linux-kernel - Re: [PATCH v2 1/2] of: overlay: Fix memory leak in of_overlay

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Date:   Tue, 5 Dec 2017 17:47:35 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     Geert Uytterhoeven <geert+renesas@...der.be>,
        Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>,
        Colin King <colin.king@...onical.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] of: overlay: Fix memory leak in of_overlay_apply()
 error path

On 12/05/17 08:58, Geert Uytterhoeven wrote:
> Hi Frank,
> 
> On Tue, Dec 5, 2017 at 2:45 PM, Frank Rowand <frowand.list@...il.com> wrote:
>> On 12/05/17 03:01, Geert Uytterhoeven wrote:
>>> On Tue, Dec 5, 2017 at 3:07 AM, Frank Rowand <frowand.list@...il.com> wrote:
>>>> Also, the previous version of the patch, and the discussion around the resulting
>>>> bug make me think that I should not have moved 'kfree(ovcs)' into
>>>> free_overlay_changeset(), because that kfree is then not very visible in the
>>>> error path of of_overlay_apply().  Could you remove 'kfree(ovcs)' from
>>>> free_overlay_changeset(), and instead call it immediately after each call
>>>> to free_overlay_changeset()?
>>>
>>> Actually I like that free_overlay_changeset() takes care of the deallocation,
>>> especially in light of the kojectification op top from bbb-overlays, which
>>> means you cannot just call kfree(ovcs) anymore (I know this won't go upstream
>>> anytime soon, but I need overlay configfs for my development and testing).
>>
>> OK, knowing that kobjectification is being considered I am willing to leave the
>> kfree(ovcs) where it is for now.
>>
>>> Perhaps the allocation of ovcs should be moved into free_overlay_changeset(),
>>
>>                                           I think this ^^^^^^^^^^^^^^^^^^^^^^^
>> is a typo, and you meant init_overlay_changeset().
> 
> Yes it is.
> 
>>> and the latter being renamed to alloc_overlay_changeset()?
>>> That way allocation and freeing become symmetrical.
>>> It would move the allocation under the mutexes, though.
>>
>> I considered moving the kzalloc() into init_overlay_changeset() when I
>> created it, but decided not to because the type of the first argument of
>> init_overlay_changeset() would change from
>>    struct overlay_changeset *
>> to
>>    struct overlay_changeset **,
>> and usage of ovcs would become _slightly_ more ugly and complex in
>> init_overlay_changeset().
> 
> I would let alloc_overlay_changeset() return struct overlay_changeset *
> instead.
> 
> If you care about why it failed, it can return ERR_PTR(error) instead of
> NULL ;-)

Yes, it should continue to return the error reason.

Thanks,

Frank


> 
> Gr{oetje,eeting}s,
> 
>                         Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
>                                 -- Linus Torvalds
>