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

[Mauricio Faria de Oliveira]

Test Steps from Debian bug, for reference.

- 1. Configure rules files:

cat <<EOF4 >/etc/iptables/rules.v4
# Generated by iptables-save v1.8.7 on Wed Nov 3 20:43:56 2021
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -s 1.0.0.1/32 -p icmp -j DROP
COMMIT
# Completed on Wed Nov  3 20:43:56 2021
EOF4

cat <<EOF6 >/etc/iptables/rules.v6
# Generated by ip6tables-save v1.8.7 on Wed Nov 3 20:43:56 2021
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [0:0]
-A INPUT -s 2606:4700:4700::1001/128 -p icmp -j DROP
COMMIT
# Completed on Wed Nov  3 20:43:56 2021
EOF6

 - 2. Flush existing rules:

iptables -F
ip6tables -F

 - 3. Add rules for 1.1.1.1:

iptables -A INPUT -p icmp -s 1.1.1.1 -j DROP
ip6tables -A INPUT -p icmp -s 2606:4700:4700::1111 -j DROP

- 4. Check rules for 1.1.1.1 are in:

iptables -nL | grep -e 1.1.1.1 -e 1.0.0.1
ip6tables -nL | grep -e 2606:4700:4700::1111 -e 2606:4700:4700::1001

- 5. Start iptables-persistent scripts:

netfilter-persistent start

Default behavior:

- 6. Check rules for 1.0.0.1 are in (rules for 1.1.1.1 are gone)

iptables -nL | grep -e 1.1.1.1 -e 1.0.0.1
ip6tables -nL | grep -e 2606:4700:4700::1111 -e 2606:4700:4700::1001

Optional behavior:

- 7. Enable the new options:

sed -i '/RESTORE_NOFLUSH/ s/^# //' /etc/default/netfilter-persistent

- 8. Repeat steps 2-5

- 9. Check rules for 1.0.0.1 _and_ 1.1.1.1 are in (rules for 1.1.1.1 are
kept)

iptables -nL | grep -e 1.1.1.1 -e 1.0.0.1
ip6tables -nL | grep -e 2606:4700:4700::1111 -e 2606:4700:4700::1001

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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]

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

  [Test Steps]

  See the Debian bug.

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

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