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SubjectRe: [PATCH v2] workqueue: fix UAF in pwq_unbound_release_workfn()
Hello, Yang.

> +static void free_pwq(struct pool_workqueue *pwq)
> +{
> + if (!pwq || --pwq->refcnt)
> + return;
> +
> + put_unbound_pool(pwq->pool);
> + kmem_cache_free(pwq_cache, pwq);
> +}
> +
> +static void free_wqattrs_ctx(struct apply_wqattrs_ctx *ctx)
> +{
> + int node;
> +
> + if (!ctx)
> + return;
> +
> + for_each_node(node)
> + free_pwq(ctx->pwq_tbl[node]);
> + free_pwq(ctx->dfl_pwq);
> +
> + free_workqueue_attrs(ctx->attrs);
> +
> + kfree(ctx);
> +}

It bothers me that we're partially replicating the free path including pwq
refcnting. Does something like the following work?

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 104e3ef04e33..0c0ab363edeb 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -3693,7 +3693,7 @@ static void pwq_unbound_release_workfn(struct work_struct *work)
* If we're the last pwq going away, @wq is already dead and no one
* is gonna access it anymore. Schedule RCU free.
*/
- if (is_last) {
+ if (is_last && !list_empty(&wq->list)) {
wq_unregister_lockdep(wq);
call_rcu(&wq->rcu, rcu_free_wq);
}
@@ -4199,6 +4199,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
}
put_online_cpus();

+ if (ret) {
+ flush_scheduled_work();
+ }
+
return ret;
}

--
tejun
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