6.1-stable review patch. If anyone has any objections, please let me know.
------------------
From: Zheng Qixing <redacted>
[ Upstream commit 5e9220389920f33b6a804d50c548cd0cd1b04634 ]
When switching IO schedulers on a block device, blkcg_activate_policy()
can race with concurrent blkcg deletion, leading to a use-after-free in
rcu_accelerate_cbs.
T1: T2:
blkg_destroy
kill(&blkg->refcnt) // blkg->refcnt=1->0
blkg_release // call_rcu(__blkg_release)
...
blkg_free_workfn
->pd_free_fn(pd)
elv_iosched_store
elevator_switch
...
iterate blkg list
blkg_get(blkg) // blkg->refcnt=0->1
list_del_init(&blkg->q_node)
blkg_put(pinned_blkg) // blkg->refcnt=1->0
blkg_release // call_rcu again
rcu_accelerate_cbs // uaf
Fix this by checking hlist_unhashed(&blkg->blkcg_node) before getting
a reference to the blkg. This is the same check used in blkg_destroy()
to detect if a blkg has already been destroyed. If the blkg is already
unhashed, skip processing it since it's being destroyed.
Fixes: f1c006f1c685 ("blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()")
Signed-off-by: Zheng Qixing <redacted>
Reviewed-by: Tang Yizhou <redacted>
Signed-off-by: Yu Kuai <yukuai@fygo.io>
Reviewed-by: Tao Cui <redacted>
Reviewed-by: Nilay Shroff <redacted>
Link: https://patch.msgid.link/20260802112525.3933753-4-yukuai@kernel.org (local)
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-cgroup.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 3f5be2105f43e..e88e493457519 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -1413,6 +1413,8 @@ int blkcg_activate_policy(struct request_queue *q,
if (blkg->pd[pol->plid])
continue;
+ if (hlist_unhashed(&blkg->blkcg_node))
+ continue;
/* If prealloc matches, use it; otherwise try GFP_NOWAIT */
if (blkg == pinned_blkg) {--
2.53.0