media: uvcvideo: Don't expose unsupported formats to userspace

When the uvcvideo driver encounters a format descriptor with an unknown
format GUID, it creates a corresponding struct uvc_format instance with
the fcc field set to 0. Since commit 50459f103edf ("media: uvcvideo:
Remove format descriptions"), the driver relies on the V4L2 core to
provide the format description string, which the V4L2 core can't do
without a valid 4CC. This triggers a WARN_ON.

As a format with a zero 4CC can't be selected, it is unusable for
applications. Ignore the format completely without creating a uvc_format
instance, which fixes the warning.

Link: https://bugzilla.kernel.org/show_bug.cgi?id=217252
Link: https://bugzilla.redhat.com/show_bug.cgi?id=2180107

Fixes: 50459f103edf ("media: uvcvideo: Remove format descriptions")
Signed-off-by: Laurent Pinchart <[e-mail]>
Reviewed-by: Ricardo Ribalda <[e-mail]>
Signed-off-by: Mauro Carvalho Chehab <[e-mail]>

drivers/media/usb/uvc/uvc_driver.c

···
 		/* Find the format descriptor from its GUID. */
 		fmtdesc = uvc_format_by_guid(&buffer[5]);
 
-		if (fmtdesc != NULL) {
-			format->fcc = fmtdesc->fcc;
-		} else {
+		if (!fmtdesc) {
+			/*
+			 * Unknown video formats are not fatal errors, the
+			 * caller will skip this descriptor.
+			 */
 			dev_info(&streaming->intf->dev,
 				 "Unknown video format %pUl\n", &buffer[5]);
-			format->fcc = 0;
+			return 0;
 		}
 
+		format->fcc = fmtdesc->fcc;
 		format->bpp = buffer[21];
 
 		/*
···
 	interval = (u32 *)&frame[nframes];
 
 	streaming->format = format;
-	streaming->nformats = nformats;
+	streaming->nformats = 0;
 
 	/* Parse the format descriptors. */
 	while (buflen > 2 && buffer[1] == USB_DT_CS_INTERFACE) {
···
 				&interval, buffer, buflen);
 			if (ret < 0)
 				goto error;
+			if (!ret)
+				break;
 
+			streaming->nformats++;
 			frame += format->nframes;
 			format++;