netdev - Re: [PATCH] unix: avoid use-after-free in ep_remove_wait

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Date:	Wed, 11 Nov 2015 19:52:08 +0100
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	Jason Baron <jbaron@...mai.com>,
	Dmitry Vyukov <dvyukov@...gle.com>,
	syzkaller <syzkaller@...glegroups.com>,
	Michal Kubecek <mkubecek@...e.cz>,
	Al Viro <viro@...iv.linux.org.uk>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	David Howells <dhowells@...hat.com>,
	Paul Moore <paul@...l-moore.com>, salyzyn@...roid.com,
	sds@...ho.nsa.gov, ying.xue@...driver.com,
	netdev <netdev@...r.kernel.org>,
	Kostya Serebryany <kcc@...gle.com>,
	Alexander Potapenko <glider@...gle.com>,
	Andrey Konovalov <andreyknvl@...gle.com>,
	Sasha Levin <sasha.levin@...cle.com>,
	Julien Tinnes <jln@...gle.com>,
	Kees Cook <keescook@...gle.com>,
	Mathias Krause <minipli@...glemail.com>
Subject: Re: [PATCH] unix: avoid use-after-free in ep_remove_wait_queue

Hi,

On Wed, Nov 11, 2015, at 17:12, Rainer Weikusat wrote:
> Hannes Frederic Sowa <hannes@...essinduktion.org> writes:
> > On Tue, Nov 10, 2015, at 22:55, Rainer Weikusat wrote:
> >> An AF_UNIX datagram socket being the client in an n:1 association with
> >> some server socket is only allowed to send messages to the server if the
> >> receive queue of this socket contains at most sk_max_ack_backlog
> >> datagrams.
> 
> [...]
> 
> > This whole patch seems pretty complicated to me.
> >
> > Can't we just remove the unix_recvq_full checks alltogether and unify
> > unix_dgram_poll with unix_poll?
> >
> > If we want to be cautious we could simply make unix_max_dgram_qlen limit
> > the number of skbs which are in flight from a sending socket. The skb
> > destructor can then decrement this. This seems much simpler.
> >
> > Would this work?
> 
> In the way this is intended to work, cf
> 
> http://marc.info/?t=115627606000002&r=1&w=2

Oh, I see, we don't limit closed but still referenced sockets. This
actually makes sense on how fd handling is implemented, just as a range
check.

Have you checked if we can somehow deregister the socket in the poll
event framework? You wrote that it does not provide such a function but
maybe it would be easy to add?

Thanks,
Hannes
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