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

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  [PATCH] media: fix media_device_unregister() to destroy media device device resource Shuah Khan <shuahkh@osg.samsung.com> - 2016-03-17 23:50 +0100
    Re: [PATCH] media: fix media_device_unregister() to destroy media  device device resource Mauro Carvalho Chehab <mchehab@osg.samsung.com> - 2016-03-18 11:00 +0100
      Re: [PATCH] media: fix media_device_unregister() to destroy media  device device resource Shuah Khan <shuahkh@osg.samsung.com> - 2016-03-18 14:40 +0100

#1360241 — [PATCH] media: fix media_device_unregister() to destroy media device device resource

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);
+	}
 
 }
 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)
 {
-- 
2.5.0

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#1360479 — 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@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

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#1360618 — Re: [PATCH] media: fix media_device_unregister() to destroy media device device resource

On 03/18/2016 03:52 AM, Mauro Carvalho Chehab wrote:
> 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?
> 

That is okay. devres_destroy() won't find the resource. The way it works
is it will try to find the resource with the match routine and data and
that step will fail it will return -ENOENT. At that point nothing more
is done.

ret = devres_destroy(dev, media_device_release_devres, NULL, NULL);
pr_debug("%s: devres_destroy() returned %d\n", __func__, ret);

devres_destroy() combines the devres_find() and remove. So we are good
here.

thanks,
-- Shuah


-- 
Shuah Khan
Sr. Linux Kernel Developer
Open Source Innovation Group
Samsung Research America (Silicon Valley)
shuahkh@osg.samsung.com | (970) 217-8978

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