linux-kernel - Re: [PATCH] media: hantro: fix use after free bug in hantro

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Date:   Mon, 13 Mar 2023 23:21:52 +0800
From:   Zheng Hacker <hackerzheng666@...il.com>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Zheng Wang <zyytlz.wz@....com>, ezequiel@...guardiasur.com.ar,
        p.zabel@...gutronix.de, mchehab@...nel.org,
        linux-media@...r.kernel.org, linux-rockchip@...ts.infradead.org,
        linux-kernel@...r.kernel.org, 1395428693sheep@...il.com,
        alex000young@...il.com
Subject: Re: [PATCH] media: hantro: fix use after free bug in hantro_remove
 due to race condition

Hans Verkuil <hverkuil@...all.nl> 于2023年3月13日周一 23:08写道：
>
> On 07/03/2023 16:41, Zheng Wang wrote:
> > In hantro_probe, vpu->watchdog_work is bound with
> > hantro_watchdog. Then hantro_end_prepare_run may
> > be called to start the work.
> >
> > If we close the file or remove the module which will
> > call hantro_release and hantro_remove to make cleanup,
> > there may be a unfinished work. The possible sequence
> > is as follows, which will cause a typical UAF bug.
> >
> > The same thing will happen in hantro_release, and use
> > ctx after freeing it.
> >
> > Fix it by canceling the work before cleanup in hantro_release.
> >
> > CPU0                  CPU1
> >
> >                     |hantro_watchdog
> > hantro_remove     |
> >   v4l2_m2m_release  |
> >     kfree(m2m_dev); |
> >                     |
> >                     | v4l2_m2m_get_curr_priv
> >                     |   m2m_dev->curr_ctx //use
> >
> > Signed-off-by: Zheng Wang <zyytlz.wz@....com>
> > ---
> >  drivers/media/platform/verisilicon/hantro_drv.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
> > diff --git a/drivers/media/platform/verisilicon/hantro_drv.c b/drivers/media/platform/verisilicon/hantro_drv.c
> > index b0aeedae7b65..80bd856a4da9 100644
> > --- a/drivers/media/platform/verisilicon/hantro_drv.c
> > +++ b/drivers/media/platform/verisilicon/hantro_drv.c
> > @@ -1099,6 +1099,7 @@ static int hantro_remove(struct platform_device *pdev)
> >
> >       v4l2_info(&vpu->v4l2_dev, "Removing %s\n", pdev->name);
> >
> > +     cancel_delayed_work(&vpu->watchdog_work);
>
> Use cancel_delayed_work_sync(): that ensures the code waits for a running
> watchdog function to finish.
>
> Ditto for the other patch.
>

Dear Hans,

Thanks for your advice. Will do in  the next version of patch :)

Best regards,
Zheng

>
> >       media_device_unregister(&vpu->mdev);
> >       hantro_remove_dec_func(vpu);
> >       hantro_remove_enc_func(vpu);
>