tcp: initialize tp->copied_seq in case of cross SYN connection

Dmitry provided a syzkaller (http://github.com/google/syzkaller)
generated program that triggers the WARNING at
net/ipv4/tcp.c:1729 in tcp_recvmsg() :

WARN_ON(tp->copied_seq != tp->rcv_nxt &&
        !(flags & (MSG_PEEK | MSG_TRUNC)));

His program is specifically attempting a Cross SYN TCP exchange,
that we support (for the pleasure of hackers ?), but it looks we
lack proper tcp->copied_seq initialization.

Thanks again Dmitry for your report and testings.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reported-by: Dmitry Vyukov <dvyukov@google.com>
Tested-by: Dmitry Vyukov <dvyukov@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index a4a0b6b..2d656ee 100644 (file)
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5683,6 +5683,7 @@ discard:
                }
 
                tp->rcv_nxt = TCP_SKB_CB(skb)->seq + 1;
+               tp->copied_seq = tp->rcv_nxt;
                tp->rcv_wup = TCP_SKB_CB(skb)->seq + 1;
 
                /* RFC1323: The window in SYN & SYN/ACK segments is