This fixes a theoretical bug indicated in:
http://bugme.osdl.org/show_bug.cgi?id=240

It prevents overflow in case the required buffer is larger than the passed
buffer.  This I found to be the minimally intrusive change.
Signed-off-by: Alexander Nyberg <alexn@dsv.su.se>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>