Bug 426081 (CVE-2007-6417)

Description of problem -- <cite Hugh Dickins>

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.

</cite>

More problem details from CVE description: 

The shmem_getpage function (mm/shmem.c) in Linux kernel 2.6.11 through
2.6.23 does not properly allocate memory in some circumstances, which
might allow local users to read sensitive kernel data or cause a
denial of service (crash).

Attaching also link to upstream commit -- contains also patch
provided from Hugh Dickins (see URL). 

More details from communication with Hugh:

<cite>
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.
announce.

</cite>