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

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Message-ID: <dd0ea27640d2420eb3b521076c643919@sphcmbx02.sunplus.com.tw>
Date:   Thu, 25 May 2023 03:22:28 +0000
From:   Wells Lu 呂芳騰 <wells.lu@...plus.com>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        "andy.shevchenko@...il.com" <andy.shevchenko@...il.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#L97
> 8)
> 
> 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

Thank you for your comments.

From the report of kmemleak, returning -ENOMEM directly causes memory leak. We 
need to free any memory allocated in this subroutine before returning -ENOMEM.

I'll send a new patch that will free the allocated memory and call of_node_put() 
when an error happens.


Best regards,
Wells Lu