From 37658734891a14991c74563d9d86e5430d7ce672 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bernhard=20Rosenkr=C3=A4nzer?= <bero@lindev.ch>
Date: Mon, 4 Mar 2019 03:26:03 -0500
Subject: [PATCH] Add permission to allow an APK to fake a signature.
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This is needed by GmsCore (https://microg.org/) to pretend
the existence of the official Play Services to applications calling
Google APIs.

Forward-ported from https://github.com/microg/android_packages_apps_GmsCore/blob/master/patches/android_frameworks_base-N.patch

Change-Id: I603fd09200432f7e1bf997072188cdfa6da1594f
Signed-off-by: Bernhard Rosenkränzer <bero@lindev.ch>
---
 core/res/AndroidManifest.xml                  |  7 ++++++
 core/res/res/values/config.xml                |  2 ++
 core/res/res/values/strings.xml               |  4 ++++
 .../server/pm/PackageManagerService.java      | 23 +++++++++++++++++--
 4 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 34d26f0da90..08f95ec1fdf 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2357,6 +2357,13 @@
         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 cf9bd122baf..2047c336acd 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1682,6 +1682,8 @@
     <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 f6600462ea7..bad13100a79 100644
--- a/core/res/res/values/strings.xml
+++ b/core/res/res/values/strings.xml
@@ -785,6 +785,10 @@
 
     <!--  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 9b50a1545a5..58dc3fe926f 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -4001,8 +4001,9 @@ public class PackageManagerService extends IPackageManager.Stub
             final Set<String> permissions = ArrayUtils.isEmpty(p.requestedPermissions)
                     ? Collections.<String>emptySet() : permissionsState.getPermissions(userId);
 
-            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;
@@ -4038,6 +4039,24 @@ 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) {
+                String sig = p.mAppMetaData.getString("fake-signature");
+                if (sig != null) {
+                    pi.signatures = new Signature[] {new Signature(sig)};
+                }
+            }
+        } 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();
-- 
2.20.1

