Re: [PATCH] PM / clock_ops: Fix clock error check in __pm_clk_add()

From: Grygorii.Strashko@xxxxxxxxxx
Date: Tue May 12 2015 - 09:55:45 EST

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@xxxxxxxxx> 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);

and of_clk_get may return ERR_PTR().

So, personally I prefer initial fix from Geert.


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