So in 4.3 there was a concept of System applications. APKs that were placed in /system/app were given system privileges. As of 4.4, there is a new concept of "privileged app". Privileged apps are stored in /system/priv-app directory and seem to be treated differently. If you look in the AOSP Source code, under PackageManagerService, you will see new methods such as
static boolean locationIsPrivileged(File path) {
try {
final String privilegedAppDir = new File(Environment.getRootDirectory(), "priv-app")
.getCanonicalPath();
return path.getCanonicalPath().startsWith(privilegedAppDir);
} catch (IOException e) {
Slog.e(TAG, "Unable to access code path " + path);
}
return false;
}
So here is an example of a situation where these differ.
public final void addActivity(PackageParser.Activity a, String type) {
...
if (!systemApp && intent.getPriority() > 0 && "activity".equals(type)) {
intent.setPriority(0);
Log.w(TAG, "Package " + a.info.applicationInfo.packageName + " has activity "
+ a.className + " with priority > 0, forcing to 0");
}
...
This affects the priority of any activities that are not defined as system applications. This seems to imply you can not add an activity to the package manager whose priority is higher than 0, unless you are a system app. This does not preclude privileged apps as far as I can tell (there is a lot of logic here, I may be wrong.).
My question is what exactly does this imply? If my app is privileged, but not system, what difference will that make? In PackageManagerService you can find various things that differ between system and privileged apps, they are not exactly the same. There should be some kind of ideology behind privileged apps, otherwise they would have just said:
if locationIsPrivileged: app.flags |= FLAG_SYSTEM
and been done with it. This is a new concept, and I think it would be important to know the difference between these kinds of apps for anyone who is doing AOSP development as of 4.4.
So after some digging, it's clear that apps in priv-app are eligible for system permissions, the same way that old apps used to be eligible to claim system permissions by being in system-app. The only official Google documentation I could find on this came in the form of a commit message:
Commit hash: ccbf84f44c9e6a5ed3c08673614826bb237afc54
Some system apps are more system than others
"signatureOrSystem" permissions are no longer available to all apps
residing en the /system partition. Instead, there is a new
/system/priv-app directory, and only apps whose APKs are in that
directory are allowed to use signatureOrSystem permissions without
sharing the platform cert. This will reduce the surface area for
possible exploits of system- bundled applications to try to gain
access to permission-guarded operations.
The ApplicationInfo.FLAG_SYSTEM flag continues to mean what it is says
in the documentation: it indicates that the application apk was
bundled on the /system partition. A new hidden flag FLAG_PRIVILEGED
has been introduced that reflects the actual right to access these
permissions.
Update: As of Android 8.0 priv-app has changed slightly with the addition of Privileged Permission Whitelisting. Beyond just being in priv-app, your app must also be added to a whitelist in order to gain various system permissions. Information on this can be found here: https://source.android.com/devices/tech/config/perms-whitelist
Related
I'm writing an Android app, that will run on custom hardware with a ROM that I have control of.
The device will run a single application (as a launcher) and once the device is deployed I (generally) do not have access to it anymore. The app also has support for updating itself.
As such, I need a way to properly handle permissions for the app i.e. permissions need to be granted automatically (including dangerous ones) if they are ever added to the manifest.
Now, the app is being signed by the same certificate as the Android OS running on the device, and the app is placed in the priv-app directory when the device is flashed.
I assumed that this would automatically grant permissions but this does not appear to be the case.
I have tried adding android:sharedUserId="android.uid.system" to the manifest, and that does indeed grant all permissions, but since there are already quite a few legacy devices "in the wild", adding this option makes it so that the app can no longer be updated (throwing a INSTALL_FAILED_SHARED_USER_INCOMPATIBLE error).
So, what is the best way to handle permissions in this case? Is there some other voodoo magic I am missing here? Should I just bite the bullet, add the sharedUserId option and manually update all devices (undesired, but possible option)?
This question has been asked before at How does Android enforce permissions?. While the discussions there are good, the question is still not fully answered.
In the development environment, exceptions are thrown when the app tries to do something that requires permissions not declared in AndroidManifest.xml. So how does the run-time system implement the run-time checking?
I guess it's most likely done in the core framework, which may or may not need support from native code. But I don't know what source code files in AOSP are relevant to this.
Android uses a lot of the standard Linux(-kernel?) mechanisms especially when it comes to hardware restrictions.
Every app gets assigned a new unique (Linux-)user id and whenever the app process is created the system creates it with that user id. The id will never change unless you remove the app. That means for accessing the lower system levels your app will appear as a certain user and every (Linux-)permission system that works with users will also apply to your app.
If you request WRITE_EXTERNAL_STORAGE in the manifest your app will also become member of the (Linux-)group (called sdcard_rw) that has permissions to write to that storage. Permissions on the filesystem are enforced to only allow writing to the system user (=owner) and the sdcard_rw group, anyone else (=other) may only read. See also Is Google blocking apps writing to SD cards
By doing that Android has to do pretty much nothing except for setting the correct UID/GIDs of the processes it spawns once the app starts and the rest is handled at lower levels. Apps that are not member of a certain group simply don't get access to certain hardware.
List of permission <> group mappings: platform.xml
There are also some (Android software) restrictions that are based on either the signature of your app and / or simply by looking up the permissions your app requested: e.g. ContextImpl#checkPermission() - but those permissions have to be checked at every entrypoint to code that allows restricted actions.
From time to time people discover ways to e.g. turn on GPS programmatically because a check like that is missing somewhere.
With regard to your second paragraph, "exceptions" are runtime faults. Permissions are not enforced at build time, only at run time.
Accessing hardware, low level operating system resources, and system files generally requires the app userid to be a member of an appropriate group which it may be assigned by the package manager as a result of having a corresponding android permission. (Familiar examples of that would be network sockets, and the sdcard write which zapl mentioned, but also system-only things like talking directly to the GSM modem or reading the raw touchscreen coordinates).
For the majority of android operations that are done by way of calling library functions which are stubs for interprocess communication to services running in a different process, the platform code running in the more privileged process on the receiving end of the ipc request checks with the package manager to find out if the calling application has the necessary android permission.
Many special permissions are only available to apps signed with the system signature - even if another app claims those in its manifest, they will not be applied by the package manager.
I am currently developing an app that reads out SMS/Emails while driving. Many users wished support for WhatsApp / KakaoTalk.
However, as there is no "official" way to receive their messages, there would be only three options, all requiring root:
The easier way of scanning their database in a given intervall.
Easy to implement.
However not battery efficient
Also the messages are not read out immediately.
An other way would be to run a service with root rights and register a receiver that listens for their push notifications. This has to be done with root, as both packages require a signature based permission for receiving their push notifications.
Harder to implement
Better user experience
Also another thing came to my mind: Would it be possible to manually add permissions to an APK after installing? In that case I could add the c2dm permissions to my package.
This would make things very easy
However, I am a little bit scared of changing my app's permissions, as this is completely against the Android Sandbox principle.
Still, if it would be possible, let me know!
The problem is, how exactly do I run a service with root rights (is it actually possible)? I know how to run shell commands or binaries with root, but I have no idea how to start a part of an APK as root.
Also, would it be possible to integrate a BroadcastReceiver into a binary? I have actually no experience with C/C++, especially in an android environment.
Can you help me with that?
Thanks.
edit: Like I said in the comment, I do not want to use an AccesibilityService, as it does not fit my needs (eg it will give me "2 unread messages" if more then one is unread, also it does not include the full body).
edit2: Just to clarify things: I know how to run commands with root. What I need to know is how to register a Broadcastreceiver, that receives a specific broadcast "normal" receivers don't get, as the Broadcast itself requires a signature based permission I don't have.
This is far from trivial but should work when the apps you want to monitor use sqlite databases or, more generically, write messages to a file when they arrive.
You will indeed need to have root access to the device as this violates the android security system:
Write a native process which runs as a daemon using the NDK and spawn it once after boot as root. You have now 3 major problems to solve:
How to find out if something changed?
This is the easy part. You would need to utilize the Linux inotify interface which should be accessible on every Android phone as the SDK has a FileObserver since API 1, so you are on the safe side here.
Another interesting approach may be to catch the C2DM messages. I have found a NDK class called BroadcastReceiver, so the NDK may be able to catch them. But I personally wouldn't do that as it feels wrong to steal intents. Also you would have to redistribute them or let them travel to real recipient, so I will not describe this in detail here. It may work, but it may be harder and should only be a fallback.
So, when you have solved this, the next problem arises:
How to read the changes in a safe way?
You have a problem, a big one, here. The file doesn't belong to the client, and the client doesn't even have the permission to know where it is (normally). So the monitored app is not aware of the client and will act like the file is exclusively owned only by itself. If they use some plain old textfile to write messages to you have to find out a way to read from it safely as it may be overwritten or extended at any time. But you may be lucky when they use sqlite, according to this it's totally valid to have more than one simultaneous reader, just only one writer. We are in the specs, everything fine again. When you have now read out the new data, more problems to solve:
How to get the new data back into the main app?
You should do only the bare minimum in this C/C++ program because it runs as root. You should also protect your app users from security breaches, so please write the program with this in mind. I have no real idea for this could work really good, but here are some thoughts:
Write the collected data into your own sqlite database (easy in C/C++ and Java),
Write the collected data into a plain file (not recommended at all, pain in the rear),
Send an Intent which contains the new data (maybe not that easy in C/C++, but easy in Java)
Use sockets/pipes/..., just every RPC mechanism you could imagine which is brought to you by Linux (same as the file, don't do it)
As stated in the text above, please be careful when you write this daemon as it is a potential security hazard. It may be hard to do this when you have no knowledge about C/C++ at all, even if you have written simple programs this should be a non trivial task.
On my search through the web I have found the NDK C++ classes I mentioned above. It can be found at Google code. I have neither experience with the NDK nor the C++ wrapper but it may be worth a look when you plan to write this.
Force, I must tell you that an Android Service do not require root access instead some actions(i.e. Access, Read, Write system resources) requires Root Permissions. Every Android Service provided in Android SDK can be run without ROOT ACCESS.
You can make the actions to execute with root permissions with the help of shell commands.
I have created an abstract class to help you with that
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.IOException;
import java.util.ArrayList;
import android.util.Log;
public abstract class RootAccess {
private static final String TAG = "RootAccess";
protected abstract ArrayList<String> runCommandsWithRootAccess();
//Check for Root Access
public static boolean hasRootAccess() {
boolean rootBoolean = false;
Process suProcess;
try {
suProcess = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(suProcess.getOutputStream());
DataInputStream is = new DataInputStream(suProcess.getInputStream());
if (os != null && is != null) {
// Getting current user's UID to check for Root Access
os.writeBytes("id\n");
os.flush();
String outputSTR = is.readLine();
boolean exitSu = false;
if (outputSTR == null) {
rootBoolean = false;
exitSu = false;
Log.d(TAG, "Can't get Root Access or Root Access deneid by user");
} else if (outputSTR.contains("uid=0")) {
//If is contains uid=0, It means Root Access is granted
rootBoolean = true;
exitSu = true;
Log.d(TAG, "Root Access Granted");
} else {
rootBoolean = false;
exitSu = true;
Log.d(TAG, "Root Access Rejected: " + is.readLine());
}
if (exitSu) {
os.writeBytes("exit\n");
os.flush();
}
}
} catch (Exception e) {
rootBoolean = false;
Log.d(TAG, "Root access rejected [" + e.getClass().getName() + "] : " + e.getMessage());
}
return rootBoolean;
}
//Execute commands with ROOT Permission
public final boolean execute() {
boolean rootBoolean = false;
try {
ArrayList<String> commands = runCommandsWithRootAccess();
if ( commands != null && commands.size() > 0) {
Process suProcess = Runtime.getRuntime().exec("su");
DataOutputStream os = new DataOutputStream(suProcess.getOutputStream());
// Execute commands with ROOT Permission
for (String currentCommand : commands) {
os.writeBytes(currentCommand + "\n");
os.flush();
}
os.writeBytes("exit\n");
os.flush();
try {
int suProcessRetval = suProcess.waitFor();
if ( suProcessRetval != 255) {
// Root Access granted
rootBoolean = true;
} else {
// Root Access denied
rootBoolean = false;
}
} catch (Exception ex) {
Log.e(TAG, "Error executing Root Action", ex);
}
}
} catch (IOException ex) {
Log.w(TAG, "Can't get Root Access", ex);
} catch (SecurityException ex) {
Log.w(TAG, "Can't get Root Access", ex);
} catch (Exception ex) {
Log.w(TAG, "Error executing operation", ex);
}
return rootBoolean;
}
}
Extend your class with RootAccess or create an instance of RootAccess class and Override runCommandsWithRootAccess() method.
running something as root is not the right way of solving this.
instead, consider an accessibility service that can watch for new notifications:
AccessibilityEvent
It is not possible to run a Service (or any other application component for that matter) as root, if you are targeting unaltered, non-rooted devices. Allowing that would make all security mechanisms in Android pointless.
It is not possible to alter the permissions of an APK at runtime either. Permissions are always granted or rejected at APK install-time. Please refer to http://developer.android.com/guide/topics/security/security.html for some more info on the subject.
"What I need to know is how to register a Broadcastreceiver, that receives a specific broadcast "normal" receivers don't get, as the Broadcast itself requires a signature based permission I don't have."
You can't. Period. End of story. And thank ghod for that.
Yes, if you use the scary rooted device facilities to have some code run as root, you can in theory do whatever you want. In practice, it may be quite hard to get around this restriction, and the platform is often designed to be that way. You will at the very least need to mess around with the state maintained and/or stored by the package manager, and will likely need to cause the user to reboot the device to get changes you make as root to actually have an impact. And of course you are then messing with deeply internal implementation details of the platform, which means breaking all over the place across different versions of the platform and different builds from different manufacturers.
you can use
pm grant your.permission
as a shell command to grant additional permissions to your app.
I think that command was added quite recently, so if you target older versions you may have to directly alter the 'packages.xml'.
It is possible to execute an app/dex file as root with the app_process command, but I haven't figured out yet how to get a valid context (with this you can use the java.io.File api to access all files, but non static android methods like bindService etc. will fail because you are running without an app context).
Of course you can change the permissions of your applications. If the permissions will be changed, the user will just have to manually update the app, and the new permission will be displayed to the user. But I do not exactly know how changing your app permission will help you in solving this problem.
Another thing I can tell you, is that you can not run a Service or whatever as root, only on rooted devices, and it will not be an easy task to root the devices through your application, and also it won't be something that many user will want.
How are you currently accessing the SMS?
If you have a BroadcastReceiveryou could set the MAX_PRIORITY for your receiver and maybe it will intercept the messages before other applications. This can be done as follows:
<receiver android:name=".SmsReceiver" >
<intent-filter android:priority="100" >
<action android:name="android.provider.Telephony.SMS_RECEIVED" />
</intent-filter>
</receiver>
You could also use the SMS Provider, which is not public now but maybe if you query at a given interval this Provider you can check for new messages. You could also have a look at this thread : Android SMS Provider if you have not done this allready.
I'm new in Android. I have an Idea to enrich user's knowledge whilst installing a desired application.
the idea is developing an application that can analyze .apk file of the application to check if it's over-privileged or not. and inform the user if this application which he's trying to install is over-privileged or not.
but since there's already a mechanism from Android which asks user's consent to grant whatever permission the application requests, I'm not sure if my application can somehow intervene this mechanism, postpone it, pause it or it can not.
I'm not sure if my application can somehow intervene this mechanism, postpone it, pause it
None of these are possible, sorry. You are welcome to create your own custom firmware that has this feature, but you cannot create this capability via an SDK application, for obvious security reasons.
I am not far from where you are ~ the entire mechanization you seek is based on an xml file in the "root" of the installation - it is called AndroidManifest.xml = all permission based issues should begin original first efforts on that file:
The AndroidManifest.xml File
Every application must have an AndroidManifest.xml file (with precisely that name) in its root directory. The manifest presents essential information about the application to the Android system, information the system must have before it can run any of the application's code. Among other things, the manifest does the following: .....
the "app-store" web based distribution system is supposed to pick that up and not only make some decisions on what to present to the user but as well differentiate to some extent what to do in the matter but as I just got a Droid-X emulator available in my installation I can tell you for a fact that "versioning" is subject to oversimplification as we cannot rely on users being tech-geeks
I'm writing an application that must not run on rooted devices. I want to store some secure data and which is possible only on non-rooted devices as nobody can access files in /data/data/package-name.
Does anyone know:
1) Is it possible to prevent the installation of an application on rooted devices? I read something about the "copy-protection mechanism" of Android Market. This feature seems to be outdated and replaced by the licensing feature. However, licensing is only possible for paid application and mine is free...
2) Is it possible to check programmatically whether a device is rooted or not? If it would be possible to do so I could simply stop the application if the device is rooted.
Any help regarding this topic is appreciated!
Execute
Runtime.getRuntime().exec("su");
and check the result code.
In other words, if you can exec su, then you have root access. it doesn't matter if the user allows or denies it, you have your answer.
I think your approach is a bit flawed. First of all, the user can first install your application and data, then "root" the device (even if rooting wipes the data, one can make the backup first). Next, the general rule is that whatever is in user's hands is not yours anymore. The hacker will find a way to get to your data sooner or later.
If you care about secure data, don't put it to device. As Android is net-centric device (yes, I know, that's subjective, but it was initially developed and positioned as such), accessing the data online is not uncommon.
What I would say is to run su and then check the output. If the user allows your app to have root, then use root to uninstall your own application (one way might be to place a script into init.d and then force a reboot).
If the user DOES NOT allow your app to run as root, then:
They DENIED your app permissions.
They are not rooted.
Now, denying permissions (and rooted) means that they have some sort of SUPERUSER management app, and that's where this next part comes in.
I would then proceed to use PackageManager to retrieve a list of all packages and then check them against the handful SuperUser management apps available, namely the ones by Koush, ChainsDD, and Chainfire
The relevant package names are:
com.noshufou.android.su
eu.chainfire.supersu
com.koushikdutta.superuser
Use those methods which will help you check for root
public static boolean findBinary(String binaryName) {
boolean found = false;
if (!found) {
String[] places = { "/sbin/", "/system/bin/", "/system/xbin/",
"/data/local/xbin/", "/data/local/bin/",
"/system/sd/xbin/", "/system/bin/failsafe/", "/data/local/" };
for (String where : places) {
if (new File(where + binaryName).exists()) {
found = true;
break;
}
}
}
return found;
}
private static boolean isRooted() {
return findBinary("su");
}
Now try to check whether the device is rooted.
if (isRooted() == true){
//Do something to prevent run this app on the device
}
else{
//Do nothing and run app normally
}
For example you can force stop the app if the device is rooted
If you are trying to protect data for the user, it's their business to worry about other apps.
If you are trying to protect data from the user, what business do you have putting it on their device?
To answer your question, they are in control of the machine so expect them to be able to trap any call to an API checking 'Is this rooted?' and lie to you. Instead, encrypt the data on the client with a key known to the client, but make it non-obvious where and how you are doing it. Generally make things annoying for whoever is looking.
Enjoy the ensuing game of whack-a-mole. Every time someone cracks into it, you'll make a better fix, they'll make a better crack, and all along the way you will be raising the barrier for cracking it.
Don't fight against freedom - why should you turn away customers with free devices anyway? - instead, if you want a particular outcome, make it so Bother To Get Data > Value Of Getting Data. Then it won't happen. If you truly must have fool-proof security, keep the data server-side.
I believe that one of the 'drawbacks' of the traditional copy protection was that it did not allow the application to be installed on rooted devices, but it also has its own share of problems and will be deprecated soon.
As for client-side checks, you simply cannot rely on a programmatic approach to detect if you're running on a rooted device or not -- anything that is in client-side code can and will be hacked and removed. You'd be surprised at how easy it is to modify even Proguard-obfuscated code. At best, you force the hacker to spend a few hours or days to edit the code and recompile. This is security through obscurity, and not a viable protection mechanism.
1) no. how would you deny installation? why would a rooted device deny installation of something the user wants to install on the fs? being the whole point of rooting that you can make the device do basically whatever.
2) no. not for your purposes. you can check if you can gain root for your application through the usual methods. so you can make a check for a positive but you cannot prove programmatically that it is not rooted, from within your app.
also, what you are asking if you can make perfect copy protection drm system - you might also be missing the point that the user can alter your application, removing your root check. if you have a checksum/crc check of some kind, the user can fake the result of that as well.