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

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Date:	Wed, 18 Nov 2015 18:35:59 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>
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, Nov 18, 2015, at 18:28, Eric Dumazet wrote:
> 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

I agree it would be better to send a RST than ACK incoming data. Just
thinking out loud, would it make sense to add a sub-state to timewait so
we RST all other packets for TIMEWAIT_LEN duration?

> 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

Thanks,
Hannes
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