use nftables on all haproxy host for better blacklisting

hosts/proxy/default.nix

@@ -20,22 +20,49 @@
       }
     ];
     defaultGateway.address = "141.56.51.254";
-    firewall = {
-      allowedTCPPorts = [
-        22
-        53 # DNS
-        80
-        443
-        1005
-        2142
-      ];
-      allowedUDPPorts = [
-        53 # DNS
-        123 # NTP
-      ];
-    };
+    firewall.enable = false;
     nftables = {
       enable = true;
+      ruleset = ''
+        table inet filter {
+          set blacklist4 {
+            type ipv4_addr
+            flags interval
+            # manage: nft add element inet filter blacklist4 { 1.2.3.0/24 }
+          }
+
+          set blacklist6 {
+            type ipv6_addr
+            flags interval
+            # manage: nft add element inet filter blacklist6 { 2001:db8::/32 }
+          }
+
+          chain input {
+            type filter hook input priority filter; policy drop;
+
+            iif "lo" accept
+            ct state established,related accept
+
+            ip saddr @blacklist4 drop
+            ip6 saddr @blacklist6 drop
+
+            # public ports
+            tcp dport { 80, 443, 1005, 2142 } accept
+
+            # lan-only: dns and ntp
+            ip saddr 141.56.51.0/24 tcp dport 53 accept
+            ip saddr 141.56.51.0/24 udp dport { 53, 123 } accept
+          }
+
+          chain forward {
+            type filter hook forward priority filter; policy drop;
+          }
+
+          chain output {
+            type filter hook output priority filter; policy accept;
+          }
+        }
+      '';
     };
   };
 
@@ -611,6 +638,47 @@
 
   stura.monitoring.extraLogInputs = [ "haproxy_geoip" ];
 
+  users.users.root.packages = [
+    (pkgs.writeShellScriptBin "nft-blacklist" ''
+      set -euo pipefail
+
+      usage() {
+        echo "Usage: nft-blacklist <add|del> <ip-or-cidr>"
+        echo "  add  - add entry to blacklist set"
+        echo "  del  - remove entry from blacklist set"
+        exit 1
+      }
+
+      [[ $# -ne 2 ]] && usage
+
+      ACTION="$1"
+      ADDR="$2"
+
+      if [[ "$ADDR" == *:* ]]; then
+        SET="blacklist6"
+      elif [[ "$ADDR" == *.* ]]; then
+        SET="blacklist4"
+      else
+        echo "Error: cannot determine address family for '$ADDR'" >&2
+        exit 1
+      fi
+
+      case "$ACTION" in
+        add)
+          ${pkgs.nftables}/bin/nft add element inet filter "$SET" "{ $ADDR }"
+          echo "Added $ADDR to $SET"
+          ;;
+        del)
+          ${pkgs.nftables}/bin/nft delete element inet filter "$SET" "{ $ADDR }"
+          echo "Removed $ADDR from $SET"
+          ;;
+        *)
+          usage
+          ;;
+      esac
+    '')
+  ];
+
   environment.systemPackages = with pkgs; [
   ];