From 1a4eda9788a542347dfc2b1684636bcbe2ee3f79 Mon Sep 17 00:00:00 2001
From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Fri, 2 Dec 2011 23:41:42 +0000
Subject: [PATCH] tcp: drop SYN+FIN messages

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@visp.net.lb>
Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 7410a8c28e14..6e33b79cb688 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5761,6 +5761,8 @@ 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;
 
-- 
2.39.5