tcp: tcp_v4_err() should be more careful

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 <edumazet@google.com>
Reported-by: soukjin bae <soukjin.bae@samsung.com>
Acked-by: Neal Cardwell <ncardwell@google.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 4 insertions, 1 deletions

diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index efc6fef692ff..ec3cea9d6828 100644
--- 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));