From: Yuchung Cheng <ycheng@google.com>
Date: Wed, 16 Jan 2019 23:05:28 +0000 (-0800)
Subject: tcp: exit if nothing to retransmit on RTO timeout
X-Git-Tag: v4.19.88~20
X-Git-Url: http://git.ipfire.org/gitweb.cgi?a=commitdiff_plain;h=d832269ac697067335952ba3a9c185027065f95c;p=thirdparty%2Fkernel%2Fstable.git

tcp: exit if nothing to retransmit on RTO timeout

commit 88f8598d0a302a08380eadefd09b9f5cb1c4c428 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
index 9d775b8df57d4..c719a41d2eba2 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;