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

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Message-ID: <CAPDyKFpTZNi63XgBgp3z4svxNcEsnZxH5qg6mZ9uTLkUm_AQSg@mail.gmail.com>
Date:   Thu, 19 Dec 2019 08:07:37 +0100
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Pan Zhang <zhangpan26@...wei.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Jaehoon Chung <jh80.chung@...sung.com>, hushiyuan@...wei.com,
        "linux-mmc@...r.kernel.org" <linux-mmc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] mmc: host: fix a possible null pointer access.

On Thu, 19 Dec 2019 at 07:28, Pan Zhang <zhangpan26@...wei.com> wrote:
>
> On Wed, 18 Dec 2019 at 7:52 p.m., Ulf Hansson <ulf.hansson@...aro.org> 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
> >>
>
> If so, there is no need to assume host->slot pointer previously(line 3419)?
>

Yeah, there is probably more cases that has unnecessary "protection".

Kind regards
Uffe