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

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Date:	Fri, 18 Mar 2016 06:52:31 -0300
From:	Mauro Carvalho Chehab <mchehab@....samsung.com>
To:	Shuah Khan <shuahkh@....samsung.com>
Cc:	tiwai@...e.de, linux-media@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] media: fix media_device_unregister() to destroy media
 device device resource

Em Thu, 17 Mar 2016 16:46:36 -0600
Shuah Khan <shuahkh@....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@....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