V4L/DVB (11945): uvcvideo: Don't accept to change the format when buffers are allocated.

Setting a new frame format or size will likely change the buffer size required
to store a complete video frame. To avoid a buffer overflow, don't allow
VIDIOC_S_FMT calls when video buffers are already allocated.
Signed-off-by: Laurent Pinchart <laurent.pinchart@skynet.be>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/uvc/uvc_queue.c

@@ -172,6 +172,20 @@ int uvc_free_buffers(struct uvc_video_queue *queue)
 	return 0;
 }
 
+/*
+ * Check if buffers have been allocated.
+ */
+int uvc_queue_allocated(struct uvc_video_queue *queue)
+{
+	int allocated;
+
+	mutex_lock(&queue->mutex);
+	allocated = queue->count != 0;
+	mutex_unlock(&queue->mutex);
+
+	return allocated;
+}
+
 static void __uvc_query_buffer(struct uvc_buffer *buf,
 		struct v4l2_buffer *v4l2_buf)
 {

drivers/media/video/uvc/uvc_v4l2.c

@@ -251,7 +251,7 @@ static int uvc_v4l2_set_format(struct uvc_video_device *video,
 	if (fmt->type != video->streaming->type)
 		return -EINVAL;
 
-	if (uvc_queue_streaming(&video->queue))
+	if (uvc_queue_allocated(&video->queue))
 		return -EBUSY;
 
 	ret = uvc_v4l2_try_format(video, fmt, &probe, &format, &frame);

drivers/media/video/uvc/uvcvideo.h

@@ -747,6 +747,7 @@ extern struct uvc_buffer *uvc_queue_next_buffer(struct uvc_video_queue *queue,
 		struct uvc_buffer *buf);
 extern unsigned int uvc_queue_poll(struct uvc_video_queue *queue,
 		struct file *file, poll_table *wait);
+extern int uvc_queue_allocated(struct uvc_video_queue *queue);
 static inline int uvc_queue_streaming(struct uvc_video_queue *queue)
 {
 	return queue->flags & UVC_QUEUE_STREAMING;