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

[Pavel Skripkin]

On Thu, 15 Jul 2021 16:08:12 +0800
Lai Jiangshan <jiangshanlai@xxxxxxxxx> wrote:

> On Wed, Jul 14, 2021 at 5:16 PM Yang Yingliang
> <yangyingliang@xxxxxxxxxx> wrote:
> 
> >
> > Fixes: 2d5f0764b526 ("workqueue: split apply_workqueue_attrs() into
> > 3 stages") Reported-by: Hulk Robot <hulkci@xxxxxxxxxx>
> > Suggested-by: Lai Jiangshan <jiangshanlai@xxxxxxxxx>
> > Signed-off-by: Yang Yingliang <yangyingliang@xxxxxxxxxx>
> > ---
> > 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@xxxxxxxxx>
> 
> Hello, Pavel
> 
> Could you have a test again, please?
> 

Hi, Lai!

Sorry for late response.

Yes, I have started local syzkaller instance just now, so I will share
the results tomorrow. 


> 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
> >


With regards,
Pavel Skripkin