comp_register_videodev() allocates a video_device with
video_device_alloc() and releases it if video_register_device() fails.

This can double free the video_device when __video_register_device()
reaches device_register() and that call fails:

  video_register_device()
    -> __video_register_device()
       -> device_register() fails
          -> put_device(&vdev->dev)
             -> v4l2_device_release()
                -> vdev->release(vdev)
                   -> video_device_release(vdev)

  comp_register_videodev()
    -> video_device_release(mdev->vdev)

Use video_device_release_empty() while registering the device so that
registration failure paths do not free mdev->vdev through vdev->release().
comp_register_videodev() then releases mdev->vdev exactly once on failure.
Restore video_device_release() after successful registration so the
registered device keeps its normal lifetime handling.

This issue was found by a static analysis tool I am developing.

Fixes: eab231c0398a ("staging: most: v4l2-aim: remove unnecessary label err_vbi_dev")
Signed-off-by: Guangshuo Li <lgs201920130244@gmail.com>
---
 drivers/staging/most/video/video.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/staging/most/video/video.c b/drivers/staging/most/video/video.c
index 04351f8ccccf..aab57768f4f7 100644
--- a/drivers/staging/most/video/video.c
+++ b/drivers/staging/most/video/video.c
@@ -420,6 +420,7 @@ static int comp_register_videodev(struct most_video_dev *mdev)
 
 	/* Fill the video capture device struct */
 	*mdev->vdev = comp_videodev_template;
+	mdev->vdev->release = video_device_release_empty;
 	mdev->vdev->v4l2_dev = &mdev->v4l2_dev;
 	mdev->vdev->lock = &mdev->lock;
 	snprintf(mdev->vdev->name, sizeof(mdev->vdev->name), "MOST: %s",
@@ -432,9 +433,13 @@ static int comp_register_videodev(struct most_video_dev *mdev)
 		v4l2_err(&mdev->v4l2_dev, "video_register_device failed (%d)\n",
 			 ret);
 		video_device_release(mdev->vdev);
+		return ret;
 	}
 
-	return ret;
+	mdev->vdev->release = video_device_release;
+
+	return 0;
+
 }
 
 static void comp_unregister_videodev(struct most_video_dev *mdev)
-- 
2.43.0