[PATCH 4.3 30/71] tcp: initialize tp->copied_seq in case of cross SYN connection

From: Greg Kroah-Hartman
Date: Sat Dec 12 2015 - 15:40:45 EST

4.3-stable review patch. If anyone has any objections, please let me know.


From: Eric Dumazet <edumazet@xxxxxxxxxx>

[ Upstream commit 142a2e7ece8d8ac0e818eb2c91f99ca894730e2a ]

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@xxxxxxxxxx>
Reported-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Tested-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
net/ipv4/tcp_input.c | 1 +
1 file changed, 1 insertion(+)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5659,6 +5659,7 @@ 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

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