From b002a94e07a8165286aa7ee4571c296b2bf8d0fc Mon Sep 17 00:00:00 2001
From: Daniel Barlow <dan@telent.net>
Date: Tue, 20 Jun 2023 20:20:32 +0100
Subject: [PATCH] rotuer: use firewallgen to make packet filter rules

---
 examples/rotuer-firewall.nix | 124 +++++++++++++++++++++++++++++++++++
 examples/rotuer.nix          |  10 ++-
 2 files changed, 133 insertions(+), 1 deletion(-)
 create mode 100644 examples/rotuer-firewall.nix

diff --git a/examples/rotuer-firewall.nix b/examples/rotuer-firewall.nix
new file mode 100644
index 0000000..d5fe5de
--- /dev/null
+++ b/examples/rotuer-firewall.nix
@@ -0,0 +1,124 @@
+let
+  drop = expr : "${expr} drop";
+  accept = expr : "${expr} accept";
+  mcast-scope = 8;
+  allow-incoming = false;
+  bogons-ip6 = {
+    type = "filter";
+    family = "ip6";
+    rules = [
+      (drop "ip6 saddr ff00::/8") # multicast saddr is illegal
+
+      (drop "ip6 saddr ::/128") # unspecified address
+      (drop "ip6 daddr ::/128")
+      (drop "ip6 saddr 2001:db8::/32") # documentation addresses
+      (drop "ip6 daddr 2001:db8::/32")
+
+      # I think this means "check FIB for (saddr, iif) to see if we
+      # could route a packet to that address using that interface",
+      # and if we can't then it was an inapproppriate source address
+      # for packets received _from_ said interface
+      (drop "fib saddr . iif oif eq 0")
+
+      (drop "icmpv6 type router-renumbering")
+      (drop "icmpv6 type 139") # Node Information Query
+      (drop "icmpv6 type 140") # Node Information Response
+      (drop "icmpv6 type 100")
+      (drop "icmpv6 type 101")
+      (drop "icmpv6 type 200")
+      (drop "icmpv6 type 201")
+      (drop "icmpv6 type 127")
+      (drop "icmpv6 type 255")
+      (drop "icmpv6 type destination-unreachable ct state invalid,untracked")
+    ];
+  };
+  forward-ip6 = {
+    type = "filter";
+    family = "ip6";
+    policy = "drop";
+    hook = "forward";
+    rules = [
+      "jump bogons-ip6"
+      (drop "ip6 saddr ::1/128") # loopback address [RFC4291]
+      (drop "ip6 daddr ::1/128")
+      (drop "ip6 saddr ::FFFF:0:0/96")# IPv4-mapped addresses
+      (drop "ip6 daddr ::FFFF:0:0/96")
+      (drop "ip6 saddr fe80::/10") # link-local unicast
+      (drop "ip6 daddr fe80::/10")
+      (drop "ip6 saddr fc00::/7") # unique-local addresses
+      (drop "ip6 daddr fc00::/7")
+      (drop "ip6 saddr 2001:10::/28") # ORCHID [RFC4843].
+      (drop "ip6 daddr 2001:10::/28")
+
+      (drop "ip6 saddr fc00::/7") # unique local source
+      (drop "ip6 daddr fc00::/7") # and/or dst addresses [RFC4193]
+
+      # multicast with wrong scopes
+      (drop
+        # dest addr first byte 0xff, low nibble of second byte <= scope
+        # https://www.mankier.com/8/nft#Payload_Expressions-Raw_Payload_Expression
+        "@nh,192,8 eq 0xff @nh,204,4 le ${toString mcast-scope}")
+
+      (accept "oifname \"int\" iifname \"ppp0\" meta l4proto udp ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" meta l4proto udp")
+
+      (accept "meta l4proto icmpv6")
+      (accept "meta l4proto ah")
+      (accept "meta l4proto esp")
+
+      # does this ever get used or does the preceding general udp accept
+      # already grab anything that might get here?
+      (accept "oifname \"ppp0\" udp dport 500") # IKE Protocol [RFC5996]. haha zyxel
+      (accept "ip6 nexthdr hip")
+
+      ## FIXME no support yet for recs 27-30 Mobility Header
+
+      (accept "oifname \"int\" iifname \"ppp0\" meta l4proto tcp ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" meta l4proto tcp")
+
+      (accept "oifname \"int\" iifname \"ppp0\" meta l4proto sctp ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" meta l4proto sctp")
+
+      (accept "oifname \"int\" iifname \"ppp0\" meta l4proto dccp ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" meta l4proto dccp")
+
+      # we can allow all reasonable inbound, or we can use an explicit
+      # allowlist to enumerate the endpoints that are allowed to
+      # accept inbound from the WAN
+      (if allow-incoming
+       then accept "oifname \"int\" iifname \"ppp0\""
+       else "oifname \"int\" iifname \"ppp0\" jump incoming-allowed-ip6"
+      )
+      # allow all outbound and any inbound that's part of a
+      # recognised (outbound-initiated) flow
+      (accept "oifname \"int\" iifname \"ppp0\" ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" ")
+    ];
+  };
+  input-ip6 = {
+    type = "filter";
+    family = "ip6";
+    policy = "drop";
+    hook = "input";
+    rules = [
+      "jump bogons-ip6"
+      (accept "meta l4proto icmpv6")
+      (if allow-incoming
+       then accept "oifname \"int\" iifname \"ppp0\""
+       else "oifname \"int\" iifname \"ppp0\" jump incoming-allowed-ip6"
+      )
+      (accept "oifname \"int\" iifname \"ppp0\"  ct state established,related")
+      (accept "iifname \"int\" oifname \"ppp0\" ")
+    ];
+  };
+
+  incoming-allowed-ip6 = {
+    type = "filter";
+    family = "ip6";
+    rules = [
+      "oifname \"int\" ip6 daddr 2001:8b0:de3a:40de::e9d tcp dport 22"
+    ];
+  };
+in {
+  inherit input-ip6 forward-ip6 bogons-ip6 incoming-allowed-ip6;
+}
diff --git a/examples/rotuer.nix b/examples/rotuer.nix
index 532fdd7..d9da607 100644
--- a/examples/rotuer.nix
+++ b/examples/rotuer.nix
@@ -226,15 +226,23 @@ in rec {
     dependencies = [ services.wan ];
   };
 
+  services.firewall =
+    let config = pkgs.firewallgen "firewall.nft" (import ./rotuer-firewall.nix);
+    in oneshot {
+      name = "firewall";
+      up = config;
+      down = "${pkgs.nftables}/bin/nft flush ruleset";
+    };
+
   services.packet_forwarding =
     let filename = "/proc/sys/net/ipv4/conf/all/forwarding";
     in oneshot {
       name = "let-the-ip-flow";
       up = ''
-        ${pkgs.nftables}/bin/nft -f ${../nat.nft}
         echo 1 > ${filename}
       '';
       down = "echo 0 > ${filename}";
+      dependencies = [ services.firewall ];
     };
 
   services.dhcp6 =