Add permission to allow an APK to fake a signature.fmo-master

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>

4 files changed, 34 insertions, 2 deletions

diff --git a/core/res/AndroidManifest.xml b/core/res/AndroidManifest.xml
index 048214a1dc0f..3cb1121eb7df 100644
--- a/core/res/AndroidManifest.xml
+++ b/core/res/AndroidManifest.xml
@@ -1924,6 +1924,13 @@
         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 dbc4324ec92a..86822a42cdda 100644
--- a/core/res/res/values/config.xml
+++ b/core/res/res/values/config.xml
@@ -1358,6 +1358,8 @@
     <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 38137f8c95a4..bae9d34c31a3 100644
--- a/core/res/res/values/strings.xml
+++ b/core/res/res/values/strings.xml
@@ -664,6 +664,10 @@
     <!--  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. -->
     <string name="permdesc_statusBar">Allows the app to disable the status bar or add and remove system icons.</string>
diff --git a/services/core/java/com/android/server/pm/PackageManagerService.java b/services/core/java/com/android/server/pm/PackageManagerService.java
index 7a547f00e607..73a0420ce112 100644
--- a/services/core/java/com/android/server/pm/PackageManagerService.java
+++ b/services/core/java/com/android/server/pm/PackageManagerService.java
@@ -3098,8 +3098,27 @@ public class PackageManagerService extends IPackageManager.Stub {
                 ? Collections.<String>emptySet() : permissionsState.getPermissions(userId);
         final PackageUserState state = ps.readUserState(userId);
 
-        return PackageParser.generatePackageInfo(p, gids, flags,
-                ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId);
+        return mayFakeSignature(p, PackageParser.generatePackageInfo(p, gids, flags,
+                ps.firstInstallTime, ps.lastUpdateTime, permissions, state, userId),
+                permissions);;
+    }
+
+    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