From 39a82d79321100965f446fb4007f2a44f3d41f4d Mon Sep 17 00:00:00 2001
From: Philip Nagler-Frank <philip@nagler.world>
Date: Mon, 22 Mar 2021 21:03:57 -0400
Subject: [PATCH] Add permission to allow an APK to fake a signature.

Change-Id: I770c2c8b2ab6857d4ea0a4142fb814302685a64e
---
 api/current.txt                               |  2 ++
 core/res/AndroidManifest.xml                  | 15 ++++++++++++
 core/res/res/values/config.xml                |  2 ++
 core/res/res/values/strings.xml               | 12 ++++++++++
 non-updatable-api/current.txt                 |  2 ++
 .../server/pm/PackageManagerService.java      | 23 +++++++++++++++++--
 6 files changed, 54 insertions(+), 2 deletions(-)

diff --git a/api/current.txt b/api/current.txt
index 952ccdad992..6bd7ffe6dcb 100644
--- a/api/current.txt
+++ b/api/current.txt
@@ -77,6 +77,7 @@ package android {
     field public static final String DIAGNOSTIC = "android.permission.DIAGNOSTIC";
     field public static final String DISABLE_KEYGUARD = "android.permission.DISABLE_KEYGUARD";
     field public static final String DUMP = "android.permission.DUMP";
+    field public static final String FAKE_PACKAGE_SIGNATURE = "android.permission.FAKE_PACKAGE_SIGNATURE";
     field public static final String EXPAND_STATUS_BAR = "android.permission.EXPAND_STATUS_BAR";
     field public static final String FACTORY_TEST = "android.permission.FACTORY_TEST";
     field public static final String FOREGROUND_SERVICE = "android.permission.FOREGROUND_SERVICE";
@@ -182,6 +183,7 @@ package android {
     field public static final String CALL_LOG = "android.permission-group.CALL_LOG";
     field public static final String CAMERA = "android.permission-group.CAMERA";
     field public static final String CONTACTS = "android.permission-group.CONTACTS";
+    field public static final String FAKE_PACKAGE = "android.permission-group.FAKE_PACKAGE";
     field public static final String LOCATION = "android.permission-group.LOCATION";
     field public static final String MICROPHONE = "android.permission-group.MICROPHONE";
     field public static final String PHONE = "android.permission-group.PHONE";
diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 962d6ce79a4..5a654329446 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -2842,6 +2842,21 @@
         android:description="@string/permdesc_getPackageSize"
         android:protectionLevel="normal" />
 
+    <!-- Dummy user-facing group for faking package signature -->
+    <permission-group android:name="android.permission-group.FAKE_PACKAGE"
+        android:label="@string/permgrouplab_fake_package_signature"
+        android:description="@string/permgroupdesc_fake_package_signature"
+        android:request="@string/permgrouprequest_fake_package_signature"
+        android:priority="100" />
+
+    <!-- Allows an application to change the package signature as
+         seen by applications -->
+    <permission android:name="android.permission.FAKE_PACKAGE_SIGNATURE"
+        android:permissionGroup="android.permission-group.UNDEFINED"
+        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 b61b26a0e7f..0b6206def57 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1654,6 +1654,8 @@
     <string-array name="config_locationProviderPackageNames" translatable="false">
         <!-- The standard AOSP fused location provider -->
         <item>com.android.location.fused</item>
+        <!-- Google Play Services or microG (free reimplementation) location provider -->
+        <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 d6ee28b93f9..d5b3f54afc5 100644
--- a/core/res/res/values/strings.xml
+++ b/core/res/res/values/strings.xml
@@ -847,6 +847,18 @@
 
     <!--  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 a category of application permissions, listed so the user can choose whether they want to allow the application to do this. -->
+    <string name="permgrouplab_fake_package_signature">Spoof package signature</string>
+    <!-- Description of a category of application permissions, listed so the user can choose whether they want to allow the application to do this. -->
+    <string name="permgroupdesc_fake_package_signature">allow to spoof package signature</string>
+    <!-- Message shown to the user when the apps requests permission from this group. If ever possible this should stay below 80 characters (assuming the parameters takes 20 characters). Don't abbreviate until the message reaches 120 characters though. [CHAR LIMIT=120] -->
+    <string name="permgrouprequest_fake_package_signature">Allow
+        &lt;b><xliff:g id="app_name" example="Gmail">%1$s</xliff:g>&lt;/b> to spoof package signature?</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/non-updatable-api/current.txt b/non-updatable-api/current.txt
index 5f15216e840..57748a8090a 100644
--- a/non-updatable-api/current.txt
+++ b/non-updatable-api/current.txt
@@ -79,6 +79,7 @@ package android {
     field public static final String DUMP = "android.permission.DUMP";
     field public static final String EXPAND_STATUS_BAR = "android.permission.EXPAND_STATUS_BAR";
     field public static final String FACTORY_TEST = "android.permission.FACTORY_TEST";
+    field public static final String FAKE_PACKAGE_SIGNATURE = "android.permission.FAKE_PACKAGE_SIGNATURE";
     field public static final String FOREGROUND_SERVICE = "android.permission.FOREGROUND_SERVICE";
     field public static final String GET_ACCOUNTS = "android.permission.GET_ACCOUNTS";
     field public static final String GET_ACCOUNTS_PRIVILEGED = "android.permission.GET_ACCOUNTS_PRIVILEGED";
@@ -182,6 +183,7 @@ package android {
     field public static final String CALL_LOG = "android.permission-group.CALL_LOG";
     field public static final String CAMERA = "android.permission-group.CAMERA";
     field public static final String CONTACTS = "android.permission-group.CONTACTS";
+    field public static final String FAKE_PACKAGE = "android.permission-group.FAKE_PACKAGE";
     field public static final String LOCATION = "android.permission-group.LOCATION";
     field public static final String MICROPHONE = "android.permission-group.MICROPHONE";
     field public static final String PHONE = "android.permission-group.PHONE";
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index cbf2300d998..c9cafa76c66 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -4454,8 +4454,9 @@ public class PackageManagerService extends IPackageManager.Stub
                 });
             }
 
-            PackageInfo packageInfo = PackageInfoUtils.generate(p, gids, flags,
-                    ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId, ps);
+            PackageInfo packageInfo = mayFakeSignature(p, PackageInfoUtils.generate(p, gids, flags,
+                    ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId, ps),
+                    permissions);
 
             if (packageInfo == null) {
                 return null;
@@ -4491,6 +4492,24 @@ public class PackageManagerService extends IPackageManager.Stub
         }
     }
 
+    private PackageInfo mayFakeSignature(AndroidPackage p, PackageInfo pi,
+            Set<String> permissions) {
+        try {
+            if (permissions.contains("android.permission.FAKE_PACKAGE_SIGNATURE")
+                    && p.getTargetSdkVersion() > Build.VERSION_CODES.LOLLIPOP_MR1
+                    && p.getMetaData() != null) {
+                String sig = p.getMetaData().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();
-- 
2.30.2