From ca07fd6d7c2fc9993da904c899af7efcb57b9bb7 Mon Sep 17 00:00:00 2001
From: JW Wang <wangchun@google.com>
Date: Tue, 13 Oct 2020 15:04:51 +0800
Subject: [PATCH] Use AtomicFile

This should guarantee the integrity of the file content and
prevent the issue like b/170697897#comment2.

Bug: 170697897
Test: atest StagedRollbackTest
Change-Id: I4c2acb80fd9c806e31aa04d6defb480dafcf2c50
---
 .../com/android/server/rollback/RollbackStore.java  | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/services/core/java/com/android/server/rollback/RollbackStore.java b/services/core/java/com/android/server/rollback/RollbackStore.java
index a4fa745c48963..44a63367dab52 100644
--- a/services/core/java/com/android/server/rollback/RollbackStore.java
+++ b/services/core/java/com/android/server/rollback/RollbackStore.java
@@ -25,6 +25,7 @@ import android.content.rollback.PackageRollbackInfo;
 import android.content.rollback.PackageRollbackInfo.RestoreInfo;
 import android.content.rollback.RollbackInfo;
 import android.os.UserHandle;
+import android.util.AtomicFile;
 import android.util.Slog;
 import android.util.SparseIntArray;
 
@@ -37,6 +38,7 @@ import org.json.JSONException;
 import org.json.JSONObject;
 
 import java.io.File;
+import java.io.FileOutputStream;
 import java.io.IOException;
 import java.io.PrintWriter;
 import java.nio.file.Files;
@@ -66,8 +68,6 @@ class RollbackStore {
     //
     // * XXX, YYY are the rollbackIds for the corresponding rollbacks.
     // * rollback.json contains all relevant metadata for the rollback.
-    //
-    // TODO: Use AtomicFile for all the .json files?
     private final File mRollbackDataDir;
 
     RollbackStore(File rollbackDataDir) {
@@ -259,6 +259,8 @@ class RollbackStore {
      * Saves the given rollback to persistent storage.
      */
     static void saveRollback(Rollback rollback) {
+        FileOutputStream fos = null;
+        AtomicFile file = new AtomicFile(new File(rollback.getBackupDir(), "rollback.json"));
         try {
             JSONObject dataJson = new JSONObject();
             dataJson.put("info", rollbackInfoToJson(rollback.info));
@@ -272,11 +274,16 @@ class RollbackStore {
             dataJson.putOpt(
                     "extensionVersions", extensionVersionsToJson(rollback.getExtensionVersions()));
 
-            PrintWriter pw = new PrintWriter(new File(rollback.getBackupDir(), "rollback.json"));
+            fos = file.startWrite();
+            PrintWriter pw = new PrintWriter(fos);
             pw.println(dataJson.toString());
             pw.close();
+            file.finishWrite(fos);
         } catch (JSONException | IOException e) {
             Slog.e(TAG, "Unable to save rollback for: " + rollback.info.getRollbackId(), e);
+            if (fos != null) {
+                file.failWrite(fos);
+            }
         }
     }