media: uvcvideo: Do not mark valid metadata as invalid

Currently, the driver performs a length check of the metadata buffer
before the actual metadata size is known and before the metadata is
decided to be copied. This results in valid metadata buffers being
incorrectly marked as invalid.

Move the length check to occur after the metadata size is determined and
is decided to be copied.

Cc: [email protected]
Fixes: 088ead2 ("media: uvcvideo: Add a metadata device node")
Reviewed-by: Laurent Pinchart <[email protected]>
Reviewed-by: Hans de Goede <[email protected]>
Signed-off-by: Ricardo Ribalda <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Hans de Goede <[email protected]>
Signed-off-by: Hans Verkuil <[email protected]>

Author: ribalda

drivers/media/usb/uvc/uvc_video.c

@@ -1442,12 +1442,6 @@ static void uvc_video_decode_meta(struct uvc_streaming *stream,
 	if (!meta_buf || length == 2)
 		return;
 
-	if (meta_buf->length - meta_buf->bytesused <
-	    length + sizeof(meta->ns) + sizeof(meta->sof)) {
-		meta_buf->error = 1;
-		return;
-	}
-
 	has_pts = mem[1] & UVC_STREAM_PTS;
 	has_scr = mem[1] & UVC_STREAM_SCR;
 
@@ -1468,6 +1462,12 @@ static void uvc_video_decode_meta(struct uvc_streaming *stream,
 				  !memcmp(scr, stream->clock.last_scr, 6)))
 		return;
 
+	if (meta_buf->length - meta_buf->bytesused <
+	    length + sizeof(meta->ns) + sizeof(meta->sof)) {
+		meta_buf->error = 1;
+		return;
+	}
+
 	meta = (struct uvc_meta_buf *)((u8 *)meta_buf->mem + meta_buf->bytesused);
 	local_irq_save(flags);
 	time = uvc_video_get_time();