[v2.6.34-stable 062/213] tcp: drop SYN+FIN messages

[Paul Gortmaker]

From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

                   -------------------
    This is a commit scheduled for the next v2.6.34 longterm release.
    http://git.kernel.org/?p=linux/kernel/git/paulg/longterm-queue-2.6.34.git
    If you see a problem with using this for longterm, please comment.
                   -------------------

commit fdf5af0daf8019cec2396cdef8fb042d80fe71fa upstream.

Denys Fedoryshchenko reported that SYN+FIN attacks were bringing his
linux machines to their limits.

Dont call conn_request() if the TCP flags includes SYN flag

Reported-by: Denys Fedoryshchenko <denys@xxxxxxxxxxx>
Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx>
Signed-off-by: David S. Miller <davem@xxxxxxxxxxxxx>
Signed-off-by: Paul Gortmaker <paul.gortmaker@xxxxxxxxxxxxx>
---
 net/ipv4/tcp_input.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index df5de7dd22d2..20af12ae55a7 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5737,6 +5737,8 @@ int tcp_rcv_state_process(struct sock *sk, struct sk_buff *skb,
 			goto discard;
 
 		if (th->syn) {
+			if (th->fin)
+				goto discard;
 			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
 				return 1;
 
-- 
1.8.5.2

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