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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Tue, 7 Mar 2023 22:59:31 +0800
Message-ID: <CAJedcCwf4st_KBxYA1dTNT3TNpyyZ_5-2o0oBP7h6kQt7Nzv3Q@mail.gmail.com>
Subject: Re: [RESEND PATCH] media: mtk-jpeg: Fix use after free bug due to
 uncanceled work
To:     Zheng Wang <zyytlz.wz@163.com>
Cc:     mchehab@kernel.org, bin.liu@mediatek.com, matthias.bgg@gmail.com,
        angelogioacchino.delregno@collabora.com,
        linux-media@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, 1395428693sheep@gmail.com,
        alex000young@gmail.com
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The timer function was inited in mtk_jpeg_probe with
mtk_jpeg_job_timeout_work function.
And the worker is started in mtk_jpeg_dec_device_run.
There are two functions (mtk_jpeg_enc_irq and mtk_jpeg_dec_irq) which
may cancel the worker.
They are used as IRQ handler function which is saved as function
pointer in a variable.
In mtk_jpeg_probe, they are registered by devm_request_irq:

ret =3D devm_request_irq(&pdev->dev,
               jpeg_irq,
               jpeg->variant->irq_handler,
               0,
               pdev->name, jpeg);
    if (ret) {
      dev_err(&pdev->dev, "Failed to request jpeg_irq %d (%d)\n",
        jpeg_irq, ret);
      return ret;
    }

However, if we remove the module without triigering the irq, the
worker will never be removed.

As for the schedule, mtk_jpeg_dec_device_run and
mtk_jpeg_enc_device_run will start the worker.
The schedule invoking is quite complicated. As far as I know, the
invoking chain is as follows:

v4l2_m2m_init->v4l2_m2m_device_run_work->v4l2_m2m_try_run

the v4l2_m2m_device_run_work is also a worker which is inited in
v4l2_m2m_init and started in
v4l2_m2m_schedule_next_job.

Before calling remove function, the  mtk_jpeg_release was invoked to
release the related resource.

v4l2_m2m_cancel_job will cancel the job by calling
m2m_dev->m2m_ops->job_abort(m2m_ctx->priv).

But this will only cancel the current queue by
list_del(&m2m_dev->curr_ctx->queue);

I think this can not cancel the posted task mentioned before. So I
think if mtk_jpeg_job_timeout_work

is working on, and use jpeg->m2m_dev after freeing it in
mtk_jpeg_remove, it wll cause UAF bug.

static int mtk_jpeg_release(struct file *file)
{
  struct mtk_jpeg_dev *jpeg =3D video_drvdata(file);
  struct mtk_jpeg_ctx *ctx =3D mtk_jpeg_fh_to_ctx(file->private_data);

  mutex_lock(&jpeg->lock);
  v4l2_ctrl_handler_free(&ctx->ctrl_hdl);
  [1] v4l2_m2m_ctx_release(ctx->fh.m2m_ctx);
  v4l2_fh_del(&ctx->fh);
  v4l2_fh_exit(&ctx->fh);
  kfree(ctx);
  mutex_unlock(&jpeg->lock);
  return 0;
}

void v4l2_m2m_ctx_release(struct v4l2_m2m_ctx *m2m_ctx)
{
  /* wait until the current context is dequeued from job_queue */
  [2] v4l2_m2m_cancel_job(m2m_ctx);

  vb2_queue_release(&m2m_ctx->cap_q_ctx.q);
  vb2_queue_release(&m2m_ctx->out_q_ctx.q);

  kfree(m2m_ctx);
}

Note that, all of this is static analysis, which may be false positive.
Feel free to tell me if there is something I've missed.

Regard,
Zheng

Zheng Hacker <hackerzheng666@gmail.com> =E4=BA=8E2023=E5=B9=B43=E6=9C=887=
=E6=97=A5=E5=91=A8=E4=BA=8C 17:27=E5=86=99=E9=81=93=EF=BC=9A
>
> Hi,
>
> Is there anyone who can help with this? I can provide more details
> like invoking chain if needed.
>
> Thanks,
> Zheng
>
> Zheng Wang <zyytlz.wz@163.com> =E4=BA=8E2023=E5=B9=B43=E6=9C=886=E6=97=A5=
=E5=91=A8=E4=B8=80 14:28=E5=86=99=E9=81=93=EF=BC=9A
> >
> > 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@163.com>
> > ---
> >  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/dri=
vers/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 =3D platform_get_drvdata(pdev);
> > -
> > +       cancel_delayed_work(&jpeg->job_timeout_work);
> >         pm_runtime_disable(&pdev->dev);
> >         video_unregister_device(jpeg->vdev);
> >         v4l2_m2m_release(jpeg->m2m_dev);
> > --
> > 2.25.1
> >