[PATCH 1/2] drm: Do not drop root privileges for a fancier younger process

[Chris Wilson]

When a second process opens the device and master transferrence is
complete, we walk the list of open devices and remove their
authentication. This also revokes our root privilege. Instead of simply
dropping the authentication, this patch reverts the authenticated state
back to its original value.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_fops.c | 5 +++--
 include/drm/drmP.h         | 1 +
 2 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index da1940ae9a2d..2f8b41c58d02 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -239,7 +239,8 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
 
 	priv->ioctl_count = 0;
 	/* for compatibility root is always authenticated */
-	priv->authenticated = capable(CAP_SYS_ADMIN);
+	priv->always_authenticated = capable(CAP_SYS_ADMIN);
+	priv->authenticated = priv->always_authenticated;
 	priv->lock_count = 0;
 
 	INIT_LIST_HEAD(&priv->lhead);
@@ -523,7 +524,7 @@ int drm_release(struct inode *inode, struct file *filp)
 		list_for_each_entry(temp, &dev->filelist, lhead) {
 			if ((temp->master == file_priv->master) &&
 			    (temp != file_priv))
-				temp->authenticated = 0;
+				temp->authenticated = temp->always_authenticated;
 		}
 
 		/**
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index 490534c990b7..3a90857bd0ee 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -412,6 +412,7 @@ struct drm_prime_file_private {
 
 /** File private data */
 struct drm_file {
+	int always_authenticated;
 	int authenticated;
 	struct pid *pid;
 	kuid_t uid;
-- 
1.8.4.rc3