Add NetworkStackPermissionStub definitions

The NetworkStackPermissionStub package is used to enforce that
permissions used by the NetworkStack are only used in packages
sharing signature with NetworkStackPermissionStub.

Permissions defined in this package are intended to be used only by the
NetworkStack: both NetworkStack and the stub APK will be signed with
a dedicated certificate to ensure that, with permissions being signature
permissions.

This APK *must* be installed, even if the NetworkStack app is not
installed, because otherwise, any application will be able to define
this permission and the system will give that application full access
to the network stack.

Test: flashed, booted
Bug: 112869080
Change-Id: Ia13a9e6a703cb7b4403697a7f7bfff0f6f3b813e

api/system-current.txt

@@ -3186,6 +3186,10 @@ package android.net {
     field public static final String EXTRA_PACKAGE_NAME = "packageName";
   }
 
+  public class NetworkStack {
+    field public static final String PERMISSION_MAINLINE_NETWORK_STACK = "android.permission.MAINLINE_NETWORK_STACK";
+  }
+
   public final class RouteInfo implements android.os.Parcelable {
     ctor public RouteInfo(android.net.IpPrefix, java.net.InetAddress, String, int);
     method public int getType();

api/test-current.txt

@@ -669,6 +669,10 @@ package android.net {
     method public boolean satisfiedByNetworkCapabilities(android.net.NetworkCapabilities);
   }
 
+  public class NetworkStack {
+    field public static final String PERMISSION_MAINLINE_NETWORK_STACK = "android.permission.MAINLINE_NETWORK_STACK";
+  }
+
   public final class RouteInfo implements android.os.Parcelable {
     ctor public RouteInfo(android.net.IpPrefix, java.net.InetAddress, String, int);
     method public int getType();

core/java/android/net/NetworkStack.java

@@ -20,7 +20,9 @@ import static android.os.IServiceManager.DUMP_FLAG_PRIORITY_NORMAL;
 
 import android.annotation.NonNull;
 import android.annotation.Nullable;
+import android.annotation.SystemApi;
 import android.annotation.SystemService;
+import android.annotation.TestApi;
 import android.content.ComponentName;
 import android.content.Context;
 import android.content.Intent;
@@ -46,9 +48,22 @@ import java.util.ArrayList;
  * @hide
  */
 @SystemService(Context.NETWORK_STACK_SERVICE)
+@SystemApi
+@TestApi
 public class NetworkStack {
     private static final String TAG = NetworkStack.class.getSimpleName();
 
+    /**
+     * Permission granted only to the NetworkStack APK, defined in NetworkStackStub with signature
+     * protection level.
+     * @hide
+     */
+    @SystemApi
+    @TestApi
+    public static final String PERMISSION_MAINLINE_NETWORK_STACK =
+            "android.permission.MAINLINE_NETWORK_STACK";
+
+    /** @hide */
     public static final String NETWORKSTACK_PACKAGE_NAME = "com.android.mainline.networkstack";
 
     private static final int NETWORKSTACK_TIMEOUT_MS = 10_000;
@@ -66,12 +81,14 @@ public class NetworkStack {
         void onNetworkStackConnected(INetworkStackConnector connector);
     }
 
+    /** @hide */
     public NetworkStack() { }
 
     /**
      * Create a DHCP server according to the specified parameters.
      *
      * <p>The server will be returned asynchronously through the provided callbacks.
+     * @hide
      */
     public void makeDhcpServer(final String ifName, final DhcpServingParamsParcel params,
             final IDhcpServerCallbacks cb) {
@@ -88,6 +105,7 @@ public class NetworkStack {
      * Create an IpClient on the specified interface.
      *
      * <p>The IpClient will be returned asynchronously through the provided callbacks.
+     * @hide
      */
     public void makeIpClient(String ifName, IIpClientCallbacks cb) {
         requestConnector(connector -> {
@@ -103,6 +121,7 @@ public class NetworkStack {
      * Create a NetworkMonitor.
      *
      * <p>The INetworkMonitor will be returned asynchronously through the provided callbacks.
+     * @hide
      */
     public void makeNetworkMonitor(
             NetworkParcelable network, String name, INetworkMonitorCallbacks cb) {
@@ -153,6 +172,7 @@ public class NetworkStack {
      * the system server on devices that do not support the network stack module. The network stack
      * connector will then be delivered asynchronously to clients that requested it before it was
      * started.
+     * @hide
      */
     public void start(Context context) {
         mNetworkStackStartRequested = true;

packages/NetworkStack/Android.bp

@@ -41,4 +41,5 @@ android_app {
         "NetworkStackLib"
     ],
     manifest: "AndroidManifest.xml",
+    required: ["NetworkStackPermissionStub"],
 }

packages/NetworkStack/AndroidManifest.xml

@@ -25,6 +25,8 @@
     <uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
     <uses-permission android:name="android.permission.CONNECTIVITY_INTERNAL" />
     <uses-permission android:name="android.permission.NETWORK_SETTINGS" />
+    <!-- Signature permission defined in NetworkStackStub -->
+    <uses-permission android:name="android.permission.MAINLINE_NETWORK_STACK" />
     <!-- Launch captive portal app as specific user -->
     <uses-permission android:name="android.permission.INTERACT_ACROSS_USERS_FULL" />
     <uses-permission android:name="android.permission.NETWORK_STACK" />

packages/NetworkStackPermissionStub/Android.bp

@@ -0,0 +1,27 @@
+//
+// Copyright (C) 2019 The Android Open Source Project
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+
+// Stub APK to define permissions for NetworkStack
+android_app {
+    name: "NetworkStackPermissionStub",
+    // TODO: mark app as hasCode=false in manifest once soong stops complaining about apps without
+    // a classes.dex.
+    srcs: ["src/**/*.java"],
+    platform_apis: true,
+    certificate: "platform",
+    privileged: true,
+    manifest: "AndroidManifest.xml",
+}

packages/NetworkStackPermissionStub/AndroidManifest.xml

@@ -0,0 +1,36 @@
+<?xml version="1.0" encoding="utf-8"?>
+<!--
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+-->
+<manifest xmlns:android="http://schemas.android.com/apk/res/android"
+    package="com.android.mainline.networkstack.permissionstub">
+    <!--
+    This package only exists to define the below permissions, and enforce that they are only
+    granted to apps sharing the same signature.
+    Permissions defined here are intended to be used only by the NetworkStack: both
+    NetworkStack and this stub APK are to be signed with a dedicated certificate to ensure
+    that, with the below permissions being signature permissions.
+
+    This APK *must* be installed, even if the NetworkStack app is not installed, because otherwise,
+    any application will be able to define this permission and the system will give that application
+    full access to the network stack.
+     -->
+    <permission android:name="android.permission.MAINLINE_NETWORK_STACK"
+                android:protectionLevel="signature"/>
+
+    <application android:name="com.android.server.NetworkStackPermissionStub"/>
+</manifest>

packages/NetworkStackPermissionStub/src/com/android/server/NetworkStackPermissionStub.java

@@ -0,0 +1,26 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.server;
+
+import android.app.Application;
+
+/**
+ * Empty application for NetworkStackStub that only exists because soong builds complain if APKs
+ * have no source file.
+ */
+public class NetworkStackPermissionStub extends Application {
+}