wireguard: allow not storing private keys in world-readable /nix/store (#27433)

* wireguard: allow not storing private keys in world-readable /nix/store

nixos/modules/services/networking/wireguard.nix

@@ -23,8 +23,23 @@ let
 
       privateKey = mkOption {
         example = "yAnz5TF+lXXJte14tji3zlMNq+hd2rYUIgJBgB3fBmk=";
-        type = types.str;
-        description = "Base64 private key generated by wg genkey.";
+        type = with types; nullOr str;
+        default = null;
+        description = ''
+          Base64 private key generated by wg genkey.
+
+          Warning: Consider using privateKeyFile instead if you do not
+          want to store the key in the world-readable Nix store.
+        '';
+      };
+
+      privateKeyFile = mkOption {
+        example = "/private/wireguard_key";
+        type = with types; nullOr str;
+        default = null;
+        description = ''
+          Private key file as generated by wg genkey.
+        '';
       };
 
       listenPort = mkOption {
@@ -91,7 +106,22 @@ let
         example = "rVXs/Ni9tu3oDBLS4hOyAUAa1qTWVA3loR8eL20os3I=";
         type = with types; nullOr str;
         description = ''
-          base64 preshared key generated by wg genpsk. Optional,
+          Base64 preshared key generated by wg genpsk. Optional,
+          and may be omitted. This option adds an additional layer of
+          symmetric-key cryptography to be mixed into the already existing
+          public-key cryptography, for post-quantum resistance.
+
+          Warning: Consider using presharedKeyFile instead if you do not
+          want to store the key in the world-readable Nix store.
+        '';
+      };
+
+      presharedKeyFile = mkOption {
+        default = null;
+        example = "/private/wireguard_psk";
+        type = with types; nullOr str;
+        description = ''
+          File pointing to preshared key as generated by wg pensk. Optional,
           and may be omitted. This option adds an additional layer of
           symmetric-key cryptography to be mixed into the already existing
           public-key cryptography, for post-quantum resistance.
@@ -134,54 +164,59 @@ let
 
   };
 
-  generateConf = name: values: pkgs.writeText "wireguard-${name}.conf" ''
-    [Interface]
-    PrivateKey = ${values.privateKey}
-    ${optionalString (values.listenPort != null)   "ListenPort = ${toString values.listenPort}"}
-
-    ${concatStringsSep "\n\n" (map (peer: ''
-    [Peer]
-    PublicKey = ${peer.publicKey}
-    ${optionalString (peer.presharedKey != null) "PresharedKey = ${peer.presharedKey}"}
-    ${optionalString (peer.allowedIPs != []) "AllowedIPs = ${concatStringsSep ", " peer.allowedIPs}"}
-    ${optionalString (peer.endpoint != null) "Endpoint = ${peer.endpoint}"}
-    ${optionalString (peer.persistentKeepalive != null) "PersistentKeepalive = ${toString peer.persistentKeepalive}"}
-    '') values.peers)}
-  '';
-
   ipCommand = "${pkgs.iproute}/bin/ip";
   wgCommand = "${pkgs.wireguard}/bin/wg";
 
   generateUnit = name: values:
+    # exactly one way to specify the private key must be set
+    assert (values.privateKey != null) != (values.privateKeyFile != null);
+    let privKey = if values.privateKeyFile != null then values.privateKeyFile else pkgs.writeText "wg-key" values.privateKey;
+    in
     nameValuePair "wireguard-${name}"
       {
         description = "WireGuard Tunnel - ${name}";
         after = [ "network.target" ];
         wantedBy = [ "multi-user.target" ];
+
         serviceConfig = {
           Type = "oneshot";
           RemainAfterExit = true;
-          ExecStart = lib.flatten([
+          ExecStart = flatten([
             values.preSetup
 
             "-${ipCommand} link del dev ${name}"
             "${ipCommand} link add dev ${name} type wireguard"
-            "${wgCommand} setconf ${name} ${generateConf name values}"
 
             (map (ip:
-            ''${ipCommand} address add ${ip} dev ${name}''
+            "${ipCommand} address add ${ip} dev ${name}"
             ) values.ips)
 
+            ("${wgCommand} set ${name} private-key ${privKey}" +
+            optionalString (values.listenPort != null) " listen-port ${toString values.listenPort}")
+
+            (map (peer:
+            assert (peer.presharedKeyFile == null) || (peer.presharedKey == null); # at most one of the two must be set
+            let psk = if peer.presharedKey != null then pkgs.writeText "wg-psk" peer.presharedKey else peer.presharedKeyFile;
+            in
+            "${wgCommand} set ${name} peer ${peer.publicKey}" +
+            optionalString (psk != null) " preshared-key ${psk}" +
+            optionalString (peer.endpoint != null) " endpoint ${peer.endpoint}" +
+            optionalString (peer.persistentKeepalive != null) " persistent-keepalive ${toString peer.persistentKeepalive}" +
+            optionalString (peer.allowedIPs != []) " allowed-ips ${concatStringsSep "," peer.allowedIPs}"
+            ) values.peers)
+
             "${ipCommand} link set up dev ${name}"
 
-            (flatten (map (peer: (map (ip:
+            (map (peer: (map (ip:
             "${ipCommand} route add ${ip} dev ${name}"
-            ) peer.allowedIPs)) values.peers))
+            ) peer.allowedIPs)) values.peers)
 
             values.postSetup
           ]);
-
-          ExecStop = [ ''${ipCommand} link del dev "${name}"'' ] ++ values.postShutdown;
+          ExecStop = flatten([
+            "${ipCommand} link del dev ${name}"
+            values.postShutdown
+          ]);
         };
       };