[PATCH 4.19 015/142] tcp: fix NULL ref in tail loss probe

Greg Kroah-Hartman
2018-12-14T12:01:40Z

From: Yuchung Cheng <ycheng@google.com>

[ Upstream commit b2b7af861122a0c0f6260155c29a1b2e594cd5b5 ]

TCP loss probe timer may fire when the retranmission queue is empty but
has a non-zero tp->packets_out counter. tcp_send_loss_probe will call
tcp_rearm_rto which triggers NULL pointer reference by fetching the
retranmission queue head in its sub-routines.

Add a more detailed warning to help catch the root cause of the inflight
accounting inconsistency.

Reported-by: Rafael Tinoco <rafael.tinoco@linaro.org>
Signed-off-by: Yuchung Cheng <ycheng@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Neal Cardwell <ncardwell@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/ipv4/tcp_output.c | 11 +++++++----
1 file changed, 7 insertions(+), 4 deletions(-)

--- a/net/ipv4/tcp_output.c
+++ b/net/ipv4/tcp_output.c
@@ -2479,15 +2479,18 @@ void tcp_send_loss_probe(struct sock *sk
goto rearm_timer;
}
skb = skb_rb_last(&sk->tcp_rtx_queue);
+ if (unlikely(!skb)) {
+ WARN_ONCE(tp->packets_out,
+ "invalid inflight: %u state %u cwnd %u mss %d\n",
+ tp->packets_out, sk->sk_state, tp->snd_cwnd, mss);
+ inet_csk(sk)->icsk_pending = 0;
+ return;
+ }

/* At most one outstanding TLP retransmission. */
if (tp->tlp_high_seq)
goto rearm_timer;

- /* Retransmit last segment. */
- if (WARN_ON(!skb))
- goto rearm_timer;
-
if (skb_still_in_host_queue(sk, skb))
goto rearm_timer;