From: Tejun Heo <tj@xxxxxxxxxx>
commit 86e6ca55b83c575ab0f2e105cf08f98e58d3d7af upstream.
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@xxxxxxxxxx>
Reported-by: Abagail ren <renzezhongucas@xxxxxxxxx>
Suggested-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxx>
Fixes: 4308a434e5e0 ("blkcg: don't offline parent blkcg first")
Cc: stable@xxxxxxxxxxxxxxx # v5.7+
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
[kovalev: in versions 5.10 and 5.15, the blkcg_unpin_online()
function was not moved to the block/blk-cgroup.c file]
Signed-off-by: Vasiliy Kovalev <kovalev@xxxxxxxxxxxx>
---
Backport to fix CVE-2024-56672
Link: https://www.cve.org/CVERecord/?id=CVE-2024-56672
---
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 0e6e84db06f674..b89099360a8673 100644
--- a/include/linux/blk-cgroup.h
+++ b/include/linux/blk-cgroup.h
@@ -428,10 +428,14 @@ 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);
}
--
2.33.8
