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

[Zheng Hacker]

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?

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
> >