It is possible to wrap the counter used to allocate the buffer for
relocation copies. This could lead to heap writing overflows.

CVE-2013-0913

v3: collapse test, improve comment
v2: move check into validate_exec_list
Signed-off-by: NKees Cook <keescook@chromium.org>
Reported-by: Pinkie Pie
Cc: stable@vger.kernel.org
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>