linux-kernel - Re: [PATCH] workqueue: Fix UAF report by KASAN in pwq_release

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Message-ID: <ZPd4yKqbvBNGV7cL@slm.duckdns.org>
Date:   Tue, 5 Sep 2023 08:51:52 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Zqiang <qiang.zhang1211@...il.com>
Cc:     jiangshanlai@...il.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] workqueue: Fix UAF report by KASAN in
 pwq_release_workfn()

Hello,

On Sat, Sep 02, 2023 at 07:50:26PM +0800, Zqiang wrote:
> diff --git a/kernel/workqueue.c b/kernel/workqueue.c
> index c85825e17df8..f3f9c9222070 100644
> --- a/kernel/workqueue.c
> +++ b/kernel/workqueue.c
> @@ -4609,6 +4609,10 @@ static int alloc_and_link_pwqs(struct workqueue_struct *wq)
>  		free_percpu(wq->cpu_pwq);
>  		wq->cpu_pwq = NULL;
>  	}
> +	wq_unregister_lockdep(wq);
> +	wq_free_lockdep(wq);
> +	free_workqueue_attrs(wq->unbound_attrs);
> +	kfree(wq);

So, this would fix the bug but it's quite confusing because we end up taking
two separate error handling paths and alloc_and_link_pwqs() ends up freeing
stuff allocated outside the function. Wouldn't it be enough to flush the
pwq_release_worker after apply_workqueue_attrs() failure so that the cleanup
operation ordering is maintained?

Thanks.

-- 
tejun