/* File permissions, written once when fs is mounted */
        struct ffs_file_perms {
                umode_t                         mode;
-               uid_t                           uid;
-               gid_t                           gid;
+               kuid_t                          uid;
+               kgid_t                          gid;
        }                               file_perms;
 
        /*
                        break;
 
                case 3:
-                       if (!memcmp(opts, "uid", 3))
-                               data->perms.uid = value;
+                       if (!memcmp(opts, "uid", 3)) {
+                               data->perms.uid = make_kuid(current_user_ns(), value);
+                               if (!uid_valid(data->perms.uid)) {
+                                       pr_err("%s: unmapped value: %lu\n", opts, value);
+                                       return -EINVAL;
+                               }
+                       }
                        else if (!memcmp(opts, "gid", 3))
-                               data->perms.gid = value;
+                               data->perms.gid = make_kgid(current_user_ns(), value);
+                               if (!gid_valid(data->perms.gid)) {
+                                       pr_err("%s: unmapped value: %lu\n", opts, value);
+                                       return -EINVAL;
+                               }
                        else
                                goto invalid;
                        break;
        struct ffs_sb_fill_data data = {
                .perms = {
                        .mode = S_IFREG | 0600,
-                       .uid = 0,
-                       .gid = 0
+                       .uid = GLOBAL_ROOT_UID,
+                       .gid = GLOBAL_ROOT_GID,
                },
                .root_mode = S_IFDIR | 0500,
        };