Working with Node::Buffers in C++ Node Addons - c++

Question

I'm working on a Node addon that encrypts data using Windows DPAPI. I'm passing two Javascript Uint8Array to the C++ code using NAN.
This is what the typescript interface looks like:
export interface DpapiBindings{
protectData(dataToEncrypt: Uint8Array, optionalEntropy: Uint8Array, scope: string): Uint8Array
}
I'd like to then create a Node::Buffer in the C++ code:
void ProtectData( Nan::NAN_METHOD_ARGS_TYPE info)
{
v8::Isolate* isolate = info.GetIsolate();
//
auto buffer = node::Buffer::Data(info[0]);
auto len = node::Buffer::Length(info[0]);
DATA_BLOB entropyBlob;
entropyBlob.pbData = nullptr;
if (!info[1]->IsNull())
{
entropyBlob.pbData = reinterpret_cast<BYTE*>(node::Buffer::Data(info[1]));
entropyBlob.cbData = node::Buffer::Length(info[1]);
}
DATA_BLOB dataIn;
DATA_BLOB dataOut;
// initialize input data
dataIn.pbData = reinterpret_cast<BYTE*>(buffer);
dataIn.cbData = len;
success = CryptProtectData(
&dataIn,
nullptr,
entropyBlob.pbData ? &entropyBlob : nullptr,
nullptr,
nullptr,
flags,
&dataOut);
auto returnBuffer = Nan::CopyBuffer(reinterpret_cast<const char*>(dataOut.pbData), dataOut.cbData).ToLocalChecked();
LocalFree(dataOut.pbData);
info.GetReturnValue().Set(returnBuffer);
}
I'm new to C++, my question is: When working with node::Buffer::Data and node::Buffer::Length in C++ code, and calling into CryptProtectData, do I need to worry about buffer overflows? If so, how do I protect against it? Should I be appending a null char to buffer and len?

Answer 1

No, you don't need to worry about overflow. The dataIn and dataOut structures are pointers with a length.
BufferCopy is not what you want to use though. You want to use: Nan::MaybeLocal<v8::Object> Nan::NewBuffer(char* data, uint32_t size).
https://github.com/nodejs/nan/blob/master/doc/buffers.md#api_nan_new_buffer
and make sure you free the dataOut.pbData memory when you're done (i see you are with the LocalFree call.) the reason it can't overflow is that CryptProtectData allocates that buffer based on the size it needs.