There wasn't any check of the size passed from userspace before trying
to allocate the memory required.

This meant that userspace might request more space than allowed,
triggering an OOM.
Signed-off-by: NSasha Levin <sasha.levin@oracle.com>
Signed-off-by: NIan Kent <raven@themaw.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>