From 56f0729a510f92151682ff6c89f69724d5595d6e Mon Sep 17 00:00:00 2001 From: Desmond Cheong Zhi Xi Date: Mon, 12 Jul 2021 12:35:08 +0800 Subject: drm: protect drm_master pointers in drm_lease.c drm_file->master pointers should be protected by drm_device.master_mutex or drm_file.master_lookup_lock when being dereferenced. However, in drm_lease.c, there are multiple instances where drm_file->master is accessed and dereferenced while neither lock is held. This makes drm_lease.c vulnerable to use-after-free bugs. We address this issue in 2 ways: 1. Add a new drm_file_get_master() function that calls drm_master_get on drm_file->master while holding on to drm_file.master_lookup_lock. Since drm_master_get increments the reference count of master, this prevents master from being freed until we unreference it with drm_master_put. 2. In each case where drm_file->master is directly accessed and eventually dereferenced in drm_lease.c, we wrap the access in a call to the new drm_file_get_master function, then unreference the master pointer once we are done using it. Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi Reviewed-by: Emil Velikov Signed-off-by: Daniel Vetter Link: https://patchwork.freedesktop.org/patch/msgid/20210712043508.11584-6-desmondcheongzx@gmail.com --- include/drm/drm_auth.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/drm/drm_auth.h') diff --git a/include/drm/drm_auth.h b/include/drm/drm_auth.h index 6bf8b2b78991..f99d3417f304 100644 --- a/include/drm/drm_auth.h +++ b/include/drm/drm_auth.h @@ -107,6 +107,7 @@ struct drm_master { }; struct drm_master *drm_master_get(struct drm_master *master); +struct drm_master *drm_file_get_master(struct drm_file *file_priv); void drm_master_put(struct drm_master **master); bool drm_is_current_master(struct drm_file *fpriv); -- cgit v1.2.3-71-gd317