netdev - Re: List corruption on epoll_ctl(EPOLL_CTL_DEL) an AF

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Message-ID: <560C9CFE.6090509@akamai.com>
Date:	Wed, 30 Sep 2015 22:39:58 -0400
From:	Jason Baron <jbaron@...mai.com>
To:	Mathias Krause <minipli@...glemail.com>
CC:	netdev@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Eric Wong <normalperson@...t.net>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Rainer Weikusat <rweikusat@...ileactivedefense.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Davide Libenzi <davidel@...ilserver.org>,
	Davidlohr Bueso <dave@...olabs.net>,
	Olivier Mauras <olivier@...ras.ch>,
	PaX Team <pageexec@...email.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"peterz@...radead.org" <peterz@...radead.org>,
	"davem@...emloft.net" <davem@...emloft.net>
Subject: Re: List corruption on epoll_ctl(EPOLL_CTL_DEL) an AF_UNIX socket

On 09/30/2015 01:54 AM, Mathias Krause wrote:
> On 29 September 2015 at 21:09, Jason Baron <jbaron@...mai.com> wrote:
>> However, if we call connect on socket 's', to connect to a new socket 'o2', we
>> drop the reference on the original socket 'o'. Thus, we can now close socket
>> 'o' without unregistering from epoll. Then, when we either close the ep
>> or unregister 'o', we end up with this list corruption. Thus, this is not a
>> race per se, but can be triggered sequentially.
> 
> Sounds profound, but the reproducers calls connect only once per
> socket. So there is no "connect to a new socket", no?
> But w/e, see below.

Yes, but it can be reproduced this way too. It can also happen with a
close() on the remote peer 'o', and a send to 'o' from 's', which the
reproducer can do as pointed out Michal. The patch I sent deals with
both cases.

Thanks,

-Jason
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