setuid.nix

# Verify that Linux builds cannot create setuid or setgid binaries.

{
  lib,
  config,
  nixpkgs,
  ...
}:

let
  pkgs = config.nodes.machine.nixpkgs.pkgs;

in
{
  name = "setuid";

  nodes.machine =
    {
      config,
      lib,
      pkgs,
      ...
    }:
    {
      virtualisation.writableStore = true;
      nix.settings.substituters = lib.mkForce [ ];
      nix.nixPath = [ "nixpkgs=${lib.cleanSource pkgs.path}" ];
      virtualisation.additionalPaths = [
        pkgs.stdenvNoCC
        pkgs.pkgsi686Linux.stdenvNoCC
      ];
    };

  testScript =
    { nodes }:
    ''
      # fmt: off
      start_all()

      # Copying to /tmp should succeed.
      machine.succeed(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" {} "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")

      # Creating a setuid binary should fail.
      machine.fail(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" {} "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        chmod 4755 /tmp/id
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")

      # Creating a setgid binary should fail.
      machine.fail(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" {} "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        chmod 2755 /tmp/id
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")

      # The checks should also work on 32-bit binaries.
      machine.fail(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> { system = "i686-linux"; }; runCommand "foo" {} "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        chmod 2755 /tmp/id
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")

      # The tests above use fchmodat(). Test chmod() as well.
      machine.succeed(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" { buildInputs = [ perl ]; } "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        perl -e \"chmod 0666, qw(/tmp/id) or die\"
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 666 ]]')

      machine.succeed("rm /tmp/id")

      machine.fail(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" { buildInputs = [ perl ]; } "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        perl -e \"chmod 04755, qw(/tmp/id) or die\"
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")

      # And test fchmod().
      machine.succeed(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" { buildInputs = [ perl ]; } "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        perl -e \"my \\\$x; open \\\$x, qw(/tmp/id); chmod 01750, \\\$x or die\"
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 1750 ]]')

      machine.succeed("rm /tmp/id")

      machine.fail(r"""
      nix-build --no-sandbox -E '(with import <nixpkgs> {}; runCommand "foo" { buildInputs = [ perl ]; } "
        mkdir -p $out
        cp ${pkgs.coreutils}/bin/id /tmp/id
        perl -e \"my \\\$x; open \\\$x, qw(/tmp/id); chmod 04777, \\\$x or die\"
      ")'
      """.strip())

      machine.succeed('[[ $(stat -c %a /tmp/id) = 555 ]]')

      machine.succeed("rm /tmp/id")
    '';
}