[Intl] Fix Heap-use-after-free

Fix Heap-use-after-free READ 2 in Intl.Segmenter
when the segments got free during the iteration
We need to keep a copy of the string in the iterator instead
of depending on the one referenced from the segments.

Bug: chromium:1121156, v8:6891
Change-Id: I26ef5baccaa470dc1bd8cc229c737f556d27160e
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2376173
Commit-Queue: Frank Tang <ftang@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69575}

src/objects/intl-objects.tq

@@ -134,6 +134,7 @@ bitfield struct JSSegmentIteratorFlags extends uint31 {
 @generateCppClass
 extern class JSSegmentIterator extends JSObject {
   icu_break_iterator: Foreign;  // Managed<icu::BreakIterator>
+  unicode_string: Foreign;      // Managed<icu::UnicodeString>
   flags: SmiTagged<JSSegmentIteratorFlags>;
 }
 

src/objects/js-segment-iterator-inl.h

@@ -22,6 +22,8 @@ TQ_OBJECT_CONSTRUCTORS_IMPL(JSSegmentIterator)
 // Base segment iterator accessors.
 ACCESSORS(JSSegmentIterator, icu_break_iterator, Managed<icu::BreakIterator>,
           kIcuBreakIteratorOffset)
+ACCESSORS(JSSegmentIterator, unicode_string, Managed<icu::UnicodeString>,
+          kUnicodeStringOffset)
 
 inline void JSSegmentIterator::set_granularity(
     JSSegmenter::Granularity granularity) {

src/objects/js-segment-iterator.cc

@@ -46,6 +46,13 @@ MaybeHandle<JSSegmentIterator> JSSegmentIterator::Create(
   Handle<Managed<icu::BreakIterator>> managed_break_iterator =
       Managed<icu::BreakIterator>::FromRawPtr(isolate, 0, break_iterator);
 
+  icu::UnicodeString* string = new icu::UnicodeString();
+  break_iterator->getText().getText(*string);
+  Handle<Managed<icu::UnicodeString>> unicode_string =
+      Managed<icu::UnicodeString>::FromRawPtr(isolate, 0, string);
+
+  break_iterator->setText(*string);
+
   // Now all properties are ready, so we can allocate the result object.
   Handle<JSObject> result = isolate->factory()->NewJSObjectFromMap(map);
   DisallowHeapAllocation no_gc;
@@ -55,6 +62,7 @@ MaybeHandle<JSSegmentIterator> JSSegmentIterator::Create(
   segment_iterator->set_flags(0);
   segment_iterator->set_granularity(granularity);
   segment_iterator->set_icu_break_iterator(*managed_break_iterator);
+  segment_iterator->set_unicode_string(*unicode_string);
 
   return segment_iterator;
 }

src/objects/js-segment-iterator.h

@@ -43,6 +43,7 @@ class JSSegmentIterator
 
   // SegmentIterator accessors.
   DECL_ACCESSORS(icu_break_iterator, Managed<icu::BreakIterator>)
+  DECL_ACCESSORS(unicode_string, Managed<icu::UnicodeString>)
 
   DECL_PRINTER(JSSegmentIterator)
 

test/intl/regress-1121156.js

+// Copyright 2020 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-intl-segmenter --expose-gc
+
+let segmenter = new Intl.Segmenter();
+let segments = segmenter.segment(undefined);
+for (let seg of segments) {
+  segments = gc();  // free segments and call gc.
+}