Netty's HttpPostRequestDecoder can OOM

Summary

The HttpPostRequestDecoder can be tricked to accumulate data. I have spotted currently two attack vectors

Details

1. While the decoder can store items on the disk if configured so, there are no limits to the number of fields the form can have, an attacher can send a chunked post consisting of many small fields that will be accumulated in the bodyListHttpData list.
2. The decoder cumulates bytes in the undecodedChunk buffer until it can decode a field, this field can cumulate data without limits

PoC

Here is a Netty branch that provides a fix + tests : https://github.com/vietj/netty/tree/post-request-decoder

Here is a reproducer with Vert.x (which uses this decoder) https://gist.github.com/vietj/f558b8ea81ec6505f1e9a6ca283c9ae3

Impact

Any Netty based HTTP server that uses the HttpPostRequestDecoder to decode a form.