Merge pull request #136605 from helsinki-systems/feat/dry-activation-scripts

nixos: Add dry activation for users/groups

6 files changed, 131 insertions, 59 deletions

diff --git a/nixos/modules/config/update-users-groups.pl b/nixos/modules/config/update-users-groups.pl
index bef08dc40207..232f886789d3 100644
--- a/nixos/modules/config/update-users-groups.pl
+++ b/nixos/modules/config/update-users-groups.pl
@@ -1,11 +1,10 @@
 use strict;
+use warnings;
 use File::Path qw(make_path);
 use File::Slurp;
+use Getopt::Long;
 use JSON;
 
-make_path("/var/lib/nixos", { mode => 0755 });
-
-
 # Keep track of deleted uids and gids.
 my $uidMapFile = "/var/lib/nixos/uid-map";
 my $uidMap = -e $uidMapFile ? decode_json(read_file($uidMapFile)) : {};
@@ -13,12 +12,19 @@ my $uidMap = -e $uidMapFile ? decode_json(read_file($uidMapFile)) : {};
 my $gidMapFile = "/var/lib/nixos/gid-map";
 my $gidMap = -e $gidMapFile ? decode_json(read_file($gidMapFile)) : {};
 
+my $is_dry = ($ENV{'NIXOS_ACTION'} // "") eq "dry-activate";
+GetOptions("dry-activate" => \$is_dry);
+make_path("/var/lib/nixos", { mode => 0755 }) unless $is_dry;
 
 sub updateFile {
     my ($path, $contents, $perms) = @_;
+    return if $is_dry;
     write_file($path, { atomic => 1, binmode => ':utf8', perms => $perms // 0644 }, $contents) or die;
 }
 
+sub nscdInvalidate {
+    system("nscd", "--invalidate", $_[0]) unless $is_dry;
+}
 
 sub hashPassword {
     my ($password) = @_;
@@ -28,6 +34,14 @@ sub hashPassword {
     return crypt($password, '$6$' . $salt . '$');
 }
 
+sub dry_print {
+    if ($is_dry) {
+        print STDERR ("$_[1] $_[2]\n")
+    } else {
+        print STDERR ("$_[0] $_[2]\n")
+    }
+}
+
 
 # Functions for allocating free GIDs/UIDs. FIXME: respect ID ranges in
 # /etc/login.defs.
@@ -51,7 +65,7 @@ sub allocGid {
     my ($name) = @_;
     my $prevGid = $gidMap->{$name};
     if (defined $prevGid && !defined $gidsUsed{$prevGid}) {
-        print STDERR "reviving group '$name' with GID $prevGid\n";
+        dry_print("reviving", "would revive", "group '$name' with GID $prevGid");
         $gidsUsed{$prevGid} = 1;
         return $prevGid;
     }
@@ -63,15 +77,14 @@ sub allocUid {
     my ($min, $max, $up) = $isSystemUser ? (400, 999, 0) : (1000, 29999, 1);
     my $prevUid = $uidMap->{$name};
     if (defined $prevUid && $prevUid >= $min && $prevUid <= $max && !defined $uidsUsed{$prevUid}) {
-        print STDERR "reviving user '$name' with UID $prevUid\n";
+        dry_print("reviving", "would revive", "user '$name' with UID $prevUid");
         $uidsUsed{$prevUid} = 1;
         return $prevUid;
     }
     return allocId(\%uidsUsed, \%uidsPrevUsed, $min, $max, $up, sub { my ($uid) = @_; getpwuid($uid) });
 }
 
-
-# Read the declared users/groups.
+# Read the declared users/groups
 my $spec = decode_json(read_file($ARGV[0]));
 
 # Don't allocate UIDs/GIDs that are manually assigned.
@@ -134,7 +147,7 @@ foreach my $g (@{$spec->{groups}}) {
     if (defined $existing) {
         $g->{gid} = $existing->{gid} if !defined $g->{gid};
         if ($g->{gid} != $existing->{gid}) {
-            warn "warning: not applying GID change of group ‘$name’ ($existing->{gid} -> $g->{gid})\n";
+            dry_print("warning: not applying", "warning: would not apply", "GID change of group ‘$name’ ($existing->{gid} -> $g->{gid})");
             $g->{gid} = $existing->{gid};
         }
         $g->{password} = $existing->{password}; # do we want this?
@@ -163,7 +176,7 @@ foreach my $name (keys %groupsCur) {
     my $g = $groupsCur{$name};
     next if defined $groupsOut{$name};
     if (!$spec->{mutableUsers} || defined $declGroups{$name}) {
-        print STDERR "removing group ‘$name’\n";
+        dry_print("removing group", "would remove group", "‘$name’");
     } else {
         $groupsOut{$name} = $g;
     }
@@ -175,7 +188,7 @@ my @lines = map { join(":", $_->{name}, $_->{password}, $_->{gid}, $_->{members}
     (sort { $a->{gid} <=> $b->{gid} } values(%groupsOut));
 updateFile($gidMapFile, to_json($gidMap));
 updateFile("/etc/group", \@lines);
-system("nscd --invalidate group");
+nscdInvalidate("group");
 
 # Generate a new /etc/passwd containing the declared users.
 my %usersOut;
@@ -196,7 +209,7 @@ foreach my $u (@{$spec->{users}}) {
     if (defined $existing) {
         $u->{uid} = $existing->{uid} if !defined $u->{uid};
         if ($u->{uid} != $existing->{uid}) {
-            warn "warning: not applying UID change of user ‘$name’ ($existing->{uid} -> $u->{uid})\n";
+            dry_print("warning: not applying", "warning: would not apply", "UID change of user ‘$name’ ($existing->{uid} -> $u->{uid})");
             $u->{uid} = $existing->{uid};
         }
     } else {
@@ -211,7 +224,7 @@ foreach my $u (@{$spec->{users}}) {
 
     # Ensure home directory incl. ownership and permissions.
     if ($u->{createHome}) {
-        make_path($u->{home}, { mode => 0700 }) if ! -e $u->{home};
+        make_path($u->{home}, { mode => 0700 }) if ! -e $u->{home} and ! $is_dry;
         chown $u->{uid}, $u->{gid}, $u->{home};
         chmod 0700, $u->{home};
     }
@@ -250,7 +263,7 @@ foreach my $name (keys %usersCur) {
     my $u = $usersCur{$name};
     next if defined $usersOut{$name};
     if (!$spec->{mutableUsers} || defined $declUsers{$name}) {
-        print STDERR "removing user ‘$name’\n";
+        dry_print("removing user", "would remove user", "‘$name’");
     } else {
         $usersOut{$name} = $u;
     }
@@ -261,7 +274,7 @@ foreach my $name (keys %usersCur) {
     (sort { $a->{uid} <=> $b->{uid} } (values %usersOut));
 updateFile($uidMapFile, to_json($uidMap));
 updateFile("/etc/passwd", \@lines);
-system("nscd --invalidate passwd");
+nscdInvalidate("passwd");
 
 
 # Rewrite /etc/shadow to add new accounts or remove dead ones.
@@ -293,7 +306,7 @@ updateFile("/etc/shadow", \@shadowNew, 0640);
     my $uid = getpwnam "root";
     my $gid = getgrnam "shadow";
     my $path = "/etc/shadow";
-    chown($uid, $gid, $path) || die "Failed to change ownership of $path: $!";
+    (chown($uid, $gid, $path) || die "Failed to change ownership of $path: $!") unless $is_dry;
 }
 
 # Rewrite /etc/subuid & /etc/subgid to include default container mappings
diff --git a/nixos/modules/config/users-groups.nix b/nixos/modules/config/users-groups.nix
index f86be3be2c65..d88162558e66 100644
--- a/nixos/modules/config/users-groups.nix
+++ b/nixos/modules/config/users-groups.nix
@@ -561,14 +561,16 @@ in {
       shadow.gid = ids.gids.shadow;
     };
 
-    system.activationScripts.users = stringAfter [ "stdio" ]
-      ''
+    system.activationScripts.users = {
+      supportsDryActivation = true;
+      text = ''
         install -m 0700 -d /root
         install -m 0755 -d /home
 
         ${pkgs.perl.withPackages (p: [ p.FileSlurp p.JSON ])}/bin/perl \
         -w ${./update-users-groups.pl} ${spec}
       '';
+    };
 
     # for backwards compatibility
     system.activationScripts.groups = stringAfter [ "users" ] "";
diff --git a/nixos/modules/system/activation/activation-script.nix b/nixos/modules/system/activation/activation-script.nix
index 3a6930314b1a..548b4de852b7 100644
--- a/nixos/modules/system/activation/activation-script.nix
+++ b/nixos/modules/system/activation/activation-script.nix
@@ -17,6 +17,41 @@ let
     '';
   });
 
+  systemActivationScript = set: onlyDry: let
+    set' = filterAttrs (_: v: onlyDry -> v.supportsDryActivation) (mapAttrs (_: v: if isString v then (noDepEntry v) // { supportsDryActivation = false; } else v) set);
+    withHeadlines = addAttributeName set';
+  in
+    ''
+      #!${pkgs.runtimeShell}
+
+      systemConfig='@out@'
+
+      export PATH=/empty
+      for i in ${toString path}; do
+          PATH=$PATH:$i/bin:$i/sbin
+      done
+
+      _status=0
+      trap "_status=1 _localstatus=\$?" ERR
+
+      # Ensure a consistent umask.
+      umask 0022
+
+      ${textClosureMap id (withHeadlines) (attrNames withHeadlines)}
+
+    '' + optionalString (!onlyDry) ''
+      # Make this configuration the current configuration.
+      # The readlink is there to ensure that when $systemConfig = /system
+      # (which is a symlink to the store), /run/current-system is still
+      # used as a garbage collection root.
+      ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
+
+      # Prevent the current configuration from being garbage-collected.
+      ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
+
+      exit $_status
+    '';
+
   path = with pkgs; map getBin
     [ coreutils
       gnugrep
@@ -28,7 +63,7 @@ let
       util-linux # needed for mount and mountpoint
     ];
 
-  scriptType = with types;
+  scriptType = withDry: with types;
     let scriptOptions =
       { deps = mkOption
           { type = types.listOf types.str;
@@ -39,6 +74,19 @@ let
           { type = types.lines;
             description = "The content of the script.";
           };
+      } // optionalAttrs withDry {
+        supportsDryActivation = mkOption
+          { type = types.bool;
+            default = false;
+            description = ''
+              Whether this activation script supports being dry-activated.
+              These activation scripts will also be executed on dry-activate
+              activations with the environment variable
+              <literal>NIXOS_ACTION</literal> being set to <literal>dry-activate
+              </literal>.  it's important that these activation scripts  don't
+              modify anything about the system when the variable is set.
+            '';
+          };
       };
     in either str (submodule { options = scriptOptions; });
 
@@ -74,47 +122,19 @@ in
         idempotent and fast.
       '';
 
-      type = types.attrsOf scriptType;
-
-      apply = set: {
-        script =
-          ''
-            #! ${pkgs.runtimeShell}
-
-            systemConfig=@out@
-
-            export PATH=/empty
-            for i in ${toString path}; do
-                PATH=$PATH:$i/bin:$i/sbin
-            done
-
-            _status=0
-            trap "_status=1 _localstatus=\$?" ERR
-
-            # Ensure a consistent umask.
-            umask 0022
-
-            ${
-              let
-                set' = mapAttrs (n: v: if isString v then noDepEntry v else v) set;
-                withHeadlines = addAttributeName set';
-              in textClosureMap id (withHeadlines) (attrNames withHeadlines)
-            }
-
-            # Make this configuration the current configuration.
-            # The readlink is there to ensure that when $systemConfig = /system
-            # (which is a symlink to the store), /run/current-system is still
-            # used as a garbage collection root.
-            ln -sfn "$(readlink -f "$systemConfig")" /run/current-system
-
-            # Prevent the current configuration from being garbage-collected.
-            ln -sfn /run/current-system /nix/var/nix/gcroots/current-system
-
-            exit $_status
-          '';
+      type = types.attrsOf (scriptType true);
+      apply = set: set // {
+        script = systemActivationScript set false;
       };
     };
 
+    system.dryActivationScript = mkOption {
+      description = "The shell script that is to be run when dry-activating a system.";
+      readOnly = true;
+      internal = true;
+      default = systemActivationScript (removeAttrs config.system.activationScripts [ "script" ]) true;
+    };
+
     system.userActivationScripts = mkOption {
       default = {};
 
@@ -137,7 +157,7 @@ in
         idempotent and fast.
       '';
 
-      type = with types; attrsOf scriptType;
+      type = with types; attrsOf (scriptType false);
 
       apply = set: {
         script = ''
diff --git a/nixos/modules/system/activation/switch-to-configuration.pl b/nixos/modules/system/activation/switch-to-configuration.pl
index dd391c8b5d78..b7a062755296 100644
--- a/nixos/modules/system/activation/switch-to-configuration.pl
+++ b/nixos/modules/system/activation/switch-to-configuration.pl
@@ -36,6 +36,8 @@ EOF
     exit 1;
 }
 
+$ENV{NIXOS_ACTION} = $action;
+
 # This is a NixOS installation if it has /etc/NIXOS or a proper
 # /etc/os-release.
 die "This is not a NixOS installation!\n" unless
@@ -360,6 +362,10 @@ if ($action eq "dry-activate") {
         if scalar @unitsToStopFiltered > 0;
     print STDERR "would NOT stop the following changed units: ", join(", ", sort(keys %unitsToSkip)), "\n"
         if scalar(keys %unitsToSkip) > 0;
+
+    print STDERR "would activate the configuration...\n";
+    system("$out/dry-activate", "$out");
+
     print STDERR "would restart systemd\n" if $restartSystemd;
     print STDERR "would restart the following units: ", join(", ", sort(keys %unitsToRestart)), "\n"
         if scalar(keys %unitsToRestart) > 0;
diff --git a/nixos/modules/system/activation/top-level.nix b/nixos/modules/system/activation/top-level.nix
index d3e4923a993f..80835d9688f2 100644
--- a/nixos/modules/system/activation/top-level.nix
+++ b/nixos/modules/system/activation/top-level.nix
@@ -56,9 +56,11 @@ let
       ''}
 
       echo "$activationScript" > $out/activate
+      echo "$dryActivationScript" > $out/dry-activate
       substituteInPlace $out/activate --subst-var out
-      chmod u+x $out/activate
-      unset activationScript
+      substituteInPlace $out/dry-activate --subst-var out
+      chmod u+x $out/activate $out/dry-activate
+      unset activationScript dryActivationScript
 
       cp ${config.system.build.bootStage2} $out/init
       substituteInPlace $out/init --subst-var-by systemConfig $out
@@ -108,6 +110,7 @@ let
       config.system.build.installBootLoader
       or "echo 'Warning: do not know how to make this configuration bootable; please enable a boot loader.' 1>&2; true";
     activationScript = config.system.activationScripts.script;
+    dryActivationScript = config.system.dryActivationScript;
     nixosLabel = config.system.nixos.label;
 
     configurationName = config.boot.loader.grub.configurationName;
diff --git a/nixos/tests/mutable-users.nix b/nixos/tests/mutable-users.nix
index e3f002d9b198..ebe32e6487ef 100644
--- a/nixos/tests/mutable-users.nix
+++ b/nixos/tests/mutable-users.nix
@@ -12,6 +12,7 @@ import ./make-test-python.nix ({ pkgs, ...} : {
     };
     mutable = { ... }: {
       users.mutableUsers = true;
+      users.users.dry-test.isNormalUser = true;
     };
   };
 
@@ -41,5 +42,32 @@ import ./make-test-python.nix ({ pkgs, ...} : {
             "${mutableSystem}/bin/switch-to-configuration test"
         )
         assert "/run/wrappers/" in machine.succeed("which passwd")
+
+    with subtest("dry-activation does not change files"):
+        machine.succeed('test -e /home/dry-test')  # home was created
+        machine.succeed('rm -rf /home/dry-test')
+
+        files_to_check = ['/etc/group',
+                          '/etc/passwd',
+                          '/etc/shadow',
+                          '/etc/subuid',
+                          '/etc/subgid',
+                          '/var/lib/nixos/uid-map',
+                          '/var/lib/nixos/gid-map',
+                          '/var/lib/nixos/declarative-groups',
+                          '/var/lib/nixos/declarative-users'
+                         ]
+        expected_hashes = {}
+        expected_stats = {}
+        for file in files_to_check:
+            expected_hashes[file] = machine.succeed(f"sha256sum {file}")
+            expected_stats[file] = machine.succeed(f"stat {file}")
+
+        machine.succeed("/run/current-system/bin/switch-to-configuration dry-activate")
+
+        machine.fail('test -e /home/dry-test')  # home was not recreated
+        for file in files_to_check:
+            assert machine.succeed(f"sha256sum {file}") == expected_hashes[file]
+            assert machine.succeed(f"stat {file}") == expected_stats[file]
   '';
 })