netdev - Re: Add a SOCK_DESTROY operation to close sockets from userspace

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Date:	Wed, 18 Nov 2015 11:19:48 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>
Cc:	Lorenzo Colitti <lorenzo@...gle.com>, netdev@...r.kernel.org,
	edumazet@...gle.com, ek@...gle.com, maze@...gle.com,
	dtor@...gle.com
Subject: Re: Add a SOCK_DESTROY operation to close sockets from userspace

Hi,

On Wed, Nov 18, 2015, at 05:04, Eric Dumazet wrote:
> On Tue, 2015-11-17 at 19:27 -0800, Stephen Hemminger wrote:
> 
> > I understand why you might want this, but it smells like the same
> > kind of problems that the "forced unmount" patch had which eventually
> > led to it not being accepted in mainline.  Lots of corner
> > cases and race conditions waiting to blow up.
> 
> Well, disconnecting a TCP socket seems straightforward, once you get a
> sk pointer.
> 
> Code looks good.
> 
> > 
> > Look at the issues that the multi-thread socket close has.
> > This looks worse.
> 
> I do not see a problem here. A RST packet has roughly same effect, and
> we do process them.
> 
> Cookies are 64bits and uniquely identify a socket.
> 
> Once you make sure the request comes from a privileged user, we are
> good.
> 
> This user could easily install some iptables rules to generate RST
> packets anyway.

I bet there will soon be a timewaitd which handles the not configurable
(David has rejected all those patches so far) timeout of TIME_WAIT
sockets. And I bet it will be used. :/

Bye,
Hannes
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