[ 11/23] tcp: drop SYN+FIN messages

From: Greg Kroah-Hartman
Date: Tue Jul 17 2012 - 20:13:17 EST

From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>

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


From: Eric Dumazet <eric.dumazet@xxxxxxxxx>

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>
Cc: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

net/ipv4/tcp_input.c | 2 ++
1 file changed, 2 insertions(+)

--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -5761,6 +5761,8 @@ int tcp_rcv_state_process(struct sock *s
goto discard;

if (th->syn) {
+ if (th->fin)
+ goto discard;
if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
return 1;

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