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

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Message-ID: <20250619155220.3577a32a@kernel.org>
Date: Thu, 19 Jun 2025 15:52:20 -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 Tue, 17 Jun 2025 18:01:25 +0200 Nicolas Dichtel wrote:
> +	if (dev == ip6n->fb_tnl_dev) {
> +		if (!data[IFLA_IPTUN_PROTO]) {
> +			NL_SET_ERR_MSG(extack,
> +				       "Only protocol can be changed for fallback tunnel");
> +			return -EINVAL;
> +		}
> +
> +		ip6_tnl_netlink_parms(data, &p);
> +		ip6_tnl0_update(netdev_priv(ip6n->fb_tnl_dev), &p);
> +		return 0;

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?

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?