nixos/sudo: add option execWheelOnly

By setting the executable's group to wheel and permissions to 4510, we
make sure that only members of the wheel group can execute sudo.

1 files changed, 25 insertions, 3 deletions

diff --git a/nixos/modules/security/sudo.nix b/nixos/modules/security/sudo.nix
index cc3ff3d11b917..2e73f8f4f311d 100644
--- a/nixos/modules/security/sudo.nix
+++ b/nixos/modules/security/sudo.nix
@@ -61,6 +61,17 @@ in
         '';
       };
 
+    security.sudo.execWheelOnly = mkOption {
+      type = types.bool;
+      default = false;
+      description = ''
+        Only allow members of the <code>wheel</code> group to execute sudo by
+        setting the executable's permissions accordingly.
+        This prevents users that are not members of <code>wheel</code> from
+        exploiting vulnerabilities in sudo such as CVE-2021-3156.
+      '';
+    };
+
     security.sudo.configFile = mkOption {
       type = types.lines;
       # Note: if syntax errors are detected in this file, the NixOS
@@ -216,9 +227,20 @@ in
         ${cfg.extraConfig}
       '';
 
-    security.wrappers = {
-      sudo.source = "${cfg.package.out}/bin/sudo";
-      sudoedit.source = "${cfg.package.out}/bin/sudoedit";
+    security.wrappers = let
+      owner = "root";
+      group = if cfg.execWheelOnly then "wheel" else "root";
+      setuid = true;
+      permissions = if cfg.execWheelOnly then "u+rx,g+x" else "u+rx,g+x,o+x";
+    in {
+      sudo = {
+        source = "${cfg.package.out}/bin/sudo";
+        inherit owner group setuid permissions;
+      };
+      sudoedit = {
+        source = "${cfg.package.out}/bin/sudoedit";
+        inherit owner group setuid permissions;
+      };
     };
 
     environment.systemPackages = [ sudo ];