Re: [PATCH v3] workqueue: fix UAF in pwq_unbound_release_workfn()

[Lai Jiangshan <jiangshanlai@gmail.com>]

On Wed, Jul 14, 2021 at 5:16 PM Yang Yingliang <yangyingliang@huawei.com> wrote:

>
> Fixes: 2d5f0764b526 ("workqueue: split apply_workqueue_attrs() into 3 stages")
> Reported-by: Hulk Robot <hulkci@huawei.com>
> Suggested-by: Lai Jiangshan <jiangshanlai@gmail.com>
> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
> ---
> v3:
>   drop the v2 and v1 changes, add check pwq in pwq_unbound_release_workfn()
> v2:
>   also use free_wqattrs_ctx() in workqueue_apply_unbound_cpumask()
> ---
>  kernel/workqueue.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
>

I'm fine with the code.

Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>

Hello, Pavel

Could you have a test again, please?

Thanks,
Lai

> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index 50142fc08902..f148eacda55a 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -3676,15 +3676,21 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
>                                                   unbound_release_work);
>         struct workqueue_struct *wq = pwq->wq;
>         struct worker_pool *pool = pwq->pool;
> -       bool is_last;
> +       bool is_last = false;
>
> -       if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
> -               return;
> +       /*
> +        * when @pwq is not linked, it doesn't hold any reference to the
> +        * @wq, and @wq is invalid to access.
> +        */
> +       if (!list_empty(&pwq->pwqs_node)) {
> +               if (WARN_ON_ONCE(!(wq->flags & WQ_UNBOUND)))
> +                       return;
>
> -       mutex_lock(&wq->mutex);
> -       list_del_rcu(&pwq->pwqs_node);
> -       is_last = list_empty(&wq->pwqs);
> -       mutex_unlock(&wq->mutex);
> +               mutex_lock(&wq->mutex);
> +               list_del_rcu(&pwq->pwqs_node);
> +               is_last = list_empty(&wq->pwqs);
> +               mutex_unlock(&wq->mutex);
> +       }
>
>         mutex_lock(&wq_pool_mutex);
>         put_unbound_pool(pool);
> --
> 2.25.1
>