If our length is greater than the size of the buffer, we
overflow the buffer

Cc: stable@vger.kernel.org
Signed-off-by: NDaniel Rosenberg <drosen@google.com>
Reviewed-by: NBenjamin Tissoires <benjamin.tissoires@redhat.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>