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

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Message-ID: <1447871712.22599.175.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 18 Nov 2015 10:35:12 -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 18:35 +0100, Hannes Frederic Sowa wrote:
> 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?

Intuitively this timewait creation looks dangerous to me, maybe from
an attack surface perspective.

An out of sequence packet sends an advisory RST packet, which is already
a hint for building some kinds of attacks.

Now if we also create a timewait socket, and its associated timer, we
also add quite a risk of memory and cpu consumption.

So I am fine you create a timewait, only if you can prove there is no
change in security.

Thanks !


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