linux-kernel - Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk

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Date:	Tue, 12 May 2015 16:55:39 +0300
From:	"Grygorii.Strashko@...aro.org" <grygorii.strashko@...aro.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>
CC:	Geert Uytterhoeven <geert+renesas@...der.be>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Kevin Hilman <khilman@...aro.org>,
	Santosh Shilimkar <santosh.shilimkar@...com>,
	Linux PM list <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk_add()

Hi Dmitry,
On 05/09/2015 12:05 AM, Dmitry Torokhov wrote:
> On Fri, May 08, 2015 at 10:59:04PM +0200, Geert Uytterhoeven wrote:
>> On Fri, May 8, 2015 at 7:19 PM, Dmitry Torokhov
>> <dmitry.torokhov@...il.com> wrote:
>>> On Fri, May 08, 2015 at 10:47:43AM +0200, Geert Uytterhoeven wrote:
>>>> In the final iteration of commit 245bd6f6af8a62a2 ("PM / clock_ops: Add
>>>> pm_clk_add_clk()"), a refcount increment was added by Grygorii Strashko.
>>>> However, the accompanying IS_ERR() check operates on the wrong clock
>>>> pointer, which is always zero at this point, i.e. not an error.
>>>> This may lead to a NULL pointer dereference later, when __clk_get()
>>>> tries to dereference an error pointer.
>>>>
>>>> Check the passed clock pointer instead to fix this.
>>>
>>> Frankly I would remove the check altogether. Why do we only check for
>>> IS_ERR and not NULL or otherwise validate the pointer? The clk is passed
>>
>> __clk_get() does the NULL check.
> 
> No, not really. It _handles_ clk being NULL and returns "everything is
> fine". In any case it is __clk_get's decision what to do.
> 
> I dislike gratuitous checks of arguments passed in. Instead of relying
> on APIs refusing grabage we better not pass garbage to these APIs in the
> first place. So I'd change it to trust that we are given a usable
> pointer and simply do:
> 
> 	if (!__clk_get(clk)) {
> 		kfree(ce);
> 		return -ENOENTl
> 	}

Not sure this is right thing to do, because this API initially 
was intended to be used as below [1]:
	clk = of_clk_get(dev->of_node, i));
 	ret = pm_clk_add_clk(dev, clk);
 	clk_put(clk);

and of_clk_get may return ERR_PTR().

So, personally I prefer initial fix from Geert.

[1] http://lists.infradead.org/pipermail/linux-arm-kernel/2014-October/296586.html

-- 
regards,
-grygorii
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