Message-ID: <1427911550.31790.56.camel@perches.com>
Subject: Re: [PATCH 1/1] ar7: replace mac address parsing
From: Joe Perches <joe@perches.com>
To: Jonas Gorski <jogo@openwrt.org>
Cc: Florian Fainelli <florian@openwrt.org>, Daniel Walter <dwalter@google.com>,
        Ralf Baechle <ralf@linux-mips.org>,
        Linux-MIPS <linux-mips@linux-mips.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Date: Wed, 01 Apr 2015 11:05:50 -0700
In-Reply-To: <CAOiHx==91cquJ0OAf-n40HB39HbtLw-5RrxhxtsJXbTyNgit8w@mail.gmail.com>
References: <20140624153959.GA19564@google.com>
	 <1403624918.29061.16.camel@joe-AO725>
	 <CAGVrzcbgds+zHbTJWnUi48Nn1xPiEjGV7PGRmUX46da2CD+G=g@mail.gmail.com>
	 <CAOiHx==91cquJ0OAf-n40HB39HbtLw-5RrxhxtsJXbTyNgit8w@mail.gmail.com>
Content-Type: text/plain; charset="ISO-8859-1"
Mime-Version: 1.0
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 2391
Lines: 59

On Wed, 2015-04-01 at 14:17 +0200, Jonas Gorski wrote:
> On Tue, Jun 24, 2014 at 9:26 PM, Florian Fainelli <florian@openwrt.org> wrote:
> > 2014-06-24 8:48 GMT-07:00 Joe Perches <joe@perches.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.
> [1] d16f7093b6eb4f3859856f6ee4ab504cbeeea0b9

Wow Jonas, a 9 month thread gestation...

Given the old code and the commit comment, I'd
say it was almost certainly safe and my issue with
the patch resolved.


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/