lxc-net fails to start when configuring IPV6

[hansvschoot]

Running on Ubuntu 22.04.3 LTS jammy
lxc-utils:
  Installed: 1:5.0.0~git2209-g5a7b9ce67-0ubuntu1.1

When configuring IPV6 on the default lxcbr0 LXC bridge in /etc/default/lxc-net, using the following:
LXC_IPV6_ADDR="fec0:1:1:1::2"
LXC_IPV6_MASK="64"
LXC_IPV6_NETWORK="fec0:1:1:1::/64"
LXC_IPV6_NAT="true"

The lxc-net service fails to start: systemctl restart lxc-net

Starting LXC network bridge setup...
Error: conflicting protocols specified: ip6 vs. ip
                             ^^^^^^^^
Failed to setup lxc-net.
lxc-net.service: Main process exited, code=exited, status=1/FAILURE
lxc-net.service: Failed with result 'exit-code'.
Failed to start LXC network bridge setup.

Turns out this is due to a syntax error in /usr/lib/x86_64-linux-gnu/lxc/lxc-net on line 174:
add rule ip6 lxc postrouting ip saddr ${LXC_IPV6_NETWORK} ip daddr != ${LXC_IPV6_NETWORK} counter masquerade;
Should mention "ip6 saddr" and "ip6 daddr" in the line, like so:
add rule ip6 lxc postrouting ip6 saddr ${LXC_IPV6_NETWORK} ip6 daddr != ${LXC_IPV6_NETWORK} counter masquerade;

After manually editing the /usr/lib/x86_64-linux-gnu/lxc/lxc-net file to include the correct ip6 syntax, lxc-net starts up fine and IPV6 networking works on my LXC containers.

This fix seems to already live in the upstream lxc project on github: https://github.com/lxc/lxc/commit/4de047f51365cc06a626ee9de49fec5f76556c66#diff-f16b43004d25f547f78c7457ba74cb05eaaa2bcf979dac8173314916ef36e7f4 and as far as I can tell made it into lxc-utils 5.0.3.
Unfortunately Ubuntu jammy ships with lxc-utils 5.0.0

[hansvschoot (hansvschoot)]

not really bug related, but in case somebody else is playing around with this and ends up here: I also needed to add a firewall rule to UFW before DHCP from my unprivileged containers started working:
 ufw allow in on lxcbr0
(this can probably be restricted a bit further to only allow DHCP requests)