[NET]: Fix sk->sk_filter field access

Function sk_filter() is called from tcp_v{4,6}_rcv() functions with arg
needlock = 0, while socket is not locked at that moment. In order to avoid
this and similar issues in the future, use rcu for sk->sk_filter field read
protection.

Signed-off-by: Dmitry Mishin <dim@openvz.org>
Signed-off-by: Alexey Kuznetsov <kuznet@ms2.inr.ac.ru>
Signed-off-by: Kirill Korotaev <dev@openvz.org>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 23b46e3..39b1798 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -1104,7 +1104,7 @@
 		goto discard_and_relse;
 	nf_reset(skb);
 
-	if (sk_filter(sk, skb, 0))
+	if (sk_filter(sk, skb))
 		goto discard_and_relse;
 
 	skb->dev = NULL;