forked from Minki/linux
[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>
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@ -309,7 +309,7 @@ static int v4l2_open(struct inode *inode, struct file *filp)
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mutex_lock(&videodev_lock);
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vdev = video_devdata(filp);
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/* return ENODEV if the video device has already been removed. */
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if (vdev == NULL) {
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if (vdev == NULL || !video_is_registered(vdev)) {
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mutex_unlock(&videodev_lock);
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return -ENODEV;
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}
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@ -624,7 +624,12 @@ void video_unregister_device(struct video_device *vdev)
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if (!vdev || !video_is_registered(vdev))
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return;
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mutex_lock(&videodev_lock);
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/* This must be in a critical section to prevent a race with v4l2_open.
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* Once this bit has been cleared video_get may never be called again.
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*/
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clear_bit(V4L2_FL_REGISTERED, &vdev->flags);
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mutex_unlock(&videodev_lock);
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device_unregister(&vdev->dev);
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}
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EXPORT_SYMBOL(video_unregister_device);
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