nixos/systemd-chroot: Rename chroot to confinement

Quoting @edolstra from [1]:

  I don't really like the name "chroot", something like "confine[ment]"
  or "restrict" seems better. Conceptually we're not providing a
  completely different filesystem tree but a restricted view of the same
  tree.

I already used "confinement" as a sub-option and I do agree that
"chroot" sounds a bit too specific (especially because not *only* chroot
is involved).

So this changes the module name and its option to use "confinement"
instead of "chroot" and also renames the "chroot.confinement" to
"confinement.mode".

[1]: https://github.com/NixOS/nixpkgs/pull/57519#issuecomment-472855704

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

nixos/tests/systemd-confinement.nix

@@ -0,0 +1,129 @@
+import ./make-test.nix {
+  name = "systemd-confinement";
+
+  machine = { pkgs, lib, ... }: let
+    testServer = pkgs.writeScript "testserver.sh" ''
+      #!${pkgs.stdenv.shell}
+      export PATH=${lib.escapeShellArg "${pkgs.coreutils}/bin"}
+      ${lib.escapeShellArg pkgs.stdenv.shell} 2>&1
+      echo "exit-status:$?"
+    '';
+
+    testClient = pkgs.writeScriptBin "chroot-exec" ''
+      #!${pkgs.stdenv.shell} -e
+      output="$(echo "$@" | nc -NU "/run/test$(< /teststep).sock")"
+      ret="$(echo "$output" | sed -nre '$s/^exit-status:([0-9]+)$/\1/p')"
+      echo "$output" | head -n -1
+      exit "''${ret:-1}"
+    '';
+
+    mkTestStep = num: { description, config ? {}, testScript }: {
+      systemd.sockets."test${toString num}" = {
+        description = "Socket for Test Service ${toString num}";
+        wantedBy = [ "sockets.target" ];
+        socketConfig.ListenStream = "/run/test${toString num}.sock";
+        socketConfig.Accept = true;
+      };
+
+      systemd.services."test${toString num}@" = {
+        description = "Confined Test Service ${toString num}";
+        confinement = (config.confinement or {}) // { enable = true; };
+        serviceConfig = (config.serviceConfig or {}) // {
+          ExecStart = testServer;
+          StandardInput = "socket";
+        };
+      } // removeAttrs config [ "confinement" "serviceConfig" ];
+
+      __testSteps = lib.mkOrder num ''
+        subtest '${lib.escape ["\\" "'"] description}', sub {
+          $machine->succeed('echo ${toString num} > /teststep');
+          ${testScript}
+        };
+      '';
+    };
+
+  in {
+    imports = lib.imap1 mkTestStep [
+      { description = "chroot-only confinement";
+        config.confinement.mode = "chroot-only";
+        testScript = ''
+          $machine->succeed(
+            'test "$(chroot-exec ls -1 / | paste -sd,)" = bin,nix',
+            'test "$(chroot-exec id -u)" = 0',
+            'chroot-exec chown 65534 /bin',
+          );
+        '';
+      }
+      { description = "full confinement with APIVFS";
+        testScript = ''
+          $machine->fail(
+            'chroot-exec ls -l /etc',
+            'chroot-exec ls -l /run',
+            'chroot-exec chown 65534 /bin',
+          );
+          $machine->succeed(
+            'test "$(chroot-exec id -u)" = 0',
+            'chroot-exec chown 0 /bin',
+          );
+        '';
+      }
+      { description = "check existence of bind-mounted /etc";
+        config.serviceConfig.BindReadOnlyPaths = [ "/etc" ];
+        testScript = ''
+          $machine->succeed('test -n "$(chroot-exec cat /etc/passwd)"');
+        '';
+      }
+      { description = "check if User/Group really runs as non-root";
+        config.serviceConfig.User = "chroot-testuser";
+        config.serviceConfig.Group = "chroot-testgroup";
+        testScript = ''
+          $machine->succeed('chroot-exec ls -l /dev');
+          $machine->succeed('test "$(chroot-exec id -u)" != 0');
+          $machine->fail('chroot-exec touch /bin/test');
+        '';
+      }
+      (let
+        symlink = pkgs.runCommand "symlink" {
+          target = pkgs.writeText "symlink-target" "got me\n";
+        } "ln -s \"$target\" \"$out\"";
+      in {
+        description = "check if symlinks are properly bind-mounted";
+        config.confinement.packages = lib.singleton symlink;
+        testScript = ''
+          $machine->fail('chroot-exec test -e /etc');
+          $machine->succeed('chroot-exec cat ${symlink} >&2');
+          $machine->succeed('test "$(chroot-exec cat ${symlink})" = "got me"');
+        '';
+      })
+      { description = "check if StateDirectory works";
+        config.serviceConfig.User = "chroot-testuser";
+        config.serviceConfig.Group = "chroot-testgroup";
+        config.serviceConfig.StateDirectory = "testme";
+        testScript = ''
+          $machine->succeed('chroot-exec touch /tmp/canary');
+          $machine->succeed('chroot-exec "echo works > /var/lib/testme/foo"');
+          $machine->succeed('test "$(< /var/lib/testme/foo)" = works');
+          $machine->succeed('test ! -e /tmp/canary');
+        '';
+      }
+    ];
+
+    options.__testSteps = lib.mkOption {
+      type = lib.types.lines;
+      description = "All of the test steps combined as a single script.";
+    };
+
+    config.environment.systemPackages = lib.singleton testClient;
+
+    config.users.groups.chroot-testgroup = {};
+    config.users.users.chroot-testuser = {
+      description = "Chroot Test User";
+      group = "chroot-testgroup";
+    };
+  };
+
+  testScript = { nodes, ... }: ''
+    $machine->waitForUnit('multi-user.target');
+    ${nodes.machine.config.__testSteps}
+  '';
+}