On Thu, 2018-01-04 at 20:22 +0100, Marcel Holtmann wrote:
Hi Thomas,I am in favor of address randomization even while it has limited affect, but at least for background scanning it is useful. However doing this via RTNL is causing a weird layer violation and all sorts of potential races and issues. This needs to be done with full awareness of cfg80211 and thus via nl80211. So iwd should do it. And iwd should just expose an on/off switch for WiFi Privacy.TL;DR: the policy of which MAC address to use (and when) is flexible and present in NetworkManager configuration. And it's more then a simple randomize on/off switch. === A smaller reason is, that some people have strong opinions and consider important which bits of the address to scramble (and choose a well known manufacturer OUI)[1]. I personally don't agree with the importance of such considerations, but I'd like NetworkManager to be the first choice for people with this particular need -- regardless of whether this need is real or only perceived. In NM you can configure how the bits are scrambled very flexible. Both while scanning[2] and while being associated[3]. More interesting is, I don't only want to have a random MAC address while scanning, but also while being associated. My permanent MAC address should never ever be reveiled. But a new random MAC address on each new association isn't exactly what you want either, because then I get a new IP address from DHCP each time and have to redo captive portal login. So, I want for each of my Wi-Fi profiles a different, stable MAC address. Actually, for public networks like a hotel, I want to use a stable MAC address for a limited amount of time. The example in [4] show how to do that in NM. ===I have nothing against an option that says generate a new MAC address for this SSID and keep using it from that time forward.
If I understand correctly, you agree that the MAC address depends on the profile.
It is a bit counterproductive if nl80211 doesn’t allow to specify the MAC address for association. Since powering down WiFi, changing the address and powering back up is something that I am strictly against. So if these things are what people really want, then neither NM nor iwd should actually do the heavy lifting for it. It should be done by the wireless stack in the kernel.
Ok, whatever works best.
That said iwd should cope Ok with the MAC address changing behind its back if it receives the RTNL notification (RTM_NEWLINK) if it isn't connected. It always updates it's copy of the address on a RTM_NEWLINK so the race condition shouldn't be present I suppose.I would think so too. NM change the MAC address via RTNL only while scanning, early during activation, and late during deactivation. As the wireless daemon does/should not autoactivate the device against NM's wish and NM determines that the device is deactivated only after an event from iwd. Hence, there shouldn't be a race of NM interfering while being connected. The race is only while scanning and iwd should just cope with that. Alternatively/additionally, a SetMacAddress() D-Bus call would avoid any race and allow to leave the decision which address to user to somebody closer to the user.It will not be as simple as that. You need to leave iwd with the decision making for connecting to known WiFi networks. It just isn’t as dumb as wpa_supplicant and from a NM perspective, you should be doing as little as you do with BlueZ or oFono. This means iwd needs to be told what to do and not just an address. It doesn’t matter if it is via a D-Bus call or RTNL. iwd remembers known networks and will connect to them if they are in range, roam automatically and also switch networks if it makes sense. That means any randomization policy would have to be executed inside iwd and not outside. As stated above, if you want different MAC addresses per SSID, then that needs to be inside iwd. So many things in the wpa_supplicant design led to “hacks” outside to add features and that really has to stop. It is not maintainable and the corner cases and race condition this architecture causes is just crazy.
For NM, at each moment not all its connection profiles are candidate
for connecting automatically. The list of which profiles can be
autoactivated depends on NM internal state, for example
- is the profile even configured to allow autoactivation?
- is the user owning the connection logged in (if it's restricted
to a user)?
- if the profile requires secrets, is somebody previledged around
to potentially provide them?
- was the connection previously manually disconnected by the user
(which marks it as blocked from autoconnecting again)
- did a previous connection attempt fail, e.g. no DHCP lease. If
it failed $configurable times, it will be blocked for a few
minutes.
With supplicant, NM intersects the list of autoconnect candidates with
the list from the scan-list, and decides which to (auto) activate. As
far as supplicant is concerned, this is not happening automatically,
and there is no race.
If I understand you, the reason to let iwd automatically pick a
network, is because iwd knows better.
But in case there are multiple autoconnect candidates that could be
activated, then NM chooses the candidate which
- has the highest autoconnect priority (configurable)
- was used the least long ago.
Indeed, NM doesn't consider the signal strength and other Wi-Fi
properties. It's a missing feature.
How is iwd choosing automatically? Choosing based on signal strength
and encryption parameters would be a nice feature, but what about non-
Wi-Fi related factors.
How will iwd allow NM to contribute to that decision?
best,
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