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I built a minimalist SPA tool using eBPF/XDP to keep ports invisible. First project in Go! (github.com)
submitted 7 months ago by to c/opensource@lemmy.ml
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Hi guys, I wanted to share a project I’ve been working on called xSpa. It's an implementation of Single Packet Authorization that works at the XDP level.

I built this because I wanted something faster and more DDoS-resilient than traditional port-knocking or SPA tools that rely on userspace processing or iptables. Here, the "drop-all" logic happens right at the driver level.

Key bits:

L1 verification (SipHash) in kernel space.

L2 (ChaCha20-Poly1305) in Go userspace.

It uses the eBPF ring buffer for communication.

This is my first Go project and my first shot at Open Source. I’m still a bit of a noob when it comes to kernel-level programming, so I’d love to get some feedback on the architecture and security. If anyone has time to check the code, I’d love to hear your thoughts on how to make it better.

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[–] 2 points 7 months ago (5 children)

What if any role did "AI" play in this project?

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  • [–] 5 points 7 months ago (3 children)

    You mean, you don’t use “init” for all your commits?

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  • [–] [S] 2 points 7 months ago (2 children)

    caught me! still learning the 'professional' way to do things. at least it's better than 'fix1', 'fix2', 'asdfgh'..

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  • [–] [S] 2 points 7 months ago

    I used AI to help with the eBPF parts since it's a new and complex topic for me. It also helped me translate the README and polish this post because English isn't my first language

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    • [–] 1 point 7 months ago (2 children)

    Sorry, I'm failing to understand what this does, mostly because your description is mixing tcpip, socket, and xdp terminology.

    It's an implementation of Single Packet Authorization that works at the XDP level.

    Sure, but to do what, exactly? Is this meant to run on Linux routers as a prefilter? Or on hosts themselves? In the second case, why not just use 802.11x?

    I don't get the use case, or what this has to do with DDOS.

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  • [–] [S] 3 points 7 months ago (1 child)

    Thanks for the feedback! You’re right, my description was a bit messy. Let me clarify the goal and the use case

    The goal to make a VPS on the public internet completely invisible to unauthorized scans while allowing access to services (like SSH) only after a valid SPA packet is received

    Traditional SPA tools (like fwknop) often use libpcap to sniff packets or iptables to block them. In both cases, unauthorized packets still hit the kernel network stack. If an attacker floods the port with junk, the kernel still spends CPU cycles processing them before they get dropped

    By using XDP, I move the "drop-all" logic to the earliest possible stage. This is where the DDoS resilience comes from we drop unauthorized traffic before sk_buff allocation, making it significantly cheaper in terms of CPU resources

    It’s designed to run on the host itself, acting as a "stealth" firewall

    A major advantage here is that xSpa doesn't touch the netfilter/iptables stack. Unlike fwknop, which has to dynamically manage firewall rules (often leading to conflicts with Docker, UFW, or complex rulesets), xSpa operates at a lower level. It’s completely independent of whatever you have going on in your iptables configuration

    And you can’t use 802.1X to protect an SSH port on a public cloud VPS

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    • [–] 1 point 7 months ago

    How have tests gone so far?

    also cool concept, you can actually get eBPF XDP to compile to FPGA on some smart NICs even further pushing it away from the core system if it works!

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