userns: Convert drm to use kuid and kgid and struct pid where appropriate

Blink Blink this had not been converted to use struct pid ages ago?

- On drm open capture the openers kuid and struct pid.
- On drm close release the kuid and struct pid
- When reporting the uid and pid convert the kuid and struct pid
  into values in the appropriate namespace.

Cc: dri-devel@lists.freedesktop.org
Acked-by: Dave Airlie <airlied@redhat.com>
Acked-by: Serge Hallyn <serge.hallyn@canonical.com>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>

drivers/gpu/drm/drm_fops.c

@@ -251,7 +251,7 @@ static int drm_open_helper(struct inode *inode, struct file *filp,
 	filp->private_data = priv;
 	priv->filp = filp;
 	priv->uid = current_euid();
-	priv->pid = task_pid_nr(current);
+	priv->pid = get_pid(task_pid(current));
 	priv->minor = idr_find(&drm_minors_idr, minor_id);
 	priv->ioctl_count = 0;
 	/* for compatibility root is always authenticated */
@@ -524,6 +524,7 @@ int drm_release(struct inode *inode, struct file *filp)
 	if (drm_core_check_feature(dev, DRIVER_PRIME))
 		drm_prime_destroy_file_private(&file_priv->prime);
 
+	put_pid(file_priv->pid);
 	kfree(file_priv);
 
 	/* ========================================================