Re: [PATCH] media: mtk-jpeg: Fix use after free bug due to uncanceled work

[Guenter Roeck]

On 3/8/23 19:58, Zheng Hacker wrote:
> Hi,
>
> Thanks for your reply. I think you're right. I don't know if there is
> other method to stop new work from enqueing. Could you please give me
> some advice about the fix?

Top-posting is discouraged.

Anyway -
I don't know the code well enough to suggest a solution.
It all depends on the driver architecture. The maintainers might
have a better idea.

A worse problem appears to be that the worker is also canceled
from mtk_jpeg_enc_irq() and mtk_jpeg_dec_irq(). Those are non-threaded
interrupt handlers which, as far as I know, must not sleep and thus
can not call cancel_delayed_work_sync(). I have no idea how to solve
that problem either.

Guenter

> Regards,
> Zheng
>
> Guenter Roeck <linux@xxxxxxxxxxxx> 于2023年3月9日周四 08:27写道：
> > On Thu, Mar 02, 2023 at 05:37:15PM +0800, Zheng Wang wrote:
> > > In mtk_jpeg_probe, &jpeg->job_timeout_work is bound with
> > > mtk_jpeg_job_timeout_work. Then mtk_jpeg_dec_device_run
> > > and mtk_jpeg_enc_device_run may be called to start the
> > > work.
> > > If we remove the module which will call mtk_jpeg_remove
> > > to make cleanup, there may be a unfinished work. The
> > > possible sequence is as follows, which will cause a
> > > typical UAF bug.
> > >
> > > Fix it by canceling the work before cleanup in the mtk_jpeg_remove
> > >
> > > CPU0                  CPU1
> > >
> > >                      |mtk_jpeg_job_timeout_work
> > > mtk_jpeg_remove     |
> > >    v4l2_m2m_release  |
> > >      kfree(m2m_dev); |
> > >                      |
> > >                      | v4l2_m2m_get_curr_priv
> > >                      |   m2m_dev->curr_ctx //use
> > >
> > > Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> > > ---
> > >   drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > > index 969516a940ba..364513e7897e 100644
> > > --- a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > > +++ b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > > @@ -1793,7 +1793,7 @@ static int mtk_jpeg_probe(struct platform_device *pdev)
> > >   static int mtk_jpeg_remove(struct platform_device *pdev)
> > >   {
> > >        struct mtk_jpeg_dev *jpeg = platform_get_drvdata(pdev);
> > > -
> > > +     cancel_delayed_work(&jpeg->job_timeout_work);
> >
> > The empty line is needed (coding style). Also, this doesn't cancel
> > the worker if it is already running. This should probably be
> > cancel_delayed_work_sync(). Even then the question is if it is
> > possible that new work is queued before the device is unregistered.
> >
> > Guenter
> >
> > >        pm_runtime_disable(&pdev->dev);
> > >        video_unregister_device(jpeg->vdev);
> > >        v4l2_m2m_release(jpeg->m2m_dev);
> > > --
> > > 2.25.1