Add support for API accessors that prohibit overwriting by accessors...

src/objects.cc

Index: src/objects.cc
===================================================================
--- src/objects.cc	(revision 654)
+++ src/objects.cc	(working copy)
@@ -2257,14 +2257,24 @@
        current != Heap::null_value();
        current = JSObject::cast(current)->GetPrototype()) {
     JSObject::cast(current)->LocalLookup(name, result);
-    if (result->IsValid() && !result->IsTransitionType()) {
-      return;
-    }
+    if (result->IsValid() && !result->IsTransitionType()) return;
   }
   result->NotFound();
 }
 
 
+// Search object and it's prototype chain for callback properties.
+void JSObject::LookupCallback(String* name, LookupResult* result) {
+  for (Object* current = this;
+       current != Heap::null_value();
+       current = JSObject::cast(current)->GetPrototype()) {
+    JSObject::cast(current)->LocalLookupRealNamedProperty(name, result);
+    if (result->IsValid() && result->type() == CALLBACKS) return;
+  }
+  result->NotFound();
+}
+
+
 Object* JSObject::DefineGetterSetter(String* name,
                                      PropertyAttributes attributes) {
   // Make sure that the top context does not change when doing callbacks or
@@ -2285,6 +2295,22 @@
   uint32_t index;
   if (name->AsArrayIndex(&index)) return Heap::undefined_value();
 
+  // Check if there is an API defined callback object which prohibits
+  // callback overwriting in this object or it's prototype chain.
+  // This mechanism is needed for instance in a browser setting, where
+  // certain accessors such as window.location should not be allowed
+  // to be overwriten because allowing overwriting could potentially

[Kasper Lund, 2008/10/30 12:32:27]

overwritten

+  // cause security problems.
+  LookupResult callback_result;
+  LookupCallback(name, &callback_result);
+  if (callback_result.IsValid()) {
+    Object* obj = callback_result.GetCallbackObject();
+    if (obj->IsAccessorInfo() &&
+        AccessorInfo::cast(obj)->prohibits_overwriting()) {
+      return Heap::undefined_value();
+    }
+  }
+
   // Lookup the name.
   LookupResult result;
   LocalLookup(name, &result);