[PATCH 2/8] drm: remove redundant drm_file->uid

[David Herrmann <dh.herrmann@gmail.com>]

Each DRM file-context caches the EUID of the process that opened the file.
It is used exclusively for debugging purposes in /proc/dri/ and friends.

Note, however, that "struct file" already caches the credentials of a
process at open-time. So lets just use drm_file->filp->f_cred->euid if
available. The pointer-chasing will not hurt us, since it is only about
debugging, anyway.

Check priv->filp for NULL before deref, to prepare for in-kernel contexts
(if they ever appear). We should not rely on "struct file" contexts to be
around at all times, anyway.

Signed-off-by: David Herrmann <dh.herrmann@gmail.com>
---
 drivers/gpu/drm/drm_fops.c  | 1 -
 drivers/gpu/drm/drm_info.c  | 4 +++-
 drivers/gpu/drm/drm_ioctl.c | 4 +++-
 include/drm/drmP.h          | 1 -
 4 files changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c
index 323c238..e9d66f5 100644
--- a/drivers/gpu/drm/drm_fops.c
+++ b/drivers/gpu/drm/drm_fops.c
@@ -199,7 +199,6 @@ static int drm_open_helper(struct file *filp, struct drm_minor *minor)
 
 	filp->private_data = priv;
 	priv->filp = filp;
-	priv->uid = current_euid();
 	priv->pid = get_pid(task_pid(current));
 	priv->minor = minor;
 
diff --git a/drivers/gpu/drm/drm_info.c b/drivers/gpu/drm/drm_info.c
index 9ae353f..247ba2b 100644
--- a/drivers/gpu/drm/drm_info.c
+++ b/drivers/gpu/drm/drm_info.c
@@ -80,6 +80,7 @@ int drm_clients_info(struct seq_file *m, void *data)
 	struct drm_info_node *node = (struct drm_info_node *) m->private;
 	struct drm_device *dev = node->minor->dev;
 	struct drm_file *priv;
+	kuid_t uid;
 
 	seq_printf(m,
 		   "%20s %5s %3s master a %5s %10s\n",
@@ -98,13 +99,14 @@ int drm_clients_info(struct seq_file *m, void *data)
 
 		rcu_read_lock(); /* locks pid_task()->comm */
 		task = pid_task(priv->pid, PIDTYPE_PID);
+		uid = priv->filp ? priv->filp->f_cred->euid : GLOBAL_ROOT_UID;
 		seq_printf(m, "%20s %5d %3d   %c    %c %5d %10u\n",
 			   task ? task->comm : "<unknown>",
 			   pid_vnr(priv->pid),
 			   priv->minor->index,
 			   drm_is_current_master(priv) ? 'y' : 'n',
 			   priv->authenticated ? 'y' : 'n',
-			   from_kuid_munged(seq_user_ns(m), priv->uid),
+			   from_kuid_munged(seq_user_ns(m), uid),
 			   priv->magic);
 		rcu_read_unlock();
 	}
diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c
index 33af4a5..49cd835 100644
--- a/drivers/gpu/drm/drm_ioctl.c
+++ b/drivers/gpu/drm/drm_ioctl.c
@@ -191,7 +191,9 @@ static int drm_getclient(struct drm_device *dev, void *data,
 		client->auth = file_priv->authenticated;
 		client->pid = pid_vnr(file_priv->pid);
 		client->uid = from_kuid_munged(current_user_ns(),
-					       file_priv->uid);
+					       file_priv->filp ?
+					       file_priv->filp->f_cred->euid :
+					       GLOBAL_ROOT_UID);
 		client->magic = 0;
 		client->iocs = 0;
 
diff --git a/include/drm/drmP.h b/include/drm/drmP.h
index d488a72..0f69f56 100644
--- a/include/drm/drmP.h
+++ b/include/drm/drmP.h
@@ -320,7 +320,6 @@ struct drm_file {
 	unsigned is_master:1;
 
 	struct pid *pid;
-	kuid_t uid;
 	drm_magic_t magic;
 	struct list_head lhead;
 	struct drm_minor *minor;
-- 
2.9.2

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