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

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Date:   Thu, 19 Dec 2019 14:28:09 +0800
From:   Pan Zhang <zhangpan26@...wei.com>
To:     <ulf.hansson@...aro.org>, <p.zabel@...gutronix.de>,
        <jh80.chung@...sung.com>, <zhangpan26@...wei.com>,
        <hushiyuan@...wei.com>
CC:     <linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: Re: [PATCH] mmc: host: fix a possible null pointer access.

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)?