Snort++ dynamic inspector questions

[Henry Foster <henryaugustfoster () gmail com>]

Hi all,

I'm working on writing a dynamic Snort++ inspector to reassemble MPTCP
streams.  I've been doing my best to RTFS, but was hoping someone could
help me with a couple questions. I feel like the answers are probably
pretty obvious, but I've been having trouble figuring them out.

1. Is it possible to craft and submit a pseudopacket for detection from a
dynamic plug-in?
I took a look at the TCP stream source and it looks like
Snort::detect_rebuilt_packet would be a good thing to use, but I'm not sure
how to go about calling it from a dynamic plug-in. I don't suppose there's
an API for submitting rebuilt packets?  Currently, for testing, I'm
overwriting the data pointer of the actual packet (p) that gets passed to the
plug-in, but doing this makes me feel dirty inside.

2. What's the best way to get all the TCP packets to my plugin?
I started with the DPX example and have been building on top of it.
Currently, I'm using IT_NETWORK and PktType::TCP, however, I've noticed
that my plugin's eval() is not getting called with ACKs / non-payload
segments from the tcp receiver -> tcp initiator. I'd like to receive all
the packets as there's some MPTCP control information that's included in
the options field of those ACK packets: I want to keep track of a nonce
that is sent when additional subflows are joining a MPTCP connection (in
the SYN/ACK of the handshake), and mptcp data sequence mappings that are
sent sometimes sent in ACKs.

Disclaimer: Right now, I'm just trying to prototype this out. The actual
plug-in code does very little work; I use Protocol Buffers to ship off the
parts of the header I need to a server written in Python that does the
actual reassembly.

Thanks!

-Henry

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