On Wed, Aug 18, 2021 at 03:38:18PM +0800, Desmond Cheong Zhi Xi wrote:
There is a window after calling drm_master_release, and before a file is freed, where drm_file can have is_master set to true, but both the drm_file and drm_device have no master.
This could result in wrongly approving permissions in drm_is_current_master_locked. Add a check that fpriv->master is non-NULl to guard against this scenario.
Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com
This should be impossible, drm_master_release is only called when the struct file is released, which means all ioctls and anything else have finished (they hold a temporary reference).
fpriv->master can change (if the drm_file becomes newly minted master and wasnt one before through the setmaster ioctl), but it cannot become NULL before it's completely gone from the system. -Daniel
drivers/gpu/drm/drm_auth.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 8c0e0dba1611..f9267b21556e 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -66,7 +66,8 @@ static bool drm_is_current_master_locked(struct drm_file *fpriv) lockdep_assert_once(lockdep_is_held(&fpriv->minor->dev->master_lookup_lock) || lockdep_is_held(&fpriv->minor->dev->master_mutex));
- return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
- return (fpriv->is_master && fpriv->master &&
drm_lease_owner(fpriv->master) == fpriv->minor->dev->master);} /** -- 2.25.1