Hi everyone!
I’m Qijia Zheng, my major is Cyberspace Security, a graduate student now studying in University of Science and Technology of China.
About me
My name is Qijia Zheng. Recently, I have conducted research in the field of wireless sensing. It is a interdisciplinary subject of wireless communication and computer vision(deep learning). Now I come to Freifunk to learn the knowledge of wifi to gain a deeper understanding of wifi communication. Also, I was attracted by the concepts of P2P and ad-hoc when I began to learn computer network. I am glad to see and be a part of such a community who brings them to reality, not just on the Internet.
About the project
Why XDP/eBPF?
eBPF can be seen as a way to bypass most kernel stacks like network stack, I/O stack and etc. Using eBPF to get information in kernel could bring less overhead and run customized programs. Also, existing eBPF projects like BCC, bpftrace provide a higher-level framework to write eBPF code, which make life easier.
What I have done?
With my mentors’ advises, I got my hands dirty with the project from a survey.
After surveying tens of wifi analysis projects, I got a list of wifi statistics and created a repo to record the survey.
I evaluated XDP and BCC on my x86 laptop equipped with AX200 NIC, but I encountered lots of barriers when implementing it.(see next section for detailed)
In addition to do a survey of some open source projects, I checked some papers about Rate adaption for mac802.11 wireless networks. The statistics of wifi traffic for transmission rate control could be classified into three groups ACK, SNR and BER, specifically they are packet loss ratio, transmission time, frame receptions, SNR, bit errors and etc.
As I got nothing from mac80211 based on AX200, I focused on collecting statistics from higher layers which basically provided by BCC and XDP project.
Official XDP repo provides a xdp_loader program. By leveraging xdp_loader, I succeded to load my XDP program on my wireless adapter to get the receiving bytes per second and other basic statistics of ethernet frames.
About MAC80211 subsystem
For some reasons, I just test XDP programs on AX200 NIC.
Obviously, we don’t have native XDP support for the driver of AX200.
I put my attention on generic XDP. After runing XDP-TCPDUMP tool provided by XDP-PROJECT repo, I got a “.pcap” file containing packets of wireless traffic captured by the tool. And the payload recorded in the file are all from struct xdp_md *ctx. However, the packets show nothing about IEEE80211 header even the wireless NIC working at monitor mode, which probably means AX200 NIC removed IEEE80211 header before XDP staff getting involved. As a result, we will not get any information about mac80211 header by implementing generic XDP on AX200.
Also, I tried bare tracing tool like kprobe, function graph to trace functions of mac80211 like ieee80211_xmit. Unluckily, I still got no output in TRACE file. That is to say, running eBPF programs attaching to kprobe to on AX200 is infeasible. But we still have some tracepoints of cfg80211.
Next step
- Switch AX200 to Atheros series to evaluate XDP on ath9k driver to unlock the potential of eBPF attaching to dynamic tracing
- Keep surveying papers related to transmission rate control topic
- Select proper machine learning algorithm to implement features and measure the model based on Precision, Recall and F1 score
Goals of the project
- By leveraging the statistics collected using eBPF, we could create a fingerprint for STAs to identify different types of devices.
- Implementing a dedicated use case that demonstrates the benefits of eBPF/XDP.
- Providing the foundation for further research in the direction of network research.
Finally
I would like to thank my mentors for offering the helps for me till now.
