OK, we do not need to do weird grab-ass stuff

package_manager/src/PathExcluder/SiteConfigurationExcluder.php

@@ -112,37 +112,16 @@ class SiteConfigurationExcluder implements EventSubscriberInterface {
     }
     $live_dir = $this->getDefaultSiteDirectoryPath($this->pathLocator->getProjectRoot());
 
-    // This is borrowed from \Symfony\Component\Filesystem\Filesystem::copy(),
-    // to ensure the correct permissions are preserved (chmod() requires
-    // permissions to be sent as an octal number, but fileperms() returns a
-    // decimal number, because PHP is just great).
-    $permissions = $this->getPermissions($staged_dir) | ($this->getPermissions($live_dir) & 0111);
+    $permissions = fileperms($live_dir);
+    if ($permissions === FALSE) {
+      throw new FileException("Could not determine permissions for '$live_dir'.");
+    }
 
     if (!$this->fileSystem->chmod($staged_dir, $permissions)) {
       throw new FileException("Could not change permissions on '$staged_dir'.");
     }
   }
 
-  /**
-   * Gets the current file permissions of a path.
-   *
-   * @param string $path
-   *   The path to examine.
-   *
-   * @return int
-   *   The current permissions of the path.
-   *
-   * @throws \Drupal\Core\File\Exception\FileException
-   *   Thrown if the file permissions cannot be determined.
-   */
-  private function getPermissions(string $path): int {
-    $permissions = fileperms($path);
-    if ($permissions === FALSE) {
-      throw new FileException("Could not determine permissions for '$path'.");
-    }
-    return $permissions;
-  }
-
   /**
    * Returns the full path to `sites/default`, relative to a root directory.
    *