path: root/flakes/secrets/flake.nix

{
  description = "Secrets handling";

  outputs = { self }: {
    nixosModule = { config, lib, pkgs, ... }: {
      # Necessary for situations where flake gets included multiple times
      key = builtins.hashString "sha256" (builtins.path { path = self.sourceInfo.outPath; name = "source"; });
      options.secrets = with lib; {
        keys = mkOption {
          type = types.attrsOf (types.submodule {
            options = {
              isTemplated = mkOption {
                type = types.bool;
                default = true;
                description = "If the file is a gucci template that needs to be resolved";
              };
              isDir = mkOption {
                type = types.bool;
                default = false;
                description = "If the entry is a directory";
              };
              group = mkOption {
                type = types.str;
                default = "root";
                description = "Group to associate to the entry";
              };
              user = mkOption {
                type = types.str;
                default = "root";
                description = "User to associate to the entry";
              };
              permissions = mkOption {
                type = types.str;
                default = "0600";
                description = "Permissions to associate to the entry";
              };
              text = mkOption {
                type = types.str;
                description = "Content of the entry";
              };
              keyDependencies = mkOption {
                default = [];
                type = types.listOf (types.either types.path types.package);
                description = ''
                  (public) system dependencies that needs to be
                  uploaded with the key.

                  keyDependencies + ignoredKeyDependencies should
                  contain the exhaustive list of the text context.

                  A warning will be thrown if there are remaning
                  dependencies from the text.
                '';
              };
              ignoredKeyDependencies = mkOption {
                default = [];
                type = types.listOf (types.either types.path types.package);
                description = ''
                  dependencies that must not be sent along with the key.

                  keyDependencies + ignoredKeyDependencies should
                  contain the exhaustive list of the text context.

                  A warning will be thrown if there are remaning
                  dependencies from the text.
                '';
              };
            };
          });
          default = {};
          description = "Keys attrs to upload to the server";
          apply = builtins.mapAttrs (dest: v: v // { inherit dest; });
        };
        gpgKeys = mkOption {
          type = types.listOf types.path;
          default = [];
          description = "GPG public keys files to encrypt to";
        };
        ageKeys = mkOption {
          type = types.listOf types.str;
          default = [];
          description = "AGE keys to encrypt to";
        };
        decryptKey = mkOption {
          type = types.str;
          default = "/etc/ssh/ssh_host_ed25519_key";
          description = "ed25519 key used to decrypt with AGE";
        };
        location = mkOption {
          type = types.path;
          default = "/var/secrets";
          description = "Location where to put the keys";
        };
        secretsVars = mkOption {
          type = types.path;
          description = "Location where the secrets variables are defined, to be used to fill the templates in secrets";
        };
        deleteSecretsVars = mkOption {
          type = types.bool;
          default = false;
          description = "Delete secrets file after deployment";
        };
        # Read-only variables
        fullPaths = mkOption {
          type = types.attrsOf types.path;
          default = builtins.mapAttrs
            (n: v: "${config.secrets.location}/${n}") config.secrets.keys;
          readOnly = true;
          description = "set of full paths to secrets";
        };
      };

      config = let
        location = config.secrets.location;
        keys = builtins.attrValues config.secrets.keys;
        empty = pkgs.runCommand "empty" { preferLocalBuild = true; } "mkdir -p $out && touch $out/done";
        fpath = v: "secrets/${v.dest}${lib.optionalString v.isTemplated ".gucci.tpl"}";
        dumpKey = v:
          if v.isDir then
            ''
              mkdir -p secrets/${v.dest}
              cat >> mods <<EOF
              ${v.user} ${v.group} ${v.permissions} secrets/${v.dest}
              EOF
            ''
          else ''
            mkdir -p secrets/$(dirname ${v.dest})
            echo -n ${lib.strings.escapeShellArg v.text} > ${fpath v}
            cat >> mods <<EOF
            ${v.user} ${v.group} ${v.permissions} ${fpath v}
            EOF
            '';
        secrets = pkgs.runCommand "secrets.tar.enc" {
          buildInputs = [ pkgs.gnupg pkgs.sops ];
          } ''
          touch mods
          tar --format=ustar --mtime='1970-01-01' -P --transform="s@${empty}@secrets@" -cf $out ${empty}/done
          ${builtins.concatStringsSep "\n" (map dumpKey keys)}
          cat mods | while read u g p k; do
          tar --no-recursion --format=ustar --mtime='1970-01-01' --owner="$u" --group="$g" --mode="$p" --append -f $out "$k"
          done
          export HOME=$(pwd)
          fingerprints=
          for key in ${builtins.concatStringsSep " " config.secrets.gpgKeys}; do
            gpg --import $key 2>/dev/null
            fingerprints=$fingerprints,$(cat $key | gpg --with-colons --import-options show-only --import 2>/dev/null | grep ^fpr | cut -d: -f10 | head -n1)
          done

          sops --age ${builtins.concatStringsSep "," config.secrets.ageKeys} --pgp ''${fingerprints#,} --input-type binary -i -e $out 2>/dev/null
          '';
        pathChmodExcl =
          let
            dirs = builtins.filter (v: v.isDir) keys;
            exclPath = builtins.concatStringsSep " -o " (map (d: " -path $TMP/${d.dest}") dirs);
          in
            lib.optionalString (builtins.length dirs > 0) " -not \\( ${exclPath} \\) ";

        checkKeyDependencies = key:
          let
            allDeps = builtins.map (n: if builtins.isPath n then "${n}" else n.drvPath) (key.keyDependencies ++ key.ignoredKeyDependencies);
            context = builtins.attrNames (builtins.getContext key.text);
            missing = builtins.foldl' (o: n: lib.remove n o) context allDeps;
          in
            lib.optional (!key.isDir && builtins.length missing > 0)
              ''
                Key ${key.dest} has non declared dependencies in its context: ${builtins.concatStringsSep " " missing}
                Add them to ignoredKeyDependencies to ignore
              '';
      in lib.mkIf (builtins.length keys > 0) {
        warnings = lib.concatMap checkKeyDependencies keys;
        # FIXME: Use lib.concatMap (k: k.keyDependencies) keys in latest nixpkgs
        system.extraDependencies = lib.concatMap (k: builtins.map (dep:
          if builtins.isPath dep then pkgs.writeText "extra-dep" "${dep}" else dep
        ) k.keyDependencies) keys;
        system.activationScripts.secrets = {
          deps = [ "users" "wrappers" ];
          text = ''
            install -m0750 -o root -g keys -d ${location}
            TMP=$(${pkgs.coreutils}/bin/mktemp -d)
            TMPWORK=$(${pkgs.coreutils}/bin/mktemp -d)
            chmod go-rwx $TMPWORK
            if [ -n "$TMP" -a -n "$TMPWORK" -a -f ${config.secrets.secretsVars} ]; then
              install -m0750 -o root -g keys -d $TMP
              ${pkgs.ssh-to-age}/bin/ssh-to-age -private-key -i ${config.secrets.decryptKey} -o $TMPWORK/keys.txt
              SOPS_AGE_KEY_FILE=$TMPWORK/keys.txt ${pkgs.sops}/bin/sops -d ${secrets} | ${pkgs.gnutar}/bin/tar --strip-components 1 -C $TMP -x
              SOPS_AGE_KEY_FILE=$TMPWORK/keys.txt ${pkgs.sops}/bin/sops -d ${config.secrets.secretsVars} > $TMPWORK/vars.yml
              if [ -f $TMPWORK/vars.yml ]; then
                find $TMP -name "*.gucci.tpl" -exec \
                  /bin/sh -c 'f="{}"; ${pkgs.gucci}/bin/gucci -f '$TMPWORK'/vars.yml "$f" > "''${f%.gucci.tpl}"; touch --reference "$f" ''${f%.gucci.tpl} ; chmod --reference="$f" ''${f%.gucci.tpl} ; chown --reference="$f" ''${f%.gucci.tpl}' \;
              fi
              find $TMP -type d ${pathChmodExcl}-exec chown root:keys {} \; -exec chmod o-rx {} \;
              ${pkgs.rsync}/bin/rsync --exclude="*.gucci.tpl" -O -c -av --delete $TMP/ ${location}
              rm -rf $TMP $TMPWORK ${lib.optionalString config.secrets.deleteSecretsVars config.secrets.secretsVars}
            fi
          '';
        };

      };
    };
  };
}