linux-kernel - Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

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Message-ID: <4BBC92D6.6040403@redhat.com>
Date:	Wed, 07 Apr 2010 10:12:38 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Nick Piggin <npiggin@...e.de>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>
Subject: Re: Ugly rmap NULL ptr deref oopsie on hibernate (was Linux 2.6.34-rc3)

On 04/07/2010 04:36 AM, Peter Zijlstra wrote:
> On Tue, 2010-04-06 at 11:28 -0700, Linus Torvalds wrote:

>>          if (empty)
>>                  anon_vma_free(anon_vma);
>>
>> *before* unlink_anon_vma's has actually does that
>>
>>          list_del(&avc->same_vma);
>>
>> and what we essentially have is a stale anon_vma_chain entry that still
>> exists on that same_vma list, and points to an anon_vma that already got
>> deleted.
>>
>> Does it matter? I really can't see that it does.
>
> I think it does, the anon_vma thing has an RCU destroyed slab, but that
> doesn't mean the anon_vma object itself is rcu delayed. The moment we
> free it it can be re-used. So the above use after free is a bug.

Peter, the avc is an anon_vma_chain, which is a different
object than the anon_vma itself.  There is no use after free
of an anon_vma object in unlink_anon_vmas + anon_vma_unlink.
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