linux-kernel - Re: [PATCH] mmc: host: fix a possible null pointer access.

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Message-ID: <CAPDyKFr8aVWVydT5U6mpuZr5_waH=bn6F8rjryfDJ15FDaAXUw@mail.gmail.com>
Date:   Wed, 18 Dec 2019 12:52:28 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Pan Zhang <zhangpan26@...wei.com>
Cc:     hushiyuan@...wei.com, Jaehoon Chung <jh80.chung@...sung.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: host: fix a possible null pointer access.

On Tue, 17 Dec 2019 at 04:18, Pan Zhang <zhangpan26@...wei.com> wrote:
>
> 3419     if (host->slot &&
> 3420         (mmc_can_gpio_cd(host->slot->mmc) ||
> 3421          !mmc_card_is_removable(host->slot->mmc))) {
> 3422         ret = clk_prepare_enable(host->biu_clk);
> 3423         if (ret)
> 3424             return ret;
> 3425     }
>
> We previously assumed 'host->slot' could be null (see line 3419).
>
> The following situation is similar, so add a judgement.
>
> Signed-off-by: Pan Zhang <zhangpan26@...wei.com>
> ---
>  drivers/mmc/host/dw_mmc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
> index fc9d4d0..8e27c52 100644
> --- a/drivers/mmc/host/dw_mmc.c
> +++ b/drivers/mmc/host/dw_mmc.c
> @@ -3454,7 +3454,7 @@ int dw_mci_runtime_resume(struct device *dev)
>         mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
>
>
> -       if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
> +       if (host->slot && (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER))
>                 dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);

This shouldn't be a problem as the ->runtime_resume() callback can't
be invoked, unless there is a slot.

>
>         /* Force setup bus to guarantee available clock output */
> --
> 2.7.4
>

Kind regards
Uffe