media: uvcvideo: Handle cameras with invalid descriptors

If the source entity does not contain any pads, do not create a link.
Reported-by: syzbot <syzkaller@googlegroups.com>
Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>

drivers/media/usb/uvc/uvc_entity.c

@@ -37,7 +37,7 @@ static int uvc_mc_create_links(struct uvc_video_chain *chain,
 			continue;
 
 		remote = uvc_entity_by_id(chain->dev, entity->baSourceID[i]);
-		if (remote == NULL)
+		if (remote == NULL || remote->num_pads == 0)
 			return -EINVAL;
 
 		source = (UVC_ENTITY_TYPE(remote) == UVC_TT_STREAMING)