[Bug 1949643] Re: iptables-persistent unconditionally drops existing iptables rules

[Mauricio Faria de Oliveira]

Thanks, Jorge!

I've sponsored the debdiffs with minor changes
(that I didn't mention previously) to B/F/H/I,
and added some stuff to the SRU template [1,2].

The changes build fine on LP PPAs for all releases.

cheers,
Mauricio

...

For reference:

- versioning:
  - B: change ubuntu2 to ubuntu1.1 (SRUs usually +0.1)
  - H/I: change ubuntu1 (same version on diff releases)
         to ubuntu0.21.{04,10}.1
- maintainer:
  - F/H/I: run update-maintainer

[1] https://wiki.ubuntu.com/SecurityTeam/UpdatePreparation#Update_the_packaging
[2] https://wiki.ubuntu.com/StableReleaseUpdates#SRU_Bug_Template

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https://bugs.launchpad.net/bugs/1949643

Title:
  iptables-persistent unconditionally drops existing iptables rules

Status in iptables-persistent package in Ubuntu:
  Fix Released
Status in iptables-persistent source package in Bionic:
  In Progress
Status in iptables-persistent source package in Focal:
  In Progress
Status in iptables-persistent source package in Hirsute:
  In Progress
Status in iptables-persistent source package in Impish:
  In Progress
Status in iptables-persistent source package in Jammy:
  Fix Released
Status in iptables-persistent package in Debian:
  Fix Released

Bug description:
  [Impact]

  The iptables-persistent plugins/{15-ip4tables,25-ip6tables}
  use ip[6]tables-restore without --noflush unconditionally.

  This doesn't play along well with ufw, which starts before
  netfilter-persistent typically, and gets its rules flushed.

  This makes `ufw status` return that ufw is disabled, which
  is misleading, as `ufw.service` is enabled and ufw actually
  loaded all its rules correctly (but they were flushed later.)

  Some images ship iptables-persistent rules, thus are subject
  to this issue if ufw is used.

  [Workaround]

  Disable the netfilter-persistent.service unit, after rules
  have been migrated to ufw.

  [Fix]

  Add options IP[6]TABLES_RESTORE_NOFLUSH (disabled by default)
  to `/etc/default/netfilter-persistent` to allow not flushing
  existing ip[6]tables rules.

  Proposed in Debian bug #998416 [1], Salsa Merge Request [2].

  [Test Steps]

  See commment #14 (based on the Debian bug.)

  [Regression Potential]

  Regressions would manifest when netfilter-persistent.service
  starts/loads rules, probably in the form  of failures to run
  ip[6]tables-restore or incorrectly (not) flushing rules.

  Note: there is _no_ behavior change is by default, so users
  have to opt-in, which should reduce the chances/numbers of
  potential regressions.

  [Links]

  [1] https://bugs.debian.org/998416
  [2] https://salsa.debian.org/debian/iptables-persistent/-/merge_requests/3

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