From 37ad9e62a2589d6cccf0dc92ff8d16617915c5bd Mon Sep 17 00:00:00 2001
From: Nulo <git@nulo.in>
Date: Thu, 17 Nov 2022 22:50:56 -0300
Subject: [PATCH] nftables

---
 modules/nftables.lua | 95 ++++++++++++++++++++++++++++++++++++++++++++
 setup.lua            |  1 +
 2 files changed, 96 insertions(+)
 create mode 100644 modules/nftables.lua

diff --git a/modules/nftables.lua b/modules/nftables.lua
new file mode 100644
index 0000000..8f8508a
--- /dev/null
+++ b/modules/nftables.lua
@@ -0,0 +1,95 @@
+modules.nftables = {}
+add_packages({ "nftables" })
+add_file("/etc/nftables.nft", [[
+#!/usr/sbin/nft -f
+
+flush ruleset
+
+table inet filter {
+	chain input {
+		type filter hook input priority 0; policy drop;
+
+		iifname lo accept \
+		comment "Accept any localhost traffic"
+
+		ct state { established, related } accept \
+		comment "Accept traffic originated from us"
+
+		ct state invalid drop \
+		comment "Drop invalid connections"
+
+		tcp dport 113 reject with icmpx type port-unreachable \
+		comment "Reject AUTH to make it fail fast"
+
+		ip protocol icmp icmp type {
+			echo-reply,  # type 0
+			destination-unreachable,  # type 3
+			echo-request,  # type 8
+			time-exceeded,  # type 11
+			parameter-problem,  # type 12
+		} accept \
+		comment "Accept ICMP"
+
+		ip6 nexthdr icmpv6 icmpv6 type {
+			destination-unreachable,  # type 1
+			packet-too-big,  # type 2
+			time-exceeded,  # type 3
+			parameter-problem,  # type 4
+			echo-request,  # type 128
+			echo-reply,  # type 129
+		} accept \
+		comment "Accept basic IPv6 functionality"
+
+		ip6 nexthdr icmpv6 icmpv6 type {
+			nd-router-solicit,  # type 133
+			nd-router-advert,  # type 134
+			nd-neighbor-solicit,  # type 135
+			nd-neighbor-advert,  # type 136
+		} ip6 hoplimit 255 accept \
+		comment "Allow IPv6 SLAAC"
+
+		ip6 nexthdr icmpv6 icmpv6 type {
+			mld-listener-query,  # type 130
+			mld-listener-report,  # type 131
+			mld-listener-reduction,  # type 132
+			mld2-listener-report,  # type 143
+		} ip6 saddr fe80::/10 accept \
+		comment "Allow IPv6 multicast listener discovery on link-local"
+
+		ip6 saddr fe80::/10 udp sport 547 udp dport 546 accept \
+		comment "Accept DHCPv6 replies from IPv6 link-local addresses"
+
+		tcp dport 80 counter accept \
+		comment "Allow HTTP"
+	}
+
+	chain forward {
+		type filter hook forward priority 0; policy drop;
+	}
+
+	chain output {
+		type filter hook output priority 0; policy accept;
+	}
+}
+
+# The state of stateful objects saved on the nftables service stop.
+include "/var/lib/nftables/*.nft"
+
+]])
+
+modules.runit.add_service("nftables", [[#!/bin/sh
+if [ ! -r /etc/nftables.nft ]; then
+	echo "No config, dropping everything"
+	nft -f /dev/stdin <<-EOF
+		flush ruleset
+		table inet filter {
+		   chain input { type filter hook input priority 0; policy drop; }
+		   chain forward { type filter hook forward priority 0; policy drop; }
+		   chain output { type filter hook output priority 0; policy drop; }
+		}
+	EOF
+	exit 1
+fi
+nft -f /etc/nftables.nft
+exec sleep infinity
+]])
diff --git a/setup.lua b/setup.lua
index 14928e7..3008658 100644
--- a/setup.lua
+++ b/setup.lua
@@ -49,6 +49,7 @@ module "hostname"
 module "dhcpcd"
 module "ntpsec"
 module "nginx"
+module "nftables"
 
 print("=> Installing and upgrading packages...")
 utils.expect_nil(alpine.make_world(root, packages))