nixos/dhparams: Add a VM test

We're going to make changes to the dhparams module so we really want to
make sure we don't break it, so having a NixOS VM test is to make sure
we don't blow things up and can iterate on it.

Signed-off-by: aszlig <aszlig@nix.build>
Cc: @Ekleog

nixos/release.nix

@@ -269,6 +269,7 @@ in rec {
   tests.containers-macvlans = callTest tests/containers-macvlans.nix {};
   tests.couchdb = callTest tests/couchdb.nix {};
   tests.deluge = callTest tests/deluge.nix {};
+  tests.dhparams = callTest tests/dhparams.nix {};
   tests.docker = callTestOnMatchingSystems ["x86_64-linux"] tests/docker.nix {};
   tests.docker-tools = callTestOnMatchingSystems ["x86_64-linux"] tests/docker-tools.nix {};
   tests.docker-tools-overlay = callTestOnMatchingSystems ["x86_64-linux"] tests/docker-tools-overlay.nix {};

nixos/tests/dhparams.nix

@@ -0,0 +1,105 @@
+let
+  common = { pkgs, ... }: {
+    security.dhparams.enable = true;
+    environment.systemPackages = [ pkgs.openssl ];
+  };
+
+in import ./make-test.nix {
+  name = "dhparams";
+
+  nodes.generation1 = { pkgs, config, ... }: {
+    imports = [ common ];
+    security.dhparams.params.foo = 16;
+    security.dhparams.params.bar = 17;
+
+    systemd.services.foo = {
+      description = "Check systemd Ordering";
+      wantedBy = [ "multi-user.target" ];
+      unitConfig = {
+        # This is to make sure that the dhparams generation of foo occurs
+        # before this service so we need this service to start as early as
+        # possible to provoke a race condition.
+        DefaultDependencies = false;
+
+        # We check later whether the service has been started or not.
+        ConditionPathExists = "${config.security.dhparams.path}/foo.pem";
+      };
+      serviceConfig.Type = "oneshot";
+      serviceConfig.RemainAfterExit = true;
+      # The reason we only provide an ExecStop here is to ensure that we don't
+      # accidentally trigger an error because a file system is not yet ready
+      # during very early startup (we might not even have the Nix store
+      # available, for example if future changes in NixOS use systemd mount
+      # units to do early file system initialisation).
+      serviceConfig.ExecStop = "${pkgs.coreutils}/bin/true";
+    };
+  };
+
+  nodes.generation2 = {
+    imports = [ common ];
+    security.dhparams.params.foo = 18;
+  };
+
+  nodes.generation3 = common;
+
+  testScript = { nodes, ... }: let
+    getParamPath = gen: name: let
+      node = "generation${toString gen}";
+      inherit (nodes.${node}.config.security.dhparams) path;
+    in "${path}/${name}.pem";
+
+    assertParamBits = gen: name: bits: let
+      path = getParamPath gen name;
+    in ''
+      $machine->nest('check bit size of ${path}', sub {
+        my $out = $machine->succeed('openssl dhparam -in ${path} -text');
+        $out =~ /^\s*DH Parameters:\s+\((\d+)\s+bit\)\s*$/m;
+        die "bit size should be ${toString bits} but it is $1 instead."
+          if $1 != ${toString bits};
+      });
+    '';
+
+    switchToGeneration = gen: let
+      node = "generation${toString gen}";
+      inherit (nodes.${node}.config.system.build) toplevel;
+      switchCmd = "${toplevel}/bin/switch-to-configuration test";
+    in ''
+      $machine->nest('switch to generation ${toString gen}', sub {
+        $machine->succeed('${switchCmd}');
+        $main::machine = ''$${node};
+      });
+    '';
+
+  in ''
+    my $machine = $generation1;
+
+    $machine->waitForUnit('multi-user.target');
+
+    subtest "verify startup order", sub {
+      $machine->succeed('systemctl is-active foo.service');
+    };
+
+    subtest "check bit sizes of dhparam files", sub {
+      ${assertParamBits 1 "foo" 16}
+      ${assertParamBits 1 "bar" 17}
+    };
+
+    ${switchToGeneration 2}
+
+    subtest "check whether bit size has changed", sub {
+      ${assertParamBits 2 "foo" 18}
+    };
+
+    subtest "ensure that dhparams file for 'bar' was deleted", sub {
+      $machine->fail('test -e ${getParamPath 1 "bar"}');
+    };
+
+    ${switchToGeneration 3}
+
+    subtest "ensure that 'security.dhparams.path' has been deleted", sub {
+      $machine->fail(
+        'test -e ${nodes.generation3.config.security.dhparams.path}'
+      );
+    };
+  '';
+}