tcp: exit if nothing to retransmit on RTO timeout

Previously TCP only warns if its RTO timer fires and the
retransmission queue is empty, but it'll cause null pointer
reference later on. It's better to avoid such catastrophic failure
and simply exit with a warning.

Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Neal Cardwell <ncardwell@google.com>
Reviewed-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 71a29e9..e7d09e3 100644 (file)
--- a/net/ipv4/tcp_timer.c
+++ b/net/ipv4/tcp_timer.c
@@ -443,10 +443,8 @@ void tcp_retransmit_timer(struct sock *sk)
                 */
                return;
        }
-       if (!tp->packets_out)
-               goto out;
-
-       WARN_ON(tcp_rtx_queue_empty(sk));
+       if (!tp->packets_out || WARN_ON_ONCE(tcp_rtx_queue_empty(sk)))
+               return;
 
        tp->tlp_high_seq = 0;