linux-kernel - Re: [PATCH] pinctrl:sunplus: Add check for kmalloc

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Date:   Tue, 23 May 2023 22:05:49 +0200
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     andy.shevchenko@...il.com,
        Wells Lu 呂芳騰 <wells.lu@...plus.com>
Cc:     Wells Lu <wellslutw@...il.com>,
        "linus.walleij@...aro.org" <linus.walleij@...aro.org>,
        "linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl:sunplus: Add check for kmalloc

Le 23/05/2023 à 21:37, andy.shevchenko@...il.com a écrit :
> Tue, May 23, 2023 at 05:39:51PM +0000, Wells Lu 呂芳騰 kirjoitti:
>>>> Fix Smatch static checker warning:
>>>> potential null dereference 'configs'. (kmalloc returns null)
> 
> ...
> 
>>>>   			configs = kmalloc(sizeof(*configs), GFP_KERNEL);
>>>> +			if (!configs)
>>>
>>>> +				return -ENOMEM;
>>>
>>> "Fixing" by adding a memory leak is not probably a good approach.
>>
>> Do you mean I need to free all memory which are allocated in this subroutine before
>> return -ENOMEM?
> 
> This is my understanding of the code. But as I said... (see below)
> 
> ...
> 
>>>>   			configs = kmalloc(sizeof(*configs), GFP_KERNEL);
>>>> +			if (!configs)
>>>> +				return -ENOMEM;
>>>
>>> Ditto.
> 
> ...
> 
>>> It might be that I'm mistaken. In this case please add an explanation why in the commit
>>> message.
> 
> ^^^
> 

Hmmm, not so sure.

Should be looked at more carefully, but
   dt_to_map_one_config		(in /drivers/pinctrl/devicetree.c)
     .dt_node_to_map
       --> sppctl_dt_node_to_map

Should dt_to_map_one_config() fail, pinctrl_dt_free_maps() is called
(see 
https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/devicetree.c#L281)

pinctrl_dt_free_maps() calls dt_free_map(), which calls .dt_free_map, so 
pinctrl_utils_free_map()
(see 
https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/sunplus/sppctl.c#L978)

Finally the needed kfree seem to be called from here.
(see 
https://elixir.bootlin.com/linux/v6.4-rc1/source/drivers/pinctrl/pinctrl-utils.c#L119)


*This should obviously be double checked*, but looks safe to me.


BUT, in the same function, the of_get_parent() should be undone in case 
of error, as done at the end of the function, in the normal path.
This one seems to be missing, should a memory allocation error occur.


Just my 2c,

CJ