netdev - Re: [PATCH net-next] ip6_tunnel: enable to change proto of fb tunnels

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Message-ID: <20250621065439.0fd2b6f6@kernel.org>
Date: Sat, 21 Jun 2025 06:54:39 -0700
From: Jakub Kicinski <kuba@...nel.org>
To: Nicolas Dichtel <nicolas.dichtel@...nd.com>
Cc: "David S . Miller" <davem@...emloft.net>, Paolo Abeni
 <pabeni@...hat.com>, Eric Dumazet <edumazet@...gle.com>, Simon Horman
 <horms@...nel.org>, netdev@...r.kernel.org
Subject: Re: [PATCH net-next] ip6_tunnel: enable to change proto of fb
 tunnels

On Fri, 20 Jun 2025 10:14:26 +0200 Nicolas Dichtel wrote:
> > Hm, I guess its in line with old school netlink behavior where we'd
> > just toss unsupported attributes on the floor. But I wonder whether
> > it'd be better to explicitly reject other attrs?  
> 
> I tried to find a (simple) way to be strict but, by default 'ip link' dumps all
> attributes and put them back in the message it sends.
> Ie, with the command 'ip link set ip6tnl0 type ip6tnl mode any' all IFLA_IPTUN_*
> attributes are set (to their current value) and only IFLA_IPTUN_PROTO has
> another value.

Ah damn.

> > Shouldn't be too painful with just one allowed:
> > 
> > 	if (!data[IFLA_IPTUN_PROTO])
> > 		goto ..
> > 
> > 	ip6_tnl_netlink_parms(data, &p);
> > 
> > 	data[IFLA_IPTUN_PROTO] = NULL;
> > 	if (memchr_inv(data, 0, sizeof() * ARRAY_SIZE(ip6_tnl_policy)))
> > 		goto ...  
> > > 	ip6_tnl0_update(netdev_priv(ip6n->fb_tnl_dev), &p);  
> > 
> > WDYT?  
> I already tried something similar, but it broke the 'ip link' command for the
> reason explained above.
> I was wondering if it's worth putting a lot of code to cover this case.
> Any thoughts?

Yes, commit message and/or even a one-line comment in the code?