[RFC PATCH mptcp-next v4] mptcp: Fast Open Mechanism

[Dmytro SHYTYI <dmytro@shytyi.net>]

This set of patches will bring "Fast Open" Option support to MPTCP.
The aim of Fast Open Mechanism is to eliminate one round trip
time from a TCP conversation by allowing data to be included as
part of the SYN segment that initiates the connection.

IETF RFC 8684: Appendix B. TCP Fast Open and MPTCP.

[PATCH v3] includes "client-server" partial support for :
1. MPTCP cookie request from client (seems to be working).
2. MPTCP cookie offering from server (seems to be working).
3. MPTCP SYN+DATA+COOKIE from client (seems to be working).
4. subsequent write + read on the opened socket (first launch
with TFO request seems to be working, hovewer the second launch
appears to have a mptcp "RST" issue).

This patch is Work In Progress transitional draft.
The differences between v3 and v4:
1. An attempt to reduce impact on existing TCP code.
2. 2 files related to mptcp_fastopen are created(*.h + *.c).
3. "subflow_v4_conn_request" is used to call "mptcp_conn_request"(
located in "mptcp_fastopen.c") to process the received packet on the
listener side when "SYN" is received during 3way handshake.
4. This chain adds "skb" to "&msk->sk_receive_queue"
("subflow_v4_conn_request"->"mptcp_conn_request"->
"mptcp_try_fastopen"->"mptcp_fastopen_create_child"->
"mptcp_fastopen_add_skb")
5. Some minor comments from mailing list are not yet included
in the current version of the PATCH.

Signed-off-by: Dmytro SHYTYI <dmytro@shytyi.net>
---
 include/net/mptcp.h        |   2 +-
 net/ipv4/tcp_output.c      |   3 +-
 net/mptcp/Makefile         |   2 +-
 net/mptcp/mptcp_fastopen.c | 476 +++++++++++++++++++++++++++++++++++++
 net/mptcp/mptcp_fastopen.h |  67 ++++++
 net/mptcp/options.c        |   7 +-
 net/mptcp/protocol.c       |   8 +-
 net/mptcp/protocol.h       |   3 +
 net/mptcp/sockopt.c        |  41 ++++
 net/mptcp/subflow.c        |   7 +-
 10 files changed, 604 insertions(+), 12 deletions(-)
 create mode 100644 net/mptcp/mptcp_fastopen.c
 create mode 100644 net/mptcp/mptcp_fastopen.h

diff --git a/include/net/mptcp.h b/include/net/mptcp.h
index 6456ea26e4c7..692197187af8 100644
--- a/include/net/mptcp.h
+++ b/include/net/mptcp.h
@@ -139,7 +139,7 @@ void mptcp_space(const struct sock *ssk, int *space, int *full_space);
 bool mptcp_syn_options(struct sock *sk, const struct sk_buff *skb,
 		       unsigned int *size, struct mptcp_out_options *opts);
 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
-			  struct mptcp_out_options *opts);
+			  struct mptcp_out_options *opts, u16 *tcp_options);
 bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 			       unsigned int *size, unsigned int remaining,
 			       struct mptcp_out_options *opts);
diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
index b4b2284ed4a2..864517e63bdf 100644
--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -747,7 +747,7 @@ static void mptcp_set_option_cond(const struct request_sock *req,
 	if (rsk_is_mptcp(req)) {
 		unsigned int size;
 
-		if (mptcp_synack_options(req, &size, &opts->mptcp)) {
+		if (mptcp_synack_options(req, &size, &opts->mptcp, &opts->options)) {
 			if (*remaining >= size) {
 				opts->options |= OPTION_MPTCP;
 				*remaining -= size;
@@ -822,7 +822,6 @@ static unsigned int tcp_syn_options(struct sock *sk, struct sk_buff *skb,
 			tp->syn_fastopen_exp = fastopen->cookie.exp ? 1 : 0;
 		}
 	}
-
 	smc_set_option(tp, opts, &remaining);
 
 	if (sk_is_mptcp(sk)) {
diff --git a/net/mptcp/Makefile b/net/mptcp/Makefile
index 8a7f68efa35f..0f1022b395ef 100644
--- a/net/mptcp/Makefile
+++ b/net/mptcp/Makefile
@@ -2,7 +2,7 @@
 obj-$(CONFIG_MPTCP) += mptcp.o
 
 mptcp-y := protocol.o subflow.o options.o token.o crypto.o ctrl.o pm.o diag.o \
-	   mib.o pm_netlink.o sockopt.o pm_userspace.o sched.o
+	   mib.o pm_netlink.o sockopt.o pm_userspace.o sched.o mptcp_fastopen.o
 
 obj-$(CONFIG_SYN_COOKIES) += syncookies.o
 obj-$(CONFIG_INET_MPTCP_DIAG) += mptcp_diag.o
diff --git a/net/mptcp/mptcp_fastopen.c b/net/mptcp/mptcp_fastopen.c
new file mode 100644
index 000000000000..cca086e178a6
--- /dev/null
+++ b/net/mptcp/mptcp_fastopen.c
@@ -0,0 +1,476 @@
+#include "mptcp_fastopen.h"
+
+int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
+			   size_t len, struct mptcp_sock *msk,
+			   size_t *copied)
+{
+	const struct iphdr *iph;
+	struct ubuf_info *uarg;
+	struct sockaddr *uaddr;
+	struct sk_buff *skb;
+	struct tcp_sock *tp;
+	struct socket *ssk;
+	int ret;
+
+	ssk = __mptcp_nmpc_socket(msk);
+	if (unlikely(!ssk))
+		goto out_EFAULT;
+	skb = tcp_stream_alloc_skb(ssk->sk, 0, ssk->sk->sk_allocation, true);
+	if (unlikely(!skb))
+		goto out_EFAULT;
+	iph = ip_hdr(skb);
+	if (unlikely(!iph))
+		goto out_EFAULT;
+	uarg = msg_zerocopy_realloc(sk, len, skb_zcopy(skb));
+	if (unlikely(!uarg))
+		goto out_EFAULT;
+	uaddr = msg->msg_name;
+
+	tp = tcp_sk(ssk->sk);
+	if (unlikely(!tp))
+		goto out_EFAULT;
+	if (!tp->fastopen_req)
+		tp->fastopen_req = kzalloc(sizeof(*tp->fastopen_req),
+					   ssk->sk->sk_allocation);
+
+	if (unlikely(!tp->fastopen_req))
+		goto out_EFAULT;
+	tp->fastopen_req->data = msg;
+	tp->fastopen_req->size = len;
+	tp->fastopen_req->uarg = uarg;
+
+	/* requests a cookie */
+	*copied = mptcp_stream_connect(sk->sk_socket, uaddr,
+				   msg->msg_namelen, msg->msg_flags);
+
+	return 0;
+out_EFAULT:
+	ret = -EFAULT;
+	return ret;
+}
+
+void mptcp_reqsk_record_syn(const struct sock *sk,
+			    struct request_sock *req,
+			    const struct sk_buff *skb)
+{
+	if (tcp_sk(sk)->save_syn) {
+		u32 length = skb_network_header_len(skb) + tcp_hdrlen(skb);
+		struct saved_syn *svd_syn;
+		u32 mac_headerlen;
+		void *base;
+
+		if (tcp_sk(sk)->save_syn == 2) {
+			base = skb_mac_header(skb);
+			mac_headerlen = skb_mac_header_len(skb);
+			length += mac_headerlen;
+		} else {
+			base = skb_network_header(skb);
+			mac_headerlen = 0;
+		}
+
+		svd_syn = kmalloc(struct_size(svd_syn, data, length),
+				    GFP_ATOMIC);
+		if (svd_syn) {
+			svd_syn->mac_hdrlen = mac_headerlen;
+			svd_syn->network_hdrlen = skb_network_header_len(skb);
+			svd_syn->tcp_hdrlen = tcp_hdrlen(skb);
+			memcpy(svd_syn->data, base, length);
+			req->saved_syn = svd_syn;
+		}
+	}
+}
+
+void mptcp_ecn_create_request(struct request_sock *req,
+			      const struct sk_buff *skb,
+			      const struct sock *listen_sk,
+			      const struct dst_entry *dst)
+{
+	const struct tcphdr *thdr = tcp_hdr(skb);
+	const struct net *net = sock_net(listen_sk);
+	bool thdr_ecn = thdr->ece && thdr->cwr;
+	bool ect_stat, ecn_okay;
+	u32 ecn_okay_dst;
+
+	if (!thdr_ecn)
+		return;
+
+	ect_stat = !INET_ECN_is_not_ect(TCP_SKB_CB(skb)->ip_dsfield);
+	ecn_okay_dst = dst_feature(dst, DST_FEATURE_ECN_MASK);
+	ecn_okay = net->ipv4.sysctl_tcp_ecn || ecn_okay_dst;
+
+	if (((!ect_stat || thdr->res1) && ecn_okay) || tcp_ca_needs_ecn(listen_sk) ||
+	    (ecn_okay_dst & DST_FEATURE_ECN_CA) ||
+	    tcp_bpf_ca_needs_ecn((struct sock *)req))
+		inet_rsk(req)->ecn_ok = 1;
+}
+
+void mptcp_openreq_init(struct request_sock *req,
+			const struct tcp_options_received *rx_opt,
+			struct sk_buff *skb, const struct sock *sk)
+{
+	struct inet_request_sock *ireq = inet_rsk(req);
+
+	req->rsk_rcv_wnd = 0;
+	tcp_rsk(req)->rcv_isn = TCP_SKB_CB(skb)->seq;
+	tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+	tcp_rsk(req)->snt_synack = 0;
+	tcp_rsk(req)->last_oow_ack_time = 0;
+	req->mss = rx_opt->mss_clamp;
+	req->ts_recent = rx_opt->saw_tstamp ? rx_opt->rcv_tsval : 0;
+	ireq->tstamp_ok = rx_opt->tstamp_ok;
+	ireq->sack_ok = rx_opt->sack_ok;
+	ireq->snd_wscale = rx_opt->snd_wscale;
+	ireq->wscale_ok = rx_opt->wscale_ok;
+	ireq->acked = 0;
+	ireq->ecn_ok = 0;
+	ireq->ir_rmt_port = tcp_hdr(skb)->source;
+	ireq->ir_num = ntohs(tcp_hdr(skb)->dest);
+	ireq->ir_mark = inet_request_mark(sk, skb);
+}
+
+void mptcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb)
+{
+	struct sock *msk = mptcp_subflow_ctx(sk)->conn;
+	struct tcp_sock *tp = tcp_sk(sk);
+
+	if (TCP_SKB_CB(skb)->end_seq == tp->rcv_nxt)
+		return;
+
+	skb = skb_clone(skb, GFP_ATOMIC);
+	if (!skb)
+		return;
+
+	skb_dst_drop(skb);
+
+	tp->segs_in = 0;
+	tcp_segs_in(tp, skb);
+	__skb_pull(skb, tcp_hdrlen(skb));
+	sk_forced_mem_schedule(sk, skb->truesize);
+	skb_set_owner_r(skb, sk);
+
+	TCP_SKB_CB(skb)->seq++;
+	TCP_SKB_CB(skb)->tcp_flags &= ~TCPHDR_SYN;
+
+	tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+
+	__skb_queue_tail(&msk->sk_receive_queue, skb);
+
+	tp->syn_data_acked = 1;
+
+	tp->bytes_received = skb->len;
+
+	if (TCP_SKB_CB(skb)->tcp_flags & TCPHDR_FIN)
+		tcp_fin(sk);
+}
+
+struct sock *mptcp_fastopen_create_child(struct sock *sk,
+					 struct sk_buff *skb,
+					 struct request_sock *req)
+{
+	struct request_sock_queue *r_sock_queue = &inet_csk(sk)->icsk_accept_queue;
+	struct tcp_sock *tp;
+	struct sock *child_sock;
+	bool own_req;
+
+	child_sock = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL,
+							 NULL, &own_req);
+	if (!child_sock)
+		return NULL;
+
+	spin_lock(&r_sock_queue->fastopenq.lock);
+	r_sock_queue->fastopenq.qlen++;
+	spin_unlock(&r_sock_queue->fastopenq.lock);
+
+	tp = tcp_sk(child_sock);
+
+	rcu_assign_pointer(tp->fastopen_rsk, req);
+	tcp_rsk(req)->tfo_listener = true;
+
+	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);
+	tp->max_window = tp->snd_wnd;
+
+	inet_csk_reset_xmit_timer(child_sock, ICSK_TIME_RETRANS,
+				  TCP_TIMEOUT_INIT, TCP_RTO_MAX);
+
+	refcount_set(&req->rsk_refcnt, 2);
+
+	tcp_init_transfer(child_sock, BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB, skb);
+
+
+	tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+	//tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;
+	//tp->copied_seq = 4;//3
+
+	mptcp_fastopen_add_skb(child_sock, skb);
+
+	tcp_rsk(req)->rcv_nxt = tp->rcv_nxt;
+	tp->rcv_wup = tp->rcv_nxt;
+
+	return child_sock;
+}
+
+bool mptcp_fastopen_queue_check(struct sock *sk)
+{
+	struct fastopen_queue *fo_queue;
+	struct request_sock *req_sock;
+
+	fo_queue = &inet_csk(sk)->icsk_accept_queue.fastopenq;
+	if (fo_queue->max_qlen == 0)
+		return false;
+
+	if (fo_queue->qlen >= fo_queue->max_qlen) {
+
+		spin_lock(&fo_queue->lock);
+		req_sock = fo_queue->rskq_rst_head;
+		if (!req_sock || time_after(req_sock->rsk_timer.expires, jiffies)) {
+			spin_unlock(&fo_queue->lock);
+			return false;
+		}
+		fo_queue->rskq_rst_head = req_sock->dl_next;
+		fo_queue->qlen--;
+		spin_unlock(&fo_queue->lock);
+		reqsk_put(req_sock);
+	}
+	return true;
+}
+
+bool mptcp_fastopen_cookie_gen_cipher(struct request_sock *req,
+				      struct sk_buff *syn,
+				      const siphash_key_t *key,
+				      struct tcp_fastopen_cookie *foc)
+{
+	if (req->rsk_ops->family == AF_INET) {
+		const struct iphdr *iph = ip_hdr(syn);
+
+		foc->val[0] = cpu_to_le64(siphash(&iph->saddr,
+					  sizeof(iph->saddr) +
+					  sizeof(iph->daddr),
+					  key));
+		foc->len = TCP_FASTOPEN_COOKIE_SIZE;
+		return true;
+	}
+
+	return false;
+}
+
+
+void mptcp_fastopen_cookie_gen(struct sock *sk,
+			       struct request_sock *req,
+			       struct sk_buff *syn,
+			       struct tcp_fastopen_cookie *foc)
+{
+	struct tcp_fastopen_context *ctx;
+
+	rcu_read_lock();
+	ctx = tcp_fastopen_get_ctx(sk);
+	if (ctx)
+		mptcp_fastopen_cookie_gen_cipher(req, syn, &ctx->key[0], foc);
+	rcu_read_unlock();
+}
+
+int mptcp_fastopen_cookie_gen_check(struct sock *sk,
+				    struct request_sock *req,
+				    struct sk_buff *syn,
+				    struct tcp_fastopen_cookie *orig,
+				    struct tcp_fastopen_cookie *valid_foc)
+{
+	struct tcp_fastopen_cookie mptcp_search_foc = { .len = -1 };
+	struct tcp_fastopen_cookie *mptcp_foc = valid_foc;
+	struct tcp_fastopen_context *mptcp_fo_ctx;
+	int i, ret = 0;
+
+	rcu_read_lock();
+	mptcp_fo_ctx = tcp_fastopen_get_ctx(sk);
+	if (!mptcp_fo_ctx)
+		goto out;
+	for (i = 0; i < tcp_fastopen_context_len(mptcp_fo_ctx); i++) {
+		mptcp_fastopen_cookie_gen_cipher(req, syn, &mptcp_fo_ctx->key[i], mptcp_foc);
+		if (tcp_fastopen_cookie_match(mptcp_foc, orig)) {
+			ret = i + 1;
+			goto out;
+		}
+		mptcp_foc = &mptcp_search_foc;
+	}
+out:
+	rcu_read_unlock();
+	return ret;
+}
+
+
+bool mptcp_fastopen_no_cookie(const struct sock *sk,
+			      const struct dst_entry *dst,
+			      int flag)
+{
+	return (sock_net(sk)->ipv4.sysctl_tcp_fastopen & flag) ||
+	       tcp_sk(sk)->fastopen_no_cookie ||
+	       (dst && dst_metric(dst, RTAX_FASTOPEN_NO_COOKIE));
+}
+
+struct sock *mptcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
+				struct request_sock *req,
+				struct tcp_fastopen_cookie *foc,
+				const struct dst_entry *dst)
+{
+	bool syn_data_status = TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1;
+	struct tcp_fastopen_cookie valid_mptcp_foc = { .len = -1 };
+	struct sock *child_sock;
+	int ret = 0;
+
+
+	if ((syn_data_status || foc->len >= 0) &&
+	      mptcp_fastopen_queue_check(sk)) {
+		foc->len = -1;
+		return NULL;
+	}
+
+	if (mptcp_fastopen_no_cookie(sk, dst, TFO_SERVER_COOKIE_NOT_REQD))
+		goto fastopen;
+
+	if (foc->len == 0) {
+		mptcp_fastopen_cookie_gen(sk, req, skb, &valid_mptcp_foc);
+	} else if (foc->len > 0) {
+		ret = mptcp_fastopen_cookie_gen_check(sk, req, skb, foc,
+						    &valid_mptcp_foc);
+		if (!ret) {
+			__asm__ ("NOP");
+		} else {
+fastopen:
+			child_sock = mptcp_fastopen_create_child(sk, skb, req);
+			if (child_sock) {
+				if (ret == 2) {
+					valid_mptcp_foc.exp = foc->exp;
+					*foc = valid_mptcp_foc;
+				} else {
+					foc->len = -1;
+				}
+				return child_sock;
+			}
+		}
+	}
+	valid_mptcp_foc.exp = foc->exp;
+	*foc = valid_mptcp_foc;
+	return NULL;
+}
+
+int mptcp_conn_request(struct request_sock_ops *rsk_ops,
+		       const struct tcp_request_sock_ops *af_ops,
+		       struct sock *sk, struct sk_buff *skb)
+{
+	struct tcp_fastopen_cookie mptcp_foc = { .len = -1 };
+	struct tcp_options_received tmp_opt_rcvd;
+	__u32 isn = TCP_SKB_CB(skb)->tcp_tw_isn;
+	struct tcp_sock *tp_sock = tcp_sk(sk);
+	struct sock *mptcp_fo_sk = NULL;
+	struct net *net = sock_net(sk);
+	struct request_sock *req_sock;
+	bool want_cookie = false;
+	struct dst_entry *dst;
+	struct flowi fl;
+
+	if (sk_acceptq_is_full(sk)) {
+		goto drop;
+	}
+
+	req_sock = inet_reqsk_alloc(rsk_ops, sk, !want_cookie);
+	if (!req_sock)
+		goto drop;
+
+	req_sock->syncookie = want_cookie;
+	tcp_rsk(req_sock)->af_specific = af_ops;
+	tcp_rsk(req_sock)->ts_off = 0;
+	tcp_rsk(req_sock)->is_mptcp = 1;
+
+	tcp_clear_options(&tmp_opt_rcvd);
+	tmp_opt_rcvd.mss_clamp = af_ops->mss_clamp;
+	tmp_opt_rcvd.user_mss  = tp_sock->rx_opt.user_mss;
+	tcp_parse_options(sock_net(sk), skb, &tmp_opt_rcvd, 0,
+			  want_cookie ? NULL : &mptcp_foc);
+
+	if (want_cookie && !tmp_opt_rcvd.saw_tstamp)
+		tcp_clear_options(&tmp_opt_rcvd);
+
+	if (IS_ENABLED(CONFIG_SMC) && want_cookie)
+		tmp_opt_rcvd.smc_ok = 0;
+
+	tmp_opt_rcvd.tstamp_ok = tmp_opt_rcvd.saw_tstamp;
+	mptcp_openreq_init(req_sock, &tmp_opt_rcvd, skb, sk);
+	inet_rsk(req_sock)->no_srccheck = inet_sk(sk)->transparent;
+
+	inet_rsk(req_sock)->ir_iif = inet_request_bound_dev_if(sk, skb);
+
+	dst = af_ops->route_req(sk, skb, &fl, req_sock);
+	if (!dst)
+		goto drop_and_free;
+
+	if (tmp_opt_rcvd.tstamp_ok)
+		tcp_rsk(req_sock)->ts_off = af_ops->init_ts_off(net, skb);
+
+	if (!want_cookie && !isn) {
+		if (!net->ipv4.sysctl_tcp_syncookies &&
+		    (net->ipv4.sysctl_max_syn_backlog - inet_csk_reqsk_queue_len(sk) <
+		     (net->ipv4.sysctl_max_syn_backlog >> 2)) &&
+		    !tcp_peer_is_proven(req_sock, dst)) {
+			goto drop_and_release;
+		}
+
+		isn = af_ops->init_seq(skb);
+	}
+
+	mptcp_ecn_create_request(req_sock, skb, sk, dst);
+
+	if (want_cookie) {
+		isn = cookie_init_sequence(af_ops, sk, skb, &req_sock->mss);
+		if (!tmp_opt_rcvd.tstamp_ok)
+			inet_rsk(req_sock)->ecn_ok = 0;
+	}
+
+	tcp_rsk(req_sock)->snt_isn = isn;
+	tcp_rsk(req_sock)->txhash = net_tx_rndhash();
+	tcp_rsk(req_sock)->syn_tos = TCP_SKB_CB(skb)->ip_dsfield;
+
+	tcp_openreq_init_rwin(req_sock, sk, dst);
+	sk_rx_queue_set(req_to_sk(req_sock), skb);
+	if (!want_cookie) {
+		mptcp_reqsk_record_syn(sk, req_sock, skb);
+		mptcp_fo_sk = mptcp_try_fastopen(sk, skb, req_sock, &mptcp_foc, dst);
+	}
+	if (mptcp_fo_sk) {
+		af_ops->send_synack(mptcp_fo_sk, dst, &fl, req_sock,
+				    &mptcp_foc, TCP_SYNACK_FASTOPEN, skb);
+		if (!inet_csk_reqsk_queue_add(sk, req_sock, mptcp_fo_sk)) {
+			reqsk_fastopen_remove(mptcp_fo_sk, req_sock, false);
+			bh_unlock_sock(mptcp_fo_sk);
+			sock_put(mptcp_fo_sk);
+			goto drop_and_free;
+		}
+		sk->sk_data_ready(sk);
+		bh_unlock_sock(mptcp_fo_sk);
+		sock_put(mptcp_fo_sk);
+
+
+	} else {
+		tcp_rsk(req_sock)->tfo_listener = false;
+		if (!want_cookie) {
+			req_sock->timeout = tcp_timeout_init((struct sock *)req_sock);
+			inet_csk_reqsk_queue_hash_add(sk, req_sock, req_sock->timeout);
+		}
+		af_ops->send_synack(sk, dst, &fl, req_sock, &mptcp_foc,
+				    !want_cookie ? TCP_SYNACK_NORMAL :
+						   TCP_SYNACK_COOKIE,
+				    skb);
+		if (want_cookie) {
+			reqsk_free(req_sock);
+			return 0;
+		}
+	}
+	reqsk_put(req_sock);
+	return 0;
+
+drop_and_release:
+	dst_release(dst);
+drop_and_free:
+	__reqsk_free(req_sock);
+drop:
+	tcp_listendrop(sk);
+	return 0;
+}
diff --git a/net/mptcp/mptcp_fastopen.h b/net/mptcp/mptcp_fastopen.h
new file mode 100644
index 000000000000..c050195c60a7
--- /dev/null
+++ b/net/mptcp/mptcp_fastopen.h
@@ -0,0 +1,67 @@
+/* SPDX-License-Identifier: GPL-2.0
+ * MPTCP Fast Open Mechanism. Copyright (c) 2021-2022, Dmytro SHYTYI.
+ */
+
+#ifndef __MPTCP_FASTOPEN_H
+#define __MPTCP_FASTOPEN_H
+
+#include <uapi/linux/mptcp.h>
+#include <net/mptcp.h>
+#include <net/sock.h>
+#include "protocol.h"
+
+int mptcp_sendmsg_fastopen(struct sock *sk, struct msghdr *msg,
+			   size_t len, struct mptcp_sock *msk,
+			   size_t *copied);
+
+void mptcp_reqsk_record_syn(const struct sock *sk,
+			    struct request_sock *req,
+			    const struct sk_buff *skb);
+
+void mptcp_ecn_create_request(struct request_sock *req,
+			      const struct sk_buff *skb,
+			      const struct sock *listen_sk,
+			      const struct dst_entry *dst);
+
+void mptcp_openreq_init(struct request_sock *req,
+			const struct tcp_options_received *rx_opt,
+			struct sk_buff *skb, const struct sock *sk);
+
+void mptcp_fastopen_add_skb(struct sock *sk, struct sk_buff *skb);
+
+struct sock *mptcp_fastopen_create_child(struct sock *sk,
+					 struct sk_buff *skb,
+					 struct request_sock *req);
+
+bool mptcp_fastopen_queue_check(struct sock *sk);
+
+bool mptcp_fastopen_cookie_gen_cipher(struct request_sock *req,
+				      struct sk_buff *syn,
+				      const siphash_key_t *key,
+				      struct tcp_fastopen_cookie *foc);
+
+void mptcp_fastopen_cookie_gen(struct sock *sk,
+			       struct request_sock *req,
+			       struct sk_buff *syn,
+			       struct tcp_fastopen_cookie *foc);
+
+int mptcp_fastopen_cookie_gen_check(struct sock *sk,
+				    struct request_sock *req,
+				    struct sk_buff *syn,
+				    struct tcp_fastopen_cookie *orig,
+				    struct tcp_fastopen_cookie *valid_foc);
+
+bool mptcp_fastopen_no_cookie(const struct sock *sk,
+			      const struct dst_entry *dst,
+			      int flag);
+
+struct sock *mptcp_try_fastopen(struct sock *sk, struct sk_buff *skb,
+				struct request_sock *req,
+				struct tcp_fastopen_cookie *foc,
+				const struct dst_entry *dst);
+
+int mptcp_conn_request(struct request_sock_ops *rsk_ops,
+		       const struct tcp_request_sock_ops *af_ops,
+		       struct sock *sk, struct sk_buff *skb);
+
+#endif /* __MPTCP_FASTOPEN_H */
diff --git a/net/mptcp/options.c b/net/mptcp/options.c
index be3b918a6d15..1ce965ee71d2 100644
--- a/net/mptcp/options.c
+++ b/net/mptcp/options.c
@@ -887,16 +887,19 @@ bool mptcp_established_options(struct sock *sk, struct sk_buff *skb,
 }
 
 bool mptcp_synack_options(const struct request_sock *req, unsigned int *size,
-			  struct mptcp_out_options *opts)
+			  struct mptcp_out_options *opts, u16 *tcp_options)
 {
 	struct mptcp_subflow_request_sock *subflow_req = mptcp_subflow_rsk(req);
+	struct inet_request_sock *ireq = inet_rsk(req);
+#define OPTION_TS               BIT(1)
+	*tcp_options ^= OPTION_TS;
 
 	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;
+		*size = TCPOLEN_MPTCP_MPC_SYNACK  - TCPOLEN_TSTAMP_ALIGNED + TCPOLEN_SACKPERM_ALIGNED;
 		pr_debug("subflow_req=%p, local_key=%llu",
 			 subflow_req, subflow_req->local_key);
 		return true;
diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
index d6aef4b13b8a..64a2635405c4 100644
--- a/net/mptcp/protocol.c
+++ b/net/mptcp/protocol.c
@@ -25,6 +25,7 @@
 #include <asm/ioctls.h>
 #include "protocol.h"
 #include "mib.h"
+#include "mptcp_fastopen.h"
 
 #define CREATE_TRACE_POINTS
 #include <trace/events/mptcp.h>
@@ -1690,9 +1691,9 @@ static int mptcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t len)
 	int ret = 0;
 	long timeo;
 
-	/* we don't support FASTOPEN yet */
+	/* we don't fully support FASTOPEN yet */
 	if (msg->msg_flags & MSG_FASTOPEN)
-		return -EOPNOTSUPP;
+		mptcp_sendmsg_fastopen(sk, msg, len, msk, &copied);
 
 	/* silently ignore everything else */
 	msg->msg_flags &= MSG_MORE | MSG_DONTWAIT | MSG_NOSIGNAL;
@@ -2681,6 +2682,7 @@ void mptcp_subflow_shutdown(struct sock *sk, struct sock *ssk, int how)
 	case TCP_SYN_SENT:
 		tcp_disconnect(ssk, O_NONBLOCK);
 		break;
+	case TCP_ESTABLISHED:
 	default:
 		if (__mptcp_check_fallback(mptcp_sk(sk))) {
 			pr_debug("Fallback");
@@ -3476,7 +3478,7 @@ static void mptcp_subflow_early_fallback(struct mptcp_sock *msk,
 	__mptcp_do_fallback(msk);
 }
 
-static int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
+int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
 				int addr_len, int flags)
 {
 	struct mptcp_sock *msk = mptcp_sk(sock->sk);
diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
index 8739794166d8..6b8784a35244 100644
--- a/net/mptcp/protocol.h
+++ b/net/mptcp/protocol.h
@@ -891,6 +891,9 @@ unsigned int mptcp_pm_get_add_addr_accept_max(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_subflows_max(const struct mptcp_sock *msk);
 unsigned int mptcp_pm_get_local_addr_max(const struct mptcp_sock *msk);
 
+int mptcp_stream_connect(struct socket *sock, struct sockaddr *uaddr,
+			 int addr_len, int flags);
+
 /* called under PM lock */
 static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
 {
diff --git a/net/mptcp/sockopt.c b/net/mptcp/sockopt.c
index 423d3826ca1e..e1ae1ef224cf 100644
--- a/net/mptcp/sockopt.c
+++ b/net/mptcp/sockopt.c
@@ -560,6 +560,8 @@ static bool mptcp_supported_sockopt(int level, int optname)
 		case TCP_TX_DELAY:
 		case TCP_INQ:
 			return true;
+		case TCP_FASTOPEN:
+			return true;
 		}
 
 		/* TCP_MD5SIG, TCP_MD5SIG_EXT are not supported, MD5 is not compatible with MPTCP */
@@ -768,6 +770,43 @@ static int mptcp_setsockopt_sol_tcp_defer(struct mptcp_sock *msk, sockptr_t optv
 	return tcp_setsockopt(listener->sk, SOL_TCP, TCP_DEFER_ACCEPT, optval, optlen);
 }
 
+static int mptcp_setsockopt_sol_tcp_fastopen(struct mptcp_sock *msk, sockptr_t optval,
+					     unsigned int optlen)
+{
+	struct mptcp_subflow_context *subflow;
+	struct sock *sk = (struct sock *)msk;
+	struct net *net = sock_net(sk);
+	int val;
+	int ret;
+
+	ret = 0;
+
+	if (copy_from_sockptr(&val, optval, sizeof(val)))
+		return -EFAULT;
+
+	lock_sock(sk);
+
+	mptcp_for_each_subflow(msk, subflow) {
+		struct sock *ssk = mptcp_subflow_tcp_sock(subflow);
+
+		lock_sock(ssk);
+
+		if (val >= 0 && ((1 << sk->sk_state) & (TCPF_CLOSE |
+		    TCPF_LISTEN))) {
+			tcp_fastopen_init_key_once(net);
+			fastopen_queue_tune(sk, val);
+		} else {
+			ret = -EINVAL;
+		}
+
+		release_sock(ssk);
+	}
+
+	release_sock(sk);
+
+	return ret;
+}
+
 static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 				    sockptr_t optval, unsigned int optlen)
 {
@@ -796,6 +835,8 @@ static int mptcp_setsockopt_sol_tcp(struct mptcp_sock *msk, int optname,
 		return mptcp_setsockopt_sol_tcp_nodelay(msk, optval, optlen);
 	case TCP_DEFER_ACCEPT:
 		return mptcp_setsockopt_sol_tcp_defer(msk, optval, optlen);
+	case TCP_FASTOPEN:
+		return mptcp_setsockopt_sol_tcp_fastopen(msk, optval, optlen);
 	}
 
 	return -EOPNOTSUPP;
diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c
index 8841e8cd9ad8..9fa71b67fd5a 100644
--- a/net/mptcp/subflow.c
+++ b/net/mptcp/subflow.c
@@ -22,6 +22,7 @@
 #endif
 #include <net/mptcp.h>
 #include <uapi/linux/mptcp.h>
+#include "mptcp_fastopen.h"
 #include "protocol.h"
 #include "mib.h"
 
@@ -542,9 +543,9 @@ static int subflow_v4_conn_request(struct sock *sk, struct sk_buff *skb)
 	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))
 		goto drop;
 
-	return tcp_conn_request(&mptcp_subflow_request_sock_ops,
-				&subflow_request_sock_ipv4_ops,
-				sk, skb);
+	return mptcp_conn_request(&mptcp_subflow_request_sock_ops,
+					  &subflow_request_sock_ipv4_ops,
+					  sk, skb);
 drop:
 	tcp_listendrop(sk);
 	return 0;
-- 
2.25.1