There was a "off by one quad word" error in there.  I don't think it is
exploitable because it will only store into a unused area, but better to plug
it.

Found and fixed by John Blackwood
Signed-off-by: NAndi Kleen <ak@suse.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NLinus Torvalds <torvalds@osdl.org>