drm: Make control nodes master-less v3

Like for render-nodes, there is no point in maintaining the master concept
for control nodes, so set the struct drm_file::master pointer to NULL.

At the same time, make sure DRM_MASTER | DRM_CONTROL_ALLOW ioctls are always
allowed when called through the control node. Previously the caller also
needed to be master.

v2: Adapt to refactoring of ioctl permission check.
v3: Formatting of logical expression. Use drm_is_control_client() instead of
    drm_is_control().
Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Brian Paul <brianp@vmware.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>

drivers/gpu/drm/drm_drv.c

@@ -306,13 +306,14 @@ static int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
 		     !file_priv->authenticated))
 		return -EACCES;
 
-	/* MASTER is only for master */
-	if (unlikely((flags & DRM_MASTER) && !file_priv->is_master))
+	/* MASTER is only for master or control clients */
+	if (unlikely((flags & DRM_MASTER) && !file_priv->is_master &&
+		     !drm_is_control_client(file_priv)))
 		return -EACCES;
 
 	/* Control clients must be explicitly allowed */
 	if (unlikely(!(flags & DRM_CONTROL_ALLOW) &&
-		     file_priv->minor->type == DRM_MINOR_CONTROL))
+		     drm_is_control_client(file_priv)))
 		return -EACCES;
 
 	/* Render clients must be explicitly allowed */

drivers/gpu/drm/drm_fops.c

@@ -232,7 +232,8 @@ 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);
-	if (!priv->minor->master && !drm_is_render_client(priv)) {
+	if (!priv->minor->master && !drm_is_render_client(priv) &&
+	    !drm_is_control_client(priv)) {
 		/* create a new master */
 		priv->minor->master = drm_master_create(priv->minor);
 		if (!priv->minor->master) {
@@ -270,7 +271,8 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
 				goto out_close;
 			}
 		}
-	} else if (!drm_is_render_client(priv)) {
+	} else if (!drm_is_render_client(priv) &&
+		   !drm_is_control_client(priv)) {
 		/* get a reference to the master */
 		priv->master = drm_master_get(priv->minor->master);
 	}

include/drm/drmP.h

@@ -1207,6 +1207,11 @@ static inline bool drm_is_render_client(struct drm_file *file_priv)
 	return file_priv->minor->type == DRM_MINOR_RENDER;
 }
 
+static inline bool drm_is_control_client(const struct drm_file *file_priv)
+{
+	return file_priv->minor->type == DRM_MINOR_CONTROL;
+}
+
 /******************************************************************/
 /** \name Internal function definitions */
 /*@{*/