netdev - [PATCH net-next 4/8] tcp: properly track retry time on passive Fast Open

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Date:   Wed, 16 Jan 2019 15:05:31 -0800
From:   Yuchung Cheng <ycheng@...gle.com>
To:     davem@...emloft.net, edumazet@...gle.com
Cc:     netdev@...r.kernel.org, ncardwell@...gle.com, soheil@...gle.com,
        Yuchung Cheng <ycheng@...gle.com>
Subject: [PATCH net-next 4/8] tcp: properly track retry time on passive Fast Open

This patch addresses a corner issue on timeout behavior of a
passive Fast Open socket.  A passive Fast Open server may write
and close the socket when it is re-trying SYN-ACK to complete
the handshake. After the handshake is completely, the server does
not properly stamp the recovery start time (tp->retrans_stamp is
0), and the socket may abort immediately on the very first FIN
timeout, instead of retying until it passes the system or user
specified limit.

Signed-off-by: Yuchung Cheng <ycheng@...gle.com>
Signed-off-by: Eric Dumazet <edumazet@...gle.com>
Reviewed-by: Neal Cardwell <ncardwell@...gle.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@...gle.com>
---
 net/ipv4/tcp_timer.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 1e61f0bd6e24..074de38bafbd 100644
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -378,6 +378,7 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
 	struct inet_connection_sock *icsk = inet_csk(sk);
 	int max_retries = icsk->icsk_syn_retries ? :
 	    sock_net(sk)->ipv4.sysctl_tcp_synack_retries + 1; /* add one more retry for fastopen */
+	struct tcp_sock *tp = tcp_sk(sk);
 	struct request_sock *req;
 
 	req = tcp_sk(sk)->fastopen_rsk;
@@ -395,6 +396,8 @@ static void tcp_fastopen_synack_timer(struct sock *sk)
 	inet_rtx_syn_ack(sk, req);
 	req->num_timeout++;
 	icsk->icsk_retransmits++;
+	if (!tp->retrans_stamp)
+		tp->retrans_stamp = tcp_time_stamp(tp);
 	inet_csk_reset_xmit_timer(sk, ICSK_TIME_RETRANS,
 			  TCP_TIMEOUT_INIT << req->num_timeout, TCP_RTO_MAX);
 }
-- 
2.20.1.97.g81188d93c3-goog