linux-kernel - Re: [PATCH 07/11] Memory compaction core

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Message-ID: <20100324155423.68c3d5b6@bike.lwn.net>
Date:	Wed, 24 Mar 2010 15:54:23 -0600
From:	Jonathan Corbet <corbet@....net>
To:	Andrea Arcangeli <aarcange@...hat.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mel@....ul.ie>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Adam Litke <agl@...ibm.com>, Avi Kivity <avi@...hat.com>,
	David Rientjes <rientjes@...gle.com>,
	Minchan Kim <minchan.kim@...il.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 07/11] Memory compaction core

On Wed, 24 Mar 2010 22:47:42 +0100
Andrea Arcangeli <aarcange@...hat.com> wrote:

> I think you mistaken a VM_BUG_ON for a:
> 
>   if (could_be_null->something) {
>      WARN_ON(1);
>      return -ESOMETHING;
>   }
> 
> adding a VM_BUG_ON(inode->something) would _still_ be as exploitable
> as the null pointer deference, because it's a DoS. It's not really a
> big deal of an exploit but it _sure_ need fixing.

Ah, but that's the point: these NULL pointer dereferences were not DoS
vulnerabilities - they were full privilege-escalation affairs.  Since
then, some problems have been fixed and some distributors have started
shipping smarter configurations.  But, on quite a few systems a NULL
dereference still has the potential to be fully exploitable; if there's
a possibility of it happening I think we should test for it.  A DoS is
a much better outcome...

jon
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