The Question:
I need to run some commands that require higher privileges from an app on a rooted device . Let's say for example, chmod 777 or accessing a a file who's permissions are --w------- (would work if permissions were --w-----w- meaning app is running as other group).
Some extra details:
- Running Android API 18 (No SELinux)
Things I have already tried:
1) Using su from java:
From this post, I have tried using su in java like so:
Process su = null;
try {
su = Runtime.getRuntime().exec("su");
su.getOutputStream().write("chmod 777 file\n".getBytes());
su.getOutputStream().write("exit\n".getBytes());
su.waitFor();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (su != null) {
su.destroy();
}
}
No error is thrown, but this does nothing.
2) Using setWritable() from java:
boolean ret = file.setWritable(true, false);
Here, ret = false indicating it had failed.
3) Using RootTools library:
Command cmd = new Command(0, "chmod 202 /sys/class/gpio/export");
try {
RootShell.getShell(true).add(cmd);
} catch (Exception e) {
Log.d(TAG,e.getMessage());
}
Running this gives me: Error! Permission denied
4) Using this answer
Using the class ExecuteAsRootBase I get: Can't get root access or denied by user.
5) Placing the app in /system/app
Still runs as u0_a38 under here for some reason! In order to get this to work I had to manually place the library .so under /system/libs. I also had to chmod 644 my .apk in order to allow it to run. I don't really understand why I am not running under root as when I use ls -l on my apk in /system/app it gives me:
-rw-r--r-- root root 1270817 2000-01-01 01:42 com.my.app.apk
6) Signing the app as a system app (not in /system/app)
This was the last thing I tried.
Following these instructions, I was able to sign and install the app. I called ps from adb shell to check if it was running as root only to find out it was running under u0_a38.
Note: When installing as a system app even after signing, I could not install the app with android:sharedUserId="android.uid.shared" as it gave me: Failure [INSTALL_FAILED_SHARED_USER_INCOMPATIBLE]. Therefore, the app signed as a system app had this line omitted from the manifest.
7) Placing signed system app in /system/app
Exactly the same this as in 5.
When I input ls -l in /system/app I get:
-rw------- root root 1303459 2000-01-01 01:02 com.my.app.apk
Yet running "id" from within the app, I know that it is actually running as:
uid=10038(u0_a38) gid=10038(u0_a38) groups=1015(sdcard_rw),1028(sdcard_r),50038(all_a38)
8) Setting android:sharedUserId="android.uid.system" regardless of error
So even though I couldn't make this install using adb install because of the error :Failure [INSTALL_FAILED_SHARED_USER_INCOMPATIBLE] I went ahead and pulled the trigger anyway. I used adb push to get the .apk into /system/app and then manually added the native library to /system/libs, rebooting the device to let the system uninstall it. I then got this error on boot:
W/PackageManager( 2652): Signature mismatch for shared user : SharedUserSetting{411d82d8 android.uid.system/1000}
D/PackageManager( 2652): No files in app dir /vendor/app
E/PackageManager( 2652): Package com.my.app has no signatures that match those in shared user android.uid.system; ignoring!
So I'm assuming there is a chance that the keys provided by the manufacturer might not be the right ones. I found them here, which is a link from the manufacturer website.
OR
This dates back a while, not sure if it is still relevant. I'm hesitant to just delete that portion of the file but I will most likely end up trying it very soon. I don't see how removing the android.uid.***** from packages.xml won't impact the apps already installed on the system.
Conclusion:
Is there anything else that can be done aside from rebuilding with new keys? Or is this pretty much everything?
