Re: [PATCH] tmpfs: restore missing clear_highpage

Adrian Bunk
2007-12-15T00:13:36Z

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@veritas.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

--

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of the darkness. There had been need of rain for many days.
"Only a promise," Lao Er said.
Pearl S. Buck - Dragon Seed