DroidCap: OS Support for Capability-based Permissions in Android

Summary

We present DroidCap, a retrofitting of Android’s central Binder IPC mechanism to change the way how permissions are being represented and managed in the system. In DroidCap, permissions are per-process Binder object capabilities. DroidCap's design removes Android’s UID-based ambient authority and allows the delegation of capabilities between processes to create least-privileged protection domains efficiently. With DroidCap, we show that object capabilities as underlying access control model integrates naturally and backward-compatible into Android’s stock permission model and application management. Thus, our Binder capabilities provide app developers with a new path to gradually adopting app compartmentalization, which we showcase at two favorite examples from the literature, privilege separated advertisement libraries and least privileged app components.