Merge pull request #197221 from azahi/endlessh-module

nixos/modules/services/security/endlessh.nix

@@ -0,0 +1,99 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.endlessh;
+in
+{
+  options.services.endlessh = {
+    enable = mkEnableOption (mdDoc "endlessh service");
+
+    port = mkOption {
+      type = types.port;
+      default = 2222;
+      example = 22;
+      description = mdDoc ''
+        Specifies on which port the endlessh daemon listens for SSH
+        connections.
+
+        Setting this to `22` may conflict with {option}`services.openssh`.
+      '';
+    };
+
+    extraOptions = mkOption {
+      type = with types; listOf str;
+      default = [ ];
+      example = [ "-6" "-d 9000" "-v" ];
+      description = mdDoc ''
+        Additional command line options to pass to the endlessh daemon.
+      '';
+    };
+
+    openFirewall = mkOption {
+      type = types.bool;
+      default = false;
+      description = lib.mdDoc ''
+        Whether to open a firewall port for the SSH listener.
+      '';
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.endlessh = {
+      description = "SSH tarpit";
+      requires = [ "network.target" ];
+      wantedBy = [ "multi-user.target" ];
+      serviceConfig =
+        let
+          needsPrivileges = cfg.port < 1024;
+          capabilities = [ "" ] ++ optionals needsPrivileges [ "CAP_NET_BIND_SERVICE" ];
+          rootDirectory = "/run/endlessh";
+        in
+        {
+          Restart = "always";
+          ExecStart = with cfg; concatStringsSep " " ([
+            "${pkgs.endlessh}/bin/endlessh"
+            "-p ${toString port}"
+          ] ++ extraOptions);
+          DynamicUser = true;
+          RootDirectory = rootDirectory;
+          BindReadOnlyPaths = [ builtins.storeDir ];
+          InaccessiblePaths = [ "-+${rootDirectory}" ];
+          RuntimeDirectory = baseNameOf rootDirectory;
+          RuntimeDirectoryMode = "700";
+          AmbientCapabilities = capabilities;
+          CapabilityBoundingSet = capabilities;
+          UMask = "0077";
+          LockPersonality = true;
+          MemoryDenyWriteExecute = true;
+          NoNewPrivileges = true;
+          PrivateDevices = true;
+          PrivateTmp = true;
+          PrivateUsers = !needsPrivileges;
+          ProtectClock = true;
+          ProtectControlGroups = true;
+          ProtectHome = true;
+          ProtectHostname = true;
+          ProtectKernelLogs = true;
+          ProtectKernelModules = true;
+          ProtectKernelTunables = true;
+          ProtectSystem = "strict";
+          ProtectProc = "noaccess";
+          ProcSubset = "pid";
+          RemoveIPC = true;
+          RestrictAddressFamilies = [ "AF_INET" "AF_INET6" ];
+          RestrictNamespaces = true;
+          RestrictRealtime = true;
+          RestrictSUIDSGID = true;
+          SystemCallArchitectures = "native";
+          SystemCallFilter = [ "@system-service" "~@resources" "~@privileged" ];
+        };
+    };
+
+    networking.firewall.allowedTCPPorts = with cfg;
+      optionals openFirewall [ port ];
+  };
+
+  meta.maintainers = with maintainers; [ azahi ];
+}