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[media] v4l2-dev: fix race condition

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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>
This commit is contained in:
Hans Verkuil 2010-11-26 06:54:53 -03:00 committed by Mauro Carvalho Chehab
parent 879aa24d63
commit ca9afe6f87
1 changed files with 6 additions and 1 deletions
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7
drivers/media/video/v4l2-dev.c
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@ -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);