[Bug 1917920] Re: magic-proxy broke with iptables 1.8.7-1ubuntu2

[Dimitri John Ledkov]

The nat fiddles are not visible inside the container network namespace.
Thus I am wondering if there is an odd interaction between namespace,
nftables based iptables vs legacy iptables. I.e. whilst the host is
configured using legacy iptables, maybe the lxd guests must be using
legacy iptables too.

I'll experiment to see if forcing to simply only use iptables-legacy
inside the lxd guest is good enough for now. Despite the hosts getting
upgraded to bionic. Cause it's only groovy that started to use nftables
based iptables.

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https://bugs.launchpad.net/bugs/1917920

Title:
  magic-proxy broke with iptables 1.8.7-1ubuntu2

Status in launchpad-buildd:
  New
Status in iptables package in Ubuntu:
  New
Status in livecd-rootfs package in Ubuntu:
  New
Status in lxd package in Ubuntu:
  New

Bug description:
  when iptables got upgraded from 1.8.5-3ubuntu4 to 1.8.7-1ubuntu2 magic
  proxy stopped working in livecd-rootfs.

  It does very simple thing:

  iptables -t nat -A OUTPUT -p tcp --dport 80 -m owner ! --uid-owner
  daemon -j REDIRECT --to 8080

  inside hirsute lxd container, with quite high privileges, in a bionic
  VM, running 4.15 kernel.

  With 1.8.5 above worked fine, with 1.8.7 somehow there was no outbound
  connectivity the very first http networking command after the above
  call would just hang indefinitely.

  However, if one does this instead:

  iptables -vv -t nat -S
  iptables-legacy -vv -t nat -S
  iptables -vv -t nat -A OUTPUT -p tcp --dport 80 -m owner ! --uid-owner daemon -j REDIRECT --to 8080

  somehow magically everything starts to work fine.

  weird.

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