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

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 {
+}