Re: [RESEND PATCH v2] media: mtk-jpeg: Fix use after free bug due to uncanceled work

[Zheng Hacker]

Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> 于2023年8月23日周三 02:51写道：

>
> Hello Zheng,
>
> On 7/7/23 12:24, 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
> > Fixes: b2f0d2724ba4 ("[media] vcodec: mediatek: Add Mediatek JPEG Decoder Driver")
> > Signed-off-by: Zheng Wang <zyytlz.wz@xxxxxxx>
> > ---
> > - v2: use cancel_delayed_work_sync instead of cancel_delayed_work suggested by Kyrie.
> > ---
> >  drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > index 0051f372a66c..6069ecf420b0 100644
> > --- a/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > +++ b/drivers/media/platform/mediatek/jpeg/mtk_jpeg_core.c
> > @@ -1816,6 +1816,7 @@ static void mtk_jpeg_remove(struct platform_device *pdev)
> >  {
> >       struct mtk_jpeg_dev *jpeg = platform_get_drvdata(pdev);
> >
> > +     cancel_delayed_work_sync(&jpeg->job_timeout_work);
> >       pm_runtime_disable(&pdev->dev);
> >       video_unregister_device(jpeg->vdev);
> >       v4l2_m2m_release(jpeg->m2m_dev);
>
> AFAICS, there is a fundamental problem here. The job_timeout_work uses
> v4l2_m2m_get_curr_priv() and at the time when driver module is unloaded,
> all the v4l contexts must be closed and released. Hence the
> v4l2_m2m_get_curr_priv() shall return NULL and crash the kernel when
> work is executed before cancel_delayed_work_sync().
>

Hi Dmitry,

Thanks for your reply. I think you're right. As m2m_dev is freed in
v4l2_m2m_release,
the invoking in v4l2_m2m_get_curr_priv might cause either UAF or null
pointer dereference
bug. I am sure that context is closed when we invoke mtk_jpeg_remove.
But I'm not sure if
context is released when mtk_jpegdec_timeout_work running.

> At the time when mtk_jpeg_remove() is invoked, there shall be no
> job_timeout_work running in background because all jobs should be
> completed before context is released. If you'll look at
> v4l2_m2m_cancel_job(), you can see that it waits for the task completion
> before closing context.

Yes, so I think the better way is to put the cancel_delayed_work_sync
invoking into
v4l2_m2m_ctx_release function?

>
> You shouldn't be able to remove driver module while it has active/opened
> v4l contexts. If you can do that, then this is yours bug that needs to
> be fixed.
>
> In addition to this all, the job_timeout_work is initialized only for
> the single-core JPEG device. I'd expect this patch should crash
> multi-core JPEG devices.
>

I think that's true. As I'm not familiar with the code here. Could you
please give me some advice about the patch?

Best regards,
Zheng

> --
> Best regards,
> Dmitry
>