drm: don't de-authenticate clients on master-close

If an active DRM-Master closes its device, we deauthenticate all clients
on that master. However, if an inactive DRM-Master closes its device, we
do nothing. This is quite inconsistent and breaks several scenarios:

 1) If this was used as security mechanism, it fails horribly if a master
    closes a device while VT switched away. Furthermore, none of the few
    drivers using ->master_*() callbacks seems to require it, anyway.

 2) If you spawn weston (or any other non-UMS compositor) in background
    while another compositor is active, both will get assigned to the
    same "drm_master" object. If the foreground compositor now exits, all
    clients of both the foreground AND background compositor will be
    de-authenticated leading to unexpected behavior.

Stop this non-sense and keep clients authenticated. We don't do this when
dropping DRM-Master (i.e., switching VTs) so don't do it on active-close
either!

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: David Herrmann <dh.herrmann@gmail.com>

2 files changed, 2 insertions, 12 deletions

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 53435e07fa8d..3299175da6ac 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -199,8 +199,7 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
         priv->minor = minor;
 
         /* for compatibility root is always authenticated */
-        priv->always_authenticated = capable(CAP_SYS_ADMIN);
-        priv->authenticated = priv->always_authenticated;
+        priv->authenticated = capable(CAP_SYS_ADMIN);
         priv->lock_count = 0;
 
         INIT_LIST_HEAD(&priv->lhead);
@@ -462,20 +461,12 @@ int drm_release(struct inode *inode, struct file *filp)
 
         if (drm_is_master(file_priv)) {
                 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))
-                                temp->authenticated = temp->always_authenticated;
-                }
 
                 /**
                  * Since the master is disappearing, so is the
                  * possibility to lock.
                  */
-
+                mutex_lock(&dev->struct_mutex);
                 if (master->lock.hw_lock) {
                         if (dev->sigdata.lock == master->lock.hw_lock)
                                 dev->sigdata.lock = NULL;
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 6ede53712d7b..e67058cc527e 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -385,7 +385,6 @@ struct drm_prime_file_private {
 
 /** File private data */
 struct drm_file {
-        unsigned always_authenticated :1;
         unsigned authenticated :1;
         /* true when the client has asked us to expose stereo 3D mode flags */
         unsigned stereo_allowed :1;