tcp: Add a tcp_filter hook before handle ack packet

Currently in both ipv4 and ipv6 code path, the ack packet received when
sk at TCP_NEW_SYN_RECV state is not filtered by socket filter or cgroup
filter since it is handled from tcp_child_process and never reaches the
tcp_filter inside tcp_v4_rcv or tcp_v6_rcv. Adding a tcp_filter hooks
here can make sure all the ingress tcp packet can be correctly filtered.

Signed-off-by: Chenbo Feng <fengc@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp_ipv4.c

@@ -1729,6 +1729,8 @@ process:
 		}
 		if (nsk == sk) {
 			reqsk_put(req);
+		} else if (tcp_filter(sk, skb)) {
+			goto discard_and_relse;
 		} else if (tcp_child_process(sk, nsk, skb)) {
 			tcp_v4_send_reset(nsk, skb);
 			goto discard_and_relse;

net/ipv6/tcp_ipv6.c

@@ -1464,6 +1464,8 @@ process:
 		if (nsk == sk) {
 			reqsk_put(req);
 			tcp_v6_restore_cb(skb);
+		} else if (tcp_filter(sk, skb)) {
+			goto discard_and_relse;
 		} else if (tcp_child_process(sk, nsk, skb)) {
 			tcp_v6_send_reset(nsk, skb);
 			goto discard_and_relse;