[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: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/video/v4l2-dev.c b/drivers/media/video/v4l2-dev.c
index 6b64fd6..359e232 100644
--- a/drivers/media/video/v4l2-dev.c
+++ b/drivers/media/video/v4l2-dev.c
@@ -309,7 +309,7 @@
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 @@
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);