linux-kernel - Re: [PATCH v4 0/3] net: unix: fix use-after-free

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Date:	Mon, 12 Oct 2015 06:36:19 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Rainer Weikusat <rweikusat@...ileactivedefense.com>
Cc:	David Miller <davem@...emloft.net>, jbaron@...mai.com,
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	minipli@...glemail.com, normalperson@...t.net,
	viro@...iv.linux.org.uk, davidel@...ilserver.org,
	dave@...olabs.net, olivier@...ras.ch, pageexec@...email.hu,
	torvalds@...ux-foundation.org, peterz@...radead.org,
	joe@...ches.com
Subject: Re: [PATCH v4 0/3] net: unix: fix use-after-free

On Mon, 2015-10-12 at 13:54 +0100, Rainer Weikusat wrote:
> David Miller <davem@...emloft.net> writes:
> > From: Jason Baron <jbaron@...mai.com>
> > Date: Fri,  9 Oct 2015 00:15:59 -0400
> >
> >> These patches are against mainline, I can re-base to net-next, please
> >> let me know.
> >> 
> >> They have been tested against: https://lkml.org/lkml/2015/9/13/195,
> >> which causes the use-after-free quite quickly and here:
> >> https://lkml.org/lkml/2015/10/2/693.
> >
> > I'd like to understand how patches that don't even compile can be
> > "tested"?
> >
> > net/unix/af_unix.c: In function ‘unix_dgram_writable’:
> > net/unix/af_unix.c:2480:3: error: ‘other_full’ undeclared (first use in this function)
> > net/unix/af_unix.c:2480:3: note: each undeclared identifier is reported only once for each function it appears in
> >
> > Could you explain how that works, I'm having a hard time understanding
> > this?
> 
> This is basicallly a workaround for the problem that it's not possible
> to tell epoll to let go of a certain wait queue: Instead of registering
> the peer_wait queue via sock_poll_wait, a wait_queue_t under control of
> the af_unix.c code is linked onto it which relays a wake up on the
> peer_wait queue to the 'ordinary' wait queue associated with the polled
> socket via custom wake function. But (at least the code I looked it) it
> enqueues a unix socket on connect which has certain side effects (in
> particular, /dev/log will have a seriously large wait queue of entirely
> uninterested peers) and in many cases, this is simply not necessary, as
> the additional peer_wait event is only interesting in case a peer of a
> fan-in socket (like /dev/log) happens to be waiting for writeabilty via
> poll/ select/ epoll/ ...
> 
> Since the wait queue handling code is now under control of the af_unix.c
> code, it can remove itself from the peer_wait queue prior to dropping
> its reference to a peer on disconnect or on detecting a dead peer in
> unix_dgram_sendmsg.
> --

Okay, but David was asking how the patch was supposed to be tested, and
applied, if it does not compile.

A patch is not only showing the idea, but must be ready for inclusion.

Please ?


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