[PATCH] drm: Fix an unwanted master inheritance v2

[Thomas Hellstrom]

Hi,

On 12/03/2015 12:12 PM, Jani Nikula wrote:
> On Wed, 02 Dec 2015, Thomas Hellstrom <thellstrom at vmware.com> wrote:
>> A client calling drmSetMaster() using a file descriptor that was opened
>> when another client was master would inherit the latter client's master
>> object and all its authenticated clients.
>>
>> This is unwanted behaviour, and when this happens, instead allocate a
>> brand new master object for the client calling drmSetMaster().
>>
>> Fixes a BUG() throw in vmw_master_set().
>>
>> Cc: <stable at vger.kernel.org>
>> Signed-off-by: Thomas Hellstrom <thellstrom at vmware.com>
> Drive-by bikeshedding, the actual change might look neater (and easier
> to revert if something falls apart) if you extracted the
> drm_new_set_master() abstraction as a separate non-functional prep
> patch. Not insisting, just a thought.
>
> BR,
> Jani.
While you're probably right, I prefer to have this as a single patch to
avoid ending up in a backporting nightmare for stable.

Thanks,
Thomas





>
>
>
>> ---
>>  drivers/gpu/drm/drm_drv.c  |  5 +++
>>  drivers/gpu/drm/drm_fops.c | 84 ++++++++++++++++++++++++++++++----------------
>>  include/drm/drmP.h         |  6 ++++
>>  3 files changed, 67 insertions(+), 28 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
>> index 9362609..7dd6728 100644
>> --- a/drivers/gpu/drm/drm_drv.c
>> +++ b/drivers/gpu/drm/drm_drv.c
>> @@ -160,6 +160,11 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
>>  		goto out_unlock;
>>  	}
>>  
>> +	if (!file_priv->allowed_master) {
>> +		ret = drm_new_set_master(dev, file_priv);
>> +		goto out_unlock;
>> +	}
>> +
>>  	file_priv->minor->master = drm_master_get(file_priv->master);
>>  	file_priv->is_master = 1;
>>  	if (dev->driver->master_set) {
>> diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
>> index c59ce4d..6b5625e 100644
>> --- a/drivers/gpu/drm/drm_fops.c
>> +++ b/drivers/gpu/drm/drm_fops.c
>> @@ -126,6 +126,60 @@ static int drm_cpu_valid(void)
>>  }
>>  
>>  /**
>> + * drm_new_set_master - Allocate a new master object and become master for the
>> + * associated master realm.
>> + *
>> + * @dev: The associated device.
>> + * @fpriv: File private identifying the client.
>> + *
>> + * This function must be called with dev::struct_mutex held.
>> + * Returns negative error code on failure. Zero on success.
>> + */
>> +int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
>> +{
>> +	struct drm_master *old_master;
>> +	int ret;
>> +
>> +	lockdep_assert_held_once(&dev->master_mutex);
>> +
>> +	/* create a new master */
>> +	fpriv->minor->master = drm_master_create(fpriv->minor);
>> +	if (!fpriv->minor->master)
>> +		return -ENOMEM;
>> +
>> +	/* take another reference for the copy in the local file priv */
>> +	old_master = fpriv->master;
>> +	fpriv->master = drm_master_get(fpriv->minor->master);
>> +
>> +	if (dev->driver->master_create) {
>> +		ret = dev->driver->master_create(dev, fpriv->master);
>> +		if (ret)
>> +			goto out_err;
>> +	}
>> +	if (dev->driver->master_set) {
>> +		ret = dev->driver->master_set(dev, fpriv, true);
>> +		if (ret)
>> +			goto out_err;
>> +	}
>> +
>> +	fpriv->is_master = 1;
>> +	fpriv->allowed_master = 1;
>> +	fpriv->authenticated = 1;
>> +	if (old_master)
>> +		drm_master_put(&old_master);
>> +
>> +	return 0;
>> +
>> +out_err:
>> +	/* drop both references and restore old master on failure */
>> +	drm_master_put(&fpriv->minor->master);
>> +	drm_master_put(&fpriv->master);
>> +	fpriv->master = old_master;
>> +
>> +	return ret;
>> +}
>> +
>> +/**
>>   * Called whenever a process opens /dev/drm.
>>   *
>>   * \param filp file pointer.
>> @@ -189,35 +243,9 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
>>  	mutex_lock(&dev->master_mutex);
>>  	if (drm_is_primary_client(priv) && !priv->minor->master) {
>>  		/* create a new master */
>> -		priv->minor->master = drm_master_create(priv->minor);
>> -		if (!priv->minor->master) {
>> -			ret = -ENOMEM;
>> +		ret = drm_new_set_master(dev, priv);
>> +		if (ret)
>>  			goto out_close;
>> -		}
>> -
>> -		priv->is_master = 1;
>> -		/* take another reference for the copy in the local file priv */
>> -		priv->master = drm_master_get(priv->minor->master);
>> -		priv->authenticated = 1;
>> -
>> -		if (dev->driver->master_create) {
>> -			ret = dev->driver->master_create(dev, priv->master);
>> -			if (ret) {
>> -				/* drop both references if this fails */
>> -				drm_master_put(&priv->minor->master);
>> -				drm_master_put(&priv->master);
>> -				goto out_close;
>> -			}
>> -		}
>> -		if (dev->driver->master_set) {
>> -			ret = dev->driver->master_set(dev, priv, true);
>> -			if (ret) {
>> -				/* drop both references if this fails */
>> -				drm_master_put(&priv->minor->master);
>> -				drm_master_put(&priv->master);
>> -				goto out_close;
>> -			}
>> -		}
>>  	} else if (drm_is_primary_client(priv)) {
>>  		/* get a reference to the master */
>>  		priv->master = drm_master_get(priv->minor->master);
>> diff --git a/include/drm/drmP.h b/include/drm/drmP.h
>> index 0b921ae..441b26e 100644
>> --- a/include/drm/drmP.h
>> +++ b/include/drm/drmP.h
>> @@ -309,6 +309,11 @@ struct drm_file {
>>  	unsigned universal_planes:1;
>>  	/* true if client understands atomic properties */
>>  	unsigned atomic:1;
>> +	/*
>> +	 * This client is allowed to gain master privileges for @master.
>> +	 * Protected by struct drm_device::master_mutex.
>> +	 */
>> +	unsigned allowed_master:1;
>>  
>>  	struct pid *pid;
>>  	kuid_t uid;
>> @@ -910,6 +915,7 @@ extern int drm_open(struct inode *inode, struct file *filp);
>>  extern ssize_t drm_read(struct file *filp, char __user *buffer,
>>  			size_t count, loff_t *offset);
>>  extern int drm_release(struct inode *inode, struct file *filp);
>> +extern int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv);
>>  
>>  				/* Mapping support (drm_vm.h) */
>>  extern unsigned int drm_poll(struct file *filp, struct poll_table_struct *wait);