iptables physdev match broken via upstream stable patchset 2023-04-06 / v5.15.93, fixed upstream in 5.15.109

[Birgit Edel]

physdev iptables match was broken in a stable update.

A fix was already committed in upstream releases
5.4.242
5.15.109
6.1.26
6.2.13 / LP: #2023929 / LP: #2026752

== Regression details ==
Discovered in version: 5.19.0-42.43~22.04.1
Last known good version: 5.19.0-41.42~22.04.1

How to tell? Add & use a bridge interface, add catchall filter (no -j ACTION needed) see if *any* bridge traffic is tracked:
# iptables -A INPUT -m physdev --physdev-in + -m comment --comment "watch me"
# iptables -nvL INPUT | grep watch

The match behaves as if the matched packets were not bridge traffic, and consistently so: negation works. Security impact highly depends on rule design. KVM hosts, probably.

bug introduced, bridge info discarded
5.4.232 dffe83a198a6c293155f99958e51ab84442424c5 LP: #2011625
5.15.93 89a69216f17005e28bd9a333662dcb3247dd0f56 LP: #2015511
6.1.11 a1512f11ec02458c0986f169f29c90a92c150cc4 LP: #2012665
6.2 2b272bb558f1d3a5aa95ed8a82253786fd1a48ba
netfilter: br_netfilter: disable sabotage_in hook after first suppression

fixed, bridge info no longer discarded
5.4.242 36f098e1e4d1a372329c6244b220047a19e60dbd
5.15.109 cb9b96c154a10dd4802b82281c9246eabe081026
6.1.26 ea854a25c8327f51f7ff529b745794a985185563
6.2.13 22134b86de9c2afe28e1f406062cd93bdcac4149
master 94623f579ce338b5fa61b5acaa5beb8aa657fb9e
netfilter: br_netfilter: fix recent physdev match breakage

related module names: xt_physdev nft_meta_bridge br_netfilter

[Birgit Edel (biredel)]

Fixed in:
Ubuntu 6.2.0-26.26~22.04.1-generic 6.2.13
Available on jammy via:
linux-image-generic-hwe-22.04-edge