From: James Morris <jmorris@redhat.com>

Here's a patch which zeroes the last byte of the mount option data copied
from userspace during mount(2).

For filesystems which parse mount options as strings (the majority), lack
of a zero terminator could cause the page to be overrun.  The source code
comments specify that the maximum size of the mount data is PAGE_SIZE-1, so
this patch will not affect any valid binary-formatted mount data.