From 4f35431eb542182d0359dcd62c4bb77f05794261 Mon Sep 17 00:00:00 2001
From: Chirayu Desai <chirayudesai1@gmail.com>
Date: Wed, 30 Jan 2019 18:18:10 +0530
Subject: [PATCH] Allow selective signature spoofing for microG

* Permission FAKE_PACKAGE_SIGNATURE required
* Only microG and FakeStore can spoof signature
* Only the official Google signature can be spoofed, the
  "fake-signature" field is unused.

Change-Id: I34745f9bf585221d17c28269f74b3e0d0c834abf
---
 core/res/AndroidManifest.xml                  |  7 +++++
 core/res/res/values/config.xml                |  2 ++
 core/res/res/values/strings.xml               |  4 +++
 .../server/pm/PackageManagerService.java      | 28 +++++++++++++++++--
 4 files changed, 39 insertions(+), 2 deletions(-)

diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 7bcd7a048db..10853678f39 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2655,6 +2655,13 @@
         android:description="@string/permdesc_getPackageSize"
         android:protectionLevel="normal" />
 
+    <!-- @hide Allows an application to change the package signature as
+	 seen by applications -->
+    <permission android:name="android.permission.FAKE_PACKAGE_SIGNATURE"
+        android:protectionLevel="dangerous"
+        android:label="@string/permlab_fakePackageSignature"
+        android:description="@string/permdesc_fakePackageSignature" />
+
     <!-- @deprecated No longer useful, see
          {@link android.content.pm.PackageManager#addPackageToPreferred}
          for details. -->
diff --git a/core/res/res/values/config.xml b/core/res/res/values/config.xml
index a84d23b624b..89754ba11ef 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1875,6 +1875,8 @@
     <string-array name="config_locationProviderPackageNames" translatable="false">
         <!-- The standard AOSP fused location provider -->
         <item>com.android.location.fused</item>
+        <!-- The (faked) microg fused location provider (a free reimplementation) -->
+        <item>com.google.android.gms</item>
     </string-array>
 
     <!-- This string array can be overriden to enable test location providers initially. -->
diff --git a/core/res/res/values/strings.xml b/core/res/res/values/strings.xml
index 7e975f68ec3..69932c6ac16 100644
--- a/core/res/res/values/strings.xml
+++ b/core/res/res/values/strings.xml
@@ -830,6 +830,10 @@
 
     <!--  Permissions -->
 
+    <!-- Title of an application permission, listed so the user can choose whether they want to allow the application to do this. -->
+    <string name="permlab_fakePackageSignature">Spoof package signature</string>
+    <!-- Description of an application permission, listed so the user can choose whether they want to allow the application to do this. -->
+    <string name="permdesc_fakePackageSignature">Allows the app to pretend to be a different app. Malicious applications might be able to use this to access private application data. Legitimate uses include an emulator pretending to be what it emulates. Grant this permission with caution only!</string>
     <!-- Title of an application permission, listed so the user can choose whether they want to allow the application to do this. -->
     <string name="permlab_statusBar">disable or modify status bar</string>
     <!-- Description of an application permission, listed so the user can choose whether they want to allow the application to do this. -->
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index 9d287a53af3..205217b3009 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -635,6 +635,11 @@ public class PackageManagerService extends IPackageManager.Stub
     private static final String[] INSTANT_APP_BROADCAST_PERMISSION =
             new String[] { android.Manifest.permission.ACCESS_INSTANT_APPS };
 
+    /**
+     * The Google signature faked by microG.
+     */
+    private static final String MICROG_FAKE_SIGNATURE = "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";
+
     final ServiceThread mHandlerThread;
 
     final PackageHandler mHandler;
@@ -4197,8 +4202,9 @@ public class PackageManagerService extends IPackageManager.Stub
                 });
             }
 
-            PackageInfo packageInfo = PackageParser.generatePackageInfo(p, gids, flags,
-                    ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId);
+            PackageInfo packageInfo = mayFakeSignature(p, PackageParser.generatePackageInfo(p, gids, flags,
+                ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId),
+                permissions);
 
             if (packageInfo == null) {
                 return null;
@@ -4234,6 +4240,24 @@ public class PackageManagerService extends IPackageManager.Stub
         }
     }
 
+    private PackageInfo mayFakeSignature(PackageParser.Package p, PackageInfo pi,
+            Set<String> permissions) {
+        try {
+            if (permissions.contains("android.permission.FAKE_PACKAGE_SIGNATURE")
+                    && p.applicationInfo.targetSdkVersion > Build.VERSION_CODES.LOLLIPOP_MR1
+                    && p.mAppMetaData != null) {
+                // Only allow microG and FakeStore
+                if (p.packageName.equals("com.google.android.gms") || p.packageName.equals("com.android.vending")) {
+                    pi.signatures = new Signature[] {new Signature(MICROG_FAKE_SIGNATURE)};
+                }
+            }
+        } catch (Throwable t) {
+            // We should never die because of any failures, this is system code!
+            Log.w("PackageManagerService.FAKE_PACKAGE_SIGNATURE", t);
+	}
+        return pi;
+    }
+
     @Override
     public void checkPackageStartable(String packageName, int userId) {
         final int callingUid = Binder.getCallingUid();
-- 
2.25.1