Re: [<PATCH v1> 1/4] mmc: core: Add check for NULL pointer access

[nguyenb@codeaurora.org]

On 2020-02-27 22:46, Ulf Hansson wrote:
> On Thu, 27 Feb 2020 at 23:06, Bao D. Nguyen <nguyenb@codeaurora.org> 
> wrote:
>> 
>> If the SD card is removed, the mmc_card pointer can be set to NULL
>> by the mmc_sd_remove() function. Check mmc_card pointer to avoid NULL
>> pointer access.
>> 
>> Signed-off-by: Bao D. Nguyen <nguyenb@codeaurora.org>
>> Signed-off-by: Asutosh Das <asutoshd@codeaurora.org>
>> ---
>>  drivers/mmc/core/bus.c  | 5 +++++
>>  drivers/mmc/core/core.c | 3 +++
>>  2 files changed, 8 insertions(+)
>> 
>> diff --git a/drivers/mmc/core/bus.c b/drivers/mmc/core/bus.c
>> index 74de3f2..4558f51 100644
>> --- a/drivers/mmc/core/bus.c
>> +++ b/drivers/mmc/core/bus.c
>> @@ -131,6 +131,11 @@ static void mmc_bus_shutdown(struct device *dev)
>>         struct mmc_host *host = card->host;
>>         int ret;
> 
> This obviously doesn't solve anything as we have already dereferenced
> the card->host above. In other words we should hit a NULL pointer
> dereference bug then.
> 
> More exactly, how do you trigger this problem?
I am porting this fix in the older kernel version 3.4. In that version 
3.4, the pointer check was needed.
Obviously, this NULL pointer check is not helping anything here as you 
pointed out. I will remove this check and resubmit.

> 
>> 
>> +       if (!card) {
>> +               dev_dbg(dev, "%s: %s: card is NULL\n", dev_name(dev), 
>> __func__);
>> +               return;
>> +       }
>> +
>>         if (dev->driver && drv->shutdown)
>>                 drv->shutdown(card);
>> 
> 
> [...]
> 
> Kind regards
> Uffe