linux-kernel - Re: [PATCH] tmpfs: restore missing clear

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Message-ID: <20071215001331.GC5403@stusta.de>
Date:	Sat, 15 Dec 2007 01:13:31 +0100
From:	Adrian Bunk <bunk@...nel.org>
To:	Hugh Dickins <hugh@...itas.com>
Cc:	Chuck Ebbert <cebbert@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Willy Tarreau <wtarreau@...a.kernel.org>, stable@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tmpfs: restore missing clear_highpage

On Wed, Dec 12, 2007 at 05:01:51AM +0000, Hugh Dickins wrote:
> On Tue, 11 Dec 2007, Chuck Ebbert wrote:
> > On 11/28/2007 01:55 PM, Hugh Dickins wrote:
> > > tmpfs was misconverted to __GFP_ZERO in 2.6.11.  There's an unusual case in
> > > which shmem_getpage receives the page from its caller instead of allocating.
> > > We must cover this case by clear_highpage before SetPageUptodate, as before.
> > > 
> > > Signed-off-by: Hugh Dickins <hugh@...itas.com>
> > > ---
> > 
> > What are the symptoms of the bug this fixes?
> 
> I've not seen it in practice, just noticed it while working on that
> area in the code.  What's the polite way of describing these things
> in public?  It's a vulnerability which might allow an attacker to
> access data from inside the kernel which should have been zeroed -
> in very limited circumstances I'd prefer not to have to devise and
> announce.
> 
> It would also be wrong data, so could for example crash any program
> rightly relying on uninitialized static data to be zeroed - in the
> unlikely event that its data was coming via this route (in most setups
> it never can do, perhaps I'd conclude that's true of all setups).  It
> has escaped notice for nearly three years, so it's not a commonplace.
> 
> Further discussion offline if you like!

Can we get or is there already a CVE number?

> Hugh

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

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