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