drivers/gpu/drm/drm_auth.c - linux - Git at Google

 /*
  * Created: Tue Feb  2 08:37:54 1999 by faith@valinux.com
  *
  * Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
  * Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
  * All Rights Reserved.
  *
  * Author Rickard E. (Rik) Faith <faith@valinux.com>
  * Author Gareth Hughes <gareth@valinux.com>
  *
  * Permission is hereby granted, free of charge, to any person obtaining a
  * copy of this software and associated documentation files (the "Software"),
  * to deal in the Software without restriction, including without limitation
  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
  * and/or sell copies of the Software, and to permit persons to whom the
  * Software is furnished to do so, subject to the following conditions:
  *
  * The above copyright notice and this permission notice (including the next
  * paragraph) shall be included in all copies or substantial portions of the
  * Software.
  *
  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
  * VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
  * OTHER DEALINGS IN THE SOFTWARE.
  */

 #include <linux/slab.h>

 #include <drm/drm_auth.h>
 #include <drm/drm_drv.h>
 #include <drm/drm_file.h>
 #include <drm/drm_lease.h>
 #include <drm/drm_print.h>

 #include "drm_internal.h"
 #include "drm_legacy.h"

 /**
  * DOC: master and authentication
  *
  * &struct drm_master is used to track groups of clients with open
  * primary/legacy device nodes. For every &struct drm_file which has had at
  * least once successfully became the device master (either through the
  * SET_MASTER IOCTL, or implicitly through opening the primary device node when
  * no one else is the current master that time) there exists one &drm_master.
  * This is noted in &drm_file.is_master. All other clients have just a pointer
  * to the &drm_master they are associated with.
  *
  * In addition only one &drm_master can be the current master for a &drm_device.
  * It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or
  * implicitly through closing/openeing the primary device node. See also
  * drm_is_current_master().
  *
  * Clients can authenticate against the current master (if it matches their own)
  * using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters,
  * this allows controlled access to the device for an entire group of mutually
  * trusted clients.
  */

 int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv)
 {
 	struct drm_auth *auth = data;
 	int ret = 0;

 	mutex_lock(&dev->master_mutex);
 	if (!file_priv->magic) {
 		ret = idr_alloc(&file_priv->master->magic_map, file_priv,
 				1, 0, GFP_KERNEL);
 		if (ret >= 0)
 			file_priv->magic = ret;
 	}
 	auth->magic = file_priv->magic;
 	mutex_unlock(&dev->master_mutex);

 	DRM_DEBUG("%u\n", auth->magic);

 	return ret < 0 ? ret : 0;
 }

 int drm_authmagic(struct drm_device *dev, void *data,
 		  struct drm_file *file_priv)
 {
 	struct drm_auth *auth = data;
 	struct drm_file *file;

 	DRM_DEBUG("%u\n", auth->magic);

 	mutex_lock(&dev->master_mutex);
 	file = idr_find(&file_priv->master->magic_map, auth->magic);
 	if (file) {
 		file->authenticated = 1;
 		idr_replace(&file_priv->master->magic_map, NULL, auth->magic);
 	}
 	mutex_unlock(&dev->master_mutex);

 	return file ? 0 : -EINVAL;
 }

 struct drm_master *drm_master_create(struct drm_device *dev)
 {
 	struct drm_master *master;

 	master = kzalloc(sizeof(*master), GFP_KERNEL);
 	if (!master)
 		return NULL;

 	kref_init(&master->refcount);
 	drm_master_legacy_init(master);
 	idr_init(&master->magic_map);
 	master->dev = dev;

 	/* initialize the tree of output resource lessees */
 	INIT_LIST_HEAD(&master->lessees);
 	INIT_LIST_HEAD(&master->lessee_list);
 	idr_init(&master->leases);
 	idr_init(&master->lessee_idr);

 	return master;
 }

 static void drm_set_master(struct drm_device *dev, struct drm_file *fpriv,
 			   bool new_master)
 {
 	dev->master = drm_master_get(fpriv->master);
 	if (dev->driver->master_set)
 		dev->driver->master_set(dev, fpriv, new_master);

 	fpriv->was_master = true;
 }

 static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv)
 {
 	struct drm_master *old_master;

 	lockdep_assert_held_once(&dev->master_mutex);

 	WARN_ON(fpriv->is_master);
 	old_master = fpriv->master;
 	fpriv->master = drm_master_create(dev);
 	if (!fpriv->master) {
 		fpriv->master = old_master;
 		return -ENOMEM;
 	}

 	fpriv->is_master = 1;
 	fpriv->authenticated = 1;

 	drm_set_master(dev, fpriv, true);

 	if (old_master)
 		drm_master_put(&old_master);

 	return 0;
 }

 /*
  * In the olden days the SET/DROP_MASTER ioctls used to return EACCES when
  * CAP_SYS_ADMIN was not set. This was used to prevent rogue applications
  * from becoming master and/or failing to release it.
  *
  * At the same time, the first client (for a given VT) is _always_ master.
  * Thus in order for the ioctls to succeed, one had to _explicitly_ run the
  * application as root or flip the setuid bit.
  *
  * If the CAP_SYS_ADMIN was missing, no other client could become master...
  * EVER :-( Leading to a) the graphics session dying badly or b) a completely
  * locked session.
  *
  *
  * As some point systemd-logind was introduced to orchestrate and delegate
  * master as applicable. It does so by opening the fd and passing it to users
  * while in itself logind a) does the set/drop master per users' request and
  * b)  * implicitly drops master on VT switch.
  *
  * Even though logind looks like the future, there are a few issues:
  *  - some platforms don't have equivalent (Android, CrOS, some BSDs) so
  * root is required _solely_ for SET/DROP MASTER.
  *  - applications may not be updated to use it,
  *  - any client which fails to drop master* can DoS the application using
  * logind, to a varying degree.
  *
  * * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER.
  *
  *
  * Here we implement the next best thing:
  *  - ensure the logind style of fd passing works unchanged, and
  *  - allow a client to drop/set master, iff it is/was master at a given point
  * in time.
  *
  * Note: DROP_MASTER cannot be free for all, as an arbitrator user could:
  *  - DoS/crash the arbitrator - details would be implementation specific
  *  - open the node, become master implicitly and cause issues
  *
  * As a result this fixes the following when using root-less build w/o logind
  * - startx
  * - weston
  * - various compositors based on wlroots
  */
 static int
 drm_master_check_perm(struct drm_device *dev, struct drm_file *file_priv)
 {
 	if (file_priv->pid == task_pid(current) && file_priv->was_master)
 		return 0;

 	if (!capable(CAP_SYS_ADMIN))
 		return -EACCES;

 	return 0;
 }

 int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 			struct drm_file *file_priv)
 {
 	int ret;

 	mutex_lock(&dev->master_mutex);

 	ret = drm_master_check_perm(dev, file_priv);
 	if (ret)
 		goto out_unlock;

 	if (drm_is_current_master(file_priv))
 		goto out_unlock;

 	if (dev->master) {
 		ret = -EBUSY;
 		goto out_unlock;
 	}

 	if (!file_priv->master) {
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	if (!file_priv->is_master) {
 		ret = drm_new_set_master(dev, file_priv);
 		goto out_unlock;
 	}

 	if (file_priv->master->lessor != NULL) {
 		DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id);
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	drm_set_master(dev, file_priv, false);
 out_unlock:
 	mutex_unlock(&dev->master_mutex);
 	return ret;
 }

 static void drm_drop_master(struct drm_device *dev,
 			    struct drm_file *fpriv)
 {
 	if (dev->driver->master_drop)
 		dev->driver->master_drop(dev, fpriv);
 	drm_master_put(&dev->master);
 }

 int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
 			 struct drm_file *file_priv)
 {
 	int ret;

 	mutex_lock(&dev->master_mutex);

 	ret = drm_master_check_perm(dev, file_priv);
 	if (ret)
 		goto out_unlock;

 	if (!drm_is_current_master(file_priv)) {
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	if (!dev->master) {
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	if (file_priv->master->lessor != NULL) {
 		DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id);
 		ret = -EINVAL;
 		goto out_unlock;
 	}

 	drm_drop_master(dev, file_priv);
 out_unlock:
 	mutex_unlock(&dev->master_mutex);
 	return ret;
 }

 int drm_master_open(struct drm_file *file_priv)
 {
 	struct drm_device *dev = file_priv->minor->dev;
 	int ret = 0;

 	/* if there is no current master make this fd it, but do not create
 	 * any master object for render clients */
 	mutex_lock(&dev->master_mutex);
 	if (!dev->master)
 		ret = drm_new_set_master(dev, file_priv);
 	else
 		file_priv->master = drm_master_get(dev->master);
 	mutex_unlock(&dev->master_mutex);

 	return ret;
 }

 void drm_master_release(struct drm_file *file_priv)
 {
 	struct drm_device *dev = file_priv->minor->dev;
 	struct drm_master *master = file_priv->master;

 	mutex_lock(&dev->master_mutex);
 	if (file_priv->magic)
 		idr_remove(&file_priv->master->magic_map, file_priv->magic);

 	if (!drm_is_current_master(file_priv))
 		goto out;

 	drm_legacy_lock_master_cleanup(dev, master);

 	if (dev->master == file_priv->master)
 		drm_drop_master(dev, file_priv);
 out:
 	if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
 		/* Revoke any leases held by this or lessees, but only if
 		 * this is the "real" master
 		 */
 		drm_lease_revoke(master);
 	}

 	/* drop the master reference held by the file priv */
 	if (file_priv->master)
 		drm_master_put(&file_priv->master);
 	mutex_unlock(&dev->master_mutex);
 }

 /**
  * drm_is_current_master - checks whether @priv is the current master
  * @fpriv: DRM file private
  *
  * Checks whether @fpriv is current master on its device. This decides whether a
  * client is allowed to run DRM_MASTER IOCTLs.
  *
  * Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
  * - the current master is assumed to own the non-shareable display hardware.
  */
 bool drm_is_current_master(struct drm_file *fpriv)
 {
 	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
 }
 EXPORT_SYMBOL(drm_is_current_master);

 /**
  * drm_master_get - reference a master pointer
  * @master: &struct drm_master
  *
  * Increments the reference count of @master and returns a pointer to @master.
  */
 struct drm_master *drm_master_get(struct drm_master *master)
 {
 	kref_get(&master->refcount);
 	return master;
 }
 EXPORT_SYMBOL(drm_master_get);

 static void drm_master_destroy(struct kref *kref)
 {
 	struct drm_master *master = container_of(kref, struct drm_master, refcount);
 	struct drm_device *dev = master->dev;

 	if (drm_core_check_feature(dev, DRIVER_MODESET))
 		drm_lease_destroy(master);

 	drm_legacy_master_rmmaps(dev, master);

 	idr_destroy(&master->magic_map);
 	idr_destroy(&master->leases);
 	idr_destroy(&master->lessee_idr);

 	kfree(master->unique);
 	kfree(master);
 }

 /**
  * drm_master_put - unreference and clear a master pointer
  * @master: pointer to a pointer of &struct drm_master
  *
  * This decrements the &drm_master behind @master and sets it to NULL.
  */
 void drm_master_put(struct drm_master **master)
 {
 	kref_put(&(*master)->refcount, drm_master_destroy);
 	*master = NULL;
 }
 EXPORT_SYMBOL(drm_master_put);

 /* Used by drm_client and drm_fb_helper */
 bool drm_master_internal_acquire(struct drm_device *dev)
 {
 	mutex_lock(&dev->master_mutex);
 	if (dev->master) {
 		mutex_unlock(&dev->master_mutex);
 		return false;
 	}

 	return true;
 }
 EXPORT_SYMBOL(drm_master_internal_acquire);

 /* Used by drm_client and drm_fb_helper */
 void drm_master_internal_release(struct drm_device *dev)
 {
 	mutex_unlock(&dev->master_mutex);
 }
 EXPORT_SYMBOL(drm_master_internal_release);
	/*
	* Created: Tue Feb 2 08:37:54 1999 by faith@valinux.com
	*
	* Copyright 1999 Precision Insight, Inc., Cedar Park, Texas.
	* Copyright 2000 VA Linux Systems, Inc., Sunnyvale, California.
	* All Rights Reserved.
	*
	* Author Rickard E. (Rik) Faith <faith@valinux.com>
	* Author Gareth Hughes <gareth@valinux.com>
	*
	* Permission is hereby granted, free of charge, to any person obtaining a
	* copy of this software and associated documentation files (the "Software"),
	* to deal in the Software without restriction, including without limitation
	* the rights to use, copy, modify, merge, publish, distribute, sublicense,
	* and/or sell copies of the Software, and to permit persons to whom the
	* Software is furnished to do so, subject to the following conditions:
	*
	* The above copyright notice and this permission notice (including the next
	* paragraph) shall be included in all copies or substantial portions of the
	* Software.
	*
	* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
	* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
	* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
	* VA LINUX SYSTEMS AND/OR ITS SUPPLIERS BE LIABLE FOR ANY CLAIM, DAMAGES OR
	* OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
	* ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
	* OTHER DEALINGS IN THE SOFTWARE.
	*/

	#include <linux/slab.h>

	#include <drm/drm_auth.h>
	#include <drm/drm_drv.h>
	#include <drm/drm_file.h>
	#include <drm/drm_lease.h>
	#include <drm/drm_print.h>

	#include "drm_internal.h"
	#include "drm_legacy.h"

	/**
	* DOC: master and authentication
	*
	* &struct drm_master is used to track groups of clients with open
	* primary/legacy device nodes. For every &struct drm_file which has had at
	* least once successfully became the device master (either through the
	* SET_MASTER IOCTL, or implicitly through opening the primary device node when
	* no one else is the current master that time) there exists one &drm_master.
	* This is noted in &drm_file.is_master. All other clients have just a pointer
	* to the &drm_master they are associated with.
	*
	* In addition only one &drm_master can be the current master for a &drm_device.
	* It can be switched through the DROP_MASTER and SET_MASTER IOCTL, or
	* implicitly through closing/openeing the primary device node. See also
	* drm_is_current_master().
	*
	* Clients can authenticate against the current master (if it matches their own)
	* using the GETMAGIC and AUTHMAGIC IOCTLs. Together with exchanging masters,
	* this allows controlled access to the device for an entire group of mutually
	* trusted clients.
	*/

	int drm_getmagic(struct drm_device dev, void data, struct drm_file *file_priv)
	{
	struct drm_auth *auth = data;
	int ret = 0;

	mutex_lock(&dev->master_mutex);
	if (!file_priv->magic) {
	ret = idr_alloc(&file_priv->master->magic_map, file_priv,
	1, 0, GFP_KERNEL);
	if (ret >= 0)
	file_priv->magic = ret;
	}
	auth->magic = file_priv->magic;
	mutex_unlock(&dev->master_mutex);

	DRM_DEBUG("%u\n", auth->magic);

	return ret < 0 ? ret : 0;
	}

	int drm_authmagic(struct drm_device dev, void data,
	struct drm_file *file_priv)
	{
	struct drm_auth *auth = data;
	struct drm_file *file;

	DRM_DEBUG("%u\n", auth->magic);

	mutex_lock(&dev->master_mutex);
	file = idr_find(&file_priv->master->magic_map, auth->magic);
	if (file) {
	file->authenticated = 1;
	idr_replace(&file_priv->master->magic_map, NULL, auth->magic);
	}
	mutex_unlock(&dev->master_mutex);

	return file ? 0 : -EINVAL;
	}

	struct drm_master drm_master_create(struct drm_device dev)
	{
	struct drm_master *master;

	master = kzalloc(sizeof(*master), GFP_KERNEL);
	if (!master)
	return NULL;

	kref_init(&master->refcount);
	drm_master_legacy_init(master);
	idr_init(&master->magic_map);
	master->dev = dev;

	/* initialize the tree of output resource lessees */
	INIT_LIST_HEAD(&master->lessees);
	INIT_LIST_HEAD(&master->lessee_list);
	idr_init(&master->leases);
	idr_init(&master->lessee_idr);

	return master;
	}

	static void drm_set_master(struct drm_device dev, struct drm_file fpriv,
	bool new_master)
	{
	dev->master = drm_master_get(fpriv->master);
	if (dev->driver->master_set)
	dev->driver->master_set(dev, fpriv, new_master);

	fpriv->was_master = true;
	}

	static int drm_new_set_master(struct drm_device dev, struct drm_file fpriv)
	{
	struct drm_master *old_master;

	lockdep_assert_held_once(&dev->master_mutex);

	WARN_ON(fpriv->is_master);
	old_master = fpriv->master;
	fpriv->master = drm_master_create(dev);
	if (!fpriv->master) {
	fpriv->master = old_master;
	return -ENOMEM;
	}

	fpriv->is_master = 1;
	fpriv->authenticated = 1;

	drm_set_master(dev, fpriv, true);

	if (old_master)
	drm_master_put(&old_master);

	return 0;
	}

	/*
	* In the olden days the SET/DROP_MASTER ioctls used to return EACCES when
	* CAP_SYS_ADMIN was not set. This was used to prevent rogue applications
	* from becoming master and/or failing to release it.
	*
	* At the same time, the first client (for a given VT) is _always_ master.
	* Thus in order for the ioctls to succeed, one had to _explicitly_ run the
	* application as root or flip the setuid bit.
	*
	* If the CAP_SYS_ADMIN was missing, no other client could become master...
	* EVER :-( Leading to a) the graphics session dying badly or b) a completely
	* locked session.
	*
	*
	* As some point systemd-logind was introduced to orchestrate and delegate
	* master as applicable. It does so by opening the fd and passing it to users
	* while in itself logind a) does the set/drop master per users' request and
	* b) * implicitly drops master on VT switch.
	*
	* Even though logind looks like the future, there are a few issues:
	* - some platforms don't have equivalent (Android, CrOS, some BSDs) so
	* root is required _solely_ for SET/DROP MASTER.
	* - applications may not be updated to use it,
	* - any client which fails to drop master* can DoS the application using
	* logind, to a varying degree.
	*
	* * Either due missing CAP_SYS_ADMIN or simply not calling DROP_MASTER.
	*
	*
	* Here we implement the next best thing:
	* - ensure the logind style of fd passing works unchanged, and
	* - allow a client to drop/set master, iff it is/was master at a given point
	* in time.
	*
	* Note: DROP_MASTER cannot be free for all, as an arbitrator user could:
	* - DoS/crash the arbitrator - details would be implementation specific
	* - open the node, become master implicitly and cause issues
	*
	* As a result this fixes the following when using root-less build w/o logind
	* - startx
	* - weston
	* - various compositors based on wlroots
	*/
	static int
	drm_master_check_perm(struct drm_device dev, struct drm_file file_priv)
	{
	if (file_priv->pid == task_pid(current) && file_priv->was_master)
	return 0;

	if (!capable(CAP_SYS_ADMIN))
	return -EACCES;

	return 0;
	}

	int drm_setmaster_ioctl(struct drm_device dev, void data,
	struct drm_file *file_priv)
	{
	int ret;

	mutex_lock(&dev->master_mutex);

	ret = drm_master_check_perm(dev, file_priv);
	if (ret)
	goto out_unlock;

	if (drm_is_current_master(file_priv))
	goto out_unlock;

	if (dev->master) {
	ret = -EBUSY;
	goto out_unlock;
	}

	if (!file_priv->master) {
	ret = -EINVAL;
	goto out_unlock;
	}

	if (!file_priv->is_master) {
	ret = drm_new_set_master(dev, file_priv);
	goto out_unlock;
	}

	if (file_priv->master->lessor != NULL) {
	DRM_DEBUG_LEASE("Attempt to set lessee %d as master\n", file_priv->master->lessee_id);
	ret = -EINVAL;
	goto out_unlock;
	}

	drm_set_master(dev, file_priv, false);
	out_unlock:
	mutex_unlock(&dev->master_mutex);
	return ret;
	}

	static void drm_drop_master(struct drm_device *dev,
	struct drm_file *fpriv)
	{
	if (dev->driver->master_drop)
	dev->driver->master_drop(dev, fpriv);
	drm_master_put(&dev->master);
	}

	int drm_dropmaster_ioctl(struct drm_device dev, void data,
	struct drm_file *file_priv)
	{
	int ret;

	mutex_lock(&dev->master_mutex);

	ret = drm_master_check_perm(dev, file_priv);
	if (ret)
	goto out_unlock;

	if (!drm_is_current_master(file_priv)) {
	ret = -EINVAL;
	goto out_unlock;
	}

	if (!dev->master) {
	ret = -EINVAL;
	goto out_unlock;
	}

	if (file_priv->master->lessor != NULL) {
	DRM_DEBUG_LEASE("Attempt to drop lessee %d as master\n", file_priv->master->lessee_id);
	ret = -EINVAL;
	goto out_unlock;
	}

	drm_drop_master(dev, file_priv);
	out_unlock:
	mutex_unlock(&dev->master_mutex);
	return ret;
	}

	int drm_master_open(struct drm_file *file_priv)
	{
	struct drm_device *dev = file_priv->minor->dev;
	int ret = 0;

	/* if there is no current master make this fd it, but do not create
	* any master object for render clients */
	mutex_lock(&dev->master_mutex);
	if (!dev->master)
	ret = drm_new_set_master(dev, file_priv);
	else
	file_priv->master = drm_master_get(dev->master);
	mutex_unlock(&dev->master_mutex);

	return ret;
	}

	void drm_master_release(struct drm_file *file_priv)
	{
	struct drm_device *dev = file_priv->minor->dev;
	struct drm_master *master = file_priv->master;

	mutex_lock(&dev->master_mutex);
	if (file_priv->magic)
	idr_remove(&file_priv->master->magic_map, file_priv->magic);

	if (!drm_is_current_master(file_priv))
	goto out;

	drm_legacy_lock_master_cleanup(dev, master);

	if (dev->master == file_priv->master)
	drm_drop_master(dev, file_priv);
	out:
	if (drm_core_check_feature(dev, DRIVER_MODESET) && file_priv->is_master) {
	/* Revoke any leases held by this or lessees, but only if
	* this is the "real" master
	*/
	drm_lease_revoke(master);
	}

	/* drop the master reference held by the file priv */
	if (file_priv->master)
	drm_master_put(&file_priv->master);
	mutex_unlock(&dev->master_mutex);
	}

	/**
	* drm_is_current_master - checks whether @priv is the current master
	* @fpriv: DRM file private
	*
	* Checks whether @fpriv is current master on its device. This decides whether a
	* client is allowed to run DRM_MASTER IOCTLs.
	*
	* Most of the modern IOCTL which require DRM_MASTER are for kernel modesetting
	* - the current master is assumed to own the non-shareable display hardware.
	*/
	bool drm_is_current_master(struct drm_file *fpriv)
	{
	return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
	}
	EXPORT_SYMBOL(drm_is_current_master);

	/**
	* drm_master_get - reference a master pointer
	* @master: &struct drm_master
	*
	* Increments the reference count of @master and returns a pointer to @master.
	*/
	struct drm_master drm_master_get(struct drm_master master)
	{
	kref_get(&master->refcount);
	return master;
	}
	EXPORT_SYMBOL(drm_master_get);

	static void drm_master_destroy(struct kref *kref)
	{
	struct drm_master *master = container_of(kref, struct drm_master, refcount);
	struct drm_device *dev = master->dev;

	if (drm_core_check_feature(dev, DRIVER_MODESET))
	drm_lease_destroy(master);

	drm_legacy_master_rmmaps(dev, master);

	idr_destroy(&master->magic_map);
	idr_destroy(&master->leases);
	idr_destroy(&master->lessee_idr);

	kfree(master->unique);
	kfree(master);
	}

	/**
	* drm_master_put - unreference and clear a master pointer
	* @master: pointer to a pointer of &struct drm_master
	*
	* This decrements the &drm_master behind @master and sets it to NULL.
	*/
	void drm_master_put(struct drm_master **master)
	{
	kref_put(&(*master)->refcount, drm_master_destroy);
	*master = NULL;
	}
	EXPORT_SYMBOL(drm_master_put);

	/* Used by drm_client and drm_fb_helper */
	bool drm_master_internal_acquire(struct drm_device *dev)
	{
	mutex_lock(&dev->master_mutex);
	if (dev->master) {
	mutex_unlock(&dev->master_mutex);
	return false;
	}

	return true;
	}
	EXPORT_SYMBOL(drm_master_internal_acquire);

	/* Used by drm_client and drm_fb_helper */
	void drm_master_internal_release(struct drm_device *dev)
	{
	mutex_unlock(&dev->master_mutex);
	}
	EXPORT_SYMBOL(drm_master_internal_release);