From: Yu Kuai <yukuai3@huawei.com>
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 use a new disk level mutex to
protect blkg_free_workfn() and blkcg_deactivate_policy).
Signed-off-by: Yu Kuai <yukuai3@huawei.com>
---
block/blk-cgroup.c | 33 +++++++++++++++++++++++++++------
include/linux/blkdev.h | 1 +
2 files changed, 28 insertions(+), 6 deletions(-)
diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
index 75f3c4460715..4098e8030e01 100644
--- a/block/blk-cgroup.c
+++ b/block/blk-cgroup.c
@@ -118,16 +118,26 @@ 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;
+ 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) {
+ if (!list_empty(&blkg->q_node))
+ 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 +472,14 @@ 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 is removed from queue list in blkg_free_workfn(), hence this
+ * function can be called from blkcg_destroy_blkgs() first, and then
+ * before blkg_free_workfn(), this function can be called again in
+ * blkg_destroy_all().
+ */
+ if (hlist_unhashed(&blkg->blkcg_node))
+ return;
for (i = 0; i < BLKCG_MAX_POLS; i++) {
struct blkcg_policy *pol = blkcg_policy[i];
@@ -478,8 +493,11 @@ static void blkg_destroy(struct blkcg_gq *blkg)
blkg->online = false;
+ /*
+ * Delay deleting list blkg->q_node to blkg_free_workfn() to synchronize
+ * pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy().
+ */
radix_tree_delete(&blkcg->blkg_tree, blkg->q->id);
- list_del_init(&blkg->q_node);
hlist_del_init_rcu(&blkg->blkcg_node);
/*
@@ -1280,6 +1298,7 @@ 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 +1539,7 @@ 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 +1558,7 @@ 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 b87ed829ab94..53ae0a7fe377 100644
--- 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;
--
2.31.1Hello,
On Wed, Jan 18, 2023 at 08:31:52PM +0800, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
>
> 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 use a new disk level mutex to
^
using
> protect blkg_free_workfn() and blkcg_deactivate_policy).
^ ^
synchronize? ()
> @@ -118,16 +118,26 @@ 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;
>
> + if (q)
> + mutex_lock(&q->blkcg_mutex);
A comment explaining what the above is synchronizing would be useful.
> +
> 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) {
> + if (!list_empty(&blkg->q_node))
We can drop the above if.
> + 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 +472,14 @@ 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 is removed from queue list in blkg_free_workfn(), hence this
> + * function can be called from blkcg_destroy_blkgs() first, and then
> + * before blkg_free_workfn(), this function can be called again in
> + * blkg_destroy_all().
How about?
* blkg stays on the queue list until 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];
> @@ -478,8 +493,11 @@ static void blkg_destroy(struct blkcg_gq *blkg)
>
> blkg->online = false;
>
> + /*
> + * Delay deleting list blkg->q_node to blkg_free_workfn() to synchronize
> + * pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy().
> + */
So, it'd be better to add a more comprehensive comment in blkg_free_workfn()
explaining why we need this synchronization and how it works and then point
to it from here.
Other than comments, it looks great to me. Thanks a lot for your patience
and seeing it through.
--
tejun
Hi,
在 2023/01/19 1:05, Tejun Heo 写道:
> Hello,
>
> On Wed, Jan 18, 2023 at 08:31:52PM +0800, Yu Kuai wrote:
>> From: Yu Kuai <yukuai3@huawei.com>
>>
>> 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 use a new disk level mutex to
> ^
> using
>
>> protect blkg_free_workfn() and blkcg_deactivate_policy).
> ^ ^
> synchronize? ()
>
>> @@ -118,16 +118,26 @@ 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;
>>
>> + if (q)
>> + mutex_lock(&q->blkcg_mutex);
>
> A comment explaining what the above is synchronizing would be useful.
>
>> +
>> 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) {
>> + if (!list_empty(&blkg->q_node))
>
> We can drop the above if.
>
>> + 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 +472,14 @@ 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 is removed from queue list in blkg_free_workfn(), hence this
>> + * function can be called from blkcg_destroy_blkgs() first, and then
>> + * before blkg_free_workfn(), this function can be called again in
>> + * blkg_destroy_all().
>
> How about?
>
> * blkg stays on the queue list until 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];
>> @@ -478,8 +493,11 @@ static void blkg_destroy(struct blkcg_gq *blkg)
>>
>> blkg->online = false;
>>
>> + /*
>> + * Delay deleting list blkg->q_node to blkg_free_workfn() to synchronize
>> + * pd_free_fn() from blkg_free_workfn() and blkcg_deactivate_policy().
>> + */
>
> So, it'd be better to add a more comprehensive comment in blkg_free_workfn()
> explaining why we need this synchronization and how it works and then point
> to it from here.
>
> Other than comments, it looks great to me. Thanks a lot for your patience
> and seeing it through.
Thanks for the suggestions, I'll send a new patch based on your
suggestions.
Kuai
>
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