From: Tejun Heo <tj@kernel.org> mainline inclusion from mainline-v6.13-rc3 commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af category: bugfix bugzilla: https://gitee.com/src-openeuler/kernel/issues/IBEAKO CVE: CVE-2024-56672 Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=... -------------------------------- blkcg_unpin_online() walks up the blkcg hierarchy putting the online pin. To walk up, it uses blkcg_parent(blkcg) but it was calling that after blkcg_destroy_blkgs(blkcg) which could free the blkcg, leading to the following UAF: ================================================================== BUG: KASAN: slab-use-after-free in blkcg_unpin_online+0x15a/0x270 Read of size 8 at addr ffff8881057678c0 by task kworker/9:1/117 CPU: 9 UID: 0 PID: 117 Comm: kworker/9:1 Not tainted 6.13.0-rc1-work-00182-gb8f52214c61a-dirty #48 Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS unknown 02/02/2022 Workqueue: cgwb_release cgwb_release_workfn Call Trace: <TASK> dump_stack_lvl+0x27/0x80 print_report+0x151/0x710 kasan_report+0xc0/0x100 blkcg_unpin_online+0x15a/0x270 cgwb_release_workfn+0x194/0x480 process_scheduled_works+0x71b/0xe20 worker_thread+0x82a/0xbd0 kthread+0x242/0x2c0 ret_from_fork+0x33/0x70 ret_from_fork_asm+0x1a/0x30 </TASK> ... Freed by task 1944: kasan_save_track+0x2b/0x70 kasan_save_free_info+0x3c/0x50 __kasan_slab_free+0x33/0x50 kfree+0x10c/0x330 css_free_rwork_fn+0xe6/0xb30 process_scheduled_works+0x71b/0xe20 worker_thread+0x82a/0xbd0 kthread+0x242/0x2c0 ret_from_fork+0x33/0x70 ret_from_fork_asm+0x1a/0x30 Note that the UAF is not easy to trigger as the free path is indirected behind a couple RCU grace periods and a work item execution. I could only trigger it with artifical msleep() injected in blkcg_unpin_online(). Fix it by reading the parent pointer before destroying the blkcg's blkg's. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Abagail ren <renzezhongucas@gmail.com> Suggested-by: Linus Torvalds <torvalds@linuxfoundation.org> Fixes: 4308a434e5e0 ("blkcg: don't offline parent blkcg first") Cc: stable@vger.kernel.org # v5.7+ Signed-off-by: Jens Axboe <axboe@kernel.dk> Conflicts: include/linux/blk-cgroup.h block/blk-cgroup.c [blkcg_unpin_online() is inline function defined in blk-cgroup.h] Signed-off-by: Yu Kuai <yukuai3@huawei.com> --- include/linux/blk-cgroup.h | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/include/linux/blk-cgroup.h b/include/linux/blk-cgroup.h index 1fe9574b4a77..0c14b195c0c2 100644 --- a/include/linux/blk-cgroup.h +++ b/include/linux/blk-cgroup.h @@ -425,10 +425,14 @@ static inline void blkcg_pin_online(struct blkcg *blkcg) static inline void blkcg_unpin_online(struct blkcg *blkcg) { do { + struct blkcg *parent; + if (!refcount_dec_and_test(&blkcg->online_pin)) break; + + parent = blkcg_parent(blkcg); blkcg_destroy_blkgs(blkcg); - blkcg = blkcg_parent(blkcg); + blkcg = parent; } while (blkcg); } -- 2.39.2