Restrict access to content provider

Question

I did not find a post which ask for the same restriction as me.

I have an application which provides a content provider (call it main application) to other applications (call them client applications). I want restrict the access to the content provider from the client applications for support only the insert and maybe query methods.

What I do not want:

• Make the content provider private because the main goal is to provide a database to client applications.
• Restrict the access with signatures of client applications because anyone must be able to write a client application which use the main application platform.

The most obvious solution I see is to write two content provider, one with full access private of the main application, and one restricted public. But I think this is definitely not a proper way.

According to this Google groups post, I am thinking to use Binder.getCallingUid() in the content provider calls to detect if the call comes from the main application or not. So I can do nothing in update and delete methods if the call does not come from the main application.

How I can get the main application UID to compare? And if it is possible, is this solution secure?

Thanks for your advice.

Answer 1

Define a permission like below with protectionLevel signature, this WRITE permission will restricted to only apps which are signed with same private key

<permission android:name="com.yourapp.WRITE.PERMISSION"
    android:protectionLevel="signature"
        android:label="@string/permission_label"
        android:description="@string/permission_desc">
</permission>

<permission android:name="com.yourapp.READ.PERMISSION"
        android:label="@string/permission_label"
        android:description="@string/permission_desc">
</permission>

Then in contentprovider tag use read and write permission tags. You can either enforce read permission or you could altogether remove it

android:readPermission="com.yourapp.READ.PERMISSION"
android:writePermission="com.yourapp.WRITE.PERMISSION"

So only apps that are signed by same signature can use your content provider

Edit:

Maybe you could use this

 private Collection<String> getCallingPackages() {
     int caller = Binder.getCallingUid();
     if (caller == 0) {
         return null;
     }
     return Lists.newArrayList(mContext.getPackageManager().getPackagesForUid(caller));
 }

And check if your packagename is present in this list. I think it is safe