V4L/DVB (13154): uvcvideo: Handle garbage at the end of streaming interface descriptors

At least one 5986:0241 webcam model includes vendor-specific descriptors
at the end of its streaming interface descriptors. Print an information
UVC_TRACE_DESCR message and try to continue parsing the descriptors
rather than bailing out with an error.
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_driver.c

@@ -426,7 +426,8 @@ static int uvc_parse_format(struct uvc_device *dev,
 	/* Parse the frame descriptors. Only uncompressed, MJPEG and frame
 	 * based formats have frame descriptors.
 	 */
-	while (buflen > 2 && buffer[2] == ftype) {
+	while (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE &&
+	       buffer[2] == ftype) {
 		frame = &format->frame[format->nframes];
 		if (ftype != UVC_VS_FRAME_FRAME_BASED)
 			n = buflen > 25 ? buffer[25] : 0;
@@ -503,12 +504,14 @@ static int uvc_parse_format(struct uvc_device *dev,
 		buffer += buffer[0];
 	}
 
-	if (buflen > 2 && buffer[2] == UVC_VS_STILL_IMAGE_FRAME) {
+	if (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE &&
+	    buffer[2] == UVC_VS_STILL_IMAGE_FRAME) {
 		buflen -= buffer[0];
 		buffer += buffer[0];
 	}
 
-	if (buflen > 2 && buffer[2] == UVC_VS_COLORFORMAT) {
+	if (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE &&
+	    buffer[2] == UVC_VS_COLORFORMAT) {
 		if (buflen < 6) {
 			uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming "
 			       "interface %d COLORFORMAT error\n",
@@ -749,6 +752,11 @@ static int uvc_parse_streaming(struct uvc_device *dev,
 		buffer += buffer[0];
 	}
 
+	if (buflen)
+		uvc_trace(UVC_TRACE_DESCR, "device %d videostreaming interface "
+			"%d has %u bytes of trailing descriptor garbage.\n",
+			dev->udev->devnum, alts->desc.bInterfaceNumber, buflen);
+
 	/* Parse the alternate settings to find the maximum bandwidth. */
 	for (i = 0; i < intf->num_altsetting; ++i) {
 		struct usb_host_endpoint *ep;