netdev - Re: [PATCH -next] net: tcp: move to timewait when receiving data post active-close

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Date:	Wed, 18 Nov 2015 09:28:56 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Hannes Frederic Sowa <hannes@...essinduktion.org>
Cc:	Florian Westphal <fw@...len.de>, netdev@...r.kernel.org,
	marcelo.leitner@...il.com
Subject: Re: [PATCH -next] net: tcp: move to timewait when receiving data
 post active-close

On Wed, 2015-11-18 at 16:54 +0100, Hannes Frederic Sowa wrote:

> Still, the RST packet can be dropped along the way. So the teardown of
> the socket on the other side might not happen.

This is why it is better to send RST for every incoming in-excess packet

Try following packetdrill test, before and after your patch :

0.000 socket(..., SOCK_STREAM, IPPROTO_TCP) = 3
0.000 setsockopt(3, SOL_SOCKET, SO_REUSEADDR, [1], 4) = 0
0.000 bind(3, ..., ...) = 0
0.000 listen(3, 1) = 0
0.100 < S 0:0(0) win 29200 <mss 1460>
0.100 > S. 0:0(0) ack 1 <mss 1460>
0.200 < . 1:1(0) ack 1 win 257
0.200 accept(3, ..., ...) = 4
// close our side.
0.210 close(4) = 0
// we should expect to see FIN now, sk moves to FIN_WAIT_1
0.210 > F. 1:1(0) ack 1 win 29200

// receive data, but sk already closed -> Reset
+.010 < P. 1:1001(1000) ack 1 win 46
+0    > R 1:1(0) win 0

// Are we properly sending a RST like prior packet did ?
+.010 < P. 1001:2001(1000) ack 1 win 46
+0    > R 1:1(0) win 0



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