[media] V4L/DVB: v4l2-ioctl: integer overflow in video_usercopy()

If ctrls->count is too high the multiplication could overflow and
array_size would be lower than expected.  Mauro and Hans Verkuil
suggested that we cap it at 1024.  That comes from the maximum
number of controls with lots of room for expantion.

$ grep V4L2_CID include/linux/videodev2.h | wc -l
211

Cc: stable <stable@vger.kernel.org>
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/v4l2-ioctl.c

@@ -2226,6 +2226,10 @@ static int check_array_args(unsigned int cmd, void *parg, size_t *array_size,
 		struct v4l2_ext_controls *ctrls = parg;
 
 		if (ctrls->count != 0) {
+			if (ctrls->count > V4L2_CID_MAX_CTRLS) {
+				ret = -EINVAL;
+				break;
+			}
 			*user_ptr = (void __user *)ctrls->controls;
 			*kernel_ptr = (void *)&ctrls->controls;
 			*array_size = sizeof(struct v4l2_ext_control)

include/linux/videodev2.h

@@ -1132,6 +1132,7 @@ struct v4l2_querymenu {
 #define V4L2_CTRL_FLAG_NEXT_CTRL	0x80000000
 
 /*  User-class control IDs defined by V4L2 */
+#define V4L2_CID_MAX_CTRLS		1024
 #define V4L2_CID_BASE			(V4L2_CTRL_CLASS_USER | 0x900)
 #define V4L2_CID_USER_BASE 		V4L2_CID_BASE
 /*  IDs reserved for driver specific controls */