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 <20211117071732.7455-1-rocco.yue@mediatek.com>
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From:   Lorenzo Colitti <lorenzo@google.com>
Date:   Wed, 17 Nov 2021 17:36:44 +0900
Message-ID: <CAKD1Yr3CMPWMmNNU6YvpBiaXVttS9T8qGVgmddijYfLSfK-Rog@mail.gmail.com>
Subject: Re: [PATCH net-next] ipv6: don't generate link-local addr in random
 or privacy mode
To:     Rocco Yue <rocco.yue@mediatek.com>
Cc:     dsahern@gmail.com, "David S . Miller" <davem@davemloft.net>,
        Jakub Kicinski <kuba@kernel.org>,
        Jonathan Corbet <corbet@lwn.net>,
        Hideaki YOSHIFUJI <yoshfuji@linux-ipv6.org>,
        David Ahern <dsahern@kernel.org>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-mediatek@lists.infradead.org, rocco.yue@gmail.com,
        chao.song@mediatek.com, yanjie.jiang@mediatek.com,
        kuohong.wang@mediatek.com, Zhuoliang.Zhang@mediatek.com,
        maze@google.com, markzzzsmith@gmail.com
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On Wed, Nov 17, 2021 at 4:22 PM Rocco Yue <rocco.yue@mediatek.com> wrote:
> Disabling the kernel's automatic link-local address generation
> doesn't mean that it violates RFC 4291, because an appropriate
> link-local addr can be added to the cellulal NIC through ioctl.

Well, it would mean that the kernel requires additional work from
userspace to respect the RFC.

> The method you mentioned can also solve the current problem, but it
> seems to introduce more logic:
>   (1) set the cellular interface addr_gen_mode to RANDOM_LL_TOKEN or PRIVACY_LL_TOKEN;
>   (2) set the cellular interface up;
>   (3) disable ipv6 first;

I don't think you need to set the interface up to disable IPv6. Also I
think that if the interface is down autoconf won't run so you don't
actually need to do this.

>   (4) set token addr through netlink;

Can't 4 be the same as 3? The same netlink message can configure both
the addr_gen_mode and the token, no?

It seems to me that the following should work, and would be much simpler.

1. Bring the interface down. All addresses are deleted.
2. Send a netlink request to set addr_gen_mode RANDOM_LL_TOKEN or
PRIVACY_LL_TOKEN and set the token.
3. Bring the interface up. Autoconf runs. The link-local address is
generated from the token. An RS is sent. When the RA is received, the
global address is generated using RFC 7217 or randomly.

Cheers,
Lorenzo