handle invalid metadata payload correctly

Summary:
After deserialize metadata, cursor location should match `frame.payload().metadataSize())` rather than just not greater than it.

Current logic may allow invalid setup frame to go through.

Reviewed By: tlj77

Differential Revision: D62332462

fbshipit-source-id: 2829f1e08f7167d438f2d9b06977e05d26406e6a

thrift/lib/cpp2/transport/rocket/server/ThriftRocketServerHandler.cpp

@@ -210,7 +210,7 @@ void ThriftRocketServerHandler::handleSetupFrame(
       reader.setInput(cursor);
       // Throws on read error
       meta.read(&reader);
-      if (reader.getCursorPosition() > frame.payload().metadataSize()) {
+      if (reader.getCursorPosition() != frame.payload().metadataSize()) {
         return connection.close(folly::make_exception_wrapper<RocketException>(
             ErrorCode::INVALID_SETUP,
             "Error deserializing SETUP payload: underflow"));
@@ -220,7 +220,7 @@ void ThriftRocketServerHandler::handleSetupFrame(
       reader.setInput(cursor);
       // Throws on read error
       meta.read(&reader);
-      if (reader.getCursorPosition() > frame.payload().metadataSize()) {
+      if (reader.getCursorPosition() != frame.payload().metadataSize()) {
         return connection.close(folly::make_exception_wrapper<RocketException>(
             ErrorCode::INVALID_SETUP,
             "Error deserializing SETUP payload: underflow"));