D-Bus Policy Governs Messages, Not the Authorization Logic Behind Them

D-Bus is widely used for local service communication on desktops and increasingly in embedded and administrative systems. Its bus daemon policy decides which messages are delivered, but it cannot judge whether a receiving method performs a safe operation. The article argues that a narrow policy still depends on the service exposing a narrow API, and that applications must enforce their own authorization after receiving a message. It recommends inventorying exported interfaces, separating system and session bus trust domains, and treating policy files as reviewable configuration. The author also notes that signals can leak sensitive data, so services should limit what they emit.