commit 4f69851fbaa26b155330be35ce8ac393e93e7442 upstream.

The "used" variables here come from the user in the ioctl and it can be
negative.  It could result in an out of bounds write.
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20191004102251.GC823@mwanda
Cc: stable@vger.kernel.org
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>