netdev - Re: [PATCH] net: ipv6: fix the address length for net

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Message-ID: <Zy45iLv7cL8OcYze@debian>
Date: Fri, 8 Nov 2024 17:17:12 +0100
From: Guillaume Nault <gnault@...hat.com>
To: Emanuele Santini <emanuele.santini.88@...il.com>
Cc: netdev@...r.kernel.org, yoshfuji@...ux-ipv6.org, friedrich@...age.de,
	kuba@...nel.org, davem@...emloft.net, pabeni@...hat.com,
	dsahern@...nel.org
Subject: Re: [PATCH] net: ipv6: fix the address length for net_device on a
 GRE tunnel

On Fri, Nov 08, 2024 at 03:24:03PM +0100, Emanuele Santini wrote:
> I'm talking about the ip6gre. I agree that setting the hardware address to 0 is appropriate.
> However, in the ip6gre_tunnel_setup function, the perm_addr field of net_device is 
> currently assigned a random Ethernet address:
> 
>         dev->flags |= IFF_NOARP;
>        - dev->addr_len = sizeof(struct in6_addr);
>        + dev->addr_len = ETH_ALEN;
>         netif_keep_dst(dev);
>         /* This perm addr will be used as interface identifier by IPv6 */
>         dev->addr_assign_type = NET_ADDR_RANDOM;
>         eth_random_addr(dev->perm_addr);
> 
> maybe this is not a valid justification to set addr_len to ETH_ALEN.

I think that having a fake permanent address for the purpose of IPv6
interface Id. generation isn't a correct justification for setting
dev->addr_len.

If setting ->perm_addr and ->addr_assign_type have side effects on the
acceptable values of ->addr_len, then the commit description should
explain that in more details.

> I will make a review setting addr_len to 0, and will resubmit the patch after successful testing.

Thanks.