blk-cgroup: synchronize pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_pol...

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>

diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 75f3c44607154bd4bb5a1f72549f1ab92d77577e..cb110fc51940aa8743705481387e29649b579771 100644 (file)
--- 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);
@@ -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);

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 89f51d68c68ad66c12e37820b27a97a0ee02cf27..b9637d63e6f0240053357f7af1b211686653438f 100644 (file)
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -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;