You've described the classic Unix security model, with minor improvements. While decent for the time it is showing its age. Specifically the difficulty in ada

You've described the classic Unix security model, with minor improvements. While decent for the time it is showing its age. Specifically the difficulty in adapting to cheap, ubiquitous computing which it wasn't designed for. If you need to keep secrets from other processes—don't run them under the same user account. Or access them remotely, although that brings other tradeoffs and difficulties.