nixos/snowflake-proxy: init

This commit introduces snowflake-proxy [1], a system to circumvent internet
censorship.

[1] https://snowflake.torproject.org/

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -120,6 +120,13 @@
           <link xlink:href="options.html#opt-services.heisenbridge.enable">services.heisenbridge</link>.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          <link xlink:href="https://snowflake.torproject.org/">snowflake-proxy</link>,
+          a system to defeat internet censorship. Available as
+          <link xlink:href="options.html#opt-services.snowflake-proxy.enable">services.snowflake-proxy</link>.
+        </para>
+      </listitem>
       <listitem>
         <para>
           <link xlink:href="https://ergo.chat">ergochat</link>, a modern

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -37,6 +37,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - [heisenbridge](https://github.com/hifi/heisenbridge), a bouncer-style Matrix IRC bridge. Available as [services.heisenbridge](options.html#opt-services.heisenbridge.enable).
 
+- [snowflake-proxy](https://snowflake.torproject.org/), a system to defeat internet censorship. Available as [services.snowflake-proxy](options.html#opt-services.snowflake-proxy.enable).
+
 - [ergochat](https://ergo.chat), a modern IRC with IRCv3 features. Available as [services.ergochat](options.html#opt-services.ergochat.enable).
 
 - [PowerDNS-Admin](https://github.com/ngoduykhanh/PowerDNS-Admin), a web interface for the PowerDNS server. Available at [services.powerdns-admin](options.html#opt-services.powerdns-admin.enable).

nixos/modules/module-list.nix

@@ -877,6 +877,7 @@
   ./services/networking/shorewall6.nix
   ./services/networking/shout.nix
   ./services/networking/sniproxy.nix
+  ./services/networking/snowflake-proxy.nix
   ./services/networking/smartdns.nix
   ./services/networking/smokeping.nix
   ./services/networking/softether.nix

nixos/modules/services/networking/snowflake-proxy.nix

@@ -0,0 +1,81 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.snowflake-proxy;
+in
+{
+  options = {
+    services.snowflake-proxy = {
+      enable = mkEnableOption "System to defeat internet censorship";
+
+      broker = mkOption {
+        description = "Broker URL (default \"https://snowflake-broker.torproject.net/\")";
+        type = with types; nullOr str;
+        default = null;
+      };
+
+      capacity = mkOption {
+        description = "Limits the amount of maximum concurrent clients allowed.";
+        type = with types; nullOr int;
+        default = null;
+      };
+
+      relay = mkOption {
+        description = "websocket relay URL (default \"wss://snowflake.bamsoftware.com/\")";
+        type = with types; nullOr str;
+        default = null;
+      };
+
+      stun = mkOption {
+        description = "STUN broker URL (default \"stun:stun.stunprotocol.org:3478\")";
+        type = with types; nullOr str;
+        default = null;
+      };
+    };
+  };
+
+  config = mkIf cfg.enable {
+    systemd.services.snowflake-proxy = {
+      wantedBy = [ "network-online.target" ];
+      serviceConfig = {
+        ExecStart =
+          "${pkgs.snowflake}/bin/proxy " + concatStringsSep " " (
+            optional (cfg.broker != null) "-broker ${cfg.broker}"
+            ++ optional (cfg.capacity != null) "-capacity ${builtins.toString cfg.capacity}"
+            ++ optional (cfg.relay != null) "-relay ${cfg.relay}"
+            ++ optional (cfg.stun != null) "-stun ${cfg.stun}"
+          );
+
+        # Security Hardening
+        # Refer to systemd.exec(5) for option descriptions.
+        CapabilityBoundingSet = "";
+
+        # implies RemoveIPC=, PrivateTmp=, NoNewPrivileges=, RestrictSUIDSGID=,
+        # ProtectSystem=strict, ProtectHome=read-only
+        DynamicUser = true;
+        LockPersonality = true;
+        PrivateDevices = true;
+        PrivateUsers = true;
+        ProcSubset = "pid";
+        ProtectClock = true;
+        ProtectControlGroups = true;
+        ProtectHome = true;
+        ProtectHostname = true;
+        ProtectKernelLogs = true;
+        ProtectProc = "invisible";
+        ProtectKernelModules = true;
+        ProtectKernelTunables = true;
+        RestrictAddressFamilies = [ "AF_INET" "AF_INET6" "AF_UNIX" ];
+        RestrictNamespaces = true;
+        RestrictRealtime = true;
+        SystemCallArchitectures = "native";
+        SystemCallFilter = "~@clock @cpu-emulation @debug @mount @obsolete @reboot @swap @privileged @resources";
+        UMask = "0077";
+      };
+    };
+  };
+
+  meta.maintainers = with maintainers; [ yayayayaka ];
+}