Date:	Mon, 28 Oct 2013 18:16:19 -0500
From:	Dan Williams <dcbw@...hat.com>
To:	David Miller <davem@...emloft.net>
Cc:	hannes@...essinduktion.org, jiri@...nulli.us, vyasevich@...il.com,
	netdev@...r.kernel.org, kuznet@....inr.ac.ru, jmorris@...ei.org,
	yoshfuji@...ux-ipv6.org, kaber@...sh.net, thaller@...hat.com,
	stephen@...workplumber.org
Subject: Re: [patch net-next] ipv6: allow userspace to create address with
 IFLA_F_TEMPORARY flag

On Mon, 2013-10-28 at 17:17 -0400, David Miller wrote:
> From: Hannes Frederic Sowa <hannes@...essinduktion.org>
> Date: Sun, 27 Oct 2013 17:48:35 +0100
> 
> > A temporary address is also bound to a non-privacy public address so
> > it's lifetime is determined by its lifetime (e.g. if you switch the
> > network and don't receive on-link information for that prefix any
> > more). NetworkManager would have to take care about that, too. It is
> > just a question of what NetworkManager wants to handle itself or lets
> > the kernel handle for it.
> 
> How much really needs to be in userspace to implement RFC4941?
> 
> I don't like the idea that even for a fully up and properly
> functioning link, if NetworkManager wedges then critical things like
> temporary address (re-)generation, will cease.

Honestly, I'd be completely happy to leave temporary address handling up
to the kernel and *not* do it in userspace; the kernel already has all
the code.  There are two problems with that though, (a) it's tied to
in-kernel RA handling, and (b) it's controlled by a CONFIG option.  Both
these are solvable.

First off, what's the reasoning behind having IPv6 privacy as a config
option?  It's off-by-default and must be explicitly turned on, so is
there any harm in removing the config?  Or is it just for
smallest-kernel-ever folks?

Would a new IFA_F_MANAGE_TEMP (or better name) work here, indicating
that for some new static address, that the kernel should create and
manage the temporary privacy addresses associated with its prefix?

Dan

> All that seems to matter is the secret used to generate the temporary
> address sequence, and perhaps things like site specific lifetime
> parameters.  These are things userland can send to the kernel in
> netlink messages.
> 
> Full disclosure that I am saying this from the perspective of someone
> who believes that one of the biggest mistakes ever was allowing the
> core of DHCP to be done in userspace.
> 
> Right now every ipv4 DHCP user ends up with their interface in
> promiscuous mode.  The DHCP client implementations are huge non-
> trivial bodies of code, and getting them to adopt the changes necessary
> to not put the interface in promiscuous mode is harder than pulling
> teeth.
> 
> If at least the DHCP protocol communications part were in the kernel,
> on the other hand, we could remove the problem quite swiftly.
> 
> This problem has existed for more than a decade, btw.  There simply
> exists no will to fix it properly, even after all this time, because
> breaking the ice on those DHCP client code bases in userbase is hard.
> 
> So I want to see less fundamental stuff about interface configuration
> and address assignment in userland, not more.
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