DO NOT MERGE: Don't trust callers to supply app info to bindBackupAgent()

Get the canonical identity and metadata about the package from the
Package Manager at time of usage rather than rely on the caller to
have gotten things right, even when the caller has the system uid.

Bug 28795098

Change-Id: I62710b15bb601fdfedd68e32349168c10725eb45
(cherry picked from commit d85a4ed)

Author: Christopher Tate

core/java/android/app/ActivityManagerNative.java

@@ -1434,9 +1434,10 @@ public boolean onTransact(int code, Parcel data, Parcel reply, int flags)
 
         case START_BACKUP_AGENT_TRANSACTION: {
             data.enforceInterface(IActivityManager.descriptor);
-            ApplicationInfo info = ApplicationInfo.CREATOR.createFromParcel(data);
+            String packageName = data.readString();
             int backupRestoreMode = data.readInt();
-            boolean success = bindBackupAgent(info, backupRestoreMode);
+            int userId = data.readInt();
+            boolean success = bindBackupAgent(packageName, backupRestoreMode, userId);
             reply.writeNoException();
             reply.writeInt(success ? 1 : 0);
             return true;
@@ -3125,13 +3126,14 @@ public IBinder peekService(Intent service, String resolvedType) throws RemoteExc
         return binder;
     }
 
-    public boolean bindBackupAgent(ApplicationInfo app, int backupRestoreMode)
+    public boolean bindBackupAgent(String packageName, int backupRestoreMode, int userId)
             throws RemoteException {
         Parcel data = Parcel.obtain();
         Parcel reply = Parcel.obtain();
         data.writeInterfaceToken(IActivityManager.descriptor);
-        app.writeToParcel(data, 0);
+        data.writeString(packageName);
         data.writeInt(backupRestoreMode);
+        data.writeInt(userId);
         mRemote.transact(START_BACKUP_AGENT_TRANSACTION, data, reply, 0);
         reply.readException();
         boolean success = reply.readInt() != 0;

core/java/android/app/IActivityManager.java

@@ -163,7 +163,7 @@ public void serviceDoneExecuting(IBinder token, int type, int startId,
             int res) throws RemoteException;
     public IBinder peekService(Intent service, String resolvedType) throws RemoteException;
 
-    public boolean bindBackupAgent(ApplicationInfo appInfo, int backupRestoreMode)
+    public boolean bindBackupAgent(String packageName, int backupRestoreMode, int userId)
             throws RemoteException;
     public void clearPendingBackup() throws RemoteException;
     public void backupAgentCreated(String packageName, IBinder agent) throws RemoteException;

services/java/com/android/server/BackupManagerService.java

@@ -1780,7 +1780,8 @@ IBackupAgent bindToAgentSynchronous(ApplicationInfo app, int mode) {
             mConnecting = true;
             mConnectedAgent = null;
             try {
-                if (mActivityManager.bindBackupAgent(app, mode)) {
+                if (mActivityManager.bindBackupAgent(app.packageName, mode,
+                        UserHandle.USER_OWNER)) {
                     Slog.d(TAG, "awaiting agent for " + app);
 
                     // success; wait for the agent to arrive

services/java/com/android/server/am/ActivityManagerService.java

@@ -12823,10 +12823,22 @@ public void serviceDoneExecuting(IBinder token, int type, int startId, int res)
     // Cause the target app to be launched if necessary and its backup agent
     // instantiated.  The backup agent will invoke backupAgentCreated() on the
     // activity manager to announce its creation.
-    public boolean bindBackupAgent(ApplicationInfo app, int backupMode) {
-        if (DEBUG_BACKUP) Slog.v(TAG, "bindBackupAgent: app=" + app + " mode=" + backupMode);
+    public boolean bindBackupAgent(String packageName, int backupMode, int userId) {
+        if (DEBUG_BACKUP) Slog.v(TAG, "bindBackupAgent: app=" + packageName + " mode=" + backupMode);
         enforceCallingPermission("android.permission.CONFIRM_FULL_BACKUP", "bindBackupAgent");
 
+        IPackageManager pm = AppGlobals.getPackageManager();
+        ApplicationInfo app = null;
+        try {
+            app = pm.getApplicationInfo(packageName, 0, userId);
+        } catch (RemoteException e) {
+            // can't happen; package manager is process-local
+        }
+        if (app == null) {
+            Slog.w(TAG, "Unable to bind backup agent for " + packageName);
+            return false;
+        }
+
         synchronized(this) {
             // !!! TODO: currently no check here that we're already bound
             BatteryStatsImpl.Uid.Pkg.Serv ss = null;