From 8e9d78ff91bef9a80ba210d1b3bce0f7101b391d Mon Sep 17 00:00:00 2001
From: Rubin Xu <rubinxu@google.com>
Date: Fri, 2 Jul 2021 14:32:03 +0100
Subject: [PATCH] Delay gargabe collection during onDestroy()

Allow the activity object to become unreachable before
iniating a gargabe collection to sanitize memory.

Bug: 189315376
Test: add device lock, confirm device lock in Settings,
      then a memory dump and search for password shards.
Change-Id: I807d74628e1355814807855ad309d86ca1fb38a1
---
 .../ConfirmDeviceCredentialBaseActivity.java      | 15 ++++++++++-----
 .../settings/password/ConfirmLockPassword.java    | 15 ++++++++++-----
 2 files changed, 20 insertions(+), 10 deletions(-)

diff --git a/src/com/android/settings/password/ConfirmDeviceCredentialBaseActivity.java b/src/com/android/settings/password/ConfirmDeviceCredentialBaseActivity.java
index 40297551152..de3ee517779 100644
--- a/src/com/android/settings/password/ConfirmDeviceCredentialBaseActivity.java
+++ b/src/com/android/settings/password/ConfirmDeviceCredentialBaseActivity.java
@@ -18,6 +18,8 @@ package com.android.settings.password;
 
 import android.app.KeyguardManager;
 import android.os.Bundle;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.UserManager;
 import android.util.Log;
 import android.view.MenuItem;
@@ -163,11 +165,14 @@ public abstract class ConfirmDeviceCredentialBaseActivity extends SettingsActivi
     @Override
     public void onDestroy() {
         super.onDestroy();
-        // Force a garbage collection immediately to remove remnant of user password shards
-        // from memory.
-        System.gc();
-        System.runFinalization();
-        System.gc();
+        // Force a garbage collection to remove remnant of user password shards from memory.
+        // Execute this with a slight delay to allow the activity lifecycle to complete and
+        // the instance to become gc-able.
+        new Handler(Looper.myLooper()).postDelayed(() -> {
+            System.gc();
+            System.runFinalization();
+            System.gc();
+        }, 5000);
     }
 
     @Override
diff --git a/src/com/android/settings/password/ConfirmLockPassword.java b/src/com/android/settings/password/ConfirmLockPassword.java
index 0278941e797..de32f139594 100644
--- a/src/com/android/settings/password/ConfirmLockPassword.java
+++ b/src/com/android/settings/password/ConfirmLockPassword.java
@@ -25,6 +25,8 @@ import android.graphics.Typeface;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.os.CountDownTimer;
+import android.os.Handler;
+import android.os.Looper;
 import android.os.SystemClock;
 import android.os.UserManager;
 import android.os.storage.StorageManager;
@@ -216,11 +218,14 @@ public class ConfirmLockPassword extends ConfirmDeviceCredentialBaseActivity {
         public void onDestroy() {
             super.onDestroy();
             mPasswordEntry.setText(null);
-            // Force a garbage collection immediately to remove remnant of user password shards
-            // from memory.
-            System.gc();
-            System.runFinalization();
-            System.gc();
+            // Force a garbage collection to remove remnant of user password shards from memory.
+            // Execute this with a slight delay to allow the activity lifecycle to complete and
+            // the instance to become gc-able.
+            new Handler(Looper.myLooper()).postDelayed(() -> {
+                System.gc();
+                System.runFinalization();
+                System.gc();
+            }, 5000);
         }
 
         private int getDefaultHeader() {