linux-kernel - Re: [PATCH v2] media: rc: Fix use-after-free bugs caused by ene_tx

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Date:   Tue, 24 Jan 2023 14:57:38 +0800 (GMT+08:00)
From:   duoming@....edu.cn
To:     "Sean Young" <sean@...s.org>
Cc:     linux-media@...r.kernel.org, maximlevitsky@...il.com,
        mchehab@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: rc: Fix use-after-free bugs caused by
 ene_tx_irqsim()

Hello,

On Mon, 23 Jan 2023 15:13:40 +0000 Sean Young wrote:

> On Mon, Jan 23, 2023 at 10:21:23PM +0800, Duoming Zhou wrote:
> > When the ene device is detaching, function ene_remove() will
> > be called. But there is no function to cancel tx_sim_timer
> > in ene_remove(), the timer handler ene_tx_irqsim() could race
> > with ene_remove(). As a result, the UAF bugs could happen,
> > the process is shown below.
> > 
> >     (cleanup routine)          |        (timer routine)
> >                                | mod_timer(&dev->tx_sim_timer, ..)
> > ene_remove()                   | (wait a time)
> >   kfree(dev) //FREE            |
> >                                | ene_tx_irqsim()
> >                                |   dev->hw_lock //USE
> >                                |   ene_tx_sample(dev) //USE
> > 
> > Fix by adding del_timer_sync(&dev->tx_sim_timer) in ene_remove(),
> > The tx_sim_timer could stop before ene device is deallocated.
> > 
> > What's more, the timer can call ene_tx_sample() which can write
> > to the io ports. So we should put rc_unregister_device() and
> > del_timer_sync(&dev->tx_sim_timer) before release_region() in
> > ene_remove().
> > 
> > Fixes: 9ea53b74df9c ("V4L/DVB: STAGING: remove lirc_ene0100 driver")
> > Signed-off-by: Duoming Zhou <duoming@....edu.cn>
> > ---
> > Changes in v2:
> >   - Move rc_unregister_device() and del_timer_sync() before release_region().
> > 
> >  drivers/media/rc/ene_ir.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/media/rc/ene_ir.c b/drivers/media/rc/ene_ir.c
> > index e09270916fb..2864360af9e 100644
> > --- a/drivers/media/rc/ene_ir.c
> > +++ b/drivers/media/rc/ene_ir.c
> > @@ -1112,8 +1112,9 @@ static void ene_remove(struct pnp_dev *pnp_dev)
> >  	spin_unlock_irqrestore(&dev->hw_lock, flags);
> >  
> >  	free_irq(dev->irq, dev);
> > -	release_region(dev->hw_io, ENE_IO_SIZE);
> >  	rc_unregister_device(dev->rdev);
> > +	del_timer_sync(&dev->tx_sim_timer);
> > +	release_region(dev->hw_io, ENE_IO_SIZE);
> >  	kfree(dev);
> >  }
> 
> I'm sorry, I think there might be a problem there: the irq is freed before
> the rc device is unregistered.
> 
> The rx receiver is disabled with ene_rx_disable() before rc_unregister_device()
> is called, which means it can be enabled again if a process opens /dev/lirc0
> between ene_rx_disable() and rc_unregister_device().
> 
> ene_remove() should call rc_unregister_device() and del_timer_sync() before
> anything else.

Thank your for your time and suggestions, I understand it.

Best regards,
Duoming Zhou