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

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Date:   Mon, 18 Sep 2023 08:06:21 -1000
From:   Tejun Heo <tj@...nel.org>
To:     Z qiang <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()

On Thu, Sep 07, 2023 at 10:13:23AM +0800, Z qiang wrote:
> >
> > On Wed, Sep 06, 2023 at 10:12:34AM +0800, Z qiang wrote:
> > > Flush the pwq_release_worker is insufficient, the call_rcu() is
> > > invoked to release wq
> > > in pwq_release_workfn(), this is also asynchronous.
> >
> > But rcu_free_pwq() doesn't access wq or anything. The last access is from
> > the work function.
> 
> The rcu_free_wq() will access wq->cpu_pwq or unbound_attrs,
> but  at this time, the kfree(wq) may have been called in alloc_workqueue().

I'm not following. The only way alloc_and_link fails is if
apply_wqattrs_prepare() fails and if prepare fails, none of the pwq's are
installed and pwq_unbound_release_workfn() won't try to free the wq as the
pwq's don't have any reference on it. So, if you flush the pwq release work
items, there can be no rcu_free_wq() in flight. Can you please try to see
whether the problem is reproducible with flushing?

Thanks.

-- 
tejun