[PATCH] ipv6: make the net.ipv6.conf.all.use_tempaddr sysctl propagate to interface settings

[Mathieu Trudel-Lapierre]

Hi,

We're trying to enable IPv6 privacy extensions by default in Ubuntu, and
I've noticed issues applying the sysctl settings: applying
net.ipv6.conf.all.use_tempaddr which I'd expect, readying docs, to be
propagated to the underlying interface-specific settings (e.g.
net.ipv6.conf.eth0.use_tempaddr) for already-available interfaces; which
does not work.

Ideally at boot-time, one would only need to set the following settings:
net.ipv6.conf.all.use_tempaddr   (to modify already-up/added interfaces)
net.ipv6.conf.default.use_tempaddr (for future new interfaces)

I wrote the attached patch which appears to correctly set the value of
net.ipv6.conf.all.use_tempaddr on the interfaces when changed. I would
be very grateful if I could get some review on that patch before
submitting it upstream.

It seems as though the issue is generally reproduced for most of the
other ipv6 settings, and my reading of
Documentation/networking/ip-sysctls.txt and net/ipv6/Kconfig (the help
entry for IPV6_PRIVACY), but I'm concentrating on just use_tempaddr
which is something we'd really need to make work.

For more information about these issues, I found
https://otrs.menandmice.com/otrs/public.pl?Action=PublicFAQ&ItemID=91
which also links two bugzilla.kernel.org bugs (which I unfortunately
can't reach). It's also been discussed in the past on netdev
(http://markmail.org/thread/pxw4o7p2k3xn5vh3#query:+page:1
+mid:pxw4o7p2k3xn5vh3+state:results ) and on debian-kernel (can't find
the thread again).

Please keep me in CC; I'm not subscribed to this list.

Regards,

--
Mathieu Trudel-Lapierre <mathieu.trudel-lapierre at canonical.com>
Freenode: cyphermox, Jabber: mathieu.tl at gmail.com
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