Re: [PATCH] media: fix media_device_unregister() to destroy media device device resource

Mauro Carvalho Chehab
2016-03-18T09:52:37Z

Em Thu, 17 Mar 2016 16:46:36 -0600
Shuah Khan <shuahkh@osg.samsung.com> escreveu:

> When all drivers except usb-core driver is unbound, destroy the media device
> resource. Other wise, media device resource will persist in a defunct state.
> This leads to use-after-free and bad access errors during a subsequent bind.
> Fix it to destroy the media device resource when last reference is released
> in media_device_unregister().
>
> Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>
> ---
> drivers/media/media-device.c | 28 ++++++++++++++++++++++------
> 1 file changed, 22 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/media-device.c b/drivers/media/media-device.c
> index 070421e..7312612 100644
> --- a/drivers/media/media-device.c
> +++ b/drivers/media/media-device.c
> @@ -822,22 +822,38 @@ printk("%s: mdev=%p\n", __func__, mdev);
> dev_dbg(mdev->dev, "Media device unregistered\n");
> }
>
> +static void media_device_release_devres(struct device *dev, void *res)
> +{
> +}
> +
> +static void media_device_destroy_devres(struct device *dev)
> +{
> + int ret;
> +
> + ret = devres_destroy(dev, media_device_release_devres, NULL, NULL);
> + pr_debug("%s: devres_destroy() returned %d\n", __func__, ret);
> +}
> +
> void media_device_unregister(struct media_device *mdev)
> {
> + int ret;
> + struct device *dev;
> printk("%s: mdev=%p\n", __func__, mdev);
> if (mdev == NULL)
> return;
>
> - mutex_lock(&mdev->graph_mutex);
> - kref_put(&mdev->kref, do_media_device_unregister);
> - mutex_unlock(&mdev->graph_mutex);
> + ret = kref_put_mutex(&mdev->kref, do_media_device_unregister,
> + &mdev->graph_mutex);
> + if (ret) {
> + /* do_media_device_unregister() has run */
> + dev = mdev->dev;
> + mutex_unlock(&mdev->graph_mutex);

> + media_device_destroy_devres(dev);

This doesn't seem right: what happens on drivers that don't use
devres to allocate struct media_device?

> + }
>
> }
> EXPORT_SYMBOL_GPL(media_device_unregister);
>
> -static void media_device_release_devres(struct device *dev, void *res)
> -{
> -}
>
> struct media_device *media_device_get_devres(struct device *dev)
> {

--
Thanks,
Mauro