users-groups service: add autoSubUidGidRange option

Previously we allocated subuids automatically for all normal users.
Make this explicitly configurable, so that one can use this for system
users too (or explicitly disable for normal users). Also don't allocate
automatically by default if a user already has ranges specified statically.

nixos/doc/manual/from_md/release-notes/rl-2205.section.xml

@@ -228,6 +228,15 @@
           to your configuration.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          Normal users (with <literal>isNormalUser = true</literal>)
+          which have non-empty <literal>subUidRanges</literal> or
+          <literal>subGidRanges</literal> set no longer have additional
+          implicit ranges allocated. To enable automatic allocation back
+          set <literal>autoSubUidGidRange = true</literal>.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-22.05-notable-changes">

nixos/doc/manual/release-notes/rl-2205.section.md

@@ -77,6 +77,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - `documentation.man` has been refactored to support choosing a man implementation other than GNU's `man-db`. For this, `documentation.man.manualPages` has been renamed to `documentation.man.man-db.manualPages`. If you want to use the new alternative man implementation `mandoc`, add `documentation.man = { enable = true; man-db.enable = false; mandoc.enable = true; }` to your configuration.
 
+- Normal users (with `isNormalUser = true`) which have non-empty `subUidRanges` or `subGidRanges` set no longer have additional implicit ranges allocated. To enable automatic allocation back set `autoSubUidGidRange = true`.
+
 ## Other Notable Changes {#sec-release-22.05-notable-changes}
 
 - The option [services.redis.servers](#opt-services.redis.servers) was added

nixos/modules/config/update-users-groups.pl

@@ -351,7 +351,7 @@ foreach my $u (values %usersOut) {
         push @subGids, $value;
     }
 
-    if($u->{isNormalUser}) {
+    if($u->{autoSubUidGidRange}) {
         my $subordinate = allocSubUid($name);
         $subUidMap->{$name} = $subordinate;
         my $value = join(":", ($name, $subordinate, 65536));

nixos/modules/config/users-groups.nix

@@ -204,6 +204,16 @@ let
         '';
       };
 
+      autoSubUidGidRange = mkOption {
+        type = types.bool;
+        default = false;
+        example = true;
+        description = ''
+          Automatically allocate subordinate user and group ids for this user.
+          Allocated range is currently always of size 65536.
+        '';
+      };
+
       createHome = mkOption {
         type = types.bool;
         default = false;
@@ -320,6 +330,9 @@ let
         (mkIf (!cfg.mutableUsers && config.initialHashedPassword != null) {
           hashedPassword = mkDefault config.initialHashedPassword;
         })
+        (mkIf (config.isNormalUser && config.subUidRanges == [] && config.subGidRanges == []) {
+          autoSubUidGidRange = mkDefault true;
+        })
       ];
 
   };
@@ -419,7 +432,7 @@ let
       { inherit (u)
           name uid group description home createHome isSystemUser
           password passwordFile hashedPassword
-          isNormalUser subUidRanges subGidRanges
+          autoSubUidGidRange subUidRanges subGidRanges
           initialPassword initialHashedPassword;
         shell = utils.toShellPath u.shell;
       }) cfg.users;