Re: Problem with IPv6 privacy addresses in 7.0

[Chris Adams <linux@cmadams.net>]

Once upon a time, Jakub Kicinski <kuba@kernel.org> said:
> On Tue, 26 May 2026 20:06:41 -0500 Chris Adams wrote:
> > > Hi! Adding more people to CC. Do you know if you upgraded from 6.18 
> > > or 6.19?  
> > 
> > It was 6.19 to 7.0.
> > 
> > > Would you be able to try testing with some commits reverted?
> > > On a quick look the candidates would be:
> > > 
> > > cb3de96eea66 ("ipv6: preserve insertion order for same-scope addresses")  
> > 
> > It's this one.
> 
> Phew, the second one was mine :)
> 
> > I figured out that it happens after stopping a VM (and I usually
> > start/stop a VM for a bit in the morning, which is why it happened more
> > than once).  So I set up a VM with a nested VM, running up-to-date
> > Fedora 44, and then was able to bisect pretty easily, and it landed on
> > this commit.
> > 
> > Fedora is using NetworkManager, and IIRC NM does some part of privacy
> > address management (right?).  NM didn't change, so maybe this commit is
> > confusing something in NM?
> 
> Sounds plausible, pretty sure we knew this commit was risky to begin
> with, but we had no direct proof that it'd break real life users.
> 
> Revert is the right course of action here. Would you be willing/able
> to send the revert with your problem description and a Fixes tag
> pointing to the reverted commit?

I did want to add a little more test note:

It's definitely an interaction with NetworkManager.  If I stop NM and
run my VM start/stop test, nothing unexpected happens after.  If NM is
running and I do my VM test, when the next router advertisement is
received, NM replaces the privacy addresses.

-- 
Chris Adams <linux@cmadams.net>