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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Sun, 8 Oct 2023 17:13:07 +0800
Message-ID: <CAJedcCwDemUSo8Hv1XYLcAkHeo2Y2RU=xX7Fv5aSRz52AixK6g@mail.gmail.com>
Subject: Re: [RESEND PATCH v2] media: mtk-jpeg: Fix use after free bug due to
 uncanceled work
To:     Dmitry Osipenko <dmitry.osipenko@collabora.com>
Cc:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>,
        Zheng Wang <zyytlz.wz@163.com>, Kyrie.Wu@mediatek.com,
        bin.liu@mediatek.com, mchehab@kernel.org, matthias.bgg@gmail.com,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, Irui.Wang@mediatek.com,
        security@kernel.org, 1395428693sheep@gmail.com,
        alex000young@gmail.com, Collabora Kernel ML <kernel@collabora.com>
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Dmitry Osipenko <dmitry.osipenko@collabora.com> =E4=BA=8E2023=E5=B9=B49=E6=
=9C=8820=E6=97=A5=E5=91=A8=E4=B8=89 02:24=E5=86=99=E9=81=93=EF=BC=9A
>
> On 8/31/23 11:18, Zheng Hacker wrote:
> >> The v4l2_m2m_ctx_release() already should wait for the job_timeout_wor=
k
> >> completion or for the interrupt fire. Apparently it doesn't work in
> >> yours case. You'll need to debug why v4l job or job_timeout_work is
> >> running after v4l2_m2m_ctx_release(), it shouldn't happen.
> >>
> > Yes, v4l2_m2m_cancel_job waits for m2m_ctx->job_flags to be  ~TRANS_RUN=
NING,
> > the mtk_jpeg_job_timeout_work will finally invoke v4l2_m2m_job_finish
> > to trigger that.
> >
> > However, this is not the only path to call v4l2_m2m_job_finish. Here
> > is a invoking chain:
> > v4l_streamon
> >   ->v4l2_m2m_ioctl_streamon
> >     ->v4l2_m2m_streamon
> >       ->v4l2_m2m_try_schedule
> >         ->v4l2_m2m_try_run
> >           ->mtk_jpeg_dec_device_run
> >             ->schedule_delayed_work(&jpeg->job_timeout_work...
> >             ->error path goto dec_end
> >             ->v4l2_m2m_job_finish
> >
> > In some specific situation, it starts the worker and also calls
> > v4l2_m2m_job_finish, which might
> > make v4l2_m2m_cancel_job continues.
>
> Then the error path should cancel the job_timeout_work, or better job
> needs to be run after the dec/enc has been started and not before.
>

Hi,

Sorry for my late reply for I just went on a long vacation.

Get it. I'll write another patch and change the summary to the lack of
canceling job in error path.

> Looking further at the code, I'm confused by this hunk:
>
>         mtk_jpeg_dec_start(comp_jpeg[hw_id]->reg_base);
>         v4l2_m2m_job_finish(jpeg->m2m_dev, ctx->fh.m2m_ctx);
>
> The job should be marked as finished when h/w has finished processing
> the job and not right after the job has been started. So the job is
> always completed and mtk_jpeg_job_timeout_work() doesn't work as
> expected, am I missing something?

After reading the code I still don't know. I didn't see any function
like mtk_jpeg_dec_end. The same thing
happens on mtk_jpeg_enc_start. I think I'd better fix the first
problem and wait for someone familiar with
the second part.

Best regards,
Zheng

>
> --
> Best regards,
> Dmitry
>