From c0390bcd64ba1fd6594fbc9f6246a1649662d683 Mon Sep 17 00:00:00 2001
From: Fergal Daly <fergal@chromium.org>
Date: Mon, 06 Apr 2026 19:49:06 -0700
Subject: [PATCH] Fix UAF in FileSystemAccessChangeSource.

`DidInitialize` calls any outstanding initialization callbacks but a
callback can delete this. The code guards against this in its access
of `initialization_callbacks_` but not `initialization_result_`.

This fix keeps a copy of the result on the stack.

This also adds a test which fails with ASAN before the fix is applied
and passes after.

The basic test code was written by Gemini.

Fixed: 497880137
Change-Id: I046831db23cb4b8e41964910e2aede9b1be0db7f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/7728464
Auto-Submit: Fergal Daly <fergal@chromium.org>
Reviewed-by: Ming-Ying Chung <mych@chromium.org>
Commit-Queue: Ming-Ying Chung <mych@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1610499}
---

diff --git a/content/browser/file_system_access/file_system_access_change_source.cc b/content/browser/file_system_access/file_system_access_change_source.cc
index 566dc1e..48bd867 100644
--- a/content/browser/file_system_access/file_system_access_change_source.cc
+++ b/content/browser/file_system_access/file_system_access_change_source.cc
@@ -71,13 +71,14 @@
   CHECK(!initialization_result_.has_value());
   CHECK(!initialization_callbacks_.empty());
 
-  initialization_result_ = std::move(result);
+  // The callbacks may cause |this| to be deleted, so we should only use
+  // stack-based objects below.
+  initialization_result_ = result->Clone();
 
-  // Move the callbacks to the stack since they may cause |this| to be deleted.
   auto initialization_callbacks = std::move(initialization_callbacks_);
   initialization_callbacks_.clear();
   for (auto& callback : initialization_callbacks) {
-    std::move(callback).Run(initialization_result_->Clone());
+    std::move(callback).Run(result->Clone());
   }
 }
 
diff --git a/content/browser/file_system_access/file_system_access_change_source_unittest.cc b/content/browser/file_system_access/file_system_access_change_source_unittest.cc
new file mode 100644
index 0000000..b0f15909
--- /dev/null
+++ b/content/browser/file_system_access/file_system_access_change_source_unittest.cc
@@ -0,0 +1,146 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/file_system_access/file_system_access_change_source.h"
+
+#include "base/files/scoped_temp_dir.h"
+#include "base/functional/bind.h"
+#include "base/memory/scoped_refptr.h"
+#include "base/task/sequenced_task_runner.h"
+#include "base/test/task_environment.h"
+#include "base/test/test_future.h"
+#include "content/browser/file_system_access/file_system_access_watch_scope.h"
+#include "storage/browser/file_system/file_system_context.h"
+#include "storage/browser/file_system/file_system_url.h"
+#include "storage/browser/quota/quota_manager_proxy.h"
+#include "storage/browser/test/test_file_system_context.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/blink/public/mojom/file_system_access/file_system_access_error.mojom.h"
+
+namespace content {
+
+namespace {
+
+class MockRawChangeObserver
+    : public FileSystemAccessChangeSource::RawChangeObserver {
+ public:
+  MOCK_METHOD(void,
+              OnRawChange,
+              (const storage::FileSystemURL& changed_url,
+               bool error,
+               const FileSystemAccessChangeSource::ChangeInfo& change_info,
+               const FileSystemAccessWatchScope& scope),
+              (override));
+  MOCK_METHOD(void,
+              OnUsageChange,
+              (size_t old_usage,
+               size_t new_usage,
+               const FileSystemAccessWatchScope& scope),
+              (override));
+  MOCK_METHOD(void,
+              OnSourceBeingDestroyed,
+              (FileSystemAccessChangeSource * source),
+              (override));
+};
+
+class FakeChangeSource : public FileSystemAccessChangeSource {
+ public:
+  FakeChangeSource(
+      FileSystemAccessWatchScope scope,
+      scoped_refptr<storage::FileSystemContext> file_system_context)
+      : FileSystemAccessChangeSource(std::move(scope),
+                                     std::move(file_system_context)) {}
+  ~FakeChangeSource() override = default;
+
+  // FileSystemAccessChangeSource:
+  void Initialize(
+      base::OnceCallback<void(blink::mojom::FileSystemAccessErrorPtr)>
+          on_source_initialized) override {
+    base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
+        FROM_HERE, base::BindOnce(std::move(on_source_initialized),
+                                  blink::mojom::FileSystemAccessError::New(
+                                      blink::mojom::FileSystemAccessStatus::kOk,
+                                      base::File::FILE_OK, "")));
+  }
+
+  void Signal(const storage::FileSystemURL& changed_url,
+              bool error = false,
+              ChangeInfo change_info = ChangeInfo()) {
+    NotifyOfChange(changed_url, error, change_info);
+  }
+};
+
+}  // namespace
+
+class FileSystemAccessChangeSourceTest : public testing::Test {
+ public:
+  FileSystemAccessChangeSourceTest()
+      : task_environment_(base::test::TaskEnvironment::MainThreadType::IO) {}
+
+  void SetUp() override {
+    ASSERT_TRUE(dir_.CreateUniqueTempDir());
+    file_system_context_ = storage::CreateFileSystemContextForTesting(
+        /*quota_manager_proxy=*/nullptr, dir_.GetPath());
+  }
+
+ protected:
+  base::test::TaskEnvironment task_environment_;
+  base::ScopedTempDir dir_;
+  scoped_refptr<storage::FileSystemContext> file_system_context_;
+};
+
+TEST_F(FileSystemAccessChangeSourceTest, CreateAndInitialize) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource source(scope, file_system_context_);
+
+  base::test::TestFuture<blink::mojom::FileSystemAccessErrorPtr> future;
+  source.EnsureInitialized(future.GetCallback());
+  EXPECT_EQ(future.Get()->status, blink::mojom::FileSystemAccessStatus::kOk);
+}
+
+TEST_F(FileSystemAccessChangeSourceTest, NotifyOfChange) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource source(scope, file_system_context_);
+
+  MockRawChangeObserver observer;
+  source.AddObserver(&observer);
+
+  EXPECT_CALL(observer, OnRawChange(testing::Eq(file_url), testing::IsFalse(),
+                                    testing::_, testing::Eq(scope)));
+  source.Signal(file_url);
+
+  source.RemoveObserver(&observer);
+}
+
+// A callback passed to `EnsureInitialized` may result in `this` being
+// destroyed. This tests that `DidInitialize` (which calls the callbacks) is
+// robust to that situation. See https://crbug.com/497880137.
+TEST_F(FileSystemAccessChangeSourceTest, TestDestroyFromInitializeCallback) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource* source = new FakeChangeSource(scope, file_system_context_);
+
+  source->EnsureInitialized(base::BindOnce(
+      [](FakeChangeSource* source, blink::mojom::FileSystemAccessErrorPtr) {
+        delete source;
+      },
+      base::Unretained(source)));
+  base::test::TestFuture<blink::mojom::FileSystemAccessErrorPtr> future;
+  source->EnsureInitialized(future.GetCallback());
+  EXPECT_EQ(future.Get()->status, blink::mojom::FileSystemAccessStatus::kOk);
+}
+
+}  // namespace content
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn

diff --git a/content/browser/file_system_access/file_system_access_change_source_unittest.cc b/content/browser/file_system_access/file_system_access_change_source_unittest.cc
new file mode 100644
index 0000000..b0f15909
--- /dev/null
+++ b/content/browser/file_system_access/file_system_access_change_source_unittest.cc
@@ -0,0 +1,146 @@
+// Copyright 2026 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/file_system_access/file_system_access_change_source.h"
+
+#include "base/files/scoped_temp_dir.h"
+#include "base/functional/bind.h"
+#include "base/memory/scoped_refptr.h"
+#include "base/task/sequenced_task_runner.h"
+#include "base/test/task_environment.h"
+#include "base/test/test_future.h"
+#include "content/browser/file_system_access/file_system_access_watch_scope.h"
+#include "storage/browser/file_system/file_system_context.h"
+#include "storage/browser/file_system/file_system_url.h"
+#include "storage/browser/quota/quota_manager_proxy.h"
+#include "storage/browser/test/test_file_system_context.h"
+#include "testing/gmock/include/gmock/gmock.h"
+#include "testing/gtest/include/gtest/gtest.h"
+#include "third_party/blink/public/mojom/file_system_access/file_system_access_error.mojom.h"
+
+namespace content {
+
+namespace {
+
+class MockRawChangeObserver
+    : public FileSystemAccessChangeSource::RawChangeObserver {
+ public:
+  MOCK_METHOD(void,
+              OnRawChange,
+              (const storage::FileSystemURL& changed_url,
+               bool error,
+               const FileSystemAccessChangeSource::ChangeInfo& change_info,
+               const FileSystemAccessWatchScope& scope),
+              (override));
+  MOCK_METHOD(void,
+              OnUsageChange,
+              (size_t old_usage,
+               size_t new_usage,
+               const FileSystemAccessWatchScope& scope),
+              (override));
+  MOCK_METHOD(void,
+              OnSourceBeingDestroyed,
+              (FileSystemAccessChangeSource * source),
+              (override));
+};
+
+class FakeChangeSource : public FileSystemAccessChangeSource {
+ public:
+  FakeChangeSource(
+      FileSystemAccessWatchScope scope,
+      scoped_refptr<storage::FileSystemContext> file_system_context)
+      : FileSystemAccessChangeSource(std::move(scope),
+                                     std::move(file_system_context)) {}
+  ~FakeChangeSource() override = default;
+
+  // FileSystemAccessChangeSource:
+  void Initialize(
+      base::OnceCallback<void(blink::mojom::FileSystemAccessErrorPtr)>
+          on_source_initialized) override {
+    base::SequencedTaskRunner::GetCurrentDefault()->PostTask(
+        FROM_HERE, base::BindOnce(std::move(on_source_initialized),
+                                  blink::mojom::FileSystemAccessError::New(
+                                      blink::mojom::FileSystemAccessStatus::kOk,
+                                      base::File::FILE_OK, "")));
+  }
+
+  void Signal(const storage::FileSystemURL& changed_url,
+              bool error = false,
+              ChangeInfo change_info = ChangeInfo()) {
+    NotifyOfChange(changed_url, error, change_info);
+  }
+};
+
+}  // namespace
+
+class FileSystemAccessChangeSourceTest : public testing::Test {
+ public:
+  FileSystemAccessChangeSourceTest()
+      : task_environment_(base::test::TaskEnvironment::MainThreadType::IO) {}
+
+  void SetUp() override {
+    ASSERT_TRUE(dir_.CreateUniqueTempDir());
+    file_system_context_ = storage::CreateFileSystemContextForTesting(
+        /*quota_manager_proxy=*/nullptr, dir_.GetPath());
+  }
+
+ protected:
+  base::test::TaskEnvironment task_environment_;
+  base::ScopedTempDir dir_;
+  scoped_refptr<storage::FileSystemContext> file_system_context_;
+};
+
+TEST_F(FileSystemAccessChangeSourceTest, CreateAndInitialize) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource source(scope, file_system_context_);
+
+  base::test::TestFuture<blink::mojom::FileSystemAccessErrorPtr> future;
+  source.EnsureInitialized(future.GetCallback());
+  EXPECT_EQ(future.Get()->status, blink::mojom::FileSystemAccessStatus::kOk);
+}
+
+TEST_F(FileSystemAccessChangeSourceTest, NotifyOfChange) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource source(scope, file_system_context_);
+
+  MockRawChangeObserver observer;
+  source.AddObserver(&observer);
+
+  EXPECT_CALL(observer, OnRawChange(testing::Eq(file_url), testing::IsFalse(),
+                                    testing::_, testing::Eq(scope)));
+  source.Signal(file_url);
+
+  source.RemoveObserver(&observer);
+}
+
+// A callback passed to `EnsureInitialized` may result in `this` being
+// destroyed. This tests that `DidInitialize` (which calls the callbacks) is
+// robust to that situation. See https://crbug.com/497880137.
+TEST_F(FileSystemAccessChangeSourceTest, TestDestroyFromInitializeCallback) {
+  auto file_path = dir_.GetPath().AppendASCII("file");
+  auto file_url = file_system_context_->CreateCrackedFileSystemURL(
+      blink::StorageKey(), storage::kFileSystemTypeLocal, file_path);
+
+  auto scope = FileSystemAccessWatchScope::GetScopeForFileWatch(file_url);
+  FakeChangeSource* source = new FakeChangeSource(scope, file_system_context_);
+
+  source->EnsureInitialized(base::BindOnce(
+      [](FakeChangeSource* source, blink::mojom::FileSystemAccessErrorPtr) {
+        delete source;
+      },
+      base::Unretained(source)));
+  base::test::TestFuture<blink::mojom::FileSystemAccessErrorPtr> future;
+  source->EnsureInitialized(future.GetCallback());
+  EXPECT_EQ(future.Get()->status, blink::mojom::FileSystemAccessStatus::kOk);
+}
+
+}  // namespace content
diff --git a/content/test/BUILD.gn b/content/test/BUILD.gn
index ec792aa..8071300 100644
--- a/content/test/BUILD.gn
+++ b/content/test/BUILD.gn
@@ -2676,6 +2676,7 @@
     "../browser/fenced_frame/redacted_fenced_frame_config_mojom_traits_unittest.cc",
     "../browser/file_system/browser_file_system_helper_unittest.cc",
     "../browser/file_system/file_system_operation_runner_unittest.cc",
+    "../browser/file_system_access/file_system_access_change_source_unittest.cc",
     "../browser/file_system_access/file_system_access_directory_handle_impl_unittest.cc",
     "../browser/file_system_access/file_system_access_file_handle_impl_unittest.cc",
     "../browser/file_system_access/file_system_access_file_modification_host_impl_unittest.cc",