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Commit ca9afe6f authored by Hans Verkuil's avatar Hans Verkuil Committed by Mauro Carvalho Chehab
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[media] v4l2-dev: fix race condition 



The unregister function had a race condition with the v4l2_open
function. Ensure that both functions test and clear the REGISTER
flag from within a critical section.

Thanks to Laurent Pinchart for finding this race.

Signed-off-by: default avatarHans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: default avatarMauro Carvalho Chehab <mchehab@redhat.com>
parent 879aa24d

drivers/media/video/v4l2-dev.c

+6 −1
Original line number Diff line number Diff line
@@ -309,7 +309,7 @@ static int v4l2_open(struct inode *inode, struct file *filp) 
	mutex_lock(&videodev_lock);

	vdev = video_devdata(filp);

	/* return ENODEV if the video device has already been removed. */

	if (vdev == NULL) {

	if (vdev == NULL || !video_is_registered(vdev)) {

		mutex_unlock(&videodev_lock);

		return -ENODEV;

	}
@@ -624,7 +624,12 @@ void video_unregister_device(struct video_device *vdev) 
	if (!vdev || !video_is_registered(vdev))

		return;



	mutex_lock(&videodev_lock);

	/* This must be in a critical section to prevent a race with v4l2_open.

	 * Once this bit has been cleared video_get may never be called again.

	 */

	clear_bit(V4L2_FL_REGISTERED, &vdev->flags);

	mutex_unlock(&videodev_lock);

	device_unregister(&vdev->dev);

}

EXPORT_SYMBOL(video_unregister_device);