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

[Zheng Hacker]

The timer function was set 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 = 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 triggering 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 function is also a worker which is set 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 using jpeg->m2m_dev after freeing it in
mtk_jpeg_remove, it will cause a UAF bug.

static int mtk_jpeg_release(struct file *file)
{
  struct mtk_jpeg_dev *jpeg = video_drvdata(file);
  struct mtk_jpeg_ctx *ctx = 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

Irui Wang (王瑞) <Irui.Wang@xxxxxxxxxxxx> 于2023年3月7日周二 18:23写道：
>
> Dear Angelo and Zheng,
>
> Thanks for your patch and comments.
>
> Dear Kyrie,
>
> Please help to check this, thanks.
>
> Best Regards
>
> On Tue, 2023-03-07 at 10:49 +0100, AngeloGioacchino Del Regno wrote:
> > Il 07/03/23 10:27, Zheng Hacker ha scritto:
> > > Hi,
> > >
> > > Is there anyone who can help with this? I can provide more details
> > > like invoking chain if needed.
> > >
> >
> > Providing more details is always good. Please do.
> >
> > Meanwhile, adding Irui Wang to the loop: he's doing mtk-jpeg.
> >
> > Regards,
> > Angelo
> >
> > > Thanks,
> > > Zheng
> > >
> > > Zheng Wang <zyytlz.wz@xxxxxxx> 于2023年3月6日周一 14:28写道：
> > > >
> > > > 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);
> > > >          pm_runtime_disable(&pdev->dev);
> > > >          video_unregister_device(jpeg->vdev);
> > > >          v4l2_m2m_release(jpeg->m2m_dev);
> > > > --
> > > > 2.25.1
> > > >
> >
> >
> >