Re: [PATCH] workqueue: Fix UAF report by KASAN in pwq_release_workfn()

[Z qiang]

>
> 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?
>

you are right .  sorry,  I ignore if apply_wqattrs_prepare() fails,
none of the pwq is installed,
the install_unbound_pwq() is not invoked. I will resend v2 and test.

Thanks
Zqiang

>
> Thanks.
>
> --
> tejun