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

[Pavel Skripkin]

On Thu, 15 Jul 2021 21:52:19 +0300
Pavel Skripkin <paskripkin@xxxxxxxxx> wrote:

> 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. 
> 

Hi, everyone!

With this patch applied my local syzbot instance didn't hit any of the
reported bugs [1].

Tested-by: Pavel Skripkin <paskripkin@xxxxxxxxx> 


Thank you!


[1] https://lore.kernel.org/lkml/20210708162417.777bff77@xxxxxxxxx/

With regards,
Pavel Skripkin

> 
> > 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
>