tcp: tcp_v4_err() should be more careful

Eric Dumazet · davem330 · commit 2c4cc9712364 · 2019-02-17T15:46:58.000-08:00
ICMP handlers are not very often stressed, we should
make them more resilient to bugs that might surface in
the future.

If there is no packet in retransmit queue, we should
avoid a NULL deref.

Signed-off-by: Eric Dumazet &lt;edumazet@google.com&gt;
Reported-by: soukjin bae &lt;soukjin.bae@samsung.com&gt;
Acked-by: Neal Cardwell &lt;ncardwell@google.com&gt;
Acked-by: Soheil Hassas Yeganeh &lt;soheil@google.com&gt;
Signed-off-by: David S. Miller &lt;davem@davemloft.net&gt;
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
@@ -536,12 +536,15 @@ int tcp_v4_err(struct sk_buff *icmp_skb, u32 info)
 		if (sock_owned_by_user(sk))
 			break;
 
+		skb = tcp_rtx_queue_head(sk);
+		if (WARN_ON_ONCE(!skb))
+			break;
+
 		icsk->icsk_backoff--;
 		icsk->icsk_rto = tp->srtt_us ? __tcp_set_rto(tp) :
 					       TCP_TIMEOUT_INIT;
 		icsk->icsk_rto = inet_csk_rto_backoff(icsk, TCP_RTO_MAX);
 
-		skb = tcp_rtx_queue_head(sk);
 
 		tcp_mstamp_refresh(tp);
 		delta_us = (u32)(tp->tcp_mstamp - tcp_skb_timestamp_us(skb));
