Commit 016818d0 authored by Neal Cardwell's avatar Neal Cardwell Committed by David S. Miller
Browse files

tcp: TCP Fast Open Server - take SYNACK RTT after completing 3WHS 



When taking SYNACK RTT samples for servers using TCP Fast Open, fix
the code to ensure that we only call tcp_valid_rtt_meas() after we
receive the ACK that completes the 3-way handshake.

Previously we were always taking an RTT sample in
tcp_v4_syn_recv_sock(). However, for TCP Fast Open connections
tcp_v4_conn_req_fastopen() calls tcp_v4_syn_recv_sock() at the time we
receive the SYN. So for TFO we must wait until tcp_rcv_state_process()
to take the RTT sample.

To fix this, we wait until after TFO calls tcp_v4_syn_recv_sock()
before we set the snt_synack timestamp, since tcp_synack_rtt_meas()
already ensures that we only take a SYNACK RTT sample if snt_synack is
non-zero. To be careful, we only take a snt_synack timestamp when
a SYNACK transmit or retransmit succeeds.

Signed-off-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 623df484

include/net/tcp.h

+1 −0
Original line number Diff line number Diff line
@@ -1125,6 +1125,7 @@ static inline void tcp_openreq_init(struct request_sock *req, 
	req->cookie_ts = 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;

	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;

net/ipv4/tcp_input.c

+1 −0
Original line number Diff line number Diff line
@@ -5983,6 +5983,7 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb, 
				 * need req so release it.

				 */

				if (req) {

					tcp_synack_rtt_meas(sk, req);

					reqsk_fastopen_remove(sk, req, false);

				} else {

					/* Make sure socket is routed, for

net/ipv4/tcp_ipv4.c

+9 −3
Original line number Diff line number Diff line
@@ -868,6 +868,8 @@ static int tcp_v4_send_synack(struct sock *sk, struct dst_entry *dst, 
					    ireq->rmt_addr,

					    ireq->opt);

		err = net_xmit_eval(err);

		if (!tcp_rsk(req)->snt_synack && !err)

			tcp_rsk(req)->snt_synack = tcp_time_stamp;

	}



	return err;
@@ -1382,6 +1384,7 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk, 
	struct request_sock_queue *queue = &inet_csk(sk)->icsk_accept_queue;

	const struct inet_request_sock *ireq = inet_rsk(req);

	struct sock *child;

	int err;



	req->retrans = 0;

	req->sk = NULL;
@@ -1393,8 +1396,11 @@ static int tcp_v4_conn_req_fastopen(struct sock *sk, 
		kfree_skb(skb_synack);

		return -1;

	}

	ip_build_and_send_pkt(skb_synack, sk, ireq->loc_addr,

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

				    ireq->rmt_addr, ireq->opt);

	err = net_xmit_eval(err);

	if (!err)

		tcp_rsk(req)->snt_synack = tcp_time_stamp;

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



	spin_lock(&queue->fastopenq->lock);
@@ -1612,7 +1618,6 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb) 
		isn = tcp_v4_init_sequence(skb);

	}

	tcp_rsk(req)->snt_isn = isn;

	tcp_rsk(req)->snt_synack = tcp_time_stamp;



	if (dst == NULL) {

		dst = inet_csk_route_req(sk, &fl4, req);
@@ -1650,6 +1655,7 @@ int tcp_v4_conn_request(struct sock *sk, struct sk_buff *skb) 
		if (err || want_cookie)

			goto drop_and_free;



		tcp_rsk(req)->snt_synack = tcp_time_stamp;

		tcp_rsk(req)->listener = NULL;

		/* Add the request_sock to the SYN table */

		inet_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);

net/ipv6/tcp_ipv6.c

+1 −1
Original line number Diff line number Diff line
@@ -1169,7 +1169,6 @@ static int tcp_v6_conn_request(struct sock *sk, struct sk_buff *skb) 
	}

have_isn:

	tcp_rsk(req)->snt_isn = isn;

	tcp_rsk(req)->snt_synack = tcp_time_stamp;



	if (security_inet_conn_request(sk, skb, req))

		goto drop_and_release;
@@ -1180,6 +1179,7 @@ have_isn: 
	    want_cookie)

		goto drop_and_free;



	tcp_rsk(req)->snt_synack = tcp_time_stamp;

	tcp_rsk(req)->listener = NULL;

	inet6_csk_reqsk_queue_hash_add(sk, req, TCP_TIMEOUT_INIT);

	return 0;

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