Ota Update in AOSP

Question

I have been trying to make a Custom ROM in android. So, far I have been able to make changes and flash in Nexus 4 successfully. But my main aim is to provide Ota updates to my ROM. Right now I am able to update the device with update.zip using adb sideload and now I want it to be done automatically through a system app. For that I have made a system app which can download the update.zip from my server. I have gone through this link without any progress: Android development RecoverySystem.installPackage() cannot write to /cache/recovery/command permission denied

I have used the following code in Asynctask to install the update:

    File update = new File("/data/update.zip");
    try {
        RecoverySystem.installPackage(mContext, update);
    } catch (IOException e) {
        e.printStackTrace();
    }

But I am getting the following error:

    W/RecoverySystem( 3900): !!! REBOOTING TO INSTALL /data/update.zip !!!
    W/System.err( 3900): java.io.FileNotFoundException: /cache/recovery/command: open failed: ENOENT (No such file or directory)
    W/System.err( 3900):    at libcore.io.IoBridge.open(IoBridge.java:456)
    W/System.err( 3900):    at java.io.FileOutputStream.<init>(FileOutputStream.java:87)
    W/System.err( 3900):    at java.io.FileOutputStream.<init>(FileOutputStream.java:72)
    W/System.err( 3900):    at java.io.FileWriter.<init>(FileWriter.java:42)
    W/System.err( 3900):    at android.os.RecoverySystem.bootCommand(RecoverySystem.java:454)
    W/com.test.ota( 3966): type=1400 audit(0.0:8): avc: denied { write } for comm=4173796E635461736B202331 name="/" dev="mmcblk0p22" ino=2 scontext=u:r:system_app:s0 tcontext=u:object_r:cache_file:s0 tclass=dir

The thing I am confused about is I am able to access data directory(which is not accessible to normal apps) when I am downloading, but I am not able to access /cache.

How should I proceed so that i don't get permission denied to system app when accessing /cache ?

My manifest file is:

    <manifest xmlns:android="http://schemas.android.com/apk/res/android"
android:sharedUserId="android.uid.system"
xmlns:tools="http://schemas.android.com/tools"
package="com.test.ota">

<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
<uses-permission android:name="android.permission.INTERNET"/>
<uses-permission android:name="android.permission.WRITE_SETTINGS" />
<uses-permission android:name="android.permission.ACCESS_SUPERUSER" />
<uses-permission android:name="android.permission.RECEIVE_BOOT_COMPLETED" />
<uses-permission android:name="android.permission.WAKE_LOCK" />
<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.VIBRATE" />
<uses-permission
    android:name="android.permission.ACCESS_CACHE_FILESYSTEM"
    tools:ignore="ProtectedPermissions"/>
<uses-permission
    android:name="android.permission.DELETE_CACHE_FILES"
    tools:ignore="ProtectedPermissions"/>
<uses-permission
    android:name="android.permission.REBOOT"
    tools:ignore="ProtectedPermissions" />
<uses-permission android:name="android.permission.RECOVERY" />

Btw, my build branch is android-5.1.1_r19

Update 1: I built using full_mako-userdebug. So, I have su when needed in adb. In adb shell when I try creating cache/recovery/command after su, it allows me to create file. But through app it is not allowing me to create file in cache/recovery/ , even though its system app. I don't want the user to root the phone just to install an ota update. Still having the same problem.

Answer 1

Although you have read access to the cache file system as a system user, you need to alter the Linux SEPolicy to give the system user write access to the /cache partition.

Add the following to file external/sepolicy/system_app.te :

allow system_app cache_file:dir create_dir_perms;
allow system_app cache_file:file create_file_perms;

Then rebuild, and you shouldn't have this error again :)

Answer 2

Please note that new File("/data/update.zip"); doesn't create new file by default, it only keeps the filename string. Check methods to create a file .

If you are sure /data/update.zip file exists, try creating /cache/recovery/command manually before running RecoverySystem.installPackage .

Answer 3

Do a grep of 'denied' on the logcat to check if selinux is preventing your app's access to the cache when executing RecoverySystem.installPackage. Alternatively, since you have su access, turn selinux temporarily off via adb setenforce 0 prior to executing RecoverySystem.installPackage.