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Subject: Re: [PATCH] clk: fix a missing-free bug in clk_cpy_name()
To:     Gen Zhang <blackgod016574@gmail.com>,
        Stephen Boyd <sboyd@kernel.org>
Cc:     mturquette@baylibre.com, linux-clk@vger.kernel.org,
        linux-kernel@vger.kernel.org
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From:   Jiri Slaby <jslaby@suse.cz>
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Message-ID: <e5b4639b-3077-59bb-6383-0c2bccdd9191@suse.cz>
Date:   Fri, 7 Jun 2019 11:10:37 +0200
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Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

On 07. 06. 19, 3:52, Gen Zhang wrote:
>>>>> @@ -3491,6 +3492,8 @@ static int clk_core_populate_parent_map(struct clk_core *core)
>>>>>                             kfree_const(parents[i].name);
>>>>>                             kfree_const(parents[i].fw_name);
>>>>>                     } while (--i >= 0);
>>>>> +                   kfree_const(parent->name);
>>>>> +                   kfree_const(parent->fw_name);
>>>>
>>>> Both of them were just freed in the loop above, no?
>>> for (i = 0, parent = parents; i < num_parents; i++, parent++)
>>> Is 'parent' the same as the one from the loop above?
>>
>> Yes. Did it change somehow?
> parent++?

parent++ is done after the loop body. Or what do you mean?

>>> Moreover, should 'parents[i].name' and 'parents[i].fw_name' be freed by
>>> kfree_const()?
>>>
>>
>> Yes? They're allocated with kstrdup_const() in clk_cpy_name(), or
>> they're NULL by virtue of the kcalloc and then kfree_const() does
>> nothing.
> I re-examined clk_cpy_name(). They are the second parameter of 
> clk_cpy_name(). The first parameter is allocated, not the second one.
> So 'parent->name' and 'parent->fw_name' should be freed, not 
> 'parents[i].name' or 'parents[i].fw_name'. Am I totally misunderstanding
> this clk_cpy_name()? :-(

The second parameter (the source) is parent_data[i].*, not parents[i].*
(the destination). parent->fw_name and parent->name are properly freed
in the do {} while loop as parents[i].name and parents[i].fw_name, given
i hasn't changed yet. I am not sure what you mean at all. Are you
uncertain about the C code flow?

thanks,
-- 
js
suse labs