linux-kernel - Re: [RFT] media: dvb_frontend: Fix use-after-free in __dvb_frontend

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Date:   Tue, 24 Oct 2017 13:42:45 +0200
From:   Andrey Konovalov <andreyknvl@...gle.com>
To:     Arvind Yadav <arvind.yadav.cs@...il.com>
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Max Kellermann <max.kellermann@...il.com>,
        Shuah Khan <shuah@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Colin Ian King <colin.king@...onical.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Kostya Serebryany <kcc@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-media@...r.kernel.org,
        syzkaller <syzkaller@...glegroups.com>,
        Matthias Schwarzott <zzam@...too.org>
Subject: Re: [RFT] media: dvb_frontend: Fix use-after-free in __dvb_frontend_free

On Tue, Oct 24, 2017 at 1:36 PM, Arvind Yadav <arvind.yadav.cs@...il.com> wrote:
> Here, dvb_free_device will free dvb_device. dvb_frontend_invoke_release
> is using  dvb_device after free.

Hi Arvind,

Matthias already suggested a fix. Also it looks like your patch is
based on an outdated tree, which doesn't contain the commit that seems
to have caused the bug (ead666000a5fe34bdc82d61838e4df2d416ea15e).

Thanks!

>
> Signed-off-by: Arvind Yadav <arvind.yadav.cs@...il.com>
> ---
> This bug report by Andrey Konovalov (usb/media/dtt200u: use-after-free
> in __dvb_frontend_free).
>
>  drivers/media/dvb-core/dvb_frontend.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/media/dvb-core/dvb_frontend.c b/drivers/media/dvb-core/dvb_frontend.c
> index 2fcba16..7f1ef12 100644
> --- a/drivers/media/dvb-core/dvb_frontend.c
> +++ b/drivers/media/dvb-core/dvb_frontend.c
> @@ -147,10 +147,10 @@ static void dvb_frontend_free(struct kref *ref)
>                 container_of(ref, struct dvb_frontend, refcount);
>         struct dvb_frontend_private *fepriv = fe->frontend_priv;
>
> -       dvb_free_device(fepriv->dvbdev);
> -
>         dvb_frontend_invoke_release(fe, fe->ops.release);
>
> +       dvb_free_device(fepriv->dvbdev);
> +
>         kfree(fepriv);
>  }
>
> --
> 1.9.1
>