Re: How does IWD handle setting MAC address?

[Marcel Holtmann <marcel holtmann org>]

Hi Thomas,

> I think a valueable feature with NetworkManager + Wi-Fi +
> wpa_supplicant is that MAC address options. 
>
> I tried to explain how that works here:
>  https://blogs.gnome.org/thaller/2016/08/26/mac-address-spoofing-in-networkmanager-1-4-0/
> and some ideas here:
>  
> https://cgit.freedesktop.org/NetworkManager/NetworkManager/tree/examples/nm-conf.d/30-anon.conf?id=b936ccd2837199d5851388122c2e44951bf20012
>
>
> Basically, NM changes the current MAC address of the Wi-Fi device under the hood.
> But only while scanning, early when activation starts, or after deactivation.
>
> Grep the sources for nm_device_hw_addr_set() and nm_device_hw_addr_set_cloned().
>
> There were/are a few issues with supplicant, where it would cope badly with NM
> externally changing the MAC address:
> E.g. https://w1.fi/cgit/hostap/commit/?id=290834df69556b903b49f2a45671cc62b44f13bb
>     http://lists.infradead.org/pipermail/hostap/2017-October/038035.html
>
> Also, some drivers don't support changing the MAC address at all. In the past,
> NM would fail badly in that case, nowadays, it should just log a warning
> and otherwise work fine.
>
>
> Anyway, how does iwd cope with NM externally changing the MAC address (via netlink)?
> Otherwise, could/does iwd provide a SetMacAddress() D-Bus method?
> I don't think iwd should contain the logic for selecting a MAC address. NM knows which
> profile is active, and it knows how to generate the desired MAC address. iwd could contain
> some MAC address randomization schemes, I don't care as long as there is a way for NM
> to explicitly set the desired MAC address.

I think that MAC address randomization should be done inside the kernel at cfg80211 level or to some level 
via nl80211 level from iwd. Doing that the hard way via RTNL and behind the back of a WiFi daemon is really a 
bad idea.

So for iwd we most likely just want to provide an option to enable privacy (aka address randomization) and 
nothing else.

Regards

Marcel