Adding upstream version 5.10.209.upstream/5.10.209

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

1 files changed, 700 insertions, 0 deletions

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);
+}