[PATCH] Reorder ACK/RST checking in LISTEN state

[PATCH] Reorder ACK/RST checking in LISTEN state

[Kris Katterjohn]

[-- Attachment #1: Type: text/plain, Size: 890 bytes --]

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.

Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>

Thanks,
Kris Katterjohn

[-- Attachment #2: ackrst.patch --]
[-- Type: text/x-patch, Size: 412 bytes --]

--- net/ipv4/tcp_input.c	2008-02-13 00:05:59.000000000 -0600
+++ net/ipv4/tcp_input.c	2008-02-13 00:10:40.000000000 -0600
@@ -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;

Re: [PATCH] Reorder ACK/RST checking in LISTEN state

[David Miller]

From: Kris Katterjohn <katterjohn@gmail.com>
Date: Wed, 13 Feb 2008 00:38:13 -0600

> 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.
> 
> Signed-off-by: Kris Katterjohn <katterjohn@gmail.com>

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.