netdev - Re: [RFC PATCH] ipv6: Use dev_addr in stable-privacy address generation

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Message-Id: <20200326.114550.2060060414897819387.davem@davemloft.net>
Date:   Thu, 26 Mar 2020 11:45:50 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     brambonne@...gle.com
Cc:     kuznet@....inr.ac.ru, yoshfuji@...ux-ipv6.org, kuba@...nel.org,
        hannes@...essinduktion.org, netdev@...r.kernel.org,
        lorenzo@...gle.com, jeffv@...gle.com
Subject: Re: [RFC PATCH] ipv6: Use dev_addr in stable-privacy address
 generation

From: "Bram Bonné" <brambonne@...gle.com>
Date: Thu, 26 Mar 2020 10:42:52 +0100

> This patch extends the IN6_ADDR_GEN_MODE_STABLE_PRIVACY address
> generation mode to use the software-defined MAC address (dev_addr)
> rather than the permanent, hardware-defined MAC address (perm_addr) of
> the interface when generating IPv6 link-local addresses.
> 
> This ensures that the IPv6 link-local address changes in line with the
> MAC address when per-network MAC address randomization is used,
> providing the expected privacy guarantees.
> 
> When no MAC address randomization is used, dev_addr corresponds to
> perm_addr, and IN6_ADDR_GEN_MODE_STABLE_PRIVACY behaves as before.
> 
> When MAC address randomization is used, this makes the MAC address
> fulfill the role of both the Net_Iface and the (optional) Network_ID
> parameters in RFC7217.
> 
> Cc: Lorenzo Colitti <lorenzo@...gle.com>
> Cc: Jeffrey Vanderstoep <jeffv@...gle.com>
> Signed-off-by: Bram Bonné <brambonne@...gle.com>

I think the current behavior is intentional in that it's supposed to use
something that is unchanging even across arbitrary administrator changes
to the in-use MAC address.