This is an android application for granting root access to other apps. To work, it needs the su binary from https://github.com/thejh/almighty_su to be installed as a setuid binary in the PATH.

Design

The only other Superuser app does a few things different - here are the reasons why this app does stuff different.

In general, the codebase of this app should be as small and simple as possible to reduce the attack surface and increase maintainability.

Volatile permission decisions

ChainsDD's Superuser allows users to grant root access only once or permanently. As an app that has obtained root access once can persist this root access anyway (e.g. by dropping a setuid executable in /system), this is only of limited use. However, it means that there must be two code paths for determining whether permissions should be granted, increasing attack surface.

Fine-grained access control

ChainsDD's Superuser grants or denies access for combinations of caller UID, wanted UID and command. However, all apps that use su just request full root access and specify /system/bin/su as command so that they don't have to obtain access for every seperate command. Therefore, this app grants access solely based on the caller's UID.

Logfiles

ChainsDD's Superuser manages logfiles about permission requests. However, as soon as an application has obtained root access, it can alter those logfiles, so they're not very useful. Also, logfiles need some kind of database with purging logic, so they create attack surface.

Architecture

When an app uses su for the first time, su will use an intent to launch thejh.almighty.AskPermissionActivity. This activity asks the user whether he wants to grant full access to the device and store the result in /data/data/thejh.almighty/uid_ok/uid:<uid> as one character (A for "allow" and D for "deny"). Afterwards, it sends SIGKILL to a child of su, thereby notifying su that it should expect a result to be present.

Reporting Bugs

Non-security bugs should be reported at https://github.com/thejh/Almighty/issues (or at https://github.com/thejh/almighty_su/issues if they mainly affect the su binary). For security-relevant bugs, please contact me at jannhorn@googlemail.com.