Re: [PATCH] net: ipv6: don't generate link-local address in any addr_gen_mode

From: Lorenzo Colitti <lorenzo@google.com>
To: David Ahern <dsahern@gmail.com>
Cc: "Rocco Yue" <rocco.yue@mediatek.com>,
	"David S . Miller" <davem@davemloft.net>,
	"Hideaki YOSHIFUJI" <yoshfuji@linux-ipv6.org>,
	"David Ahern" <dsahern@kernel.org>,
	"Jakub Kicinski" <kuba@kernel.org>,
	"Matthias Brugger" <matthias.bgg@gmail.com>,
	"Linux NetDev" <netdev@vger.kernel.org>,
	lkml <linux-kernel@vger.kernel.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org, wsd_upstream@mediatek.com,
	rocco.yue@gmail.com, chao.song@mediatek.com,
	"Kuohong Wang (王國鴻)" <kuohong.wang@mediatek.com>,
	"Zhuoliang Zhang (张卓亮)" <zhuoliang.zhang@mediatek.com>
Subject: Re: [PATCH] net: ipv6: don't generate link-local address in any addr_gen_mode
Date: Thu, 9 Sep 2021 15:20:51 +0900	[thread overview]
Message-ID: <CAKD1Yr2aijPe_aq+SRm-xv0ZPoz_gKjYrEX97R1NJyYpSnv4zg@mail.gmail.com> (raw)
In-Reply-To: <62c9f5b7-84bd-d809-4e33-39fed7a9d780@gmail.com>

David,

sorry for reviving this discussion, but it felt better than starting a
new thread about this. We (Android) added a vendor hook for this, but
IMO that's the wrong solution and I think we'd still like to see this
fixed the right way.

> I think another addr_gen_mode is better than a separate sysctl. It looks
> like IN6_ADDR_GEN_MODE_STABLE_PRIVACY and IN6_ADDR_GEN_MODE_RANDOM are
> the ones used for RAs, so add something like:
>
> IN6_ADDR_GEN_MODE_STABLE_PRIVACY_NO_LLA,
> IN6_ADDR_GEN_MODE_RANDOM_NO_LLA,

I think the real requirement here (which wasn't clear in this thread)
is that the network needs to control the interface ID (i.e., the
bottom 64 bits) of the link-local address, but the device is free to
use whatever interface IDs to form global addresses. See:
https://www.etsi.org/deliver/etsi_ts/129000_129099/129061/15.03.00_60/ts_129061v150300p.pdf

How do you think that would best be implemented?

1. The actual interface ID could be passed in using IFLA_INET6_TOKEN,
but there is only one token, so that would cause all future addresses
to use the token, disabling things like privacy addresses (bad).
2. We could add new IN6_ADDR_GEN_MODE_STABLE_PRIVACY_LL_TOKEN,
IN6_ADDR_GEN_MODE_RANDOM_LL_TOKEN, etc., but we'd need to add one such
mode for every new mode we add.
3. We could add a separate sysctl for the link-local address, but you
said that per-device sysctls aren't free.
4. We could change the behaviour so that if the user configures a
token and then sets IN6_ADDR_GEN_MODE_*, then we use the token only
for the link-local address. But that would impact backwards
compatibility.

Thoughts?

Cheers,
Lorenzo