infrastructure/modules/dgn-runners/default.nix

/* Copyright 2023 Clan contributers, Tom-Hubrecht

   Permission is hereby granted, free of charge, to any person obtaining a copy
   of this software and associated documentation files (the "Software"), to
   deal in the Software without restriction, including without limitation the
   rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
   sell copies of the Software, and to permit persons to whom the Software is
   furnished to do so, subject to the following conditions:

   The above copyright notice and this permission notice shall be included in
   all copies or substantial portions of the Software.

   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
   IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
   AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
   LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
   FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
   DEALINGS IN THE SOFTWARE.
*/

{ config, pkgs, lib, ... }:

let
  inherit (lib) mkEnableOption mkOption types;

  storeDeps = pkgs.runCommand "store-deps" { } ''
    mkdir -p $out/bin
    for dir in ${builtins.toString cfg.dependencies}; do
      for bin in "$dir"/bin/*; do
        ln -s "$bin" "$out/bin/$(basename "$bin")"
      done
    done

    # Add SSL CA certs
    mkdir -p $out/etc/ssl/certs
    cp -a "${pkgs.cacert}/etc/ssl/certs/ca-bundle.crt" $out/etc/ssl/certs/ca-bundle.crt
  '';

  cfg = config.dgn-runners;

  storePaths = "nix-store --query -R ${builtins.toString (cfg.dependencies ++ [ pkgs.path ])}";
in {
  options.dgn-runners = {
    enable = mkEnableOption "Forgero Actions Runners.";

    nbRunners = mkOption {
      type = types.ints.positive;
      default = 4;
    };

    storePath = mkOption {
      type = types.str;
      default = "/data/slow/nix";
    };

    dependencies = mkOption { type = with types; listOf package; };
  };

  config = lib.mkIf cfg.enable {
    dgn-runners.dependencies = [
      pkgs.bash
      pkgs.colmena
      pkgs.coreutils
      pkgs.findutils
      pkgs.gawk
      pkgs.git
      pkgs.gnugrep
      pkgs.jq
      pkgs.nix
      pkgs.nodejs
      pkgs.npins
      pkgs.openssh
      pkgs.tea
    ];

    # everything here has no dependencies on the store
    systemd.services = {
      forgejo-nix-store = {
        wantedBy = [ "multi-user.target" ];
        path = [ pkgs.curl pkgs.nix ];
        script = ''
          dest=${cfg.storePath}

          echo "[+] Performing an installation of Nix at $dest."

          if ! [ -e "$dest" ]; then
            echo "[+] Directory $dest does not exist, creating it."
            mkdir -m 0755 $dest
          fi

          mkdir -p "$dest/store" "$dest/var/nix"

          # Copy the required store paths
          for i in $(${storePaths} | sed -e 's|/nix/store/||'); do
            i_tmp="$dest/store/$i.$$"
            if [ -e "$i_tmp" ]; then
                rm -rf "$i_tmp"
            fi
            if ! [ -e "$dest/store/$i" ]; then
                cp -RPp "/nix/store/$i" "$i_tmp"
                chmod -R a-w "$i_tmp"
                chmod +w "$i_tmp"
                mv "$i_tmp" "$dest/store/$i"
                chmod -w "$dest/store/$i"
            fi
          done

          # Dump the corresponding db
          nix-store --dump-db $(${storePaths}) | sed -e "s|/nix|$dest|" > .storeinfo

          # Switch to the new store
          export NIX_ROOT="$dest"
          export NIX_STORE_DIR="$NIX_ROOT/store"
          export NIX_DATA_DIR="$NIX_ROOT/share"
          export NIX_STATE_DIR="$NIX_ROOT/var/nix"

          nix-store --load-db < .storeinfo

          # Setup the permissions to nixuser
          chown -R nixuser:nixuser ${cfg.storePath}
        '';

        serviceConfig = {
          RuntimeDirectory = "forgejo-store-nix";
          WorkingDirectory = "/run/forgejo-store-nix";
          Type = "oneshot";
          RemainAfterExit = true;
        };
      };

      forgejo-runner-nix-image = {
        wantedBy = [ "multi-user.target" ];
        after = [ "podman.service" "forgejo-nix-store.service" ];
        requires = [ "podman.service" "forgejo-nix-store.service" ];
        path = [
          config.virtualisation.podman.package
          pkgs.gnutar
          pkgs.shadow
          pkgs.getent
        ];

        # we also include etc here because the cleanup job also wants the nixuser to be present
        script = ''
          set -eux -o pipefail

          mkdir -p etc/nix

          # Create an unpriveleged user that we can use also without the run-as-user.sh script
          touch etc/passwd etc/group
          groupid=$(cut -d: -f3 < <(getent group nixuser))
          userid=$(cut -d: -f3 < <(getent passwd nixuser))
          groupadd --prefix $(pwd) --gid "$groupid" nixuser
          emptypassword='$6$1ero.LwbisiU.h3D$GGmnmECbPotJoPQ5eoSTD6tTjKnSWZcjHoVTkxFLZP17W9hRi/XkmCiAMOfWruUwy8gMjINrBMNODc7cYEo4K.'
          useradd --prefix $(pwd) -p "$emptypassword" -m -d /tmp -u "$userid" -g "$groupid" -G nixuser nixuser

          cat <<NIX_CONFIG > etc/nix/nix.conf
          accept-flake-config = true
          experimental-features = nix-command flakes
          NIX_CONFIG

          cat <<NSSWITCH > etc/nsswitch.conf
          passwd:    files mymachines systemd
          group:     files mymachines systemd
          shadow:    files

          hosts:     files mymachines dns myhostname
          networks:  files

          ethers:    files
          services:  files
          protocols: files
          rpc:       files
          NSSWITCH

          # list the content as it will be imported into the container
          tar -cv . | tar -tvf -
          tar -cv . | podman import - forgejo-runner-nix
        '';

        serviceConfig = {
          RuntimeDirectory = "forgejo-runner-nix-image";
          WorkingDirectory = "/run/forgejo-runner-nix-image";
          Type = "oneshot";
          RemainAfterExit = true;
        };
      };
    } // lib.genAttrs
      (builtins.genList (n: "forgejo-runner-nix${builtins.toString n}")
        cfg.nbRunners) (name: {
          after = [ "forgejo-runner-nix-image.service" ];
          requires = [ "forgejo-runner-nix-image.service" ];

          # TODO: systemd confinment
          serviceConfig = {
            # Hardening (may overlap with DynamicUser=)
            # The following options are only for optimizing output of systemd-analyze
            AmbientCapabilities = "";
            CapabilityBoundingSet = "";
            # ProtectClock= adds DeviceAllow=char-rtc r
            DeviceAllow = "";
            NoNewPrivileges = true;
            PrivateDevices = true;
            PrivateMounts = true;
            PrivateTmp = true;
            PrivateUsers = true;
            ProtectClock = true;
            ProtectControlGroups = true;
            ProtectHome = true;
            ProtectHostname = true;
            ProtectKernelLogs = true;
            ProtectKernelModules = true;
            ProtectKernelTunables = true;
            ProtectSystem = "strict";
            RemoveIPC = true;
            RestrictNamespaces = true;
            RestrictRealtime = true;
            RestrictSUIDSGID = true;
            UMask = "0066";
            ProtectProc = "invisible";
            SystemCallFilter = [
              "~@clock"
              "~@cpu-emulation"
              "~@module"
              "~@mount"
              "~@obsolete"
              "~@raw-io"
              "~@reboot"
              "~@swap"
              # needed by go?
              #"~@resources"
              "~@privileged"
              "~capset"
              "~setdomainname"
              "~sethostname"
            ];
            RestrictAddressFamilies =
              [ "AF_INET" "AF_INET6" "AF_UNIX" "AF_NETLINK" ];

            # Needs network access
            PrivateNetwork = false;
            # Cannot be true due to Node
            MemoryDenyWriteExecute = false;

            # The more restrictive "pid" option makes `nix` commands in CI emit
            # "GC Warning: Couldn't read /proc/stat"
            # You may want to set this to "pid" if not using `nix` commands
            ProcSubset = "all";
            # Coverage programs for compiled code such as `cargo-tarpaulin` disable
            # ASLR (address space layout randomization) which requires the
            # `personality` syscall
            # You may want to set this to `true` if not using coverage tooling on
            # compiled code
            LockPersonality = false;

            # Note that this has some interactions with the User setting; so you may
            # want to consult the systemd docs if using both.
            DynamicUser = true;
          };
        });

    users = {
      users.nixuser = {
        group = "nixuser";
        description = "Used for running nix ci jobs";
        home = "/var/empty";
        isSystemUser = true;
      };
      groups.nixuser = { };
    };

    virtualisation = {
      podman = {
        enable = true;

        defaultNetwork.settings = {
          dns_enable = true;
          ipv6_enabled = true;
        };
      };

      containers.storage.settings = {
        storage = {
          driver = "overlay";
          graphroot = "/data/slow/containers/storage";
          runroot = "/run/containers/storage";
        };
      };
    };

    dgn-secrets.sources = [ ./. ];

    services.gitea-actions-runner.instances = lib.genAttrs
      (builtins.genList (n: "runner${builtins.toString n}") cfg.nbRunners)
      (name: {
        enable = true;
        name = "nix-runner";
        # take the git root url from the forgejo config
        # only possible if you've also configured your forgejo though the same nix config
        # otherwise you need to set it manually
        url = "https://git.dgnum.eu";
        # use your favourite nix secret manager to get a path for this
        tokenFile = config.age.secrets."dgn_runners-token_file".path;

        labels = [ "nix:docker://forgejo-runner-nix" ];
        settings = {
          container = {
            options = builtins.toString [
              "-e NIX_BUILD_SHELL=/bin/bash"
              "-e PAGER=cat"
              "-e PATH=/bin"
              "-e NIX_PATH=nixpkgs=${builtins.toString pkgs.path}"
              "--device /dev/kvm"
              "-e SSL_CERT_FILE=/etc/ssl/certs/ca-bundle.crt"
              "-v ${cfg.storePath}:/nix"
              "-v ${storeDeps}/bin:/bin"
              "-v ${storeDeps}/etc/ssl:/etc/ssl"
              "--cpus=4"
              "--device=/dev/kvm"
              "--user nixuser"
            ];

            # the default network that also respects our dns server settings
            network = "host";
            valid_volumes =
              [ cfg.storePath "${storeDeps}/bin" "${storeDeps}/etc/ssl" ];
          };
        };
      });
  };
}