Fix forging of object's identity hashes.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 80a53bf158a4c521fe1020456d1765ebb528c7bd..196e1a55f5bb14a4a1e45b8d27654a7761aba6b3 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -2655,26 +2655,38 @@ int v8::Object::GetIdentityHash() {
   ENTER_V8;
   HandleScope scope;
   i::Handle<i::JSObject> self = Utils::OpenHandle(this);
-  i::Handle<i::Object> hidden_props(i::GetHiddenProperties(self, true));
-  i::Handle<i::Object> hash_symbol = i::Factory::identity_hash_symbol();
-  i::Handle<i::Object> hash = i::GetProperty(hidden_props, hash_symbol);
-  int hash_value;
-  if (hash->IsSmi()) {
-    hash_value = i::Smi::cast(*hash)->value();
-  } else {
-    int attempts = 0;
-    do {
-      // Generate a random 32-bit hash value but limit range to fit
-      // within a smi.
-      hash_value = i::V8::Random() & i::Smi::kMaxValue;
-      attempts++;
-    } while (hash_value == 0 && attempts < 30);
-    hash_value = hash_value != 0 ? hash_value : 1;  // never return 0
-    i::SetProperty(hidden_props,
-                   hash_symbol,
-                   i::Handle<i::Object>(i::Smi::FromInt(hash_value)),
-                   static_cast<PropertyAttributes>(None));
+  i::Handle<i::Object> hidden_props_obj(i::GetHiddenProperties(self, true));
+  if (!hidden_props_obj->IsJSObject()) {
+    // We failed to create hidden properties.  That's a detached
+    // global proxy.
+    ASSERT(hidden_props_obj->IsUndefined());
+    return 0;
   }
+  i::Handle<i::JSObject> hidden_props =
+      i::Handle<i::JSObject>::cast(hidden_props_obj);
+  i::Handle<i::String> hash_symbol = i::Factory::identity_hash_symbol();
+  if (hidden_props->HasLocalProperty(*hash_symbol)) {
+    i::Handle<i::Object> hash = i::GetProperty(hidden_props, hash_symbol);
+    CHECK(!hash.is_null());
+    CHECK(hash->IsSmi());
+    return i::Smi::cast(*hash)->value();
+  }
+
+  int hash_value;
+  int attempts = 0;
+  do {
+    // Generate a random 32-bit hash value but limit range to fit
+    // within a smi.
+    hash_value = i::V8::Random() & i::Smi::kMaxValue;
+    attempts++;
+  } while (hash_value == 0 && attempts < 30);
+  hash_value = hash_value != 0 ? hash_value : 1;  // never return 0
+  CHECK(!i::SetLocalPropertyIgnoreAttributes(
+          hidden_props,
+          hash_symbol,
+          i::Handle<i::Object>(i::Smi::FromInt(hash_value)),
+          static_cast<PropertyAttributes>(None)).is_null());
+
   return hash_value;
 }