A Summer of Code

Here I write my final report of Google Summer of Code 2018 for mitmproxy, under the Honeynet organization. I’ll include pretty much all the work done for the organization, together with the ideas behind every step. Use it to get the code, or read about my work and contact me while I extend it, to be part of this awesome team :)

Shortly, my project for these months was to develop a new serialization module for mitmproxy Flows. This is useful in a number of ways, most of them underlined in my GSoC project overview. One peculiar idea was to exploit this module to implement a Hybrid SQLite DB which could serve as the storage layer for mitmproxy – not only solving RAM chugging issues, but serving as the foundation to implement persistence in the software, aka Sessions.

Testing

Before spending time and resources to properly implement a serialization interface under Google Protocol Buffers, one crucial point was to test the libraries (protobuf and sqlite), gathering some fact to ensure that serializing wouldn’t have too much impact on performances. In the meantime, it proved to be a good time to learn more about asyncio code in Python, which anyway is the approach adopted by mitmproxy since release 4.

Pull Requests

This has been my first PR for GSoC. It included a lot of testing code: a dummy serialization interface, and two addons which measured dumping time in comparison with tnetstrings(dumpwatcher), and throughput to SQLite DB when flows are streaming costantly(streamtester). I, later in time, adjusted that code - using the new, complete protobuf interface - to be used as a benchmarking script in test folder:

This can be used as it is just by running the script, as with every other mitmproxy script. It can be modified by tweaking params, or saving path, or flow dimensions and fields.

Refactoring the View API

Building a new storage layer means building a new View. This addon, in fact, handles the logic to implement the ordered, filtered storage every tool (web or console) offers in its interface. The View offers an API exposed via commands to the tools, but some of the code still accessed the addon internally. So, I started cleaning up the API, extending it, and clearing most of the “illegal” accesses to the addon.

Pull Requests

The cleanup is not completed yet. It will be a gradual process, involving changes in some other area of mitmproxy, to be reworked in conjuction with other devs. Nevertheless, it was a good start and helped a lot understanding how and where mitmproxy stores its flows :)

Building the Protocol Buffer Interface

Here we go. Serializing flows with protobufs. My idea, during the whole process, was to mirror the functionalities that tnetstrings and state_objects offered, bringing all the logic into: a .proto file, providing a clear format for Flows, and the protobuf module, where all the conversion code was implemented.

Pull Requests

The code is merged and can be used by every tool, script or addon interfacing with mitmproxy by importing mitmproxy.io.protobuf, calling protobuf.dumps, protobuf.loads methods. Everything should be clear enough reading the code and its usage in the the other PRs which use this interface.

A New Storage Layer for Sessions

Having a functioning, fast enough dumping interface handy, I proceeded with building the foundations for Session storage. In particular, I have developed an addon (Session) which implements the logic to use the Hybrid DB (indexed protobuf blobs of flows) as the storage layer for mitmproxy.

Pull Requests

The two PRs are widely commented, so I’ll avoid adding redundancy here.

The End…?

I’m grateful for the GSoC experience. It encouraged me to explore the Open Source community, find many amazing developers and persons, while constantly improving my skills and knowledge. I have found an awesome environment in mitmproxy, and while the GSoC period ends, my journey with this organization does not. Enjoy!

Pietro Francesco Tirenna - madt1m