In this paper, we proposed a sniffer to detect permission smells from developer and third-party libraries' code. Moreover, we conducted an empirical study to investigate unnecessary permissions on large real-world Android apps. Our analysis indicates that permission smell extensively exists in Android apps. According to the results, permission smells exist in most Android apps. In particular, third-party libraries request permission for functionalities that are not used by developers, which cause more smells. Moreover, most developers do not properly disable unnecessary permissions that are declared for third-party libraries. We discussed the impacts of permission smells on user experiences. As a result, the existence of permission smell does not impact the number of downloads. However, apps that have more unnecessary permissions have received lower ratings from users.

Android, Code Smell, Permission, Empirical Study, Security Risk