tcp: TCP Fast Open Server - main code path

{

	struct tcp_sock *tp = tcp_sk(sk);

	/* If the retrans timer is currently being used by Fast Open

	 * for SYN-ACK retrans purpose, stay put.

	 */

	if (tp->fastopen_rsk)

		return;

	if (!tp->packets_out) {

		inet_csk_clear_xmit_timer(sk, ICSK_TIME_RETRANS);

	} else {

		tcp_send_synack(sk);

#if 0

		/* Note, we could accept data and URG from this segment.

		 * There are no obstacles to make this.

		 * There are no obstacles to make this (except that we must

		 * either change tcp_recvmsg() to prevent it from returning data

		 * before 3WHS completes per RFC793, or employ TCP Fast Open).

		 *

		 * However, if we ignore data in ACKless segments sometimes,

		 * we have no reasons to accept it sometimes.

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct inet_connection_sock *icsk = inet_csk(sk);

	struct request_sock *req;

	int queued = 0;

	tp->rx_opt.saw_tstamp = 0;

		return 0;

	}

	if (!tcp_validate_incoming(sk, skb, th, 0))

	req = tp->fastopen_rsk;

	if (req != NULL) {

		BUG_ON(sk->sk_state != TCP_SYN_RECV &&

		    sk->sk_state != TCP_FIN_WAIT1);

		if (tcp_check_req(sk, skb, req, NULL, true) == NULL)

			goto discard;

	} else if (!tcp_validate_incoming(sk, skb, th, 0))

		return 0;

	/* step 5: check the ACK field */

		switch (sk->sk_state) {

		case TCP_SYN_RECV:

			if (acceptable) {

				/* Once we leave TCP_SYN_RECV, we no longer

				 * need req so release it.

				 */

				if (req) {

					reqsk_fastopen_remove(sk, req, false);

				} else {

					/* Make sure socket is routed, for

					 * correct metrics.

					 */

					icsk->icsk_af_ops->rebuild_header(sk);

					tcp_init_congestion_control(sk);

					tcp_mtup_init(sk);

					tcp_init_buffer_space(sk);

					tp->copied_seq = tp->rcv_nxt;

				}

				smp_mb();

				tcp_set_state(sk, TCP_ESTABLISHED);

				sk->sk_state_change(sk);

				if (tp->rx_opt.tstamp_ok)

					tp->advmss -= TCPOLEN_TSTAMP_ALIGNED;

				/* Make sure socket is routed, for

				 * correct metrics.

				if (req) {

					/* Re-arm the timer because data may

					 * have been sent out. This is similar

					 * to the regular data transmission case

					 * when new data has just been ack'ed.

					 *

					 * (TFO) - we could try to be more

					 * aggressive and retranmitting any data

					 * sooner based on when they were sent

					 * out.

					 */

				icsk->icsk_af_ops->rebuild_header(sk);

					tcp_rearm_rto(sk);

				} else

					tcp_init_metrics(sk);

				tcp_init_congestion_control(sk);

				/* Prevent spurious tcp_cwnd_restart() on

				 * first data packet.

				 */

				tp->lsndtime = tcp_time_stamp;

				tcp_mtup_init(sk);

				tcp_initialize_rcv_mss(sk);

				tcp_init_buffer_space(sk);

				tcp_fast_path_on(tp);

			} else {

				return 1;

			break;

		case TCP_FIN_WAIT1:

			/* If we enter the TCP_FIN_WAIT1 state and we are a

			 * Fast Open socket and this is the first acceptable

			 * ACK we have received, this would have acknowledged

			 * our SYNACK so stop the SYNACK timer.

			 */

			if (acceptable && req != NULL) {

				/* We no longer need the request sock. */

				reqsk_fastopen_remove(sk, req, false);

				tcp_rearm_rto(sk);

			}

			if (tp->snd_una == tp->write_seq) {

				struct dst_entry *dst;

	const int code = icmp_hdr(icmp_skb)->code;

	struct sock *sk;

	struct sk_buff *skb;

	struct request_sock *req;

	__u32 seq;

	__u32 remaining;

	int err;

	icsk = inet_csk(sk);

	tp = tcp_sk(sk);

	req = tp->fastopen_rsk;

	seq = ntohl(th->seq);

	if (sk->sk_state != TCP_LISTEN &&

	    !between(seq, tp->snd_una, tp->snd_nxt)) {

	    !between(seq, tp->snd_una, tp->snd_nxt) &&

	    (req == NULL || seq != tcp_rsk(req)->snt_isn)) {

		/* For a Fast Open socket, allow seq to be snt_isn. */

		NET_INC_STATS_BH(net, LINUX_MIB_OUTOFWINDOWICMPS);

		goto out;

	}

		    !icsk->icsk_backoff)

			break;

		/* XXX (TFO) - revisit the following logic for TFO */

		if (sock_owned_by_user(sk))

			break;

		goto out;

	}

	/* XXX (TFO) - if it's a TFO socket and has been accepted, rather

	 * than following the TCP_SYN_RECV case and closing the socket,

	 * we ignore the ICMP error and keep trying like a fully established

	 * socket. Is this the right thing to do?

	 */

	if (req && req->sk == NULL)

		goto out;

	switch (sk->sk_state) {

		struct request_sock *req, **prev;

	case TCP_LISTEN:

	case TCP_SYN_SENT:

	case TCP_SYN_RECV:  /* Cannot happen.

			       It can f.e. if SYNs crossed.

			       It can f.e. if SYNs crossed,

			       or Fast Open.

			     */

		if (!sock_owned_by_user(sk)) {

			sk->sk_err = err;

static void tcp_v4_reqsk_send_ack(struct sock *sk, struct sk_buff *skb,

				  struct request_sock *req)

{

	tcp_v4_send_ack(skb, tcp_rsk(req)->snt_isn + 1,

			tcp_rsk(req)->rcv_isn + 1, req->rcv_wnd,

	/* sk->sk_state == TCP_LISTEN -> for regular TCP_SYN_RECV

	 * sk->sk_state == TCP_SYN_RECV -> for Fast Open.

	 */

	tcp_v4_send_ack(skb, (sk->sk_state == TCP_LISTEN) ?

			tcp_rsk(req)->snt_isn + 1 : tcp_sk(sk)->snd_nxt,

			tcp_rsk(req)->rcv_nxt, req->rcv_wnd,

			req->ts_recent,

			0,

			tcp_md5_do_lookup(sk, (union tcp_md5_addr *)&ip_hdr(skb)->daddr,

};

#endif

static bool tcp_fastopen_check(struct sock *sk, struct sk_buff *skb,

			       struct request_sock *req,

			       struct tcp_fastopen_cookie *foc,

			       struct tcp_fastopen_cookie *valid_foc)

{

	bool skip_cookie = false;

	struct fastopen_queue *fastopenq;

	if (likely(!fastopen_cookie_present(foc))) {

		/* See include/net/tcp.h for the meaning of these knobs */

		if ((sysctl_tcp_fastopen & TFO_SERVER_ALWAYS) ||

		    ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_REQD) &&

		    (TCP_SKB_CB(skb)->end_seq != TCP_SKB_CB(skb)->seq + 1)))

			skip_cookie = true; /* no cookie to validate */

		else

			return false;

	}

	fastopenq = inet_csk(sk)->icsk_accept_queue.fastopenq;

	/* A FO option is present; bump the counter. */

	NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPFASTOPENPASSIVE);

	/* Make sure the listener has enabled fastopen, and we don't

	 * exceed the max # of pending TFO requests allowed before trying

	 * to validating the cookie in order to avoid burning CPU cycles

	 * unnecessarily.

	 *

	 * XXX (TFO) - The implication of checking the max_qlen before

	 * processing a cookie request is that clients can't differentiate

	 * between qlen overflow causing Fast Open to be disabled

	 * temporarily vs a server not supporting Fast Open at all.

	 */

	if ((sysctl_tcp_fastopen & TFO_SERVER_ENABLE) == 0 ||

	    fastopenq == NULL || fastopenq->max_qlen == 0)

		return false;

	if (fastopenq->qlen >= fastopenq->max_qlen) {

		struct request_sock *req1;

		spin_lock(&fastopenq->lock);

		req1 = fastopenq->rskq_rst_head;

		if ((req1 == NULL) || time_after(req1->expires, jiffies)) {

			spin_unlock(&fastopenq->lock);

			NET_INC_STATS_BH(sock_net(sk),

			    LINUX_MIB_TCPFASTOPENLISTENOVERFLOW);

			/* Avoid bumping LINUX_MIB_TCPFASTOPENPASSIVEFAIL*/

			foc->len = -1;

			return false;

		}

		fastopenq->rskq_rst_head = req1->dl_next;

		fastopenq->qlen--;

		spin_unlock(&fastopenq->lock);

		reqsk_free(req1);

	}

	if (skip_cookie) {

		tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

		return true;

	}

	if (foc->len == TCP_FASTOPEN_COOKIE_SIZE) {

		if ((sysctl_tcp_fastopen & TFO_SERVER_COOKIE_NOT_CHKED) == 0) {

			tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);

			if ((valid_foc->len != TCP_FASTOPEN_COOKIE_SIZE) ||

			    memcmp(&foc->val[0], &valid_foc->val[0],

			    TCP_FASTOPEN_COOKIE_SIZE) != 0)

				return false;

			valid_foc->len = -1;

		}

		/* Acknowledge the data received from the peer. */

		tcp_rsk(req)->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

		return true;

	} else if (foc->len == 0) { /* Client requesting a cookie */

		tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);

		NET_INC_STATS_BH(sock_net(sk),

		    LINUX_MIB_TCPFASTOPENCOOKIEREQD);

	} else {

		/* Client sent a cookie with wrong size. Treat it

		 * the same as invalid and return a valid one.

		 */

		tcp_fastopen_cookie_gen(ip_hdr(skb)->saddr, valid_foc);

	}

	return false;

}

static int tcp_v4_conn_req_fastopen(struct sock *sk,

				    struct sk_buff *skb,

				    struct sk_buff *skb_synack,

				    struct request_sock *req,

				    struct request_values *rvp)

{

	struct tcp_sock *tp = tcp_sk(sk);

	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

	const struct inet_request_sock *ireq = inet_rsk(req);

	struct sock *child;

	req->retrans = 0;

	req->sk = NULL;

	child = inet_csk(sk)->icsk_af_ops->syn_recv_sock(sk, skb, req, NULL);

	if (child == NULL) {

		NET_INC_STATS_BH(sock_net(sk),

				 LINUX_MIB_TCPFASTOPENPASSIVEFAIL);

		kfree_skb(skb_synack);

		return -1;

	}

	ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,

			ireq->rmt_addr, ireq->opt);

	/* XXX (TFO) - is it ok to ignore error and continue? */

	spin_lock(&queue->fastopenq->lock);

	queue->fastopenq->qlen++;

	spin_unlock(&queue->fastopenq->lock);

	/* Initialize the child socket. Have to fix some values to take

	 * into account the child is a Fast Open socket and is created

	 * only out of the bits carried in the SYN packet.

	 */

	tp = tcp_sk(child);

	tp->fastopen_rsk = req;

	/* Do a hold on the listner sk so that if the listener is being

	 * closed, the child that has been accepted can live on and still

	 * access listen_lock.

	 */

	sock_hold(sk);

	tcp_rsk(req)->listener = sk;

	/* RFC1323: The window in SYN & SYN/ACK segments is never

	 * scaled. So correct it appropriately.

	 */

	tp->snd_wnd = ntohs(tcp_hdr(skb)->window);

	/* Activate the retrans timer so that SYNACK can be retransmitted.

	 * The request socket is not added to the SYN table of the parent

	 * because it's been added to the accept queue directly.

	 */

	inet_csk_reset_xmit_timer(child, ICSK_TIME_RETRANS,

	    TCP_TIMEOUT_INIT, TCP_RTO_MAX);

	/* Add the child socket directly into the accept queue */

	inet_csk_reqsk_queue_add(sk, req, child);

	/* Now finish processing the fastopen child socket. */

	inet_csk(child)->icsk_af_ops->rebuild_header(child);

	tcp_init_congestion_control(child);

	tcp_mtup_init(child);

	tcp_init_buffer_space(child);

	tcp_init_metrics(child);

	/* Queue the data carried in the SYN packet. We need to first

	 * bump skb's refcnt because the caller will attempt to free it.

	 *

	 * XXX (TFO) - we honor a zero-payload TFO request for now.

	 * (Any reason not to?)

	 */

	if (TCP_SKB_CB(skb)->end_seq == TCP_SKB_CB(skb)->seq + 1) {

		/* Don't queue the skb if there is no payload in SYN.

		 * XXX (TFO) - How about SYN+FIN?

		 */

		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

	} else {

		skb = skb_get(skb);

		skb_dst_drop(skb);

		__skb_pull(skb, tcp_hdr(skb)->doff * 4);

		skb_set_owner_r(skb, child);

		__skb_queue_tail(&child->sk_receive_queue, skb);

		tp->rcv_nxt = TCP_SKB_CB(skb)->end_seq;

	}

	sk->sk_data_ready(sk, 0);

	bh_unlock_sock(child);

	sock_put(child);

	WARN_ON(req->sk == NULL);

	return 0;

}

int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb)

{

	struct tcp_extend_values tmp_ext;

	__be32 daddr = ip_hdr(skb)->daddr;

	__u32 isn = TCP_SKB_CB(skb)->when;

	bool want_cookie = false;

	struct flowi4 fl4;

	struct tcp_fastopen_cookie foc = { .len = -1 };

	struct tcp_fastopen_cookie valid_foc = { .len = -1 };

	struct sk_buff *skb_synack;

	int do_fastopen;

	/* Never answer to SYNs send to broadcast or multicast */

	if (skb_rtable(skb)->rt_flags & (RTCF_BROADCAST | RTCF_MULTICAST))

	tcp_clear_options(&tmp_opt);

	tmp_opt.mss_clamp = TCP_MSS_DEFAULT;

	tmp_opt.user_mss  = tp->rx_opt.user_mss;

	tcp_parse_options(skb, &tmp_opt, &hash_location, 0, NULL);

	tcp_parse_options(skb, &tmp_opt, &hash_location, 0,

	    want_cookie ? NULL : &foc);

	if (tmp_opt.cookie_plus > 0 &&

	    tmp_opt.saw_tstamp &&

		isn = cookie_v4_init_sequence(sk, skb, &req->mss);

		req->cookie_ts = tmp_opt.tstamp_ok;

	} else if (!isn) {

		struct flowi4 fl4;

		/* VJ's idea. We save last timestamp seen

		 * from the destination in peer table, when entering

		 * state TIME-WAIT, and check against it before

	tcp_rsk(req)->snt_isn = isn;

	tcp_rsk(req)->snt_synack = tcp_time_stamp;

	if (tcp_v4_send_synack(sk, dst, req,

	if (dst == NULL) {

		dst = inet_csk_route_req(sk, &fl4, req);

		if (dst == NULL)

			goto drop_and_free;

	}

	do_fastopen = tcp_fastopen_check(sk, skb, req, &foc, &valid_foc);

	/* We don't call tcp_v4_send_synack() directly because we need

	 * to make sure a child socket can be created successfully before

	 * sending back synack!

	 *

	 * XXX (TFO) - Ideally one would simply call tcp_v4_send_synack()

	 * (or better yet, call tcp_send_synack() in the child context

	 * directly, but will have to fix bunch of other code first)

	 * after syn_recv_sock() except one will need to first fix the

	 * latter to remove its dependency on the current implementation

	 * of tcp_v4_send_synack()->tcp_select_initial_window().

	 */

	skb_synack = tcp_make_synack(sk, dst, req,

	    (struct request_values *)&tmp_ext,

			       skb_get_queue_mapping(skb),

			       want_cookie) ||

	    want_cookie)

	    fastopen_cookie_present(&valid_foc) ? &valid_foc : NULL);

	if (skb_synack) {

		__tcp_v4_send_check(skb_synack, ireq->loc_addr, ireq->rmt_addr);

		skb_set_queue_mapping(skb_synack, skb_get_queue_mapping(skb));

	} else

		goto drop_and_free;

	if (likely(!do_fastopen)) {

		int err;

		err = ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,

		     ireq->rmt_addr, ireq->opt);

		err = net_xmit_eval(err);

		if (err || want_cookie)

			goto drop_and_free;

		tcp_rsk(req)->listener = NULL;

		/* Add the request_sock to the SYN table */

		inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);

		if (fastopen_cookie_present(&foc) && foc.len != 0)

			NET_INC_STATS_BH(sock_net(sk),

			    LINUX_MIB_TCPFASTOPENPASSIVEFAIL);

	} else if (tcp_v4_conn_req_fastopen(sk, skb, skb_synack, req,

	    (struct request_values *)&tmp_ext))

		goto drop_and_free;

	return 0;

drop_and_release:

			 tcp_cookie_values_release);

		tp->cookie_values = NULL;

	}

	BUG_ON(tp->fastopen_rsk != NULL);

	/* If socket is aborted during connect operation */

	tcp_free_fastopen_req(tp);

	const struct tcp_sock *tp = tcp_sk(sk);

	const struct inet_connection_sock *icsk = inet_csk(sk);

	const struct inet_sock *inet = inet_sk(sk);

	struct fastopen_queue *fastopenq = icsk->icsk_accept_queue.fastopenq;

	__be32 dest = inet->inet_daddr;

	__be32 src = inet->inet_rcv_saddr;

	__u16 destp = ntohs(inet->inet_dport);

		jiffies_to_clock_t(icsk->icsk_ack.ato),

		(icsk->icsk_ack.quick << 1) | icsk->icsk_ack.pingpong,

		tp->snd_cwnd,

		tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh,

		sk->sk_state == TCP_LISTEN ?

		    (fastopenq ? fastopenq->max_qlen : 0) :

		    (tcp_in_initial_slowstart(tp) ? -1 : tp->snd_ssthresh),

		len);

}