modules/pppd: init

additions over upstream pppd module:
* symlinks for peer config (to hide usernames)
* added default options (/etc/ppp/options)
* full link up/down script support

2 files changed, 245 insertions, 0 deletions

diff --git a/common.nix b/common.nix
index 31fedc9..98cf87f 100644
--- a/common.nix
+++ b/common.nix
@@ -6,9 +6,11 @@ let
   host = config.networking.hostName;
 in
 {
+  disabledModules = [ "services/networking/pppd.nix" ];
   imports = [
     ./modules/userdata.nix
     ./modules/dev.nix
+    ./modules/pppd.nix
   ];
 
   # boot
diff --git a/modules/pppd.nix b/modules/pppd.nix
new file mode 100644
index 0000000..3a5e3a0
--- /dev/null
+++ b/modules/pppd.nix
@@ -0,0 +1,243 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+
+let
+  cfg = config.services.pppd;
+  shTypes = [ "ip-up" "ip-down" "ipv6-up" "ipv6-down" ];
+in
+{
+  meta = {
+    maintainers = with maintainers; [ danderson ];
+  };
+
+  options.services.pppd = {
+    enable = mkEnableOption (lib.mdDoc "pppd");
+
+    package = mkOption {
+      default = pkgs.ppp;
+      defaultText = literalExpression "pkgs.ppp";
+      type = types.package;
+      description = lib.mdDoc "pppd package to use.";
+    };
+
+    config = mkOption {
+      type = types.lines;
+      default = "";
+      description = lib.mdDoc "default config for pppd";
+    };
+
+    script = mkOption {
+      default = {};
+      description = lib.mdoc ''
+        script which is executed when the link is available for sending and
+        receiving IP packets or when the link is no longer available for sending
+        and receiving IP packets, see pppd(8) for more details
+      '';
+      type = types.attrsOf (types.submodule (
+        { name, ... }:
+        {
+          options = {
+            name = mkOption {
+              type = types.str;
+              default = name;
+              example = "01-ddns.sh";
+              description = lib.mdDoc "Name of the script.";
+            };
+            type = mkOption {
+              default = "ip-up";
+              type = types.enum shTypes;
+              description = lib.mdDoc "Type of the script.";
+            };
+            text = mkOption {
+              type = types.lines;
+              default = "";
+              description = lib.mdDoc "Shell commands to be executed.";
+            };
+          };
+        }
+      ));
+    };
+
+    peers = mkOption {
+      default = {};
+      description = lib.mdDoc "pppd peers.";
+      type = types.attrsOf (types.submodule (
+        { name, ... }:
+        {
+          options = {
+            name = mkOption {
+              type = types.str;
+              default = name;
+              example = "dialup";
+              description = lib.mdDoc "Name of the PPP peer.";
+            };
+
+            enable = mkOption {
+              type = types.bool;
+              default = true;
+              example = false;
+              description = lib.mdDoc "Whether to enable this PPP peer.";
+            };
+
+            autostart = mkOption {
+              type = types.bool;
+              default = true;
+              example = false;
+              description = lib.mdDoc "Whether the PPP session is automatically started at boot time.";
+            };
+
+            config = mkOption {
+              type = types.lines;
+              default = "";
+              description = lib.mdDoc "pppd configuration for this peer, see the pppd(8) man page.";
+            };
+
+            configFile = mkOption {
+              type = types.nullOr types.path;
+              default = null;
+              example = literalExpression "/run/secrets/ppp/peer/options";
+              description = lib.mdDoc "pppd configuration file for this peer, see the pppd(8) man page.";
+            };
+          };
+        }
+      ));
+    };
+  };
+
+  config = let
+    enabledConfigs = filter (f: f.enable) (attrValues cfg.peers);
+
+    defaultCfg = if (cfg.config != "") then {
+      "ppp/options".text = cfg.config;
+    } else {};
+
+    mkPeers = peerCfg: with peerCfg; let
+      key = if (configFile == null) then "text" else "source";
+      val = if (configFile == null) then peerCfg.config else configFile;
+    in
+    {
+      name = "ppp/peers/${name}";
+      value.${key} = val;
+    };
+
+    enabledSh = filter (s: s.text != "") (attrValues cfg.script);
+    mkMsh = name : {
+      name = "ppp/${name}";
+      value.mode = "0755";
+      value.text = ''
+        #!/bin/sh
+
+        # see the pppd(8) man page
+        for s in /etc/ppp/${name}.d/*.sh; do
+            [ -x "$s" ] && "$s" "$@"
+        done
+      '';
+    };
+    mkUsh = shCfg : {
+      name = "ppp/${shCfg.type}.d/${shCfg.name}.sh";
+      value.mode = "0755";
+      value.text = ''
+        #!/bin/sh
+
+        ${shCfg.text}
+      '';
+    };
+
+    mkSystemd = peerCfg: {
+      name = "pppd-${peerCfg.name}";
+      value = {
+        restartTriggers = [ config.environment.etc."ppp/peers/${peerCfg.name}".source ];
+        before = [ "network.target" ];
+        wants = [ "network.target" ];
+        after = [ "network-pre.target" ];
+        environment = {
+          # pppd likes to write directly into /var/run. This is rude
+          # on a modern system, so we use libredirect to transparently
+          # move those files into /run/pppd.
+          LD_PRELOAD = "${pkgs.libredirect}/lib/libredirect.so";
+          NIX_REDIRECTS = "/var/run=/run/pppd";
+        };
+        serviceConfig = let
+          capabilities = [
+            "CAP_BPF"
+            "CAP_SYS_TTY_CONFIG"
+            "CAP_NET_ADMIN"
+            "CAP_NET_RAW"
+          ];
+        in
+        {
+          ExecStart = "${getBin cfg.package}/sbin/pppd call ${peerCfg.name} nodetach nolog";
+          Restart = "always";
+          RestartSec = 5;
+
+          AmbientCapabilities = capabilities;
+          CapabilityBoundingSet = capabilities;
+          KeyringMode = "private";
+          LockPersonality = true;
+          MemoryDenyWriteExecute = true;
+          NoNewPrivileges = true;
+          PrivateMounts = true;
+          PrivateTmp = true;
+          ProtectControlGroups = true;
+          ProtectHome = true;
+          ProtectHostname = true;
+          ProtectKernelModules = true;
+          # pppd can be configured to tweak kernel settings.
+          ProtectKernelTunables = false;
+          ProtectSystem = "strict";
+          RemoveIPC = true;
+          RestrictAddressFamilies = [
+            "AF_ATMPVC"
+            "AF_ATMSVC"
+            "AF_INET"
+            "AF_INET6"
+            "AF_IPX"
+            "AF_NETLINK"
+            "AF_PACKET"
+            "AF_PPPOX"
+            "AF_UNIX"
+          ];
+          RestrictNamespaces = true;
+          RestrictRealtime = true;
+          RestrictSUIDSGID = true;
+          SecureBits = "no-setuid-fixup-locked noroot-locked";
+          SystemCallFilter = "@system-service";
+          SystemCallArchitectures = "native";
+
+          # All pppd instances on a system must share a runtime
+          # directory in order for PPP multilink to work correctly. So
+          # we give all instances the same /run/pppd directory to store
+          # things in.
+          #
+          # For the same reason, we can't set PrivateUsers=true, because
+          # all instances need to run as the same user to access the
+          # multilink database.
+          RuntimeDirectory = "pppd";
+          RuntimeDirectoryPreserve = true;
+        };
+        wantedBy = mkIf peerCfg.autostart [ "multi-user.target" ];
+      };
+    };
+
+    etcFiles = listToAttrs (map mkPeers enabledConfigs) //
+               listToAttrs (map mkMsh shTypes) //
+               listToAttrs (map mkUsh enabledSh) //
+               defaultCfg;
+
+    systemdConfigs = listToAttrs (map mkSystemd enabledConfigs);
+
+  in mkIf cfg.enable {
+    assertions = map (peerCfg: {
+      assertion = (peerCfg.configFile == null || peerCfg.config == "");
+      message = ''
+        Please specify either
+        'services.pppd.${peerCfg.name}.config' or
+        'services.pppd.${peerCfg.name}.configFile'.
+      '';
+    }) enabledConfigs;
+
+    environment.etc = etcFiles;
+    systemd.services = systemdConfigs;
+  };
+}