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 <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Acked-by: Daniel Vetter <daniel@ffwll.ch>

3 files changed, 64 insertions, 47 deletions

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index c7792b1d1773..a0ce39c96f8e 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -231,12 +231,11 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
 
         /* 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;
                 }
@@ -244,29 +243,23 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
                 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;
                         }
                 }
@@ -274,7 +267,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
                 /* 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);
@@ -302,6 +295,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
         return 0;
 
 out_close:
+        mutex_unlock(&dev->master_mutex);
         if (dev->driver->postclose)
                 dev->driver->postclose(dev, priv);
 out_prime_destroy:
@@ -489,11 +483,13 @@ int drm_release(struct inode *inode, struct file *filp)
         }
         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))
@@ -512,6 +508,7 @@ int drm_release(struct inode *inode, struct file *filp)
                         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 */
@@ -521,10 +518,13 @@ int drm_release(struct inode *inode, struct file *filp)
                 }
         }
 
-        /* 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);
 
diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c
index a378af49ed2e..fac6f9834257 100644
--- a/drivers/gpu/drm/drm_stub.c
+++ b/drivers/gpu/drm/drm_stub.c
@@ -144,6 +144,7 @@ static void drm_master_destroy(struct kref *kref)
         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);
 
@@ -171,6 +172,7 @@ static void drm_master_destroy(struct kref *kref)
 
         drm_ht_remove(&master->magiclist);
 
+        mutex_unlock(&dev->struct_mutex);
         kfree(master);
 }
 
@@ -186,19 +188,20 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
 {
         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->master)
-                return -EINVAL;
+        if (file_priv->minor->master) {
+                ret = -EINVAL;
+                goto out_unlock;
+        }
 
-        if (file_priv->minor->master)
-                return -EINVAL;
+        if (!file_priv->master) {
+                ret = -EINVAL;
+                goto out_unlock;
+        }
 
-        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) {
@@ -208,27 +211,33 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data,
                         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;
 }
 
 /*
@@ -559,6 +568,7 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
         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)) {
@@ -612,6 +622,7 @@ err_minors:
         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;
 }
@@ -633,6 +644,8 @@ static void drm_dev_release(struct kref *ref)
         drm_minor_free(dev, DRM_MINOR_CONTROL);
 
         kfree(dev->devname);
+
+        mutex_destroy(&dev->master_mutex);
         kfree(dev);
 }
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 3d594ca7fa62..4e24a1a0daeb 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -405,7 +405,8 @@ struct drm_prime_file_private {
 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;
 
@@ -684,28 +685,29 @@ struct drm_gem_object {
 
 #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
@@ -1020,7 +1022,8 @@ struct drm_minor {
         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;
 };
 
@@ -1070,6 +1073,7 @@ struct drm_device {
         /*@{ */
         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 */