linux-kernel - Re: [PATCH 1/1] ar7: replace mac address parsing

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Date:	Wed, 1 Apr 2015 14:17:16 +0200
From:	Jonas Gorski <jogo@...nwrt.org>
To:	Florian Fainelli <florian@...nwrt.org>
Cc:	Joe Perches <joe@...ches.com>, Daniel Walter <dwalter@...gle.com>,
	Ralf Baechle <ralf@...ux-mips.org>,
	Linux-MIPS <linux-mips@...ux-mips.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] ar7: replace mac address parsing

On Tue, Jun 24, 2014 at 9:26 PM, Florian Fainelli <florian@...nwrt.org> wrote:
> 2014-06-24 8:48 GMT-07:00 Joe Perches <joe@...ches.com>:
>> On Tue, 2014-06-24 at 16:39 +0100, Daniel Walter wrote:
>>> Replace sscanf() with mac_pton().
>> []
>>> diff --git a/arch/mips/ar7/platform.c b/arch/mips/ar7/platform.c
>> []
>>> @@ -307,10 +307,7 @@ static void __init cpmac_get_mac(int instance, unsigned char *dev_addr)
>>>       }
>>>
>>>       if (mac) {
>>> -             if (sscanf(mac, "%hhx:%hhx:%hhx:%hhx:%hhx:%hhx",
>>> -                                     &dev_addr[0], &dev_addr[1],
>>> -                                     &dev_addr[2], &dev_addr[3],
>>> -                                     &dev_addr[4], &dev_addr[5]) != 6) {
>>> +             if (!mac_pton(mac, dev_addr)) {
>>
>> There is a slight functional change with this conversion.
>>
>> mac_pton is strict about leading 0's and requires a 17 char strlen.
>
> I do not have my devices handy, but I am fairly positive the use of
> sscanf() was exactly for that, we may or may not have leading zeroes.
> I am feeling a little uncomfortable with random code changes like that
> without being actually able to test on real hardware that has a
> variety of bootloaders and environment variables.

One of my two devices has a mac address with one of the numbers being
< 16, and it uses a fixed length mac:

(psbl) printenv
...
HWA_0           00:16:B6:2A:A4:3B

Also looking at the history[1] of this code, it looks like this was
just an optimization of an earlier code which did expect 17 char len:

       for (i = 0; i < 6; i++)
               dev_addr[i] = (char2hex(mac[i * 3]) << 4) +
                       char2hex(mac[i * 3 + 1]);


So I'm tempted to say it should not cause any issues. But my sample
size is rather small.


Regards
Jonas


[1] d16f7093b6eb4f3859856f6ee4ab504cbeeea0b9
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