linux-kernel - Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt

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Message-Id: <04d2eb4a-7365-495a-ab74-704febac2789@app.fastmail.com>
Date:   Fri, 14 Oct 2022 17:29:41 +0100
From:   "Lorenz Bauer" <oss@....io>
To:     shaozhengchao <shaozhengchao@...wei.com>,
        "Stanislav Fomichev" <sdf@...gle.com>
Cc:     "Alexei Starovoitov" <ast@...nel.org>,
        "Daniel Borkmann" <daniel@...earbox.net>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org, yuehaibing@...wei.com
Subject: Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt_len

On Thu, 13 Oct 2022, at 11:44, shaozhengchao wrote:
> 	Sorry, I haven't fully understood your intentions yet.
> Can you explain it more detail?

I'll try! Roughly, we do the following:

1. Create a BPF_PROG_TYPE_SOCKET_FILTER program that just returns 0
2. Load the program into the kernel
3. Call BPF_PROG_RUN with data_size_in == 14

After your bugfix, it seems like step 3 is rejected due to data_size_in == 14. We had to increase data_size_in to 15 to
avoid this, see [0].

This breaks user space, so it would be great if you could fix this in a way that doesn't refuse BPF_PROG_RUN with
data_size_in == 14. Since I don't understand the original problem very well I can't tell you what the best fix is however.

0: https://github.com/cilium/ebpf/commit/a38fb6b5a46ab3b5639ea4d421232a10013596c0

Thanks
Lorenz