linux-kernel - Re: [PATCH] mmc: dw_mmc: Fix potential null pointer risk

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Date: Thu, 7 Mar 2024 22:02:56 +0300
From: Aleksandr Mishin <amishin@...rgos.ru>
To: Ulf Hansson <ulf.hansson@...aro.org>
CC: Jaehoon Chung <jh80.chung@...sung.com>, Wen Zhiwei <wenzhiwei@...inos.cn>,
	<linux-mmc@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<lvc-project@...uxtesting.org>
Subject: Re: [PATCH] mmc: dw_mmc: Fix potential null pointer risk



07.03.2024 13:57, Ulf Hansson wrote:
> On Thu, 7 Mar 2024 at 09:53, Aleksandr Mishin <amishin@...rgos.ru> wrote:
>>
>> In dw_mci_runtime_resume() 'host->slot' could be null, but check is not cover all corresponding code.
>> Fix this bug by changing check place.
> 
> In fact host->slot can never be NULL in dw_mci_runtime_resume() or in
> dw_mci_runtime_suspend().
> 
> A better fix would thus be to remove the redundant checks.
> 
> Kind regards
> Uffe
> 
>>
>> Found by Linux Verification Center (linuxtesting.org) with SVACE.
>>
>> Fixes: 4a835afd808a (mmc: dw_mmc: Fix potential null pointer risk)
>> Signed-off-by: Aleksandr Mishin <amishin@...rgos.ru>
>> ---
>>   drivers/mmc/host/dw_mmc.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/mmc/host/dw_mmc.c b/drivers/mmc/host/dw_mmc.c
>> index 829af2c98a44..a4f124452abc 100644
>> --- a/drivers/mmc/host/dw_mmc.c
>> +++ b/drivers/mmc/host/dw_mmc.c
>> @@ -3570,8 +3570,10 @@ int dw_mci_runtime_resume(struct device *dev)
>>                     DW_MCI_ERROR_FLAGS);
>>          mci_writel(host, CTRL, SDMMC_CTRL_INT_ENABLE);
>>
>> +       if (!host->slot)
>> +               goto err;
>>
>> -       if (host->slot && host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
>> +       if (host->slot->mmc->pm_flags & MMC_PM_KEEP_POWER)
>>                  dw_mci_set_ios(host->slot->mmc, &host->slot->mmc->ios);
>>
>>          /* Force setup bus to guarantee available clock output */
>> --
>> 2.30.2
>>
>>
> 

At the same time there are few checks such as "if (host->slot)" in 
dw_mci_runtime_resume() and commit 
4a835afd808a3dbbac44bb399a902b822dc7445c message contains: "we 
previously assumed 'host->slot' could be null, null pointer judgment 
should be added" and replaces "if (host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)" with "if (host->slot && host->slot->mmc->pm_flags & 
MMC_PM_KEEP_POWER)"
So where is the truth?

-- 
Kind regadrds
Aleksandr