Commit a41e8a88 authored Sep 26, 2019 by Eric Dumazet Committed by David S. Miller Sep 27, 2019

tcp: better handle TCP_USER_TIMEOUT in SYN_SENT state



Yuchung Cheng and Marek Majkowski independently reported a weird
behavior of TCP_USER_TIMEOUT option when used at connect() time.

When the TCP_USER_TIMEOUT is reached, tcp_write_timeout()
believes the flow should live, and the following condition
in tcp_clamp_rto_to_user_timeout() programs one jiffie timers :

    remaining = icsk->icsk_user_timeout - elapsed;
    if (remaining <= 0)
        return 1; /* user timeout has passed; fire ASAP */

This silly situation ends when the max syn rtx count is reached.

This patch makes sure we honor both TCP_SYNCNT and TCP_USER_TIMEOUT,
avoiding these spurious SYN packets.

Fixes: b701a99e ("tcp: Add tcp_clamp_rto_to_user_timeout() helper to improve accuracy")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Yuchung Cheng <ycheng@google.com>
Reported-by: Marek Majkowski <marek@cloudflare.com>
Cc: Jon Maxwell <jmaxwell37@gmail.com>
Link: https://marc.info/?l=linux-netdev&m=156940118307949&w=2


Acked-by: Jon Maxwell <jmaxwell37@gmail.com>
Tested-by: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: Marek Majkowski <marek@cloudflare.com>
Acked-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

parent 174e2381

net/ipv4/tcp_timer.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -210,7 +210,7 @@ static int tcp_write_timeout(struct sock *sk)
		struct inet_connection_sock *icsk = inet_csk(sk);
		struct tcp_sock *tp = tcp_sk(sk);
		struct net *net = sock_net(sk);
		bool expired, do_reset;
		bool expired = false, do_reset;
		int retry_until;

		if ((1 << sk->sk_state) & (TCPF_SYN_SENT \| TCPF_SYN_RECV)) {
		@@ -242,9 +242,10 @@ static int tcp_write_timeout(struct sock *sk)
		if (tcp_out_of_resources(sk, do_reset))
		return 1;
		}
		}
		if (!expired)
		expired = retransmits_timed_out(sk, retry_until,
		icsk->icsk_user_timeout);
		}
		tcp_fastopen_active_detect_blackhole(sk, expired);

		if (BPF_SOCK_OPS_TEST_FLAG(tp, BPF_SOCK_OPS_RTO_CB_FLAG))

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