+bool uid_is_valid(uid_t uid) {
+
+ /* Some libc APIs use UID_INVALID as special placeholder */
+ if (uid == (uid_t) 0xFFFFFFFF)
+ return false;
+
+ /* A long time ago UIDs where 16bit, hence explicitly avoid the 16bit -1 too */
+ if (uid == (uid_t) 0xFFFF)
+ return false;
+
+ return true;
+}
+