tcp: adjust rto_base in retransmits_timed_out()

BugLink: https://bugs.launchpad.net/bugs/1848047
[ Upstream commit 3256a2d6ab1f71f9a1bd2d7f6f18eb8108c48d17 ]

The cited commit exposed an old retransmits_timed_out() bug
which assumed it could call tcp_model_timeout() with
TCP_RTO_MIN as rto_base for all states.

But flows in SYN_SENT or SYN_RECV state uses a different
RTO base (1 sec instead of 200 ms, unless BPF choses
another value)

This caused a reduction of SYN retransmits from 6 to 4 with
the default /proc/sys/net/ipv4/tcp_syn_retries value.

Fixes: a41e8a88b06e ("tcp: better handle TCP_USER_TIMEOUT in SYN_SENT state")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Marek Majkowski <marek@cloudflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 3e8b38c73d8ce253f3b2271d7bff16fed608a379..483323332d745ffe31a9a3c7c14faef8bef60115 100644 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -198,8 +198,13 @@ static bool retransmits_timed_out(struct sock *sk,
                return false;
 
        start_ts = tcp_sk(sk)->retrans_stamp;
-       if (likely(timeout == 0))
-               timeout = tcp_model_timeout(sk, boundary, TCP_RTO_MIN);
+       if (likely(timeout == 0)) {
+               unsigned int rto_base = TCP_RTO_MIN;
+
+               if ((1 << sk->sk_state) & (TCPF_SYN_SENT | TCPF_SYN_RECV))
+                       rto_base = tcp_timeout_init(sk);
+               timeout = tcp_model_timeout(sk, boundary, rto_base);
+       }
 
        return (s32)(tcp_time_stamp(tcp_sk(sk)) - start_ts - timeout) >= 0;
 }