[heap-profiler] Fix a use-after-free when snapshots are deleted

If a caller starts the sampling heap profiler and takes a snapshot, and
then deletes the snapshot before the sampling has completed, a
use-after-free will occur on the StringsStorage pointer.

The same issue applies for StartTrackingHeapObjects which shares the
same StringsStorage object.

Bug: v8:8373
Change-Id: I5d69d60d3f9465f9dd3b3bef107c204e0fda0643
Reviewed-on: https://chromium-review.googlesource.com/c/1301477
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57114}

Author: psmarshall

src/profiler/heap-profiler.cc

@@ -23,9 +23,14 @@ HeapProfiler::~HeapProfiler() = default;
 
 void HeapProfiler::DeleteAllSnapshots() {
   snapshots_.clear();
-  names_.reset(new StringsStorage());
+  MaybeClearStringsStorage();
 }
 
+void HeapProfiler::MaybeClearStringsStorage() {
+  if (snapshots_.empty() && !sampling_heap_profiler_ && !allocation_tracker_) {
+    names_.reset(new StringsStorage());
+  }
+}
 
 void HeapProfiler::RemoveSnapshot(HeapSnapshot* snapshot) {
   snapshots_.erase(
@@ -126,6 +131,7 @@ bool HeapProfiler::StartSamplingHeapProfiler(
 
 void HeapProfiler::StopSamplingHeapProfiler() {
   sampling_heap_profiler_.reset();
+  MaybeClearStringsStorage();
 }
 
 
@@ -159,6 +165,7 @@ void HeapProfiler::StopHeapObjectsTracking() {
   ids_->StopHeapObjectsTracking();
   if (allocation_tracker_) {
     allocation_tracker_.reset();
+    MaybeClearStringsStorage();
     heap()->RemoveHeapObjectAllocationTracker(this);
   }
 }

src/profiler/heap-profiler.h

@@ -92,6 +92,8 @@ class HeapProfiler : public HeapObjectAllocationTracker {
                     v8::PersistentValueVector<v8::Object>* objects);
 
  private:
+  void MaybeClearStringsStorage();
+
   Heap* heap() const;
 
   // Mapping from HeapObject addresses to objects' uids.

test/cctest/test-heap-profiler.cc

@@ -3920,3 +3920,45 @@ TEST(WeakReference) {
   const v8::HeapSnapshot* snapshot = heap_profiler->TakeHeapSnapshot();
   CHECK(ValidateSnapshot(snapshot));
 }
+
+TEST(Bug8373_1) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  v8::HeapProfiler* heap_profiler = env->GetIsolate()->GetHeapProfiler();
+
+  heap_profiler->StartSamplingHeapProfiler(100);
+
+  heap_profiler->TakeHeapSnapshot();
+  // Causes the StringsStorage to be deleted.
+  heap_profiler->DeleteAllHeapSnapshots();
+
+  // Triggers an allocation sample that tries to use the StringsStorage.
+  for (int i = 0; i < 2 * 1024; ++i) {
+    CompileRun(
+        "new Array(64);"
+        "new Uint8Array(16);");
+  }
+
+  heap_profiler->StopSamplingHeapProfiler();
+}
+
+TEST(Bug8373_2) {
+  LocalContext env;
+  v8::HandleScope scope(env->GetIsolate());
+  v8::HeapProfiler* heap_profiler = env->GetIsolate()->GetHeapProfiler();
+
+  heap_profiler->StartTrackingHeapObjects(true);
+
+  heap_profiler->TakeHeapSnapshot();
+  // Causes the StringsStorage to be deleted.
+  heap_profiler->DeleteAllHeapSnapshots();
+
+  // Triggers an allocations that try to use the StringsStorage.
+  for (int i = 0; i < 2 * 1024; ++i) {
+    CompileRun(
+        "new Array(64);"
+        "new Uint8Array(16);");
+  }
+
+  heap_profiler->StopTrackingHeapObjects();
+}