From ac0654daf06a9d01fd264d96c00c8ab47b90cb73 Mon Sep 17 00:00:00 2001
From: sommerfeld <sommerfeld@sommerfeld.dev>
Date: Wed, 13 May 2026 13:43:22 +0100
Subject: feat(net): nftables laptop firewall

Default-deny inbound, allow outbound. Scoped to 'inet filter' with
'destroy table' on reload so podman/netavark tables are preserved.

- meta/base.txt: add nftables
- systemd-units/system/base.txt: enable nftables.service
- etc/nftables.conf: laptop ruleset (loopback, ct state, ICMP/ICMPv6
  essentials, DHCPv6 client, default-drop input/forward, accept output)
- etc/sysctl.d/99-sysctl.conf: rp_filter=2, no redirects, no source-route,
  log_martians
- README.md: firewall section with reload caveat
---
 etc/nftables.conf           | 50 +++++++++++++++++++++++++++++++++++++++++++++
 etc/sysctl.d/99-sysctl.conf | 13 ++++++++++++
 2 files changed, 63 insertions(+)
 create mode 100644 etc/nftables.conf

(limited to 'etc')

diff --git a/etc/nftables.conf b/etc/nftables.conf
new file mode 100644
index 0000000..c7eada2
--- /dev/null
+++ b/etc/nftables.conf
@@ -0,0 +1,50 @@
+#!/usr/bin/nft -f
+# Laptop firewall: default-deny inbound, allow outbound.
+# Scoped to `inet filter` so podman/netavark tables are preserved on reload.
+
+destroy table inet filter
+
+table inet filter {
+    chain input {
+        type filter hook input priority filter; policy drop;
+
+        iif "lo" accept
+        ct state vmap { established : accept, related : accept, invalid : drop }
+
+        # IPv4 ICMP essentials
+        ip protocol icmp icmp type {
+            echo-request,
+            destination-unreachable,
+            time-exceeded,
+            parameter-problem
+        } accept
+
+        # IPv6 ICMP: NDP, PMTUD, echo, MLD
+        meta l4proto icmpv6 icmpv6 type {
+            destination-unreachable,
+            packet-too-big,
+            time-exceeded,
+            parameter-problem,
+            echo-request,
+            nd-router-solicit,
+            nd-router-advert,
+            nd-neighbor-solicit,
+            nd-neighbor-advert,
+            mld-listener-query,
+            mld-listener-report,
+            mld-listener-done,
+            mld2-listener-report
+        } accept
+
+        # DHCPv6 client
+        ip6 saddr fe80::/10 udp dport 546 accept
+    }
+
+    chain forward {
+        type filter hook forward priority filter; policy drop;
+    }
+
+    chain output {
+        type filter hook output priority filter; policy accept;
+    }
+}
diff --git a/etc/sysctl.d/99-sysctl.conf b/etc/sysctl.d/99-sysctl.conf
index 6d21fda..3177c28 100644
--- a/etc/sysctl.d/99-sysctl.conf
+++ b/etc/sysctl.d/99-sysctl.conf
@@ -17,3 +17,16 @@ net.ipv4.tcp_mtu_probing = 1
 net.core.default_qdisc = cake
 net.ipv4.tcp_congestion_control = bbr
 vm.vfs_cache_pressure = 50
+
+# Network hardening
+net.ipv4.conf.all.rp_filter = 2
+net.ipv4.conf.default.rp_filter = 2
+net.ipv4.conf.all.accept_redirects = 0
+net.ipv4.conf.default.accept_redirects = 0
+net.ipv6.conf.all.accept_redirects = 0
+net.ipv6.conf.default.accept_redirects = 0
+net.ipv4.conf.all.send_redirects = 0
+net.ipv4.conf.default.send_redirects = 0
+net.ipv4.conf.all.accept_source_route = 0
+net.ipv6.conf.all.accept_source_route = 0
+net.ipv4.conf.all.log_martians = 1
-- 
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