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From:   Ulf Hansson <ulf.hansson@linaro.org>
Date:   Fri, 21 Jan 2022 13:41:27 +0100
Message-ID: <CAPDyKFpu0mGchoqdzE-qKc6=9ogncnTCwN8AR7g1wcMZLyRFsw@mail.gmail.com>
Subject: Re: [PATCH] moxart: fix potential use-after-free on remove path
To:     Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     linux-kernel@vger.kernel.org, Xiyu Yang <xiyuyang19@fudan.edu.cn>,
        Xin Xiong <xiongx18@fudan.edu.cn>,
        Xin Tan <tanxin.ctf@gmail.com>,
        Tony Lindgren <tony@atomide.com>,
        Yang Li <yang.lee@linux.alibaba.com>,
        linux-mmc@vger.kernel.org, stable <stable@vger.kernel.org>,
        whitehat002 <hackyzh002@gmail.com>
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On Fri, 14 Jan 2022 at 08:59, Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> It was reported that the mmc host structure could be accessed after it
> was freed in moxart_remove(), so fix this by saving the base register of
> the device and using it instead of the pointer dereference.
>
> Cc: Ulf Hansson <ulf.hansson@linaro.org>
> Cc: Xiyu Yang <xiyuyang19@fudan.edu.cn>
> Cc: Xin Xiong <xiongx18@fudan.edu.cn>
> Cc: Xin Tan <tanxin.ctf@gmail.com>
> Cc: Tony Lindgren <tony@atomide.com>
> Cc: Yang Li <yang.lee@linux.alibaba.com>
> Cc: linux-mmc@vger.kernel.org
> Cc: stable <stable@vger.kernel.org>
> Reported-by: whitehat002 <hackyzh002@gmail.com>
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/mmc/host/moxart-mmc.c | 9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mmc/host/moxart-mmc.c b/drivers/mmc/host/moxart-mmc.c
> index 16d1c7a43d33..f5d96940a9b8 100644
> --- a/drivers/mmc/host/moxart-mmc.c
> +++ b/drivers/mmc/host/moxart-mmc.c
> @@ -697,6 +697,7 @@ static int moxart_remove(struct platform_device *pdev)
>  {
>         struct mmc_host *mmc = dev_get_drvdata(&pdev->dev);
>         struct moxart_host *host = mmc_priv(mmc);
> +       void __iomem *base = host->base;
>
>         dev_set_drvdata(&pdev->dev, NULL);
>
> @@ -707,10 +708,10 @@ static int moxart_remove(struct platform_device *pdev)
>         mmc_remove_host(mmc);
>         mmc_free_host(mmc);
>
> -       writel(0, host->base + REG_INTERRUPT_MASK);
> -       writel(0, host->base + REG_POWER_CONTROL);
> -       writel(readl(host->base + REG_CLOCK_CONTROL) | CLK_OFF,
> -              host->base + REG_CLOCK_CONTROL);

Rather than doing it like this, I think it would be easier to move
mmc_free_host() below this part. That's usually what mmc host drivers
do clean up things in ->remove().

> +       writel(0, base + REG_INTERRUPT_MASK);
> +       writel(0, base + REG_POWER_CONTROL);
> +       writel(readl(base + REG_CLOCK_CONTROL) | CLK_OFF,
> +              base + REG_CLOCK_CONTROL);
>
>         return 0;
>  }

Kind regards
Uffe