diff --git a/[refs] b/[refs]
index accbfb8669ec..a92300e6ed27 100644
--- a/[refs]
+++ b/[refs]
@@ -1,2 +1,2 @@
 ---
-refs/heads/master: b6fe83e9525a03b3141e5857eb7d8af219db94e5
+refs/heads/master: e371589917011efe6ff8c7dfb4e9e81934ac5855
diff --git a/trunk/net/ipv4/tcp_input.c b/trunk/net/ipv4/tcp_input.c
index 8aaec5536111..fdd49f1b7a52 100644
--- a/trunk/net/ipv4/tcp_input.c
+++ b/trunk/net/ipv4/tcp_input.c
@@ -5296,8 +5296,11 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 		 * an acknowledgment should be sent in reply (unless the RST
 		 * bit is set, if so drop the segment and return)".
 		 */
-		if (!th->rst)
+		if (!th->rst) {
+			if (th->syn)
+				goto syn_challenge;
 			tcp_send_dupack(sk, skb);
+		}
 		goto discard;
 	}
 
@@ -5327,6 +5330,7 @@ static bool tcp_validate_incoming(struct sock *sk, struct sk_buff *skb,
 	 * RFC 5691 4.2 : Send a challenge ack
 	 */
 	if (th->syn) {
+syn_challenge:
 		if (syn_inerr)
 			TCP_INC_STATS_BH(sock_net(sk), TCP_MIB_INERRS);
 		NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPSYNCHALLENGE);