Reorder ACK/RST checking in LISTEN state

Hey everyone,

[I'm not subscribed, so please CC me on any replies]

I've attached a patch that changes the order of the ACK and RST checking in the LISTEN state in tcp_rcv_state_process() in tcp_input.c

Before: If an ACK/RST packet is received, then tcp_rcv_state_process() would return 1 because of the ACK. Then (following the function calls in tcp_ipv4.c and tcp_minisocks.c), tcp_v4_send_reset() is called--but since there is a RST in the packet it just returns. After this, the kfree_skb() is called. The same goes in tcp_ipv6.c as well.

But if the order of the ACK and RST checking is reversed, __kfree_skb() is called in tcp_rcv_state_process() because of the RST and the function returns 0, which skips that other useless stuff.

This is the order specified on page 65 of RFC 793 anyway.

Thanks,
Kris Katterjohn

@@ -4962,12 +4962,12 @@ int tcp_rcv_state_process(struct sock *s
 		goto discard;
 
 	case TCP_LISTEN:
-		if (th->ack)
-			return 1;
-
 		if (th->rst)
 			goto discard;
 
+		if (th->ack)
+			return 1;
+
 		if (th->syn) {
 			if (icsk->icsk_af_ops->conn_request(sk, skb) < 0)
 				return 1;

From: Kris Katterjohn <[email protected]>
Date: Wed, 13 Feb 2008 00:38:13 -0600

This code has been like this for I don't know how many years, the end result is the same both before and after your patch, and the added expense of the existing code is frankly trivial.

I really don't want to apply this, it doesn't buy us anything, sorry.