Adding upstream version 6.1.76.upstream/6.1.76

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

1 files changed, 1633 insertions, 0 deletions

diff --git a/net/mptcp/options.c b/net/mptcp/options.c
new file mode 100644
index 000000000..a718ebcb5
--- /dev/null
+++ b/net/mptcp/options.c
@@ -0,0 +1,1633 @@
+// SPDX-License-Identifier: GPL-2.0
+/* Multipath TCP
+ *
+ * Copyright (c) 2017 - 2019, Intel Corporation.
+ */
+
+#define pr_fmt(fmt) "MPTCP: " fmt
+
+#include <linux/kernel.h>
+#include <crypto/sha2.h>
+#include <net/tcp.h>
+#include <net/mptcp.h>
+#include "protocol.h"
+#include "mib.h"
+
+#include <trace/events/mptcp.h>
+
+static bool mptcp_cap_flag_sha256(u8 flags)
+{
+	return (flags & MPTCP_CAP_FLAG_MASK) == MPTCP_CAP_HMAC_SHA256;
+}
+
+static void mptcp_parse_option(const struct sk_buff *skb,
+			       const unsigned char *ptr, int opsize,
+			       struct mptcp_options_received *mp_opt)
+{
+	u8 subtype = *ptr >> 4;
+	int expected_opsize;
+	u8 version;
+	u8 flags;
+	u8 i;
+
+	switch (subtype) {
+	case MPTCPOPT_MP_CAPABLE:
+		/* strict size checking */
+		if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_SYN)) {
+			if (skb->len > tcp_hdr(skb)->doff << 2)
+				expected_opsize = TCPOLEN_MPTCP_MPC_ACK_DATA;
+			else
+				expected_opsize = TCPOLEN_MPTCP_MPC_ACK;
+		} else {
+			if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_ACK)
+				expected_opsize = TCPOLEN_MPTCP_MPC_SYNACK;
+			else
+				expected_opsize = TCPOLEN_MPTCP_MPC_SYN;
+		}
+
+		/* Cfr RFC 8684 Section 3.3.0:
+		 * If a checksum is present but its use had
+		 * not been negotiated in the MP_CAPABLE handshake, the receiver MUST
+		 * close the subflow with a RST, as it is not behaving as negotiated.
+		 * If a checksum is not present when its use has been negotiated, the
+		 * receiver MUST close the subflow with a RST, as it is considered
+		 * broken
+		 * We parse even option with mismatching csum presence, so that
+		 * later in subflow_data_ready we can trigger the reset.
+		 */
+		if (opsize != expected_opsize &&
+		    (expected_opsize != TCPOLEN_MPTCP_MPC_ACK_DATA ||
+		     opsize != TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM))
+			break;
+
+		/* try to be gentle vs future versions on the initial syn */
+		version = *ptr++ & MPTCP_VERSION_MASK;
+		if (opsize != TCPOLEN_MPTCP_MPC_SYN) {
+			if (version != MPTCP_SUPPORTED_VERSION)
+				break;
+		} else if (version < MPTCP_SUPPORTED_VERSION) {
+			break;
+		}
+
+		flags = *ptr++;
+		if (!mptcp_cap_flag_sha256(flags) ||
+		    (flags & MPTCP_CAP_EXTENSIBILITY))
+			break;
+
+		/* RFC 6824, Section 3.1:
+		 * "For the Checksum Required bit (labeled "A"), if either
+		 * host requires the use of checksums, checksums MUST be used.
+		 * In other words, the only way for checksums not to be used
+		 * is if both hosts in their SYNs set A=0."
+		 */
+		if (flags & MPTCP_CAP_CHECKSUM_REQD)
+			mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
+
+		mp_opt->deny_join_id0 = !!(flags & MPTCP_CAP_DENY_JOIN_ID0);
+
+		mp_opt->suboptions |= OPTIONS_MPTCP_MPC;
+		if (opsize >= TCPOLEN_MPTCP_MPC_SYNACK) {
+			mp_opt->sndr_key = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		if (opsize >= TCPOLEN_MPTCP_MPC_ACK) {
+			mp_opt->rcvr_key = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		if (opsize >= TCPOLEN_MPTCP_MPC_ACK_DATA) {
+			/* Section 3.1.:
+			 * "the data parameters in a MP_CAPABLE are semantically
+			 * equivalent to those in a DSS option and can be used
+			 * interchangeably."
+			 */
+			mp_opt->suboptions |= OPTION_MPTCP_DSS;
+			mp_opt->use_map = 1;
+			mp_opt->mpc_map = 1;
+			mp_opt->use_ack = 0;
+			mp_opt->data_len = get_unaligned_be16(ptr);
+			ptr += 2;
+		}
+		if (opsize == TCPOLEN_MPTCP_MPC_ACK_DATA_CSUM) {
+			mp_opt->csum = get_unaligned((__force __sum16 *)ptr);
+			mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
+			ptr += 2;
+		}
+		pr_debug("MP_CAPABLE version=%x, flags=%x, optlen=%d sndr=%llu, rcvr=%llu len=%d csum=%u",
+			 version, flags, opsize, mp_opt->sndr_key,
+			 mp_opt->rcvr_key, mp_opt->data_len, mp_opt->csum);
+		break;
+
+	case MPTCPOPT_MP_JOIN:
+		if (opsize == TCPOLEN_MPTCP_MPJ_SYN) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_SYN;
+			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
+			mp_opt->join_id = *ptr++;
+			mp_opt->token = get_unaligned_be32(ptr);
+			ptr += 4;
+			mp_opt->nonce = get_unaligned_be32(ptr);
+			ptr += 4;
+			pr_debug("MP_JOIN bkup=%u, id=%u, token=%u, nonce=%u",
+				 mp_opt->backup, mp_opt->join_id,
+				 mp_opt->token, mp_opt->nonce);
+		} else if (opsize == TCPOLEN_MPTCP_MPJ_SYNACK) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_SYNACK;
+			mp_opt->backup = *ptr++ & MPTCPOPT_BACKUP;
+			mp_opt->join_id = *ptr++;
+			mp_opt->thmac = get_unaligned_be64(ptr);
+			ptr += 8;
+			mp_opt->nonce = get_unaligned_be32(ptr);
+			ptr += 4;
+			pr_debug("MP_JOIN bkup=%u, id=%u, thmac=%llu, nonce=%u",
+				 mp_opt->backup, mp_opt->join_id,
+				 mp_opt->thmac, mp_opt->nonce);
+		} else if (opsize == TCPOLEN_MPTCP_MPJ_ACK) {
+			mp_opt->suboptions |= OPTION_MPTCP_MPJ_ACK;
+			ptr += 2;
+			memcpy(mp_opt->hmac, ptr, MPTCPOPT_HMAC_LEN);
+			pr_debug("MP_JOIN hmac");
+		}
+		break;
+
+	case MPTCPOPT_DSS:
+		pr_debug("DSS");
+		ptr++;
+
+		/* we must clear 'mpc_map' be able to detect MP_CAPABLE
+		 * map vs DSS map in mptcp_incoming_options(), and reconstruct
+		 * map info accordingly
+		 */
+		mp_opt->mpc_map = 0;
+		flags = (*ptr++) & MPTCP_DSS_FLAG_MASK;
+		mp_opt->data_fin = (flags & MPTCP_DSS_DATA_FIN) != 0;
+		mp_opt->dsn64 = (flags & MPTCP_DSS_DSN64) != 0;
+		mp_opt->use_map = (flags & MPTCP_DSS_HAS_MAP) != 0;
+		mp_opt->ack64 = (flags & MPTCP_DSS_ACK64) != 0;
+		mp_opt->use_ack = (flags & MPTCP_DSS_HAS_ACK);
+
+		pr_debug("data_fin=%d dsn64=%d use_map=%d ack64=%d use_ack=%d",
+			 mp_opt->data_fin, mp_opt->dsn64,
+			 mp_opt->use_map, mp_opt->ack64,
+			 mp_opt->use_ack);
+
+		expected_opsize = TCPOLEN_MPTCP_DSS_BASE;
+
+		if (mp_opt->use_ack) {
+			if (mp_opt->ack64)
+				expected_opsize += TCPOLEN_MPTCP_DSS_ACK64;
+			else
+				expected_opsize += TCPOLEN_MPTCP_DSS_ACK32;
+		}
+
+		if (mp_opt->use_map) {
+			if (mp_opt->dsn64)
+				expected_opsize += TCPOLEN_MPTCP_DSS_MAP64;
+			else
+				expected_opsize += TCPOLEN_MPTCP_DSS_MAP32;
+		}
+
+		/* Always parse any csum presence combination, we will enforce
+		 * RFC 8684 Section 3.3.0 checks later in subflow_data_ready
+		 */
+		if (opsize != expected_opsize &&
+		    opsize != expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM)
+			break;
+
+		mp_opt->suboptions |= OPTION_MPTCP_DSS;
+		if (mp_opt->use_ack) {
+			if (mp_opt->ack64) {
+				mp_opt->data_ack = get_unaligned_be64(ptr);
+				ptr += 8;
+			} else {
+				mp_opt->data_ack = get_unaligned_be32(ptr);
+				ptr += 4;
+			}
+
+			pr_debug("data_ack=%llu", mp_opt->data_ack);
+		}
+
+		if (mp_opt->use_map) {
+			if (mp_opt->dsn64) {
+				mp_opt->data_seq = get_unaligned_be64(ptr);
+				ptr += 8;
+			} else {
+				mp_opt->data_seq = get_unaligned_be32(ptr);
+				ptr += 4;
+			}
+
+			mp_opt->subflow_seq = get_unaligned_be32(ptr);
+			ptr += 4;
+
+			mp_opt->data_len = get_unaligned_be16(ptr);
+			ptr += 2;
+
+			if (opsize == expected_opsize + TCPOLEN_MPTCP_DSS_CHECKSUM) {
+				mp_opt->suboptions |= OPTION_MPTCP_CSUMREQD;
+				mp_opt->csum = get_unaligned((__force __sum16 *)ptr);
+				ptr += 2;
+			}
+
+			pr_debug("data_seq=%llu subflow_seq=%u data_len=%u csum=%d:%u",
+				 mp_opt->data_seq, mp_opt->subflow_seq,
+				 mp_opt->data_len, !!(mp_opt->suboptions & OPTION_MPTCP_CSUMREQD),
+				 mp_opt->csum);
+		}
+
+		break;
+
+	case MPTCPOPT_ADD_ADDR:
+		mp_opt->echo = (*ptr++) & MPTCP_ADDR_ECHO;
+		if (!mp_opt->echo) {
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT)
+				mp_opt->addr.family = AF_INET;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+			else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6 ||
+				 opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT)
+				mp_opt->addr.family = AF_INET6;
+#endif
+			else
+				break;
+		} else {
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT)
+				mp_opt->addr.family = AF_INET;
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+			else if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE ||
+				 opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT)
+				mp_opt->addr.family = AF_INET6;
+#endif
+			else
+				break;
+		}
+
+		mp_opt->suboptions |= OPTION_MPTCP_ADD_ADDR;
+		mp_opt->addr.id = *ptr++;
+		mp_opt->addr.port = 0;
+		mp_opt->ahmac = 0;
+		if (mp_opt->addr.family == AF_INET) {
+			memcpy((u8 *)&mp_opt->addr.addr.s_addr, (u8 *)ptr, 4);
+			ptr += 4;
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR_PORT ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR_BASE_PORT) {
+				mp_opt->addr.port = htons(get_unaligned_be16(ptr));
+				ptr += 2;
+			}
+		}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		else {
+			memcpy(mp_opt->addr.addr6.s6_addr, (u8 *)ptr, 16);
+			ptr += 16;
+			if (opsize == TCPOLEN_MPTCP_ADD_ADDR6_PORT ||
+			    opsize == TCPOLEN_MPTCP_ADD_ADDR6_BASE_PORT) {
+				mp_opt->addr.port = htons(get_unaligned_be16(ptr));
+				ptr += 2;
+			}
+		}
+#endif
+		if (!mp_opt->echo) {
+			mp_opt->ahmac = get_unaligned_be64(ptr);
+			ptr += 8;
+		}
+		pr_debug("ADD_ADDR%s: id=%d, ahmac=%llu, echo=%d, port=%d",
+			 (mp_opt->addr.family == AF_INET6) ? "6" : "",
+			 mp_opt->addr.id, mp_opt->ahmac, mp_opt->echo, ntohs(mp_opt->addr.port));
+		break;
+
+	case MPTCPOPT_RM_ADDR:
+		if (opsize < TCPOLEN_MPTCP_RM_ADDR_BASE + 1 ||
+		    opsize > TCPOLEN_MPTCP_RM_ADDR_BASE + MPTCP_RM_IDS_MAX)
+			break;
+
+		ptr++;
+
+		mp_opt->suboptions |= OPTION_MPTCP_RM_ADDR;
+		mp_opt->rm_list.nr = opsize - TCPOLEN_MPTCP_RM_ADDR_BASE;
+		for (i = 0; i < mp_opt->rm_list.nr; i++)
+			mp_opt->rm_list.ids[i] = *ptr++;
+		pr_debug("RM_ADDR: rm_list_nr=%d", mp_opt->rm_list.nr);
+		break;
+
+	case MPTCPOPT_MP_PRIO:
+		if (opsize != TCPOLEN_MPTCP_PRIO)
+			break;
+
+		mp_opt->suboptions |= OPTION_MPTCP_PRIO;
+		mp_opt->backup = *ptr++ & MPTCP_PRIO_BKUP;
+		pr_debug("MP_PRIO: prio=%d", mp_opt->backup);
+		break;
+
+	case MPTCPOPT_MP_FASTCLOSE:
+		if (opsize != TCPOLEN_MPTCP_FASTCLOSE)
+			break;
+
+		ptr += 2;
+		mp_opt->rcvr_key = get_unaligned_be64(ptr);
+		ptr += 8;
+		mp_opt->suboptions |= OPTION_MPTCP_FASTCLOSE;
+		pr_debug("MP_FASTCLOSE: recv_key=%llu", mp_opt->rcvr_key);
+		break;
+
+	case MPTCPOPT_RST:
+		if (opsize != TCPOLEN_MPTCP_RST)
+			break;
+
+		if (!(TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST))
+			break;
+
+		mp_opt->suboptions |= OPTION_MPTCP_RST;
+		flags = *ptr++;
+		mp_opt->reset_transient = flags & MPTCP_RST_TRANSIENT;
+		mp_opt->reset_reason = *ptr;
+		pr_debug("MP_RST: transient=%u reason=%u",
+			 mp_opt->reset_transient, mp_opt->reset_reason);
+		break;
+
+	case MPTCPOPT_MP_FAIL:
+		if (opsize != TCPOLEN_MPTCP_FAIL)
+			break;
+
+		ptr += 2;
+		mp_opt->suboptions |= OPTION_MPTCP_FAIL;
+		mp_opt->fail_seq = get_unaligned_be64(ptr);
+		pr_debug("MP_FAIL: data_seq=%llu", mp_opt->fail_seq);
+		break;
+
+	default:
+		break;
+	}
+}
+
+void mptcp_get_options(const struct sk_buff *skb,
+		       struct mptcp_options_received *mp_opt)
+{
+	const struct tcphdr *th = tcp_hdr(skb);
+	const unsigned char *ptr;
+	int length;
+
+	/* initialize option status */
+	mp_opt->suboptions = 0;
+
+	length = (th->doff * 4) - sizeof(struct tcphdr);
+	ptr = (const unsigned char *)(th + 1);
+
+	while (length > 0) {
+		int opcode = *ptr++;
+		int opsize;
+
+		switch (opcode) {
+		case TCPOPT_EOL:
+			return;
+		case TCPOPT_NOP:	/* Ref: RFC 793 section 3.1 */
+			length--;
+			continue;
+		default:
+			if (length < 2)
+				return;
+			opsize = *ptr++;
+			if (opsize < 2) /* "silly options" */
+				return;
+			if (opsize > length)
+				return;	/* don't parse partial options */
+			if (opcode == TCPOPT_MPTCP)
+				mptcp_parse_option(skb, ptr, opsize, mp_opt);
+			ptr += opsize - 2;
+			length -= opsize;
+		}
+	}
+}
+
+bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
+		       unsigned int *size, struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	/* we will use snd_isn to detect first pkt [re]transmission
+	 * in mptcp_established_options_mp()
+	 */
+	subflow->snd_isn = TCP_SKB_CB(skb)->end_seq;
+	if (subflow->request_mptcp) {
+		opts->suboptions = OPTION_MPTCP_MPC_SYN;
+		opts->csum_reqd = mptcp_is_checksum_enabled(sock_net(sk));
+		opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
+		*size = TCPOLEN_MPTCP_MPC_SYN;
+		return true;
+	} else if (subflow->request_join) {
+		pr_debug("remote_token=%u, nonce=%u", subflow->remote_token,
+			 subflow->local_nonce);
+		opts->suboptions = OPTION_MPTCP_MPJ_SYN;
+		opts->join_id = subflow->local_id;
+		opts->token = subflow->remote_token;
+		opts->nonce = subflow->local_nonce;
+		opts->backup = subflow->request_bkup;
+		*size = TCPOLEN_MPTCP_MPJ_SYN;
+		return true;
+	}
+	return false;
+}
+
+static void clear_3rdack_retransmission(struct sock *sk)
+{
+	struct inet_connection_sock *icsk = inet_csk(sk);
+
+	sk_stop_timer(sk, &icsk->icsk_delack_timer);
+	icsk->icsk_ack.timeout = 0;
+	icsk->icsk_ack.ato = 0;
+	icsk->icsk_ack.pending &= ~(ICSK_ACK_SCHED | ICSK_ACK_TIMER);
+}
+
+static bool mptcp_established_options_mp(struct sock *sk, struct sk_buff *skb,
+					 bool snd_data_fin_enable,
+					 unsigned int *size,
+					 unsigned int remaining,
+					 struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	struct mptcp_ext *mpext;
+	unsigned int data_len;
+	u8 len;
+
+	/* When skb is not available, we better over-estimate the emitted
+	 * options len. A full DSS option (28 bytes) is longer than
+	 * TCPOLEN_MPTCP_MPC_ACK_DATA(22) or TCPOLEN_MPTCP_MPJ_ACK(24), so
+	 * tell the caller to defer the estimate to
+	 * mptcp_established_options_dss(), which will reserve enough space.
+	 */
+	if (!skb)
+		return false;
+
+	/* MPC/MPJ needed only on 3rd ack packet, DATA_FIN and TCP shutdown take precedence */
+	if (subflow->fully_established || snd_data_fin_enable ||
+	    subflow->snd_isn != TCP_SKB_CB(skb)->seq ||
+	    sk->sk_state != TCP_ESTABLISHED)
+		return false;
+
+	if (subflow->mp_capable) {
+		mpext = mptcp_get_ext(skb);
+		data_len = mpext ? mpext->data_len : 0;
+
+		/* we will check ops->data_len in mptcp_write_options() to
+		 * discriminate between TCPOLEN_MPTCP_MPC_ACK_DATA and
+		 * TCPOLEN_MPTCP_MPC_ACK
+		 */
+		opts->data_len = data_len;
+		opts->suboptions = OPTION_MPTCP_MPC_ACK;
+		opts->sndr_key = subflow->local_key;
+		opts->rcvr_key = subflow->remote_key;
+		opts->csum_reqd = READ_ONCE(msk->csum_enabled);
+		opts->allow_join_id0 = mptcp_allow_join_id0(sock_net(sk));
+
+		/* Section 3.1.
+		 * The MP_CAPABLE option is carried on the SYN, SYN/ACK, and ACK
+		 * packets that start the first subflow of an MPTCP connection,
+		 * as well as the first packet that carries data
+		 */
+		if (data_len > 0) {
+			len = TCPOLEN_MPTCP_MPC_ACK_DATA;
+			if (opts->csum_reqd) {
+				/* we need to propagate more info to csum the pseudo hdr */
+				opts->data_seq = mpext->data_seq;
+				opts->subflow_seq = mpext->subflow_seq;
+				opts->csum = mpext->csum;
+				len += TCPOLEN_MPTCP_DSS_CHECKSUM;
+			}
+			*size = ALIGN(len, 4);
+		} else {
+			*size = TCPOLEN_MPTCP_MPC_ACK;
+		}
+
+		pr_debug("subflow=%p, local_key=%llu, remote_key=%llu map_len=%d",
+			 subflow, subflow->local_key, subflow->remote_key,
+			 data_len);
+
+		return true;
+	} else if (subflow->mp_join) {
+		opts->suboptions = OPTION_MPTCP_MPJ_ACK;
+		memcpy(opts->hmac, subflow->hmac, MPTCPOPT_HMAC_LEN);
+		*size = TCPOLEN_MPTCP_MPJ_ACK;
+		pr_debug("subflow=%p", subflow);
+
+		/* we can use the full delegate action helper only from BH context
+		 * If we are in process context - sk is flushing the backlog at
+		 * socket lock release time - just set the appropriate flag, will
+		 * be handled by the release callback
+		 */
+		if (sock_owned_by_user(sk))
+			set_bit(MPTCP_DELEGATE_ACK, &subflow->delegated_status);
+		else
+			mptcp_subflow_delegate(subflow, MPTCP_DELEGATE_ACK);
+		return true;
+	}
+	return false;
+}
+
+static void mptcp_write_data_fin(struct mptcp_subflow_context *subflow,
+				 struct sk_buff *skb, struct mptcp_ext *ext)
+{
+	/* The write_seq value has already been incremented, so the actual
+	 * sequence number for the DATA_FIN is one less.
+	 */
+	u64 data_fin_tx_seq = READ_ONCE(mptcp_sk(subflow->conn)->write_seq) - 1;
+
+	if (!ext->use_map || !skb->len) {
+		/* RFC6824 requires a DSS mapping with specific values
+		 * if DATA_FIN is set but no data payload is mapped
+		 */
+		ext->data_fin = 1;
+		ext->use_map = 1;
+		ext->dsn64 = 1;
+		ext->data_seq = data_fin_tx_seq;
+		ext->subflow_seq = 0;
+		ext->data_len = 1;
+	} else if (ext->data_seq + ext->data_len == data_fin_tx_seq) {
+		/* If there's an existing DSS mapping and it is the
+		 * final mapping, DATA_FIN consumes 1 additional byte of
+		 * mapping space.
+		 */
+		ext->data_fin = 1;
+		ext->data_len++;
+	}
+}
+
+static bool mptcp_established_options_dss(struct sock *sk, struct sk_buff *skb,
+					  bool snd_data_fin_enable,
+					  unsigned int *size,
+					  unsigned int remaining,
+					  struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	unsigned int dss_size = 0;
+	struct mptcp_ext *mpext;
+	unsigned int ack_size;
+	bool ret = false;
+	u64 ack_seq;
+
+	opts->csum_reqd = READ_ONCE(msk->csum_enabled);
+	mpext = skb ? mptcp_get_ext(skb) : NULL;
+
+	if (!skb || (mpext && mpext->use_map) || snd_data_fin_enable) {
+		unsigned int map_size = TCPOLEN_MPTCP_DSS_BASE + TCPOLEN_MPTCP_DSS_MAP64;
+
+		if (mpext) {
+			if (opts->csum_reqd)
+				map_size += TCPOLEN_MPTCP_DSS_CHECKSUM;
+
+			opts->ext_copy = *mpext;
+		}
+
+		remaining -= map_size;
+		dss_size = map_size;
+		if (skb && snd_data_fin_enable)
+			mptcp_write_data_fin(subflow, skb, &opts->ext_copy);
+		opts->suboptions = OPTION_MPTCP_DSS;
+		ret = true;
+	}
+
+	/* passive sockets msk will set the 'can_ack' after accept(), even
+	 * if the first subflow may have the already the remote key handy
+	 */
+	opts->ext_copy.use_ack = 0;
+	if (!READ_ONCE(msk->can_ack)) {
+		*size = ALIGN(dss_size, 4);
+		return ret;
+	}
+
+	ack_seq = READ_ONCE(msk->ack_seq);
+	if (READ_ONCE(msk->use_64bit_ack)) {
+		ack_size = TCPOLEN_MPTCP_DSS_ACK64;
+		opts->ext_copy.data_ack = ack_seq;
+		opts->ext_copy.ack64 = 1;
+	} else {
+		ack_size = TCPOLEN_MPTCP_DSS_ACK32;
+		opts->ext_copy.data_ack32 = (uint32_t)ack_seq;
+		opts->ext_copy.ack64 = 0;
+	}
+	opts->ext_copy.use_ack = 1;
+	opts->suboptions = OPTION_MPTCP_DSS;
+	WRITE_ONCE(msk->old_wspace, __mptcp_space((struct sock *)msk));
+
+	/* Add kind/length/subtype/flag overhead if mapping is not populated */
+	if (dss_size == 0)
+		ack_size += TCPOLEN_MPTCP_DSS_BASE;
+
+	dss_size += ack_size;
+
+	*size = ALIGN(dss_size, 4);
+	return true;
+}
+
+static u64 add_addr_generate_hmac(u64 key1, u64 key2,
+				  struct mptcp_addr_info *addr)
+{
+	u16 port = ntohs(addr->port);
+	u8 hmac[SHA256_DIGEST_SIZE];
+	u8 msg[19];
+	int i = 0;
+
+	msg[i++] = addr->id;
+	if (addr->family == AF_INET) {
+		memcpy(&msg[i], &addr->addr.s_addr, 4);
+		i += 4;
+	}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+	else if (addr->family == AF_INET6) {
+		memcpy(&msg[i], &addr->addr6.s6_addr, 16);
+		i += 16;
+	}
+#endif
+	msg[i++] = port >> 8;
+	msg[i++] = port & 0xFF;
+
+	mptcp_crypto_hmac_sha(key1, key2, msg, i, hmac);
+
+	return get_unaligned_be64(&hmac[SHA256_DIGEST_SIZE - sizeof(u64)]);
+}
+
+static bool mptcp_established_options_add_addr(struct sock *sk, struct sk_buff *skb,
+					       unsigned int *size,
+					       unsigned int remaining,
+					       struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	bool drop_other_suboptions = false;
+	unsigned int opt_size = *size;
+	bool echo;
+	int len;
+
+	/* add addr will strip the existing options, be sure to avoid breaking
+	 * MPC/MPJ handshakes
+	 */
+	if (!mptcp_pm_should_add_signal(msk) ||
+	    (opts->suboptions & (OPTION_MPTCP_MPJ_ACK | OPTION_MPTCP_MPC_ACK)) ||
+	    !mptcp_pm_add_addr_signal(msk, skb, opt_size, remaining, &opts->addr,
+		    &echo, &drop_other_suboptions))
+		return false;
+
+	if (drop_other_suboptions)
+		remaining += opt_size;
+	len = mptcp_add_addr_len(opts->addr.family, echo, !!opts->addr.port);
+	if (remaining < len)
+		return false;
+
+	*size = len;
+	if (drop_other_suboptions) {
+		pr_debug("drop other suboptions");
+		opts->suboptions = 0;
+
+		/* note that e.g. DSS could have written into the memory
+		 * aliased by ahmac, we must reset the field here
+		 * to avoid appending the hmac even for ADD_ADDR echo
+		 * options
+		 */
+		opts->ahmac = 0;
+		*size -= opt_size;
+	}
+	opts->suboptions |= OPTION_MPTCP_ADD_ADDR;
+	if (!echo) {
+		opts->ahmac = add_addr_generate_hmac(msk->local_key,
+						     msk->remote_key,
+						     &opts->addr);
+	}
+	pr_debug("addr_id=%d, ahmac=%llu, echo=%d, port=%d",
+		 opts->addr.id, opts->ahmac, echo, ntohs(opts->addr.port));
+
+	return true;
+}
+
+static bool mptcp_established_options_rm_addr(struct sock *sk,
+					      unsigned int *size,
+					      unsigned int remaining,
+					      struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	struct mptcp_rm_list rm_list;
+	int i, len;
+
+	if (!mptcp_pm_should_rm_signal(msk) ||
+	    !(mptcp_pm_rm_addr_signal(msk, remaining, &rm_list)))
+		return false;
+
+	len = mptcp_rm_addr_len(&rm_list);
+	if (len < 0)
+		return false;
+	if (remaining < len)
+		return false;
+
+	*size = len;
+	opts->suboptions |= OPTION_MPTCP_RM_ADDR;
+	opts->rm_list = rm_list;
+
+	for (i = 0; i < opts->rm_list.nr; i++)
+		pr_debug("rm_list_ids[%d]=%d", i, opts->rm_list.ids[i]);
+
+	return true;
+}
+
+static bool mptcp_established_options_mp_prio(struct sock *sk,
+					      unsigned int *size,
+					      unsigned int remaining,
+					      struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	/* can't send MP_PRIO with MPC, as they share the same option space:
+	 * 'backup'. Also it makes no sense at all
+	 */
+	if (!subflow->send_mp_prio || (opts->suboptions & OPTIONS_MPTCP_MPC))
+		return false;
+
+	/* account for the trailing 'nop' option */
+	if (remaining < TCPOLEN_MPTCP_PRIO_ALIGN)
+		return false;
+
+	*size = TCPOLEN_MPTCP_PRIO_ALIGN;
+	opts->suboptions |= OPTION_MPTCP_PRIO;
+	opts->backup = subflow->request_bkup;
+
+	pr_debug("prio=%d", opts->backup);
+
+	return true;
+}
+
+static noinline bool mptcp_established_options_rst(struct sock *sk, struct sk_buff *skb,
+						   unsigned int *size,
+						   unsigned int remaining,
+						   struct mptcp_out_options *opts)
+{
+	const struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	if (remaining < TCPOLEN_MPTCP_RST)
+		return false;
+
+	*size = TCPOLEN_MPTCP_RST;
+	opts->suboptions |= OPTION_MPTCP_RST;
+	opts->reset_transient = subflow->reset_transient;
+	opts->reset_reason = subflow->reset_reason;
+	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPRSTTX);
+
+	return true;
+}
+
+static bool mptcp_established_options_fastclose(struct sock *sk,
+						unsigned int *size,
+						unsigned int remaining,
+						struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+
+	if (likely(!subflow->send_fastclose))
+		return false;
+
+	if (remaining < TCPOLEN_MPTCP_FASTCLOSE)
+		return false;
+
+	*size = TCPOLEN_MPTCP_FASTCLOSE;
+	opts->suboptions |= OPTION_MPTCP_FASTCLOSE;
+	opts->rcvr_key = msk->remote_key;
+
+	pr_debug("FASTCLOSE key=%llu", opts->rcvr_key);
+	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFASTCLOSETX);
+	return true;
+}
+
+static bool mptcp_established_options_mp_fail(struct sock *sk,
+					      unsigned int *size,
+					      unsigned int remaining,
+					      struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+
+	if (likely(!subflow->send_mp_fail))
+		return false;
+
+	if (remaining < TCPOLEN_MPTCP_FAIL)
+		return false;
+
+	*size = TCPOLEN_MPTCP_FAIL;
+	opts->suboptions |= OPTION_MPTCP_FAIL;
+	opts->fail_seq = subflow->map_seq;
+
+	pr_debug("MP_FAIL fail_seq=%llu", opts->fail_seq);
+	MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFAILTX);
+
+	return true;
+}
+
+bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
+			       unsigned int *size, unsigned int remaining,
+			       struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	unsigned int opt_size = 0;
+	bool snd_data_fin;
+	bool ret = false;
+
+	opts->suboptions = 0;
+
+	if (unlikely(__mptcp_check_fallback(msk) && !mptcp_check_infinite_map(skb)))
+		return false;
+
+	if (unlikely(skb && TCP_SKB_CB(skb)->tcp_flags & TCPHDR_RST)) {
+		if (mptcp_established_options_fastclose(sk, &opt_size, remaining, opts) ||
+		    mptcp_established_options_mp_fail(sk, &opt_size, remaining, opts)) {
+			*size += opt_size;
+			remaining -= opt_size;
+		}
+		/* MP_RST can be used with MP_FASTCLOSE and MP_FAIL if there is room */
+		if (mptcp_established_options_rst(sk, skb, &opt_size, remaining, opts)) {
+			*size += opt_size;
+			remaining -= opt_size;
+		}
+		return true;
+	}
+
+	snd_data_fin = mptcp_data_fin_enabled(msk);
+	if (mptcp_established_options_mp(sk, skb, snd_data_fin, &opt_size, remaining, opts))
+		ret = true;
+	else if (mptcp_established_options_dss(sk, skb, snd_data_fin, &opt_size, remaining, opts)) {
+		unsigned int mp_fail_size;
+
+		ret = true;
+		if (mptcp_established_options_mp_fail(sk, &mp_fail_size,
+						      remaining - opt_size, opts)) {
+			*size += opt_size + mp_fail_size;
+			remaining -= opt_size - mp_fail_size;
+			return true;
+		}
+	}
+
+	/* we reserved enough space for the above options, and exceeding the
+	 * TCP option space would be fatal
+	 */
+	if (WARN_ON_ONCE(opt_size > remaining))
+		return false;
+
+	*size += opt_size;
+	remaining -= opt_size;
+	if (mptcp_established_options_add_addr(sk, skb, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	} else if (mptcp_established_options_rm_addr(sk, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	}
+
+	if (mptcp_established_options_mp_prio(sk, &opt_size, remaining, opts)) {
+		*size += opt_size;
+		remaining -= opt_size;
+		ret = true;
+	}
+
+	return ret;
+}
+
+bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
+			  struct mptcp_out_options *opts)
+{
+	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+
+	if (subflow_req->mp_capable) {
+		opts->suboptions = OPTION_MPTCP_MPC_SYNACK;
+		opts->sndr_key = subflow_req->local_key;
+		opts->csum_reqd = subflow_req->csum_reqd;
+		opts->allow_join_id0 = subflow_req->allow_join_id0;
+		*size = TCPOLEN_MPTCP_MPC_SYNACK;
+		pr_debug("subflow_req=%p, local_key=%llu",
+			 subflow_req, subflow_req->local_key);
+		return true;
+	} else if (subflow_req->mp_join) {
+		opts->suboptions = OPTION_MPTCP_MPJ_SYNACK;
+		opts->backup = subflow_req->backup;
+		opts->join_id = subflow_req->local_id;
+		opts->thmac = subflow_req->thmac;
+		opts->nonce = subflow_req->local_nonce;
+		pr_debug("req=%p, bkup=%u, id=%u, thmac=%llu, nonce=%u",
+			 subflow_req, opts->backup, opts->join_id,
+			 opts->thmac, opts->nonce);
+		*size = TCPOLEN_MPTCP_MPJ_SYNACK;
+		return true;
+	}
+	return false;
+}
+
+static bool check_fully_established(struct mptcp_sock *msk, struct sock *ssk,
+				    struct mptcp_subflow_context *subflow,
+				    struct sk_buff *skb,
+				    struct mptcp_options_received *mp_opt)
+{
+	/* here we can process OoO, in-window pkts, only in-sequence 4th ack
+	 * will make the subflow fully established
+	 */
+	if (likely(subflow->fully_established)) {
+		/* on passive sockets, check for 3rd ack retransmission
+		 * note that msk is always set by subflow_syn_recv_sock()
+		 * for mp_join subflows
+		 */
+		if (TCP_SKB_CB(skb)->seq == subflow->ssn_offset + 1 &&
+		    TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq &&
+		    subflow->mp_join && (mp_opt->suboptions & OPTIONS_MPTCP_MPJ) &&
+		    !subflow->request_join)
+			tcp_send_ack(ssk);
+		goto fully_established;
+	}
+
+	/* we must process OoO packets before the first subflow is fully
+	 * established. OoO packets are instead a protocol violation
+	 * for MP_JOIN subflows as the peer must not send any data
+	 * before receiving the forth ack - cfr. RFC 8684 section 3.2.
+	 */
+	if (TCP_SKB_CB(skb)->seq != subflow->ssn_offset + 1) {
+		if (subflow->mp_join)
+			goto reset;
+		return subflow->mp_capable;
+	}
+
+	if (((mp_opt->suboptions & OPTION_MPTCP_DSS) && mp_opt->use_ack) ||
+	    ((mp_opt->suboptions & OPTION_MPTCP_ADD_ADDR) && !mp_opt->echo)) {
+		/* subflows are fully established as soon as we get any
+		 * additional ack, including ADD_ADDR.
+		 */
+		subflow->fully_established = 1;
+		WRITE_ONCE(msk->fully_established, true);
+		goto fully_established;
+	}
+
+	/* If the first established packet does not contain MP_CAPABLE + data
+	 * then fallback to TCP. Fallback scenarios requires a reset for
+	 * MP_JOIN subflows.
+	 */
+	if (!(mp_opt->suboptions & OPTIONS_MPTCP_MPC)) {
+		if (subflow->mp_join)
+			goto reset;
+		subflow->mp_capable = 0;
+		pr_fallback(msk);
+		mptcp_do_fallback(ssk);
+		return false;
+	}
+
+	if (mp_opt->deny_join_id0)
+		WRITE_ONCE(msk->pm.remote_deny_join_id0, true);
+
+	if (unlikely(!READ_ONCE(msk->pm.server_side)))
+		pr_warn_once("bogus mpc option on established client sk");
+	mptcp_subflow_fully_established(subflow, mp_opt);
+
+fully_established:
+	/* if the subflow is not already linked into the conn_list, we can't
+	 * notify the PM: this subflow is still on the listener queue
+	 * and the PM possibly acquiring the subflow lock could race with
+	 * the listener close
+	 */
+	if (likely(subflow->pm_notified) || list_empty(&subflow->node))
+		return true;
+
+	subflow->pm_notified = 1;
+	if (subflow->mp_join) {
+		clear_3rdack_retransmission(ssk);
+		mptcp_pm_subflow_established(msk);
+	} else {
+		mptcp_pm_fully_established(msk, ssk, GFP_ATOMIC);
+	}
+	return true;
+
+reset:
+	mptcp_subflow_reset(ssk);
+	return false;
+}
+
+u64 __mptcp_expand_seq(u64 old_seq, u64 cur_seq)
+{
+	u32 old_seq32, cur_seq32;
+
+	old_seq32 = (u32)old_seq;
+	cur_seq32 = (u32)cur_seq;
+	cur_seq = (old_seq & GENMASK_ULL(63, 32)) + cur_seq32;
+	if (unlikely(cur_seq32 < old_seq32 && before(old_seq32, cur_seq32)))
+		return cur_seq + (1LL << 32);
+
+	/* reverse wrap could happen, too */
+	if (unlikely(cur_seq32 > old_seq32 && after(old_seq32, cur_seq32)))
+		return cur_seq - (1LL << 32);
+	return cur_seq;
+}
+
+static void ack_update_msk(struct mptcp_sock *msk,
+			   struct sock *ssk,
+			   struct mptcp_options_received *mp_opt)
+{
+	u64 new_wnd_end, new_snd_una, snd_nxt = READ_ONCE(msk->snd_nxt);
+	struct sock *sk = (struct sock *)msk;
+	u64 old_snd_una;
+
+	mptcp_data_lock(sk);
+
+	/* avoid ack expansion on update conflict, to reduce the risk of
+	 * wrongly expanding to a future ack sequence number, which is way
+	 * more dangerous than missing an ack
+	 */
+	old_snd_una = msk->snd_una;
+	new_snd_una = mptcp_expand_seq(old_snd_una, mp_opt->data_ack, mp_opt->ack64);
+
+	/* ACK for data not even sent yet? Ignore.*/
+	if (unlikely(after64(new_snd_una, snd_nxt)))
+		new_snd_una = old_snd_una;
+
+	new_wnd_end = new_snd_una + tcp_sk(ssk)->snd_wnd;
+
+	if (after64(new_wnd_end, msk->wnd_end))
+		msk->wnd_end = new_wnd_end;
+
+	/* this assumes mptcp_incoming_options() is invoked after tcp_ack() */
+	if (after64(msk->wnd_end, READ_ONCE(msk->snd_nxt)))
+		__mptcp_check_push(sk, ssk);
+
+	if (after64(new_snd_una, old_snd_una)) {
+		msk->snd_una = new_snd_una;
+		__mptcp_data_acked(sk);
+	}
+	mptcp_data_unlock(sk);
+
+	trace_ack_update_msk(mp_opt->data_ack,
+			     old_snd_una, new_snd_una,
+			     new_wnd_end, msk->wnd_end);
+}
+
+bool mptcp_update_rcv_data_fin(struct mptcp_sock *msk, u64 data_fin_seq, bool use_64bit)
+{
+	/* Skip if DATA_FIN was already received.
+	 * If updating simultaneously with the recvmsg loop, values
+	 * should match. If they mismatch, the peer is misbehaving and
+	 * we will prefer the most recent information.
+	 */
+	if (READ_ONCE(msk->rcv_data_fin))
+		return false;
+
+	WRITE_ONCE(msk->rcv_data_fin_seq,
+		   mptcp_expand_seq(READ_ONCE(msk->ack_seq), data_fin_seq, use_64bit));
+	WRITE_ONCE(msk->rcv_data_fin, 1);
+
+	return true;
+}
+
+static bool add_addr_hmac_valid(struct mptcp_sock *msk,
+				struct mptcp_options_received *mp_opt)
+{
+	u64 hmac = 0;
+
+	if (mp_opt->echo)
+		return true;
+
+	hmac = add_addr_generate_hmac(msk->remote_key,
+				      msk->local_key,
+				      &mp_opt->addr);
+
+	pr_debug("msk=%p, ahmac=%llu, mp_opt->ahmac=%llu\n",
+		 msk, hmac, mp_opt->ahmac);
+
+	return hmac == mp_opt->ahmac;
+}
+
+/* Return false if a subflow has been reset, else return true */
+bool mptcp_incoming_options(struct sock *sk, struct sk_buff *skb)
+{
+	struct mptcp_subflow_context *subflow = mptcp_subflow_ctx(sk);
+	struct mptcp_sock *msk = mptcp_sk(subflow->conn);
+	struct mptcp_options_received mp_opt;
+	struct mptcp_ext *mpext;
+
+	if (__mptcp_check_fallback(msk)) {
+		/* Keep it simple and unconditionally trigger send data cleanup and
+		 * pending queue spooling. We will need to acquire the data lock
+		 * for more accurate checks, and once the lock is acquired, such
+		 * helpers are cheap.
+		 */
+		mptcp_data_lock(subflow->conn);
+		if (sk_stream_memory_free(sk))
+			__mptcp_check_push(subflow->conn, sk);
+		__mptcp_data_acked(subflow->conn);
+		mptcp_data_unlock(subflow->conn);
+		return true;
+	}
+
+	mptcp_get_options(skb, &mp_opt);
+
+	/* The subflow can be in close state only if check_fully_established()
+	 * just sent a reset. If so, tell the caller to ignore the current packet.
+	 */
+	if (!check_fully_established(msk, sk, subflow, skb, &mp_opt))
+		return sk->sk_state != TCP_CLOSE;
+
+	if (unlikely(mp_opt.suboptions != OPTION_MPTCP_DSS)) {
+		if ((mp_opt.suboptions & OPTION_MPTCP_FASTCLOSE) &&
+		    msk->local_key == mp_opt.rcvr_key) {
+			WRITE_ONCE(msk->rcv_fastclose, true);
+			mptcp_schedule_work((struct sock *)msk);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFASTCLOSERX);
+		}
+
+		if ((mp_opt.suboptions & OPTION_MPTCP_ADD_ADDR) &&
+		    add_addr_hmac_valid(msk, &mp_opt)) {
+			if (!mp_opt.echo) {
+				mptcp_pm_add_addr_received(sk, &mp_opt.addr);
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ADDADDR);
+			} else {
+				mptcp_pm_add_addr_echoed(msk, &mp_opt.addr);
+				mptcp_pm_del_add_timer(msk, &mp_opt.addr, true);
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_ECHOADD);
+			}
+
+			if (mp_opt.addr.port)
+				MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_PORTADD);
+		}
+
+		if (mp_opt.suboptions & OPTION_MPTCP_RM_ADDR)
+			mptcp_pm_rm_addr_received(msk, &mp_opt.rm_list);
+
+		if (mp_opt.suboptions & OPTION_MPTCP_PRIO) {
+			mptcp_pm_mp_prio_received(sk, mp_opt.backup);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPPRIORX);
+		}
+
+		if (mp_opt.suboptions & OPTION_MPTCP_FAIL) {
+			mptcp_pm_mp_fail_received(sk, mp_opt.fail_seq);
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPFAILRX);
+		}
+
+		if (mp_opt.suboptions & OPTION_MPTCP_RST) {
+			subflow->reset_seen = 1;
+			subflow->reset_reason = mp_opt.reset_reason;
+			subflow->reset_transient = mp_opt.reset_transient;
+			MPTCP_INC_STATS(sock_net(sk), MPTCP_MIB_MPRSTRX);
+		}
+
+		if (!(mp_opt.suboptions & OPTION_MPTCP_DSS))
+			return true;
+	}
+
+	/* we can't wait for recvmsg() to update the ack_seq, otherwise
+	 * monodirectional flows will stuck
+	 */
+	if (mp_opt.use_ack)
+		ack_update_msk(msk, sk, &mp_opt);
+
+	/* Zero-data-length packets are dropped by the caller and not
+	 * propagated to the MPTCP layer, so the skb extension does not
+	 * need to be allocated or populated. DATA_FIN information, if
+	 * present, needs to be updated here before the skb is freed.
+	 */
+	if (TCP_SKB_CB(skb)->seq == TCP_SKB_CB(skb)->end_seq) {
+		if (mp_opt.data_fin && mp_opt.data_len == 1 &&
+		    mptcp_update_rcv_data_fin(msk, mp_opt.data_seq, mp_opt.dsn64))
+			mptcp_schedule_work((struct sock *)msk);
+
+		return true;
+	}
+
+	mpext = skb_ext_add(skb, SKB_EXT_MPTCP);
+	if (!mpext)
+		return true;
+
+	memset(mpext, 0, sizeof(*mpext));
+
+	if (likely(mp_opt.use_map)) {
+		if (mp_opt.mpc_map) {
+			/* this is an MP_CAPABLE carrying MPTCP data
+			 * we know this map the first chunk of data
+			 */
+			mptcp_crypto_key_sha(subflow->remote_key, NULL,
+					     &mpext->data_seq);
+			mpext->data_seq++;
+			mpext->subflow_seq = 1;
+			mpext->dsn64 = 1;
+			mpext->mpc_map = 1;
+			mpext->data_fin = 0;
+		} else {
+			mpext->data_seq = mp_opt.data_seq;
+			mpext->subflow_seq = mp_opt.subflow_seq;
+			mpext->dsn64 = mp_opt.dsn64;
+			mpext->data_fin = mp_opt.data_fin;
+		}
+		mpext->data_len = mp_opt.data_len;
+		mpext->use_map = 1;
+		mpext->csum_reqd = !!(mp_opt.suboptions & OPTION_MPTCP_CSUMREQD);
+
+		if (mpext->csum_reqd)
+			mpext->csum = mp_opt.csum;
+	}
+
+	return true;
+}
+
+static void mptcp_set_rwin(struct tcp_sock *tp, struct tcphdr *th)
+{
+	const struct sock *ssk = (const struct sock *)tp;
+	struct mptcp_subflow_context *subflow;
+	u64 ack_seq, rcv_wnd_old, rcv_wnd_new;
+	struct mptcp_sock *msk;
+	u32 new_win;
+	u64 win;
+
+	subflow = mptcp_subflow_ctx(ssk);
+	msk = mptcp_sk(subflow->conn);
+
+	ack_seq = READ_ONCE(msk->ack_seq);
+	rcv_wnd_new = ack_seq + tp->rcv_wnd;
+
+	rcv_wnd_old = atomic64_read(&msk->rcv_wnd_sent);
+	if (after64(rcv_wnd_new, rcv_wnd_old)) {
+		u64 rcv_wnd;
+
+		for (;;) {
+			rcv_wnd = atomic64_cmpxchg(&msk->rcv_wnd_sent, rcv_wnd_old, rcv_wnd_new);
+
+			if (rcv_wnd == rcv_wnd_old)
+				break;
+
+			rcv_wnd_old = rcv_wnd;
+			if (before64(rcv_wnd_new, rcv_wnd_old)) {
+				MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICTUPDATE);
+				goto raise_win;
+			}
+			MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDCONFLICT);
+		}
+		return;
+	}
+
+	if (rcv_wnd_new != rcv_wnd_old) {
+raise_win:
+		win = rcv_wnd_old - ack_seq;
+		tp->rcv_wnd = min_t(u64, win, U32_MAX);
+		new_win = tp->rcv_wnd;
+
+		/* Make sure we do not exceed the maximum possible
+		 * scaled window.
+		 */
+		if (unlikely(th->syn))
+			new_win = min(new_win, 65535U) << tp->rx_opt.rcv_wscale;
+		if (!tp->rx_opt.rcv_wscale &&
+		    READ_ONCE(sock_net(ssk)->ipv4.sysctl_tcp_workaround_signed_windows))
+			new_win = min(new_win, MAX_TCP_WINDOW);
+		else
+			new_win = min(new_win, (65535U << tp->rx_opt.rcv_wscale));
+
+		/* RFC1323 scaling applied */
+		new_win >>= tp->rx_opt.rcv_wscale;
+		th->window = htons(new_win);
+		MPTCP_INC_STATS(sock_net(ssk), MPTCP_MIB_RCVWNDSHARED);
+	}
+}
+
+__sum16 __mptcp_make_csum(u64 data_seq, u32 subflow_seq, u16 data_len, __wsum sum)
+{
+	struct csum_pseudo_header header;
+	__wsum csum;
+
+	/* cfr RFC 8684 3.3.1.:
+	 * the data sequence number used in the pseudo-header is
+	 * always the 64-bit value, irrespective of what length is used in the
+	 * DSS option itself.
+	 */
+	header.data_seq = cpu_to_be64(data_seq);
+	header.subflow_seq = htonl(subflow_seq);
+	header.data_len = htons(data_len);
+	header.csum = 0;
+
+	csum = csum_partial(&header, sizeof(header), sum);
+	return csum_fold(csum);
+}
+
+static __sum16 mptcp_make_csum(const struct mptcp_ext *mpext)
+{
+	return __mptcp_make_csum(mpext->data_seq, mpext->subflow_seq, mpext->data_len,
+				 ~csum_unfold(mpext->csum));
+}
+
+static void put_len_csum(u16 len, __sum16 csum, void *data)
+{
+	__sum16 *sumptr = data + 2;
+	__be16 *ptr = data;
+
+	put_unaligned_be16(len, ptr);
+
+	put_unaligned(csum, sumptr);
+}
+
+void mptcp_write_options(struct tcphdr *th, __be32 *ptr, struct tcp_sock *tp,
+			 struct mptcp_out_options *opts)
+{
+	const struct sock *ssk = (const struct sock *)tp;
+	struct mptcp_subflow_context *subflow;
+
+	/* Which options can be used together?
+	 *
+	 * X: mutually exclusive
+	 * O: often used together
+	 * C: can be used together in some cases
+	 * P: could be used together but we prefer not to (optimisations)
+	 *
+	 *  Opt: | MPC  | MPJ  | DSS  | ADD  |  RM  | PRIO | FAIL |  FC  |
+	 * ------|------|------|------|------|------|------|------|------|
+	 *  MPC  |------|------|------|------|------|------|------|------|
+	 *  MPJ  |  X   |------|------|------|------|------|------|------|
+	 *  DSS  |  X   |  X   |------|------|------|------|------|------|
+	 *  ADD  |  X   |  X   |  P   |------|------|------|------|------|
+	 *  RM   |  C   |  C   |  C   |  P   |------|------|------|------|
+	 *  PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|
+	 *  FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|
+	 *  FC   |  X   |  X   |  X   |  X   |  X   |  X   |  X   |------|
+	 *  RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |
+	 * ------|------|------|------|------|------|------|------|------|
+	 *
+	 * The same applies in mptcp_established_options() function.
+	 */
+	if (likely(OPTION_MPTCP_DSS & opts->suboptions)) {
+		struct mptcp_ext *mpext = &opts->ext_copy;
+		u8 len = TCPOLEN_MPTCP_DSS_BASE;
+		u8 flags = 0;
+
+		if (mpext->use_ack) {
+			flags = MPTCP_DSS_HAS_ACK;
+			if (mpext->ack64) {
+				len += TCPOLEN_MPTCP_DSS_ACK64;
+				flags |= MPTCP_DSS_ACK64;
+			} else {
+				len += TCPOLEN_MPTCP_DSS_ACK32;
+			}
+		}
+
+		if (mpext->use_map) {
+			len += TCPOLEN_MPTCP_DSS_MAP64;
+
+			/* Use only 64-bit mapping flags for now, add
+			 * support for optional 32-bit mappings later.
+			 */
+			flags |= MPTCP_DSS_HAS_MAP | MPTCP_DSS_DSN64;
+			if (mpext->data_fin)
+				flags |= MPTCP_DSS_DATA_FIN;
+
+			if (opts->csum_reqd)
+				len += TCPOLEN_MPTCP_DSS_CHECKSUM;
+		}
+
+		*ptr++ = mptcp_option(MPTCPOPT_DSS, len, 0, flags);
+
+		if (mpext->use_ack) {
+			if (mpext->ack64) {
+				put_unaligned_be64(mpext->data_ack, ptr);
+				ptr += 2;
+			} else {
+				put_unaligned_be32(mpext->data_ack32, ptr);
+				ptr += 1;
+			}
+		}
+
+		if (mpext->use_map) {
+			put_unaligned_be64(mpext->data_seq, ptr);
+			ptr += 2;
+			put_unaligned_be32(mpext->subflow_seq, ptr);
+			ptr += 1;
+			if (opts->csum_reqd) {
+				/* data_len == 0 is reserved for the infinite mapping,
+				 * the checksum will also be set to 0.
+				 */
+				put_len_csum(mpext->data_len,
+					     (mpext->data_len ? mptcp_make_csum(mpext) : 0),
+					     ptr);
+			} else {
+				put_unaligned_be32(mpext->data_len << 16 |
+						   TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
+			}
+			ptr += 1;
+		}
+
+		/* We might need to add MP_FAIL options in rare cases */
+		if (unlikely(OPTION_MPTCP_FAIL & opts->suboptions))
+			goto mp_fail;
+	} else if (OPTIONS_MPTCP_MPC & opts->suboptions) {
+		u8 len, flag = MPTCP_CAP_HMAC_SHA256;
+
+		if (OPTION_MPTCP_MPC_SYN & opts->suboptions) {
+			len = TCPOLEN_MPTCP_MPC_SYN;
+		} else if (OPTION_MPTCP_MPC_SYNACK & opts->suboptions) {
+			len = TCPOLEN_MPTCP_MPC_SYNACK;
+		} else if (opts->data_len) {
+			len = TCPOLEN_MPTCP_MPC_ACK_DATA;
+			if (opts->csum_reqd)
+				len += TCPOLEN_MPTCP_DSS_CHECKSUM;
+		} else {
+			len = TCPOLEN_MPTCP_MPC_ACK;
+		}
+
+		if (opts->csum_reqd)
+			flag |= MPTCP_CAP_CHECKSUM_REQD;
+
+		if (!opts->allow_join_id0)
+			flag |= MPTCP_CAP_DENY_JOIN_ID0;
+
+		*ptr++ = mptcp_option(MPTCPOPT_MP_CAPABLE, len,
+				      MPTCP_SUPPORTED_VERSION,
+				      flag);
+
+		if (!((OPTION_MPTCP_MPC_SYNACK | OPTION_MPTCP_MPC_ACK) &
+		    opts->suboptions))
+			goto mp_capable_done;
+
+		put_unaligned_be64(opts->sndr_key, ptr);
+		ptr += 2;
+		if (!((OPTION_MPTCP_MPC_ACK) & opts->suboptions))
+			goto mp_capable_done;
+
+		put_unaligned_be64(opts->rcvr_key, ptr);
+		ptr += 2;
+		if (!opts->data_len)
+			goto mp_capable_done;
+
+		if (opts->csum_reqd) {
+			put_len_csum(opts->data_len,
+				     __mptcp_make_csum(opts->data_seq,
+						       opts->subflow_seq,
+						       opts->data_len,
+						       ~csum_unfold(opts->csum)),
+				     ptr);
+		} else {
+			put_unaligned_be32(opts->data_len << 16 |
+					   TCPOPT_NOP << 8 | TCPOPT_NOP, ptr);
+		}
+		ptr += 1;
+
+		/* MPC is additionally mutually exclusive with MP_PRIO */
+		goto mp_capable_done;
+	} else if (OPTIONS_MPTCP_MPJ & opts->suboptions) {
+		if (OPTION_MPTCP_MPJ_SYN & opts->suboptions) {
+			*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+					      TCPOLEN_MPTCP_MPJ_SYN,
+					      opts->backup, opts->join_id);
+			put_unaligned_be32(opts->token, ptr);
+			ptr += 1;
+			put_unaligned_be32(opts->nonce, ptr);
+			ptr += 1;
+		} else if (OPTION_MPTCP_MPJ_SYNACK & opts->suboptions) {
+			*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+					      TCPOLEN_MPTCP_MPJ_SYNACK,
+					      opts->backup, opts->join_id);
+			put_unaligned_be64(opts->thmac, ptr);
+			ptr += 2;
+			put_unaligned_be32(opts->nonce, ptr);
+			ptr += 1;
+		} else {
+			*ptr++ = mptcp_option(MPTCPOPT_MP_JOIN,
+					      TCPOLEN_MPTCP_MPJ_ACK, 0, 0);
+			memcpy(ptr, opts->hmac, MPTCPOPT_HMAC_LEN);
+			ptr += 5;
+		}
+	} else if (OPTION_MPTCP_ADD_ADDR & opts->suboptions) {
+		u8 len = TCPOLEN_MPTCP_ADD_ADDR_BASE;
+		u8 echo = MPTCP_ADDR_ECHO;
+
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		if (opts->addr.family == AF_INET6)
+			len = TCPOLEN_MPTCP_ADD_ADDR6_BASE;
+#endif
+
+		if (opts->addr.port)
+			len += TCPOLEN_MPTCP_PORT_LEN;
+
+		if (opts->ahmac) {
+			len += sizeof(opts->ahmac);
+			echo = 0;
+		}
+
+		*ptr++ = mptcp_option(MPTCPOPT_ADD_ADDR,
+				      len, echo, opts->addr.id);
+		if (opts->addr.family == AF_INET) {
+			memcpy((u8 *)ptr, (u8 *)&opts->addr.addr.s_addr, 4);
+			ptr += 1;
+		}
+#if IS_ENABLED(CONFIG_MPTCP_IPV6)
+		else if (opts->addr.family == AF_INET6) {
+			memcpy((u8 *)ptr, opts->addr.addr6.s6_addr, 16);
+			ptr += 4;
+		}
+#endif
+
+		if (!opts->addr.port) {
+			if (opts->ahmac) {
+				put_unaligned_be64(opts->ahmac, ptr);
+				ptr += 2;
+			}
+		} else {
+			u16 port = ntohs(opts->addr.port);
+
+			if (opts->ahmac) {
+				u8 *bptr = (u8 *)ptr;
+
+				put_unaligned_be16(port, bptr);
+				bptr += 2;
+				put_unaligned_be64(opts->ahmac, bptr);
+				bptr += 8;
+				put_unaligned_be16(TCPOPT_NOP << 8 |
+						   TCPOPT_NOP, bptr);
+
+				ptr += 3;
+			} else {
+				put_unaligned_be32(port << 16 |
+						   TCPOPT_NOP << 8 |
+						   TCPOPT_NOP, ptr);
+				ptr += 1;
+			}
+		}
+	} else if (unlikely(OPTION_MPTCP_FASTCLOSE & opts->suboptions)) {
+		/* FASTCLOSE is mutually exclusive with others except RST */
+		*ptr++ = mptcp_option(MPTCPOPT_MP_FASTCLOSE,
+				      TCPOLEN_MPTCP_FASTCLOSE,
+				      0, 0);
+		put_unaligned_be64(opts->rcvr_key, ptr);
+		ptr += 2;
+
+		if (OPTION_MPTCP_RST & opts->suboptions)
+			goto mp_rst;
+		return;
+	} else if (unlikely(OPTION_MPTCP_FAIL & opts->suboptions)) {
+mp_fail:
+		/* MP_FAIL is mutually exclusive with others except RST */
+		subflow = mptcp_subflow_ctx(ssk);
+		subflow->send_mp_fail = 0;
+
+		*ptr++ = mptcp_option(MPTCPOPT_MP_FAIL,
+				      TCPOLEN_MPTCP_FAIL,
+				      0, 0);
+		put_unaligned_be64(opts->fail_seq, ptr);
+		ptr += 2;
+
+		if (OPTION_MPTCP_RST & opts->suboptions)
+			goto mp_rst;
+		return;
+	} else if (unlikely(OPTION_MPTCP_RST & opts->suboptions)) {
+mp_rst:
+		*ptr++ = mptcp_option(MPTCPOPT_RST,
+				      TCPOLEN_MPTCP_RST,
+				      opts->reset_transient,
+				      opts->reset_reason);
+		return;
+	}
+
+	if (OPTION_MPTCP_PRIO & opts->suboptions) {
+		subflow = mptcp_subflow_ctx(ssk);
+		subflow->send_mp_prio = 0;
+
+		*ptr++ = mptcp_option(MPTCPOPT_MP_PRIO,
+				      TCPOLEN_MPTCP_PRIO,
+				      opts->backup, TCPOPT_NOP);
+
+		MPTCP_INC_STATS(sock_net((const struct sock *)tp),
+				MPTCP_MIB_MPPRIOTX);
+	}
+
+mp_capable_done:
+	if (OPTION_MPTCP_RM_ADDR & opts->suboptions) {
+		u8 i = 1;
+
+		*ptr++ = mptcp_option(MPTCPOPT_RM_ADDR,
+				      TCPOLEN_MPTCP_RM_ADDR_BASE + opts->rm_list.nr,
+				      0, opts->rm_list.ids[0]);
+
+		while (i < opts->rm_list.nr) {
+			u8 id1, id2, id3, id4;
+
+			id1 = opts->rm_list.ids[i];
+			id2 = i + 1 < opts->rm_list.nr ? opts->rm_list.ids[i + 1] : TCPOPT_NOP;
+			id3 = i + 2 < opts->rm_list.nr ? opts->rm_list.ids[i + 2] : TCPOPT_NOP;
+			id4 = i + 3 < opts->rm_list.nr ? opts->rm_list.ids[i + 3] : TCPOPT_NOP;
+			put_unaligned_be32(id1 << 24 | id2 << 16 | id3 << 8 | id4, ptr);
+			ptr += 1;
+			i += 4;
+		}
+	}
+
+	if (tp)
+		mptcp_set_rwin(tp, th);
+}
+
+__be32 mptcp_get_reset_option(const struct sk_buff *skb)
+{
+	const struct mptcp_ext *ext = mptcp_get_ext(skb);
+	u8 flags, reason;
+
+	if (ext) {
+		flags = ext->reset_transient;
+		reason = ext->reset_reason;
+
+		return mptcp_option(MPTCPOPT_RST, TCPOLEN_MPTCP_RST,
+				    flags, reason);
+	}
+
+	return htonl(0u);
+}
+EXPORT_SYMBOL_GPL(mptcp_get_reset_option);