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

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Message-Id: <1447862057.909111.443349025.5B7D067D@webmail.messagingengine.com>
Date:	Wed, 18 Nov 2015 16:54:17 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Florian Westphal <fw@...len.de>
Cc:	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 16:46, Eric Dumazet wrote:
> On Wed, 2015-11-18 at 16:36 +0100, Florian Westphal wrote:
> 
> > Yes, but we kill the socket.
> > 
> > I should have added
> > 
> > 0.400 `ss -nito state time-wait`
> > 
> > as last line...
> > 
> > Before patch: no output
> > after patch: tw socket shown.
> > 
> > The on-wire behavior doesn't change unless further packets arrive.
> > Old behaviour: more RST
> > New behaviour: acks+tw timer restart
> 
> Just add few more incoming packets to the packetdrill test then ?
> 
> Also, is your customer really _not_ using TCP timestamps ?

Windows mostly does not use TCP timestamps. Also we have cases were
security folks tell customers to turn off timestamps as they enable
attackers to guess uptime. :(

> This is kind of a requirement for port reuse anyway.
> 
> Anyway, having a TIMEWAIT setup after sending a RST makes little sense
> to me.
> 
> When a RST packet is sent, the remote peer will forget everything about
> this previous connection, and another connect() might reuse the tuple
> and I do not think we should forbid this. Normal PAWS checks were
> invented for a good reason.

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

Bye,
Hannes
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