nixos/opensnitch: Add option to configure rules

nixos/doc/manual/from_md/release-notes/rl-2305.section.xml

@@ -83,7 +83,10 @@
     <itemizedlist spacing="compact">
       <listitem>
         <para>
-          Create the first release note entry in this section!
+          The module for the application firewall
+          <literal>opensnitch</literal> got the ability to configure
+          rules. Available as
+          <link linkend="opt-services.opensnitch.rules">services.opensnitch.rules</link>
         </para>
       </listitem>
     </itemizedlist>

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -33,4 +33,4 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 <!-- To avoid merge conflicts, consider adding your item at an arbitrary place in the list instead. -->
 
-- Create the first release note entry in this section!
+- The module for the application firewall `opensnitch` got the ability to configure rules. Available as [services.opensnitch.rules](#opt-services.opensnitch.rules)

nixos/modules/services/security/opensnitch.nix

@@ -5,10 +5,47 @@ with lib;
 let
   cfg = config.services.opensnitch;
   format = pkgs.formats.json {};
+
+  predefinedRules = flip mapAttrs cfg.rules (name: cfg: {
+    file = pkgs.writeText "rule" (builtins.toJSON cfg);
+  });
+
 in {
   options = {
     services.opensnitch = {
-      enable = mkEnableOption (lib.mdDoc "Opensnitch application firewall");
+      enable = mkEnableOption (mdDoc "Opensnitch application firewall");
+
+      rules = mkOption {
+        default = {};
+        example = literalExpression ''
+          {
+            "tor" = {
+              "name" = "tor";
+              "enabled" = true;
+              "action" = "allow";
+              "duration" = "always";
+              "operator" = {
+                "type" ="simple";
+                "sensitive" = false;
+                "operand" = "process.path";
+                "data" = "''${lib.getBin pkgs.tor}/bin/tor";
+              };
+            };
+          };
+        '';
+
+        description = mdDoc ''
+          Declarative configuration of firewall rules.
+          All rules will be stored in `/var/lib/opensnitch/rules`.
+          See [upstream documentation](https://github.com/evilsocket/opensnitch/wiki/Rules)
+          for available options.
+        '';
+
+        type = types.submodule {
+          freeformType = format.type;
+        };
+      };
+
       settings = mkOption {
         type = types.submodule {
           freeformType = format.type;
@@ -18,15 +55,15 @@ in {
 
               Address = mkOption {
                 type = types.str;
-                description = lib.mdDoc ''
+                description = mdDoc ''
                   Unix socket path (unix:///tmp/osui.sock, the "unix:///" part is
                   mandatory) or TCP socket (192.168.1.100:50051).
                 '';
               };
 
               LogFile = mkOption {
                 type = types.path;
-                description = lib.mdDoc ''
+                description = mdDoc ''
                   File to write logs to (use /dev/stdout to write logs to standard
                   output).
                 '';
@@ -36,7 +73,7 @@ in {
 
             DefaultAction = mkOption {
               type = types.enum [ "allow" "deny" ];
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Default action whether to block or allow application internet
                 access.
               '';
@@ -46,36 +83,36 @@ in {
               type = types.enum [
                 "once" "always" "until restart" "30s" "5m" "15m" "30m" "1h"
               ];
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Default duration of firewall rule.
               '';
             };
 
             InterceptUnknown = mkOption {
               type = types.bool;
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Wheter to intercept spare connections.
               '';
             };
 
             ProcMonitorMethod = mkOption {
               type = types.enum [ "ebpf" "proc" "ftrace" "audit" ];
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Which process monitoring method to use.
               '';
             };
 
             LogLevel = mkOption {
               type = types.enum [ 0 1 2 3 4 ];
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Default log level from 0 to 4 (debug, info, important, warning,
                 error).
               '';
             };
 
             Firewall = mkOption {
               type = types.enum [ "iptables" "nftables" ];
-              description = lib.mdDoc ''
+              description = mdDoc ''
                 Which firewall backend to use.
               '';
             };
@@ -84,24 +121,23 @@ in {
 
               MaxEvents = mkOption {
                 type = types.int;
-                description = lib.mdDoc ''
+                description = mdDoc ''
                   Max events to send to the GUI.
                 '';
               };
 
               MaxStats = mkOption {
                 type = types.int;
-                description = lib.mdDoc ''
+                description = mdDoc ''
                   Max stats per item to keep in backlog.
                 '';
               };
 
             };
           };
         };
-        description = lib.mdDoc ''
-          opensnitchd configuration. Refer to
-          <https://github.com/evilsocket/opensnitch/wiki/Configurations>
+        description = mdDoc ''
+          opensnitchd configuration. Refer to [upstream documentation](https://github.com/evilsocket/opensnitch/wiki/Configurations)
           for details on supported values.
         '';
       };
@@ -118,6 +154,25 @@ in {
       services.opensnitchd.wantedBy = [ "multi-user.target" ];
     };
 
+    systemd.services.opensnitchd.preStart = mkIf (cfg.rules != {}) (let
+      rules = flip mapAttrsToList predefinedRules (file: content: {
+        inherit (content) file;
+        local = "/var/lib/opensnitch/rules/${file}.json";
+      });
+    in ''
+      # Remove all firewall rules from `/var/lib/opensnitch/rules` that are symlinks to a store-path,
+      # but aren't declared in `cfg.rules` (i.e. all networks that were "removed" from
+      # `cfg.rules`).
+      find /var/lib/opensnitch/rules -type l -lname '${builtins.storeDir}/*' ${optionalString (rules != {}) ''
+        -not \( ${concatMapStringsSep " -o " ({ local, ... }:
+          "-name '${baseNameOf local}*'")
+        rules} \) \
+      ''} -delete
+      ${concatMapStrings ({ file, local }: ''
+        ln -sf '${file}' "${local}"
+      '') rules}
+    '');
+
     environment.etc."opensnitchd/default-config.json".source = format.generate "default-config.json" cfg.settings;
 
   };