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blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy() 

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>
This commit is contained in:
Yu Kuai 2023-01-19 19:03:50 +08:00 committed by Jens Axboe
parent dfd6200a09
commit f1c006f1c6
2 changed files with 30 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
block/blk-cgroup.c
View File

@ -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);
@ -462,9 +478,14 @@ 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];
@ -479,7 +500,6 @@ 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);
/*
@ -1280,6 +1300,7 @@ 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)
@ -1520,6 +1541,7 @@ 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);
@ -1538,6 +1560,7 @@ 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);

1
include/linux/blkdev.h
View File

@ -485,6 +485,7 @@ 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;