From 2da1f51f911ecd545593c81708b27ddf47bf12ba Mon Sep 17 00:00:00 2001
From: Simon Giesecke <sgiesecke@mozilla.com>
Date: Fri, 14 Feb 2020 14:39:40 +0100
Subject: [PATCH] [IndexedDB] Ensure that strong references to newly created
 cursors are kept until the DOM Binding is created.

This fixes random crashes on websites that use IndexedDB cursors.
See also BZ bug 1599420
---
 dom/indexedDB/ActorsChild.cpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/dom/indexedDB/ActorsChild.cpp b/dom/indexedDB/ActorsChild.cpp
index 30dc9b6dab..85f876cdc1 100644
--- a/dom/indexedDB/ActorsChild.cpp
+++ b/dom/indexedDB/ActorsChild.cpp
@@ -3291,6 +3291,10 @@ BackgroundCursorChild::HandleResponse(
   auto& responses =
     const_cast<nsTArray<ObjectStoreCursorResponse>&>(aResponses);
 
+  // If a new cursor is created, we need to keep a reference to it until the
+  // ResultHelper creates a DOM Binding.
+  RefPtr<IDBCursor> newCursor;
+
   for (ObjectStoreCursorResponse& response : responses) {
     StructuredCloneReadInfo cloneReadInfo(Move(response.cloneInfo()));
     cloneReadInfo.mDatabase = mTransaction->Database();
@@ -3300,8 +3304,6 @@ BackgroundCursorChild::HandleResponse(
                                     nullptr,
                                     cloneReadInfo.mFiles);
 
-    RefPtr<IDBCursor> newCursor;
-
     if (mCursor) {
       mCursor->Reset(Move(response.key()), Move(cloneReadInfo));
     } else {