commit fdf5af0daf8019cec2396cdef8fb042d80fe71fa
author Eric Dumazet <eric.dumazet@gmail.com> Fri Dec 02 23:41:42 2011 +0000
committer David S. Miller <davem@davemloft.net> Sun Dec 04 01:25:19 2011 -0500
tree 2423b611659756f2b6553b8d1aa2c117b248c884
parent 78a8a36fe0b2cee5a0a7360107815cbcad5b4003

tcp: drop SYN+FIN messages

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>

net/ipv4/tcp_input.c

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index 78dd38c..0cbb440 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5811,6 +5811,8 @@
 			goto discard;
 
 		if (th->syn) {
+			if (th->fin)
+				goto discard;
 			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
 				return 1;