Re: [PATCH] tmpfs: restore missing clear_highpage

[Hugh Dickins <hugh@veritas.com>]

On Sat, 15 Dec 2007, Adrian Bunk wrote:
> 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?

I've not asked for one, so I don't suppose there is one: do go ahead
and get one if you wish (though of course it would have been better
earlier, so 2.6.22.15 and 2.6.23.10 could have cited it along with
their fix: sorry about that).

Hugh