Android Security

1. 1
Android Security - Permission

2. 2
Agenda
• What is permission
• System prebuilt vs APK Custom
• Request a permission
• Grant permission
• Enforce Permission
• Runtime permission

3. 3
What is Permission
• Applications (UIDs) are assigned permissions
• Permissions are needed to control access to
System resources (logs, battery, etc.)
Sensitive data (SMS, contacts, e-mails, etc.)
System interfaces (Internet, send SMS, etc.)
• Application (developers) can also
define own permissions to
protect application interfaces
• A string

4. 4
Permission Group
Divide permissions into some groups based on
functionality.
In M, Permission is granted by group.

5. 5
Permission Level
• Normal
Lower-risk permission, auto grant in installation
• Dangerous
Higher-risk permission, Need user grant.(Runtime grant/revoke
in M)
• Signature
Auto grant in installation if caller/callee are signed by same
certification
• SignatureOrSystem
Auto grant in installation if caller/callee are signed by same
certification or caller is in system image.

6. 6
System Prebuilt
In frameworks/base/core/res/AndroidManifest.xml
<permission android:name="android.permission.READ_CONTACTS"
android:permissionGroup="android.permission-group.CONTACTS"
android:label="@string/permlab_readContacts"
android:description="@string/permdesc_readContacts"
android:protectionLevel="dangerous" />

7. 7
APK Custom
In AndroidManifest.xml of APK
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.example.android.myapp" >
<permission
android:name="com.example.app.DO_X"
android:label="@string/do_x_label"
android:description="@string/do_x_desc"
android:permissionGroup="android.permission-group.PERSONAL_INFO"
android:protectionLevel="dangerous" />
…
</manifest>

8. 8
Permission Conflict
Multiple applications may attempt to define the
same permission name
• "first definition wins" principle.
• Android 4.4.3+ gives precedence to system
applications
• Android 5.0+ blocks installation completely for
applications attempting to define an existing
permission if they are signed with a different key
than the first definer

9. 9
Request Permission
Declare in AndroidMainifest.xml
<manifest package="com.XXX">
<uses-permission android:name="android.permission.XXX" />
…
</manifest>

10. 10
Grant Permission
Grant the permission when installation before M.

11. 11
Grant Permission
• Android cannot grant permissions that don’t
exist yet
If an application requires a permission which is not existing in system,
the system will not grant the permission to the requesting application.
• An application who defines <permission> is
uninstalled, the permission records are
removed from the system’s known permissions
list.
Any applications currently holding that permission will still have the
permission granted to them until they are updated/reinstalled.

12. 12
Grant Permission (2)
Assign permission in prebuilt etc/permission/platform.xml
<assign-permission name="android.permission.MODIFY_AUDIO_SETTINGS"
uid="media" />
 Assign higher-level permissions to system processes
running under a specific UID that do not have a
corresponding package.
 Allows specific core system users to perform the given
operations with the higher-level framework

13. 13
Enforce Permission
• Kernel
• Java components
• Native daemons

14. 14
Enforce Permission - Kernel
Access to files/device nodes/and local sockets is
regulated by Kernel.
Permission <map> Supplementary GIDs
<permission name="android.permission.ACCESS_FM_RADIO" >
<group gid="media" />
</permission>
JNI
APK
Device Node
Security check
APK has a special permission
which is mapped to GroupB in
platform.xml
Group B
UserID :arbitrary

15. 15
Java Components - Static
Managed by ActivityManagerService
Components who
uses permission
Components who declares
permission
Check by AMS

16. 16
Java Components - Dynamic
Programmatically check
if (mContext.checkCallingOrSelfPermission(android.Manifest.permission.XX)
!= PackageManager.PERMISSION_GRANTED) {
throw new SecurityException("Requires XXX permission");
}

17. 17
Native daemons
Dynamic Programmatically check

18. 18
Runtime Permission
• Support in M
• Dangerous permissions can
be granted/revoked in runtime.
• Other permission will be
granted in installation automatically.
• Only has to grant permission
once per app for each permission group.
• No difference for permission enforce

19. 19
Runtime Permission - Revoke
Before M: Not allowed
From M: Revocable from Settings.

20. 20
Runtime Permission - Caller
• Always Check for Permissions
• Handle Lack of Permissions Gracefully
if (checkSelfPermission(Manifest.permission.READ_CONTACTS)
!= PackageManager.PERMISSION_GRANTED) {
if (shouldShowRequestPermissionRationale(
Manifest.permission.READ_CONTACTS)) {
}
requestPermissions(new
String[]{Manifest.permission.READ_CONTACTS},
MY_PERMISSIONS_REQUEST_READ_CONTACTS);
return;
}