NixOS · Apr 20, 2020 · May 4, 2020 · May 6, 2020 · May 8, 2020 · May 9, 2020
diff --git a/nixos/doc/manual/release-notes/rl-2009.xml b/nixos/doc/manual/release-notes/rl-2009.xml
@@ -77,7 +77,9 @@
 
   <itemizedlist>
    <listitem>
-    <para />
+    <para>
+      There is a new <xref linkend="opt-security.doas.enable"/> module that provides <command>doas</command>, a lighter alternative to <command>sudo</command> with many of the same features.
+    </para>
    </listitem>
   </itemizedlist>
 

diff --git a/nixos/modules/module-list.nix b/nixos/modules/module-list.nix
@@ -200,6 +200,7 @@
   ./security/rtkit.nix
   ./security/wrappers/default.nix
   ./security/sudo.nix
+  ./security/doas.nix
   ./security/systemd-confinement.nix
   ./security/tpm2.nix
   ./services/admin/oxidized.nix

diff --git a/nixos/modules/security/doas.nix b/nixos/modules/security/doas.nix
@@ -0,0 +1,274 @@
+{ config, lib, pkgs, ... }:
+
+with lib;
+let
+  cfg = config.security.doas;
+
+  inherit (pkgs) doas;
+
+  mkUsrString = user: toString user;
+
+  mkGrpString = group: ":${toString group}";
+
+  mkOpts = rule: concatStringsSep " " [
+    (optionalString rule.noPass "nopass")
+    (optionalString rule.persist "persist")
+    (optionalString rule.keepEnv "keepenv")
+    "setenv { SSH_AUTH_SOCK ${concatStringsSep " " rule.setEnv} }"
+  ];
+
+  mkArgs = rule:
+    if (isNull rule.args) then ""
+    else if (length rule.args == 0) then "args"
+    else "args ${concatStringsSep " " rule.args}";
+
+  mkRule = rule:
+    let
+      opts = mkOpts rule;
+
+      as = optionalString (!isNull rule.runAs) "as ${rule.runAs}";
+
+      cmd = optionalString (!isNull rule.cmd) "cmd ${rule.cmd}";
+
+      args = mkArgs rule;
+    in
+    optionals (length cfg.extraRules > 0) [
+      (
+        optionalString (length rule.users > 0)
+          (map (usr: "permit ${opts} ${mkUsrString usr} ${as} ${cmd} ${args}") rule.users)
+      )
+      (
+        optionalString (length rule.groups > 0)
+          (map (grp: "permit ${opts} ${mkGrpString grp} ${as} ${cmd} ${args}") rule.groups)
+      )
+    ];
+in
+{
+
+  ###### interface
+
+  options.security.doas = {
+
+    enable = mkOption {
+      type = with types; bool;
+      default = false;
+      description = ''
+        Whether to enable the <command>doas</command> command, which allows
+        non-root users to execute commands as root.
+      '';
+    };
+
+    wheelNeedsPassword = mkOption {
+      type = with types; bool;
+      default = true;
+      description = ''
+        Whether users of the <code>wheel</code> group must provide a password to
+        run commands as super user via <command>doas</command>.
+      '';
+    };
+
+    extraRules = mkOption {
+      default = [];
+      description = ''
+        Define specific rules to be set in the
+        <filename>/etc/doas.conf</filename> file. More specific rules should
+        come after more general ones in order to yield the expected behavior.
+        You can use <code>mkBefore</code> and/or <code>mkAfter</code> to ensure
+        this is the case when configuration options are merged.
+      '';
+      example = literalExample ''
+        [
+          # Allow execution of any command by any user in group doas, requiring
+          # a password and keeping any previously-defined environment variables.
+          { groups = [ "doas" ]; noPass = false; keepEnv = true; }
+
+          # Allow execution of "/home/root/secret.sh" by user `backup` OR user
+          # `database` OR any member of the group with GID `1006`, without a
+          # password.
+          { users = [ "backup" "database" ]; groups = [ 1006 ];
+            cmd = "/home/root/secret.sh"; noPass = true; }
+
+          # Allow any member of group `bar` to run `/home/baz/cmd1.sh` as user
+          # `foo` with argument `hello-doas`.
+          { groups = [ "bar" ]; runAs = "foo";
+            cmd = "/home/baz/cmd1.sh"; args = [ "hello-doas" ]; }
+
+          # Allow any member of group `bar` to run `/home/baz/cmd2.sh` as user
+          # `foo` with no arguments.
+          { groups = [ "bar" ]; runAs = "foo";
+            cmd = "/home/baz/cmd2.sh"; args = [ ]; }
+
+          # Allow user `abusers` to execute "nano" and unset the value of
+          # SSH_AUTH_SOCK, override the value of ALPHA to 1, and inherit the
+          # value of BETA from the current environment.
+          { users = [ "abusers" ]; cmd = "nano";
+            setEnv = [ "-SSH_AUTH_SOCK" "ALPHA=1" "BETA" ]; }
+        ]
+      '';
+      type = with types; listOf (
+        submodule {
+          options = {
+
+            noPass = mkOption {
+              type = with types; bool;
+              default = false;
+              description = ''
+                If <code>true</code>, the user is not required to enter a
+                password.
+              '';
+            };
+
+            persist = mkOption {
+              type = with types; bool;
+              default = false;
+              description = ''
+                If <code>true</code>, do not ask for a password again for some
+                time after the user successfully authenticates.
+              '';
+            };
+
+            keepEnv = mkOption {
+              type = with types; bool;
+              default = false;
+              description = ''
+                If <code>true</code>, environment variables other than those
+                listed in
+                <citerefentry><refentrytitle>doas</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+                are kept when creating the environment for the new process.
+              '';
+            };
+
+            setEnv = mkOption {
+              type = with types; listOf str;
+              default = [];
+              description = ''
+                Keep or set the specified variables. Variables may also be
+                removed with a leading '-' or set using
+                <code>variable=value</code>. If the first character of
+                <code>value</code> is a '$', the value to be set is taken from
+                the existing environment variable of the indicated name. This
+                option is processed after the default environment has been
+                created.
+
+                NOTE: All rules have <code>setenv { SSH_AUTH_SOCK }</code> by
+                default. To prevent <code>SSH_AUTH_SOCK</code> from being
+                inherited, add <code>"-SSH_AUTH_SOCK"</code> anywhere in this
+                list.
+              '';
+            };
+
+            users = mkOption {
+              type = with types; listOf (either str int);
+              default = [];
+              description = "The usernames / UIDs this rule should apply for.";
+            };
+
+            groups = mkOption {
+              type = with types; listOf (either str int);
+              default = [];
+              description = "The groups / GIDs this rule should apply for.";
+            };
+
+            runAs = mkOption {
+              type = with types; nullOr str;
+              default = null;
+              description = ''
+                Which user or group the specified command is allowed to run as.
+                When set to <code>null</code> (the default), all users are
+                allowed.
+
+                A user can be specified using just the username:
+                <code>"foo"</code>. It is also possible to only allow running as
+                a specific group with <code>":bar"</code>.
+              '';
+            };
+
+            cmd = mkOption {
+              type = with types; nullOr str;
+              default = null;
+              description = ''
+                The command the user is allowed to run. When set to
+                <code>null</code> (the default), all commands are allowed.
+
+                NOTE: It is best practice to specify absolute paths. If a
+                relative path is specified, only a restricted PATH will be
+                searched.
+              '';
+            };
+
+            args = mkOption {
+              type = with types; nullOr (listOf str);
+              default = null;
+              description = ''
+                Arguments that must be provided to the command. When set to
+                <code>[]</code>, the command must be run without any arguments.
+              '';
+            };
+          };
+        }
+      );
+    };
+
+    extraConfig = mkOption {
+      type = with types; lines;
+      default = "";
+      description = ''
+        Extra configuration text appended to <filename>doas.conf</filename>.
+      '';
+    };
+  };
+
+
+  ###### implementation
+
+  config = mkIf cfg.enable {
+
+    security.doas.extraRules = [
+      {
+        groups = [ "wheel" ];
+        noPass = !cfg.wheelNeedsPassword;
+      }
+    ];
+
+    security.wrappers = {
+      doas.source = "${doas}/bin/doas";
+    };
+
+    environment.systemPackages = [
+      doas
+    ];
+
+    security.pam.services.doas = {
+      allowNullPassword = true;
+      sshAgentAuth = true;
+    };
+
+    environment.etc."doas.conf" = {
+      source = pkgs.runCommand "doas-conf"
+        {
+          src = pkgs.writeText "doas-conf-in" ''
+            # To modify this file, set the NixOS options
+            # `security.doas.extraRules` or `security.doas.extraConfig`. To
+            # completely replace the contents of this file, use
+            # `environment.etc."doas.conf"`.
+
+            # "root" is allowed to do anything.
+            permit nopass keepenv root
+
+            # extraRules
+            ${concatStringsSep "\n" (lists.flatten (map mkRule cfg.extraRules))}
+
+            # extraConfig
+            ${cfg.extraConfig}
+          '';
+          preferLocalBuild = true;
+        }
+        # Make sure that the doas.conf file is syntactically valid.
+        "${pkgs.buildPackages.doas}/bin/doas -C $src && cp $src $out";
+      mode = "0440";
+    };
+
+  };
+
+  meta.maintainers = with maintainers; [ cole-h ];
+}
diff --git a/nixos/tests/all-tests.nix b/nixos/tests/all-tests.nix
@@ -68,6 +68,7 @@ in
   deluge = handleTest ./deluge.nix {};
   dhparams = handleTest ./dhparams.nix {};
   dnscrypt-proxy2 = handleTestOn ["x86_64-linux"] ./dnscrypt-proxy2.nix {};
+  doas = handleTest ./doas.nix {};
   docker = handleTestOn ["x86_64-linux"] ./docker.nix {};
   oci-containers = handleTestOn ["x86_64-linux"] ./oci-containers.nix {};
   docker-edge = handleTestOn ["x86_64-linux"] ./docker-edge.nix {};

diff --git a/nixos/tests/doas.nix b/nixos/tests/doas.nix
@@ -0,0 +1,83 @@
+# Some tests to ensure doas is working properly.
+import ./make-test-python.nix (
+  { lib, ... }: {
+    name = "doas";
+    meta = with lib.maintainers; {
+      maintainers = [ cole-h ];
+    };
+
+    machine =
+      { ... }:
+        {
+          users.groups = { foobar = {}; barfoo = {}; baz = { gid = 1337; }; };
+          users.users = {
+            test0 = { isNormalUser = true; extraGroups = [ "wheel" ]; };
+            test1 = { isNormalUser = true; };
+            test2 = { isNormalUser = true; extraGroups = [ "foobar" ]; };
+            test3 = { isNormalUser = true; extraGroups = [ "barfoo" ]; };
+            test4 = { isNormalUser = true; extraGroups = [ "baz" ]; };
+            test5 = { isNormalUser = true; };
+            test6 = { isNormalUser = true; };
+            test7 = { isNormalUser = true; };
+          };
+
+          security.doas = {
+            enable = true;
+            wheelNeedsPassword = false;
+
+            extraRules = [
+              { users = [ "test1" ]; groups = [ "foobar" ]; }
+              { users = [ "test2" ]; noPass = true; setEnv = [ "CORRECT" "HORSE=BATTERY" ]; }
+              { groups = [ "barfoo" 1337 ]; noPass = true; }
+              { users = [ "test5" ]; noPass = true; keepEnv = true; runAs = "test1"; }
+              { users = [ "test6" ]; noPass = true; keepEnv = true; setEnv = [ "-STAPLE" ]; }
+              { users = [ "test7" ]; noPass = true; setEnv = [ "-SSH_AUTH_SOCK" ]; }
+            ];
+          };
+        };
+
+    testScript = ''
+      with subtest("users in wheel group should have passwordless doas"):
+          machine.succeed('su - test0 -c "doas -u root true"')
+
+      with subtest("test1 user should not be able to use doas without password"):
+          machine.fail('su - test1 -c "doas -n -u root true"')
+
+      with subtest("test2 user should be able to keep some env"):
+          if "CORRECT=1" not in machine.succeed('su - test2 -c "CORRECT=1 doas env"'):
+              raise Exception("failed to keep CORRECT")
+
+          if "HORSE=BATTERY" not in machine.succeed('su - test2 -c "doas env"'):
+              raise Exception("failed to setenv HORSE=BATTERY")
+
+      with subtest("users in group 'barfoo' shouldn't require password"):
+          machine.succeed("doas -u test3 doas -n -u root true")
+
+      with subtest("users in group 'baz' (GID 1337) shouldn't require password"):
+          machine.succeed("doas -u test4 doas -n -u root echo true")
+
+      with subtest("test5 user should be able to run commands under test1"):
+          machine.succeed("doas -u test5 doas -n -u test1 true")
+
+      with subtest("test5 user should not be able to run commands under root"):
+          machine.fail("doas -u test5 doas -n -u root true")
+
+      with subtest("test6 user should be able to keepenv"):
+          envs = ["BATTERY=HORSE", "CORRECT=false"]
+          out = machine.succeed(
+              'su - test6 -c "BATTERY=HORSE CORRECT=false STAPLE=Tr0ub4dor doas env"'
+          )
+
+          if not all(env in out for env in envs):
+              raise Exception("failed to keep BATTERY or CORRECT")
+          if "STAPLE=Tr0ub4dor" in out:
+              raise Exception("failed to exclude STAPLE")
+
+      with subtest("test7 should not have access to SSH_AUTH_SOCK"):
+          if "SSH_AUTH_SOCK=HOLEY" in machine.succeed(
+              'su - test7 -c "SSH_AUTH_SOCK=HOLEY doas env"'
+          ):
+              raise Exception("failed to exclude SSH_AUTH_SOCK")
+    '';
+  }
+)