This patch series addresses potential use-after-free errors when dereferencing pointers to struct drm_master. These were identified after one such bug was caught by Syzbot in drm_getunique(): https://syzkaller.appspot.com/bug?id=148d2f1dfac64af52ffd27b661981a540724f80...
The series is broken up into two patches:
1. Implement a locked version of drm_is_current_master() function that's used within drm_auth.c.
2. Identify areas in drm_lease.c where pointers to struct drm_master are dereferenced, and ensure that the master pointers are not freed during use.
Changes in v2 -> v3: - Patch 1: Move the definition of drm_is_current_master and the _locked version higher up in drm_auth.c to avoid needing a forward declaration of drm_is_current_master_locked. As suggested by Daniel Vetter.
- Patch 2: Instead of leaking drm_device.master_mutex into drm_lease.c to protect drm_master pointers, add a new drm_file_get_master() function that returns drm_file->master while increasing its reference count, to prevent drm_file->master from being freed. As suggested by Daniel Vetter.
Changes in v1 -> v2: - Patch 2: Move the lock and assignment before the DRM_DEBUG_LEASE in drm_mode_get_lease_ioctl, as suggested by Emil Velikov.
Desmond Cheong Zhi Xi (2): drm: add a locked version of drm_is_current_master drm: protect drm_master pointers in drm_lease.c
drivers/gpu/drm/drm_auth.c | 73 +++++++++++++++++++++++++++---------- drivers/gpu/drm/drm_lease.c | 57 ++++++++++++++++++++--------- include/drm/drm_auth.h | 1 + include/drm/drm_file.h | 15 ++++++-- 4 files changed, 107 insertions(+), 39 deletions(-)