On Thu, Aug 26, 2021 at 10:01:16AM +0800, Desmond Cheong Zhi Xi wrote: > drm_master_release can be called on a drm_file without a master, which > results in a null ptr dereference of file_priv->master->magic_map. The > three cases are: > > 1. Error path in drm_open_helper > drm_open(): > drm_open_helper(): > drm_master_open(): > drm_new_set_master(); <--- returns -ENOMEM, > drm_file.master not set > drm_file_free(): > drm_master_release(); <--- NULL ptr dereference > (file_priv->master->magic_map) > > 2. Error path in mock_drm_getfile > mock_drm_getfile(): > anon_inode_getfile(); <--- returns error, drm_file.master not set > drm_file_free(): > drm_master_release(); <--- NULL ptr dereference > (file_priv->master->magic_map) > > 3. In drm_client_close, as drm_client_open doesn't set up a master > > drm_file.master is set up in drm_open_helper through the call to > drm_master_open, so we mirror it with a call to drm_master_release in > drm_close_helper, and remove drm_master_release from drm_file_free to > avoid the null ptr dereference. > > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> I guess we should also have a cc: stable on this one? I think this bug existed since pretty much forever, but maybe more prominent with the drm_client stuff added a while ago. -Daniel > --- > drivers/gpu/drm/drm_file.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) > > diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c > index ed25168619fc..90b62f360da1 100644 > --- a/drivers/gpu/drm/drm_file.c > +++ b/drivers/gpu/drm/drm_file.c > @@ -282,9 +282,6 @@ void drm_file_free(struct drm_file *file) > > drm_legacy_ctxbitmap_flush(dev, file); > > - if (drm_is_primary_client(file)) > - drm_master_release(file); > - > if (dev->driver->postclose) > dev->driver->postclose(dev, file); > > @@ -305,6 +302,9 @@ static void drm_close_helper(struct file *filp) > list_del(&file_priv->lhead); > mutex_unlock(&dev->filelist_mutex); > > + if (drm_is_primary_client(file_priv)) > + drm_master_release(file_priv); > + > drm_file_free(file_priv); > } > > -- > 2.25.1 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch
