I am just playing with a certain scenario of
inter-application-communication, and trying to circumvent the problem that
in
Android the main activity of an application can't be secured by a custom
permisssion (as in that case it can't be launched at all).
I tried to use two activities instead: 1) The main activity which is not
protected. 2) When a button is clicked, the main activity
sends an explicit Intent to start the second activity. That one performs
some sensitive work and is protected by a custom permission
("toy.test.permission.ACTIVATE_SECOND_ACTIVITY").
The idea being that if the main activity is either started by the user from
the launcher or by a foreign maliscious application using
an explicit intent, we can warn the user before he pushes the button to
proceed.
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_activity);
final Button start = (Button) findViewById(R.id.start);
start.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent activateIntent = new Intent(MainActivity.this,
SecondActivity.class);
startActivity(activateIntent);
finish();
}
}); ....
The Manifest.xml file looks like that:
<application
android:icon="@drawable/icon"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name=".MainActivity"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name=".SecondActivity"
android:label="@string/second_activity_name"
android:theme="@style/AppTheme"
android:permission="toy.test.permission.ACTIVATE_SECOND_ACTIVITY" >
<intent-filter>
<action android:name="toy.test.action.ACTIVATE_SECOND_ACTIVITY"
/>
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>
</activity>
</application>
In addition, the SecondActivity can be started from a friend application by
either an implicit or an explicit Intent with
actionString="toy.test.action.ACTIVATE_SECOND_ACTIVITY"
using the permission "toy.test.permission.ACTIVATE_SECOND_ACTIVITY".
The friend application's declaration of the permission in its Manifest is
like that:
<permission
android:name="toy.test.permission.ACTIVATE_SECOND_ACTIVITY"
android:description="@string/activate_activity_permission_description"
android:label="@string/activate_activity_permission_label"
android:permissionGroup="android.permission-group.PERSONAL_INFO"
android:protectionLevel="signature" />
Now the difference between android 2.3.3 and android 4.2:
==========================================
On an android 4.2 device or emulator, the SecondActivity can be started
from the MainActivity by clicking the Start button without any problems,
although
the application does not ask explicitly for the permission
"toy.test.permission.ACTIVATE_SECOND_ACTIVITY".
However, on an android 2.3.3 emulator, the SecondActivity can't be started
because of SecurityException:
FATAL EXCEPTION: main
java.lang.SecurityException: Permission Denial: starting Intent {
cmp=toy.test/.SecondActivity }
from ProcessRecord{406827d0 405:toy.test/10034} (pid=405, uid=10034)
requires
toy.test.permission.ACTIVATE_SECOND_ACTIVITY
Question:
=========
I am confused: Was the permission enforcement changed between the two
Android versions? And is it on purpose that android 4.2 allows such
situations,
i.e. activation of the SecondActivity without permission? (Of course, that
would be useful.)
Let me specify my question: If android 4.2 now newly allows on purpose (as
opposed to android 2.3.3) to start the SecondActivity from the
MainActivity,
would this scenario allow to secure the SecondActivity against maliscious
attacks? I.e. the SecondActivity could only be started either directly from
the MainActivity or from a friend application (implicit or explicit Intent)
which asked for the signature permission, shown below. Is this correct or
do
I overlook something here?
Thanks a lot for any answers,
puffin137
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