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>

1 files changed, 2 insertions, 4 deletions

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 71a29e9c0620..e7d09e3705b8 100644
--- 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;