[PATCH-block,v3,0/2] blk-cgroup: Fix potential UAF & flush rstat at blkgs destruction path

Message

Waiman Long Dec. 13, 2022, 6:44 p.m. UTC

v3:
  - Drop v2 patch 2 as it may not be needed.
  - Replace css_tryget() with percpu_ref_is_zero() in patch 1 as
    suggested by Tejun.
  - Expand comment on patch 2 to elaborate the reason for this patch.

 v2:
  - Remove unnecessary rcu_read_{lock|unlock} from
    cgroup_rstat_css_cpu_flush() in patch 3.

It was found that blkcg_destroy_blkgs() may be called with all blkcg
references gone. This may potentially cause user-after-free and so should
be fixed. The second patch flushes rstat when blkcg_destroy_blkgs().

Waiman Long (2):
  bdi, blk-cgroup: Fix potential UAF of blkcg
  blk-cgroup: Flush stats at blkgs destruction path

 block/blk-cgroup.c     | 22 ++++++++++++++++++++++
 include/linux/cgroup.h |  1 +
 kernel/cgroup/rstat.c  | 18 ++++++++++++++++++
 mm/backing-dev.c       |  8 ++++++--
 4 files changed, 47 insertions(+), 2 deletions(-)