netdev - Re: [PATCH 03/10] net/fec: add mac field into platform data and consolidate fec_get

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Date:	Thu, 30 Dec 2010 10:12:44 +0800
From:	Shawn Guo <shawn.guo@...escale.com>
To:	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>
CC:	Baruch Siach <baruch@...s.co.il>, <davem@...emloft.net>,
	<gerg@...pgear.com>, <eric@...rea.com>, <bryan.wu@...onical.com>,
	<r64343@...escale.com>, <B32542@...escale.com>,
	<lw@...o-electronics.de>, <w.sang@...gutronix.de>,
	<s.hauer@...gutronix.de>, <linux-arm-kernel@...ts.infradead.org>,
	<netdev@...r.kernel.org>
Subject: Re: [PATCH 03/10] net/fec: add mac field into platform data and
 consolidate fec_get_mac

Hi Uwe,

On Wed, Dec 29, 2010 at 01:42:21PM +0100, Uwe Kleine-König wrote:
> Hello Shawn,
> 
> On Wed, Dec 29, 2010 at 07:58:09PM +0800, Shawn Guo wrote:
> > On Wed, Dec 29, 2010 at 11:31:38AM +0100, Uwe Kleine-König wrote:
> > > On Wed, Dec 29, 2010 at 06:05:21PM +0800, Shawn Guo wrote:
> > > > On Wed, Dec 29, 2010 at 08:53:30AM +0200, Baruch Siach wrote:
> > > > 	if (iap == fec_mac_default)
> > > > 		dev->dev_addr[ETH_ALEN-1] = fec_mac_default[ETH_ALEN-1] + fep->pdev->id;
> > > Can this overflow?  (I didn't check the code, so my concern might be
> > > completely stupid here.)
> > No. dev->dev_addr points to netdev_hw_addr->addr, which is a 32 bytes array.
> I didn't mean an out-of-bound access, but what is if
> fec_mac_default[ETH_ALEN-1] is 0xff and you add 1?  Does that result in
> 0x100 or 0?  What if id is <0?  For big ids you might even handle a
> carry to indixes <ETH_ALEN-2.
> 
First of all, all my patch did is changing fep->index to,
fep->pdev->id, which should not bring any problem you are concerned.

Secondly, I do not understand how the overflow on 
fec_mac_default[ETH_ALEN-1] can result in a carry on the next array
element. Here is what I'm seeing with fec_mac=00:04:9f:01:30:ff.

eth0      Link encap:Ethernet  HWaddr 00:04:9F:01:30:FF
eth1      Link encap:Ethernet  HWaddr 00:04:9F:01:30:00

-- 
Regards,
Shawn

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