drm/vmwgfx: Allow dropped masters render-node like access on legacy nodes v2

Applications like gnome-shell may try to render after dropping master
privileges. Since the driver should now be safe against this scenario,
allow those applications to use their legacy node like a render node.

v2: Add missing return statement.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Sinclair Yeh <syeh@vmware.com>

drivers/gpu/drm/vmwgfx/vmwgfx_drv.c

@@ -1052,10 +1052,15 @@ static struct vmw_master *vmw_master_check(struct drm_device *dev,
 	}
 
 	/*
-	 * Check if we were previously master, but now dropped.
+	 * Check if we were previously master, but now dropped. In that
+	 * case, allow at least render node functionality.
 	 */
 	if (vmw_fp->locked_master) {
 		mutex_unlock(&dev->master_mutex);
+
+		if (flags & DRM_RENDER_ALLOW)
+			return NULL;
+
 		DRM_ERROR("Dropped master trying to access ioctl that "
 			  "requires authentication.\n");
 		return ERR_PTR(-EACCES);

drivers/gpu/drm/vmwgfx/vmwgfx_surface.c

@@ -911,6 +911,12 @@ vmw_surface_handle_reference(struct vmw_private *dev_priv,
 				  "surface reference.\n");
 			return -EACCES;
 		}
+		if (ACCESS_ONCE(vmw_fpriv(file_priv)->locked_master)) {
+			DRM_ERROR("Locked master refused legacy "
+				  "surface reference.\n");
+			return -EACCES;
+		}
+
 		handle = u_handle;
 	}