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 aa890e3e4e509..45881f8c79130 100644 --- a/block/blk-cgroup.c +++ b/block/blk-cgroup.c @@ -118,16 +118,32 @@ 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); @@ -458,9 +474,14 @@ 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]; @@ -472,7 +493,6 @@ 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);
/* @@ -1273,6 +1293,7 @@ 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) @@ -1510,6 +1531,7 @@ 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); @@ -1528,6 +1550,7 @@ 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 43d4e073b1115..10ee92db680c9 100644 --- a/include/linux/blkdev.h +++ b/include/linux/blkdev.h @@ -484,6 +484,7 @@ 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;