linux-kernel - Re: [PATCH] of: overlay: Fix uninitialized vars in dup_and_fixup_symbol

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Date:   Tue, 19 Sep 2017 22:16:06 +0200
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Frank Rowand <frowand.list@...il.com>
Cc:     Pantelis Antoniou <pantelis.antoniou@...sulko.com>,
        Rob Herring <robh+dt@...nel.org>,
        Grant Likely <grant.likely@...aro.org>,
        Arnd Bergmann <arnd@...db.de>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: overlay: Fix uninitialized vars in dup_and_fixup_symbol_prop()

Hi Frank,

On Tue, Sep 19, 2017 at 8:27 PM, Frank Rowand <frowand.list@...il.com> wrote:
> On 09/10/17 03:26, Geert Uytterhoeven wrote:
>> With gcc 4.1.2:
>>
>>     drivers/of/overlay.c: In function ‘dup_and_fixup_symbol_prop’:
>>     drivers/of/overlay.c:108: warning: ‘overlay_name_len’ may be used uninitialized in this function
>>     drivers/of/overlay.c:100: warning: ‘ovinfo’ may be used uninitialized in this function
>>
>> Indeed, if ov->count == 0, both variables are uninitialized, which may
>> lead to a crash when dereferencing ovinfo later.
>>
>> Currently this is a false positive, as the sole creator of of_overlay
>> structures (of_build_overlay_info(), introduced in commit
>> 7518b5890d8ac366 ("of/overlay: Introduce DT overlay support") checks for
>> this.
>>
>> To prevent future issues, add a check for a zero ov->count to
>> dup_and_fixup_symbol_prop().  Note that this does not get rid of the
>> actual compiler warning.
>>
>> Fixes: d1651b03c2df75db ("of: overlay: add overlay symbols to live device tree")
>> Signed-off-by: Geert Uytterhoeven <geert@...ux-m68k.org>
>> ---
>>  drivers/of/overlay.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/of/overlay.c b/drivers/of/overlay.c
>> index 8ecfee31ab6d3874..ebe19e0f8e4d1f4b 100644
>> --- a/drivers/of/overlay.c
>> +++ b/drivers/of/overlay.c
>> @@ -108,7 +108,7 @@ static struct property *dup_and_fixup_symbol_prop(struct of_overlay *ov,
>>       int overlay_name_len;
>>       int target_path_len;
>>
>> -     if (!prop->value)
>> +     if (!ov->count || !prop->value)
>>               return NULL;
>>       symbol_path = prop->value;
>>
>
> I did not see this patch due to an overzealous spam filter.  I noticed it
> when Rob replied with his applied email.
>
> This check is not needed to prevent accessing overlay_name_len and ovinfo
> when ov->count == 0.  That is already prevented by:
>
>         if (k >= ov->count)
>                 goto err_free;
>
> because k will be zero and ov->count will be zero.

Thank you, I stand corrected.

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