setcon

Run command with specific selinux context for Android

Usage

Get prebuilts from releases.

Push the binary matching your architecture via adb. For example arm64-v8a.

$ adb root
$ adb push <path-to-prebuilts>/arm64-v8a/setcon /data

Run it and see help.

$ adb shell chmod u+x /data/setcon
$ adb shell /data/setcon --help
setcon by LibXZR <i@xzr.moe>
Run command with specific selinux context
Usage:
 setcon <context> <command>
Example:
 setcon u:r:untrusted_app:s0 sh

It can be used to test sepolicy.

$ adb shell /data/setcon u:r:untrusted_app:s0 ls /
ls: /: Permission denied
$ adb logcat | grep avc
09-27 21:41:08.443 27787 27787 W ls      : type=1400 audit(0.0:180): avc: denied { read } for name="/" dev="dm-2" ino=2 scontext=u:r:untrusted_app:s0 tcontext=u:object_r:rootfs:s0 tclass=dir permissive=0

Also a getcon binary is included in the prebuilt package. It simply prints current selinux context.

$ adb shell /data/getcon
u:r:su:s0

Building

It's easy to build it with Android NDK.

$ export PATH="/path/to/your/ndk:${PATH}"
$ git clone https://github.com/libxzr/setcon
......
$ cd setcon
$ ndk-build
......
$ tree libs          
libs
├── arm64-v8a
│   ├── getcon
│   └── setcon
├── armeabi-v7a
│   ├── getcon
│   └── setcon
├── x86
│   ├── getcon
│   └── setcon
└── x86_64
    ├── getcon
    └── setcon

Why?

You may wonder we already have runcon in toybox, why bother to rewrite?

It's quite interesting that runcon itself can be denied by SELinux :)

$ adb root
$ adb shell runcon u:r:priv_app:s0:c512,c768 sh
runcon: exec sh: Permission denied
$ adb logcat | grep avc
10-02 18:43:27.027  5376  5376 W runcon  : type=1400 audit(0.0:124): avc: denied { entrypoint } for path="/system/bin/sh" dev="dm-2" ino=539 scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:shell_exec:s0 tclass=file permissive=0
10-02 18:43:27.027  5376  5376 W runcon  : type=1400 audit(0.0:125): avc: denied { entrypoint } for path="/vendor/bin/sh" dev="dm-4" ino=261 scontext=u:r:priv_app:s0:c512,c768 tcontext=u:object_r:vendor_shell_exec:s0 tclass=file permissive=0

License

MIT