+#include <trace/define_trace.h>