netdev - Kernel panic on bpf_skb_pull

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Date:   Fri, 24 Mar 2023 16:23:59 +0000
From:   Farbod Shahinfar <farbod.shahinfar@...imi.it>
To:     "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Kernel panic on bpf_skb_pull_data

Hello everyone,

I am performing some test with BPF SK_SKB and I have encountered a 
scenario resulting in kernel panic. I use a BPF_SK_SKB_STREAM_PARSER 
program to parse a request which might be spanning multiple TCP 
segments. If the end of request is detected in the parser program it 
returns skb->len, passing the request to the 
BPF_SK_SKB_STREAM_VERDICT program, and otherwise it returns 0, waiting 
for more data to be received. You can find the BPF program attached 
(bpf_test.c). Is there an assumption that the program violates?

To reproduce the crashing scenario, I use the python script attached 
(client.py) which sends data in chunks toward the bpf program. Usually, 
the kernel crashes on the 3rd segment.

To provide more information, I have attached some crash logs. I have 
tested this on kernel version 6.1.0 (slightly modified) and version 
6.2.8 (unmodified, obtained from kernel.org). It seems that the panic 
happens when invoking the bpf_skb_pull_data.

Is this a known issue or is there any information that I can provide to help resolve it?

Sincerely, 
Farbod Shahinfar

PhD student at Politecnico di Milano
https://fshahinfar1.github.io/

View attachment "kernel_crash_log_ver_6.2.8.txt" of type "text/plain" (6600 bytes)

View attachment "kernel_crash_log_ver_6.1.0.txt" of type "text/plain" (5368 bytes)

View attachment "client_py.txt" of type "text/plain" (1108 bytes)

View attachment "bpf_test.c" of type "text/x-csrc" (1460 bytes)