Re: [PATCH-block v2 1/3] bdi, blk-cgroup: Fix potential UAF of blkcg

Waiman Long
2022-12-12T22:17:51Z

On 12/12/22 17:13, Tejun Heo wrote:
> On Sun, Dec 11, 2022 at 05:20:56PM -0500, Waiman Long wrote:
>> static void blkcg_destroy_blkgs(struct blkcg *blkcg)
>> {
>> + /*
>> + * blkcg_destroy_blkgs() shouldn't be called with all the blkcg
>> + * references gone.
>> + */
>> + if (WARN_ON_ONCE(!css_tryget(&blkcg->css)))
>> + return;
> Wouldn't it make more sense to use percpu_ref_is_zero()? It's not like the
> obtained extra reference does anything, right?

Yes, that makes sense. Will incorporate the change in the next version.

Thanks,
Longman