From mboxrd@z Thu Jan  1 00:00:00 1970
From: Shawn Guo <shawn.guo@freescale.com>
Subject: Re: [PATCH 03/10] net/fec: add mac field into platform data and
 consolidate fec_get_mac
Date: Thu, 30 Dec 2010 10:12:44 +0800
Message-ID: <20101230021243.GA20155@freescale.com>
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Cc: Baruch Siach <baruch@tkos.co.il>, <davem@davemloft.net>,
	<gerg@snapgear.com>, <eric@eukrea.com>, <bryan.wu@canonical.com>,
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To: Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=
	<u.kleine-koenig@pengutronix.de>
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In-Reply-To: <20101229124220.GD14221@pengutronix.de>
Sender: netdev-owner@vger.kernel.org
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Hi Uwe,

On Wed, Dec 29, 2010 at 01:42:21PM +0100, Uwe Kleine-K=F6nig wrote:
> Hello Shawn,
>=20
> 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-K=F6nig 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 =3D=3D fec_mac_default)
> > > > 		dev->dev_addr[ETH_ALEN-1] =3D fec_mac_default[ETH_ALEN-1] + f=
ep->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 byt=
es 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.
>=20
=46irst 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=20
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=3D00:04:9f: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

--=20
Regards,
Shawn