[DO NOT MERGE] Check caller's uid in backupAgentCreated callback

AM.backupAgentCreated() should enforce that caller belongs the package called in the API.

Bug: 289549315
Test: atest android.security.cts.ActivityManagerTest#testActivityManager_backupAgentCreated_rejectIfCallerUidNotEqualsPackageUid
Change-Id: I9f3ae5ec0b8f00e020d471cc0eddf8bd8bdbb82d

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

@@ -2982,6 +2982,22 @@ public class ActivityManagerService extends IActivityManager.Stub
         }
     }
 
+    /**
+     * Enforces that the uid of the caller matches the uid of the package.
+     *
+     * @param packageName the name of the package to match uid against.
+     * @param callingUid the uid of the caller.
+     * @throws SecurityException if the calling uid doesn't match uid of the package.
+     */
+    private void enforceCallingPackage(String packageName, int callingUid) {
+        final int userId = UserHandle.getUserId(callingUid);
+        final int packageUid = getPackageManagerInternal().getPackageUid(packageName,
+                /*flags=*/ 0, userId);
+        if (packageUid != callingUid) {
+            throw new SecurityException(packageName + " does not belong to uid " + callingUid);
+        }
+    }
+
     @Override
     public void setPackageScreenCompatMode(String packageName, int mode) {
         mActivityTaskManager.setPackageScreenCompatMode(packageName, mode);
@@ -12951,13 +12967,16 @@ public class ActivityManagerService extends IActivityManager.Stub
     // A backup agent has just come up
     @Override
     public void backupAgentCreated(String agentPackageName, IBinder agent, int userId) {
+        final int callingUid = Binder.getCallingUid();
+        enforceCallingPackage(agentPackageName, callingUid);
+
         // Resolve the target user id and enforce permissions.
-        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), Binder.getCallingUid(),
+        userId = mUserController.handleIncomingUser(Binder.getCallingPid(), callingUid,
                 userId, /* allowAll */ false, ALLOW_FULL_ONLY, "backupAgentCreated", null);
         if (DEBUG_BACKUP) {
             Slog.v(TAG_BACKUP, "backupAgentCreated: " + agentPackageName + " = " + agent
                     + " callingUserId = " + UserHandle.getCallingUserId() + " userId = " + userId
-                    + " callingUid = " + Binder.getCallingUid() + " uid = " + Process.myUid());
+                    + " callingUid = " + callingUid + " uid = " + Process.myUid());
         }
 
         synchronized(this) {