Make sure api interceptors don't change the store target w/o storing

src/objects.cc

 // Copyright 2015 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.
 
 #include "src/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 4291 matching lines @@
         // might still call into setters up the prototype chain.
         return JSObject::SetPropertyWithFailedAccessCheck(it, value,
                                                           should_throw);
 
       case LookupIterator::JSPROXY:
         return JSProxy::SetProperty(it->GetHolder<JSProxy>(), it->GetName(),
                                     value, it->GetReceiver(), language_mode);
 
       case LookupIterator::INTERCEPTOR:
         if (it->HolderIsReceiverOrHiddenPrototype()) {
+          Handle<Map> store_target_map =
+              handle(it->GetStoreTarget()->map(), it->isolate());
           Maybe<bool> result =
               JSObject::SetPropertyWithInterceptor(it, should_throw, value);
           if (result.IsNothing() || result.FromJust()) return result;
+          // Interceptor modified the store target but failed to set the
+          // property.
+          Utils::ApiCheck(*store_target_map == it->GetStoreTarget()->map(),
+                          it->IsElement() ? "v8::IndexedPropertySetterCallback"
+                                          : "v8::NamedPropertySetterCallback",
+                          "Interceptor silently changed store target.");
         } else {
+          Handle<JSObject> store_target = it->GetStoreTarget();
           Maybe<PropertyAttributes> maybe_attributes =
               JSObject::GetPropertyAttributesWithInterceptor(it);
           if (!maybe_attributes.IsJust()) return Nothing<bool>();
           if (maybe_attributes.FromJust() == ABSENT) break;
           if ((maybe_attributes.FromJust() & READ_ONLY) != 0) {
             return WriteToReadOnlyProperty(it, value, should_throw);
           }
+          // Interceptor modified the store target but failed to set the
+          // property.
+          Utils::ApiCheck(*store_target == *it->GetStoreTarget(),

[Toon Verwaest, 2016/06/21 13:09:24]

Don't you want to do exactly the same check in both cases?

+                          it->IsElement() ? "v8::IndexedPropertySetterCallback"
+                                          : "v8::NamedPropertySetterCallback",
+                          "Interceptor silently changed store target.");
           *found = false;
           return Nothing<bool>();
         }
         break;
 
       case LookupIterator::ACCESSOR: {
         if (it->IsReadOnly()) {
           return WriteToReadOnlyProperty(it, value, should_throw);
         }
         Handle<Object> accessors = it->GetAccessors();
@@ skipping 14525 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8