[PATCH 3/3] drm: allow render capable master with DRM_AUTH ioctls

[Emil Velikov]

From: Emil Velikov <emil.velikov at collabora.com>

There are cases (in mesa and applications) where one would open the
primary node without properly authenticating the client.

Sometimes we don't check if the authentication succeeds, but there's
also cases we simply forget to do it. Mesa has been fixed recently
although, there's the question of older drivers or other apps that
exbibit this behaviour.

To workaround this, some users resort to running their apps under sudo.
Which admittedly isn't always a good idea.

Since any DRIVER_RENDER driver has sufficient isolation between clients,
we can use that, for unauthenticated [primary node] ioctls that require
DRM_AUTH. But only if the respective ioctl is tagged as DRM_RENDER_ALLOW.

As an added bonus this allows us to use vgem in userspace with zero
change to some (but not all) existing programs.

Signed-off-by: Emil Velikov <emil.velikov at collabora.com>
---
 drivers/gpu/drm/drm_ioctl.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 2221c8857fb0..4c775b775395 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -521,13 +521,17 @@ int drm_version(struct drm_device *dev, void *data,
  */
 int drm_ioctl_permit(u32 flags, struct drm_file *file_priv)
 {
+	const struct drm_device *dev = file_priv->minor->dev;
+
 	/* ROOT_ONLY is only for CAP_SYS_ADMIN */
 	if (unlikely((flags & DRM_ROOT_ONLY) && !capable(CAP_SYS_ADMIN)))
 		return -EACCES;
 
-	/* AUTH is only for authenticated or render client */
+	/* AUTH is only for authenticated/render capable master or render client */
 	if (unlikely((flags & DRM_AUTH) && !drm_is_render_client(file_priv) &&
-		     !file_priv->authenticated))
+		     !file_priv->authenticated &&
+		     !(drm_core_check_feature(dev, DRIVER_RENDER) &&
+		       (flags & DRM_RENDER_ALLOW))))
 		return -EACCES;
 
 	/* MASTER is only for master or control clients */
-- 
2.19.2