drm: Protect the master management with a drm_device::master_mutex v3

The master management was previously protected by the drm_device::struct_mutex.
In order to avoid locking order violations in a reworked dropped master
security check in the vmwgfx driver, break it out into a separate master_mutex.
Locking order is master_mutex -> struct_mutex.

Also remove drm_master::blocked since it's not used.

v2: Add an inline comment about what drm_device::master_mutex is protecting.
v3: Remove unneeded struct_mutex locks. Fix error returns in
drm_setmaster_ioctl().

Signed-off-by: Thomas Hellstrom <[e-mail]>
Reviewed-by: Brian Paul <[e-mail]>
Reviewed-by: David Herrmann <[e-mail]>
Acked-by: Daniel Vetter <[e-mail]>

drivers/gpu/drm/drm_fops.c

···
 
 	/* if there is no current master make this fd it, but do not create
 	 * any master object for render clients */
-	mutex_lock(&dev->struct_mutex);
+	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) {
-			mutex_unlock(&dev->struct_mutex);
 			ret = -ENOMEM;
 			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;
 
-		mutex_unlock(&dev->struct_mutex);
 		if (dev->driver->master_create) {
 			ret = dev->driver->master_create(dev, priv->master);
 			if (ret) {
-				mutex_lock(&dev->struct_mutex);
 				/* drop both references if this fails */
 				drm_master_put(&priv->minor->master);
 				drm_master_put(&priv->master);
-				mutex_unlock(&dev->struct_mutex);
 				goto out_close;
 			}
 		}
-		mutex_lock(&dev->struct_mutex);
 		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);
-				mutex_unlock(&dev->struct_mutex);
 				goto out_close;
 			}
 		}
···
 		/* get a reference to the master */
 		priv->master = drm_master_get(priv->minor->master);
 	}
-	mutex_unlock(&dev->struct_mutex);
+	mutex_unlock(&dev->master_mutex);
 
 	mutex_lock(&dev->struct_mutex);
 	list_add(&priv->lhead, &dev->filelist);
···
 	return 0;
 
 out_close:
+	mutex_unlock(&dev->master_mutex);
 	if (dev->driver->postclose)
 		dev->driver->postclose(dev, priv);
 out_prime_destroy:
···
 	}
 	mutex_unlock(&dev->ctxlist_mutex);
 
-	mutex_lock(&dev->struct_mutex);
+	mutex_lock(&dev->master_mutex);
 
 	if (file_priv->is_master) {
 		struct drm_master *master = file_priv->master;
 		struct drm_file *temp;
+
+		mutex_lock(&dev->struct_mutex);
 		list_for_each_entry(temp, &dev->filelist, lhead) {
 			if ((temp->master == file_priv->master) &&
 			    (temp != file_priv))
···
 			master->lock.file_priv = NULL;
 			wake_up_interruptible_all(&master->lock.lock_queue);
 		}
+		mutex_unlock(&dev->struct_mutex);
 
 		if (file_priv->minor->master == file_priv->master) {
 			/* drop the reference held my the minor */
···
 		}
 	}
 
-	/* drop the reference held my the file priv */
+	/* drop the master reference held by the file priv */
 	if (file_priv->master)
 		drm_master_put(&file_priv->master);
 	file_priv->is_master = 0;
+	mutex_unlock(&dev->master_mutex);
+
+	mutex_lock(&dev->struct_mutex);
 	list_del(&file_priv->lhead);
 	mutex_unlock(&dev->struct_mutex);
 

drivers/gpu/drm/drm_stub.c

···
 	struct drm_device *dev = master->minor->dev;
 	struct drm_map_list *r_list, *list_temp;
 
+	mutex_lock(&dev->struct_mutex);
 	if (dev->driver->master_destroy)
 		dev->driver->master_destroy(dev, master);
 
···
 
 	drm_ht_remove(&master->magiclist);
 
+	mutex_unlock(&dev->struct_mutex);
 	kfree(master);
 }
 
···
 {
 	int ret = 0;
 
+	mutex_lock(&dev->master_mutex);
 	if (file_priv->is_master)
-		return 0;
+		goto out_unlock;
 
-	if (file_priv->minor->master && file_priv->minor->master != file_priv->master)
-		return -EINVAL;
+	if (file_priv->minor->master) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
 
-	if (!file_priv->master)
-		return -EINVAL;
+	if (!file_priv->master) {
+		ret = -EINVAL;
+		goto out_unlock;
+	}
 
-	if (file_priv->minor->master)
-		return -EINVAL;
-
-	mutex_lock(&dev->struct_mutex);
 	file_priv->minor->master = drm_master_get(file_priv->master);
 	file_priv->is_master = 1;
 	if (dev->driver->master_set) {
···
 			drm_master_put(&file_priv->minor->master);
 		}
 	}
-	mutex_unlock(&dev->struct_mutex);
 
+out_unlock:
+	mutex_unlock(&dev->master_mutex);
 	return ret;
 }
 
 int drm_dropmaster_ioctl(struct drm_device *dev, void *data,
 			 struct drm_file *file_priv)
 {
+	int ret = -EINVAL;
+
+	mutex_lock(&dev->master_mutex);
 	if (!file_priv->is_master)
-		return -EINVAL;
+		goto out_unlock;
 
 	if (!file_priv->minor->master)
-		return -EINVAL;
+		goto out_unlock;
 
-	mutex_lock(&dev->struct_mutex);
+	ret = 0;
 	if (dev->driver->master_drop)
 		dev->driver->master_drop(dev, file_priv, false);
 	drm_master_put(&file_priv->minor->master);
 	file_priv->is_master = 0;
-	mutex_unlock(&dev->struct_mutex);
-	return 0;
+
+out_unlock:
+	mutex_unlock(&dev->master_mutex);
+	return ret;
 }
 
 /*
···
 	spin_lock_init(&dev->event_lock);
 	mutex_init(&dev->struct_mutex);
 	mutex_init(&dev->ctxlist_mutex);
+	mutex_init(&dev->master_mutex);
 
 	dev->anon_inode = drm_fs_inode_new();
 	if (IS_ERR(dev->anon_inode)) {
···
 	drm_minor_free(dev, DRM_MINOR_CONTROL);
 	drm_fs_inode_free(dev->anon_inode);
 err_free:
+	mutex_destroy(&dev->master_mutex);
 	kfree(dev);
 	return NULL;
 }
···
 	drm_minor_free(dev, DRM_MINOR_CONTROL);
 
 	kfree(dev->devname);
+
+	mutex_destroy(&dev->master_mutex);
 	kfree(dev);
 }
 

include/drm/drmP.h

···
 struct drm_file {
 	unsigned always_authenticated :1;
 	unsigned authenticated :1;
-	unsigned is_master :1; /* this file private is a master for a minor */
+	/* Whether we're master for a minor. Protected by master_mutex */
+	unsigned is_master :1;
 	/* true when the client has asked us to expose stereo 3D mode flags */
 	unsigned stereo_allowed :1;
 
···
 
 #include <drm/drm_crtc.h>
 
-/* per-master structure */
+/**
+ * struct drm_master - drm master structure
+ *
+ * @refcount: Refcount for this master object.
+ * @minor: Link back to minor char device we are master for. Immutable.
+ * @unique: Unique identifier: e.g. busid. Protected by drm_global_mutex.
+ * @unique_len: Length of unique field. Protected by drm_global_mutex.
+ * @unique_size: Amount allocated. Protected by drm_global_mutex.
+ * @magiclist: Hash of used authentication tokens. Protected by struct_mutex.
+ * @magicfree: List of used authentication tokens. Protected by struct_mutex.
+ * @lock: DRI lock information.
+ * @driver_priv: Pointer to driver-private information.
+ */
 struct drm_master {
-
-	struct kref refcount; /* refcount for this master */
-
-	struct drm_minor *minor; /**< link back to minor we are a master for */
-
-	char *unique;			/**< Unique identifier: e.g., busid */
-	int unique_len;			/**< Length of unique field */
-	int unique_size;		/**< amount allocated */
-
-	int blocked;			/**< Blocked due to VC switch? */
-
-	/** \name Authentication */
-	/*@{ */
+	struct kref refcount;
+	struct drm_minor *minor;
+	char *unique;
+	int unique_len;
+	int unique_size;
 	struct drm_open_hash magiclist;
 	struct list_head magicfree;
-	/*@} */
-
-	struct drm_lock_data lock;	/**< Information on hardware lock */
-
-	void *driver_priv; /**< Private structure for driver to use */
+	struct drm_lock_data lock;
+	void *driver_priv;
 };
 
 /* Size of ringbuffer for vblank timestamps. Just double-buffer
···
 	struct list_head debugfs_list;
 	struct mutex debugfs_lock; /* Protects debugfs_list. */
 
-	struct drm_master *master; /* currently active master for this node */
+	/* currently active master for this node. Protected by master_mutex */
+	struct drm_master *master;
 	struct drm_mode_group mode_group;
 };
 
···
 	/*@{ */
 	spinlock_t count_lock;		/**< For inuse, drm_device::open_count, drm_device::buf_use */
 	struct mutex struct_mutex;	/**< For others */
+	struct mutex master_mutex;      /**< For drm_minor::master and drm_file::is_master */
 	/*@} */
 
 	/** \name Usage Counters */