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From:   Zheng Hacker <hackerzheng666@gmail.com>
Date:   Wed, 15 Mar 2023 16:59:29 +0800
Message-ID: <CAJedcCwxbiEv4cOEyWpgrNNLZybP4O8Ubu6hpiMpmg1wL8xP1g@mail.gmail.com>
Subject: Re: [PATCH v2] media: cedrus: fix use after free bug in cedrus_remove
 due to race condition
To:     =?UTF-8?Q?Jernej_=C5=A0krabec?= <jernej.skrabec@gmail.com>
Cc:     mchehab@kernel.org, Zheng Wang <zyytlz.wz@163.com>,
        hverkuil@xs4all.nl, wens@csie.org, samuel@sholland.org,
        linux-media@vger.kernel.org, linux-staging@lists.linux.dev,
        linux-arm-kernel@lists.infradead.org, linux-sunxi@lists.linux.dev,
        linux-kernel@vger.kernel.org, 1395428693sheep@gmail.com,
        alex000young@gmail.com
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Jernej =C5=A0krabec <jernej.skrabec@gmail.com> =E4=BA=8E2023=E5=B9=B43=E6=
=9C=8815=E6=97=A5=E5=91=A8=E4=B8=89 03:53=E5=86=99=E9=81=93=EF=BC=9A
>
> Dne ponedeljek, 13. marec 2023 ob 17:31:20 CET je Zheng Wang napisal(a):
> > In cedrus_probe, dev->watchdog_work is bound with cedrus_watchdog funct=
ion.
> > In cedrus_device_run, it will started by schedule_delayed_work. If ther=
e is
> > an unfinished work in cedrus_remove, there may be a race condition and
> > trigger UAF bug.
> >
> > CPU0                  CPU1
> >
> >                     |cedrus_watchdog
> >
> > cedrus_remove       |
> >   v4l2_m2m_release  |
> >   kfree(m2m_dev)    |
> >
> >                     | v4l2_m2m_get_curr_priv
> >                     |
> >                     |   m2m_dev //use
> >
> > Fix it by canceling the worker in cedrus_remove.
> >
> > Fixes: 7c38a551bda1 ("media: cedrus: Add watchdog for job completion")
> > Signed-off-by: Zheng Wang <zyytlz.wz@163.com>
> > ---
> > v2:
> > - use cancel_delayed_work_sync instead and add Fixes
> > label suggested by Hans Verkuil
> > ---
> >  drivers/staging/media/sunxi/cedrus/cedrus.c | 1 +
> >  1 file changed, 1 insertion(+)
> >
>
> Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
>

Thanks for your review.

Best regards,
Zheng

> Best regards,
> Jernej
>
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus.c
> > b/drivers/staging/media/sunxi/cedrus/cedrus.c index
> > a43d5ff66716..a50a4d0a8f71 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus.c
> > @@ -547,6 +547,7 @@ static int cedrus_remove(struct platform_device *pd=
ev)
> >  {
> >       struct cedrus_dev *dev =3D platform_get_drvdata(pdev);
> >
> > +     cancel_delayed_work_sync(&dev->watchdog_work);
> >       if (media_devnode_is_registered(dev->mdev.devnode)) {
> >               media_device_unregister(&dev->mdev);
> >               v4l2_m2m_unregister_media_controller(dev->m2m_dev);
>
>
>
>