Re: [PATCH] moxart: fix potential use-after-free on remove path

[Ulf Hansson]

On Fri, 14 Jan 2022 at 08:59, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> 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@xxxxxxxxxx>
> Cc: Xiyu Yang <xiyuyang19@xxxxxxxxxxxx>
> Cc: Xin Xiong <xiongx18@xxxxxxxxxxxx>
> Cc: Xin Tan <tanxin.ctf@xxxxxxxxx>
> Cc: Tony Lindgren <tony@xxxxxxxxxxx>
> Cc: Yang Li <yang.lee@xxxxxxxxxxxxxxxxx>
> Cc: linux-mmc@xxxxxxxxxxxxxxx
> Cc: stable <stable@xxxxxxxxxxxxxxx>
> Reported-by: whitehat002 <hackyzh002@xxxxxxxxx>
> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> ---
>  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