SenDroid: Auditing Sensor Access in Android System-Wide

Abstract

Sensors are widely used in modern mobile devices (e.g., smartphones, watches) and may gather abundant information from environments as well as about users, e.g., photos, sounds and locations. The rich set of sensor data enables various applications (e.g., health monitoring) and personalized apps as well. However, the powerful sensing abilities provide opportunities for attackers to steal both personal sensitive data and commercial secrets like never before. Unfortunately, the current design of smart devices only provides a coarse access control on sensors and does not have the capability to audit sensing. We argue that knowing how often the sensors are accessed and how much sensor data are collected is the first-line defense against sensor data breach. Such an ability is yet to be designed. In this paper, we propose a framework that allows users to acquire sensor data usages. In particular, we leverage a hook-based track method to track sensor accesses. Thus, with no need to change the source codes of the Android system and applications, we can intercept sensing operations to graphic sensors, audio sensors, location sensors, and standard sensors, and audit them from four aspects: flow audit, frequency audit, duration audit and invoker audit. Then, we implement a prototype, referred to as senDroid, which visually shows the quantitative usages of these sensors in real time at a performance overhead of [0.04-8.05] percent. senDroid allows Android users to audit the applications even when they bypass the Android framework via JNI invocations or when the malicious codes are dynamically loaded from the server side. Our empirical study on 1,489 popular apps in three well-known Android app markets shows that 26.32 percent apps access sensors when the apps are launched, and 11.01 percent apps access sensors while the apps run in the background. Furthermore, we analyze the relevance between sensor usage patterns and third-party libraries, and reverse-engineering on suspicious third-party libraries shows that 77.27 percent apps access sensors via third-party libraries. Our results call attentions to address the users' privacy concerns caused by sensor access.