On Tue, Jun 15, 2021 at 10:36:44AM +0800, Desmond Cheong Zhi Xi wrote:
While checking the master status of the DRM file in drm_is_current_master(), the device's master mutex should be held. Without the mutex, the pointer fpriv->master may be freed concurrently by another process calling drm_setmaster_ioctl(). This could lead to use-after-free errors when the pointer is subsequently dereferenced in drm_lease_owner().
The callers of drm_is_current_master() from drm_auth.c hold the device's master mutex, but external callers do not. Hence, we implement drm_is_current_master_locked() to be used within drm_auth.c, and modify drm_is_current_master() to grab the device's master mutex before checking the master status.
Reported-by: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Desmond Cheong Zhi Xi desmondcheongzx@gmail.com Reviewed-by: Emil Velikov emil.l.velikov@gmail.com
drivers/gpu/drm/drm_auth.c | 23 +++++++++++++++++++---- 1 file changed, 19 insertions(+), 4 deletions(-)
diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index 232abbba3686..c6bf52c310a9 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -61,6 +61,8 @@
- trusted clients.
*/
+static bool drm_is_current_master_locked(struct drm_file *fpriv);
A bit a bikeshed, but we try to avoid forward declarations when they're not needed. If you don't want to tear apart drm_is_current_master and the _locked version then just move them together.
Can you pls do that and respin?
Otherwise looks all great. -Daniel
int drm_getmagic(struct drm_device *dev, void *data, struct drm_file *file_priv) { struct drm_auth *auth = data; @@ -223,7 +225,7 @@ int drm_setmaster_ioctl(struct drm_device *dev, void *data, if (ret) goto out_unlock;
- if (drm_is_current_master(file_priv))
if (drm_is_current_master_locked(file_priv)) goto out_unlock;
if (dev->master) {
@@ -272,7 +274,7 @@ int drm_dropmaster_ioctl(struct drm_device *dev, void *data, if (ret) goto out_unlock;
- if (!drm_is_current_master(file_priv)) {
- if (!drm_is_current_master_locked(file_priv)) { ret = -EINVAL; goto out_unlock; }
@@ -321,7 +323,7 @@ void drm_master_release(struct drm_file *file_priv) if (file_priv->magic) idr_remove(&file_priv->master->magic_map, file_priv->magic);
- if (!drm_is_current_master(file_priv))
if (!drm_is_current_master_locked(file_priv)) goto out;
drm_legacy_lock_master_cleanup(dev, master);
@@ -342,6 +344,13 @@ void drm_master_release(struct drm_file *file_priv) mutex_unlock(&dev->master_mutex); }
+static bool drm_is_current_master_locked(struct drm_file *fpriv) +{
- lockdep_assert_held_once(&fpriv->master->dev->master_mutex);
- return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
+}
/**
- drm_is_current_master - checks whether @priv is the current master
- @fpriv: DRM file private
@@ -354,7 +363,13 @@ void drm_master_release(struct drm_file *file_priv) */ bool drm_is_current_master(struct drm_file *fpriv) {
- return fpriv->is_master && drm_lease_owner(fpriv->master) == fpriv->minor->dev->master;
- bool ret;
- mutex_lock(&fpriv->master->dev->master_mutex);
- ret = drm_is_current_master_locked(fpriv);
- mutex_unlock(&fpriv->master->dev->master_mutex);
- return ret;
} EXPORT_SYMBOL(drm_is_current_master);
-- 2.25.1