[PATCH AUTOSEL 6.1 10/21] blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy()

Sasha Levin
2023-02-26T03:44:04Z

From: Yu Kuai <yukuai3@huawei.com>

[ Upstream commit f1c006f1c6850c14040f8337753a63119bba39b9 ]

Currently parent pd can be freed before child pd:

t1: remove cgroup C1
blkcg_destroy_blkgs
blkg_destroy
list_del_init(&blkg->q_node)
// remove blkg from queue list
percpu_ref_kill(&blkg->refcnt)
blkg_release
call_rcu

t2: from t1
__blkg_release
blkg_free
schedule_work
t4: deactivate policy
blkcg_deactivate_policy
pd_free_fn
// parent of C1 is freed first
t3: from t2
blkg_free_workfn
pd_free_fn

If policy(for example, ioc_timer_fn() from iocost) access parent pd from
child pd after pd_offline_fn(), then UAF can be triggered.

Fix the problem by delaying 'list_del_init(&blkg->q_node)' from
blkg_destroy() to blkg_free_workfn(), and using a new disk level mutex to
synchronize blkg_free_workfn() and blkcg_deactivate_policy().

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20230119110350.2287325-4-yukuai1@huaweicloud.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
block/blk-cgroup.c | 35 +++++++++++++++++++++++++++++------
include/linux/blkdev.h | 1 +
2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 8d1b7757f1e4f..f8b21bead6552 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -87,16 +87,32 @@ static void blkg_free_workfn(struct work_struct *work)
{
struct blkcg_gq *blkg = container_of(work, struct blkcg_gq,
free_work);
+ struct request_queue *q = blkg->q;
int i;

+ /*
+ * pd_free_fn() can also be called from blkcg_deactivate_policy(),
+ * in order to make sure pd_free_fn() is called in order, the deletion
+ * of the list blkg->q_node is delayed to here from blkg_destroy(), and
+ * blkcg_mutex is used to synchronize blkg_free_workfn() and
+ * blkcg_deactivate_policy().
+ */
+ if (q)
+ mutex_lock(&q->blkcg_mutex);
+
for (i = 0; i < BLKCG_MAX_POLS; i++)
if (blkg->pd[i])
blkcg_policy[i]->pd_free_fn(blkg->pd[i]);

if (blkg->parent)
blkg_put(blkg->parent);
- if (blkg->q)
- blk_put_queue(blkg->q);
+
+ if (q) {
+ list_del_init(&blkg->q_node);
+ mutex_unlock(&q->blkcg_mutex);
+ blk_put_queue(q);
+ }
+
free_percpu(blkg->iostat_cpu);
percpu_ref_exit(&blkg->refcnt);
kfree(blkg);
@@ -425,9 +441,14 @@ static void blkg_destroy(struct blkcg_gq *blkg)
lockdep_assert_held(&blkg->q->queue_lock);
lockdep_assert_held(&blkcg->lock);

- /* Something wrong if we are trying to remove same group twice */
- WARN_ON_ONCE(list_empty(&blkg->q_node));
- WARN_ON_ONCE(hlist_unhashed(&blkg->blkcg_node));
+ /*
+ * blkg stays on the queue list until blkg_free_workfn(), see details in
+ * blkg_free_workfn(), hence this function can be called from
+ * blkcg_destroy_blkgs() first and again from blkg_destroy_all() before
+ * blkg_free_workfn().
+ */
+ if (hlist_unhashed(&blkg->blkcg_node))
+ return;

for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
@@ -439,7 +460,6 @@ static void blkg_destroy(struct blkcg_gq *blkg)
blkg->online = false;

radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
- list_del_init(&blkg->q_node);
hlist_del_init_rcu(&blkg->blkcg_node);

/*
@@ -1226,6 +1246,7 @@ int blkcg_init_disk(struct gendisk *disk)
int ret;

INIT_LIST_HEAD(&q->blkg_list);
+ mutex_init(&q->blkcg_mutex);

new_blkg = blkg_alloc(&blkcg_root, disk, GFP_KERNEL);
if (!new_blkg)
@@ -1463,6 +1484,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
if (queue_is_mq(q))
blk_mq_freeze_queue(q);

+ mutex_lock(&q->blkcg_mutex);
spin_lock_irq(&q->queue_lock);

__clear_bit(pol->plid, q->blkcg_pols);
@@ -1481,6 +1503,7 @@ void blkcg_deactivate_policy(struct request_queue *q,
}

spin_unlock_irq(&q->queue_lock);
+ mutex_unlock(&q->blkcg_mutex);

if (queue_is_mq(q))
blk_mq_unfreeze_queue(q);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 891f8cbcd0436..1680b6e1e5362 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -487,6 +487,7 @@ struct request_queue {
DECLARE_BITMAP (blkcg_pols, BLKCG_MAX_POLS);
struct blkcg_gq *root_blkg;
struct list_head blkg_list;
+ struct mutex blkcg_mutex;
#endif

struct queue_limits limits;
--
2.39.0