From: sdf@google.com
To: Lorenz Bauer <oss@lmb.io>
Cc: shaozhengchao <shaozhengchao@huawei.com>,
Alexei Starovoitov <ast@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
yuehaibing@huawei.com
Subject: Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt_len
Date: Fri, 14 Oct 2022 09:55:40 -0700 [thread overview]
Message-ID: <Y0mUjLXEpVuheSUc@google.com> (raw)
In-Reply-To: <04d2eb4a-7365-495a-ab74-704febac2789@app.fastmail.com>
On 10/14, Lorenz Bauer wrote:
> 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.
The problem was that we were able to generate skb with len=0 via
BPF_PROG_RUN. Prohibiting those cases breaks backwards compatibility, so
we either have to:
a) (preferred?) accept inputs with <14, but maybe internally pad to 14
bytes to make the core stack happy
b) revert the patch and instead have length checks at runtime; doesn't seem
to
be worth the penalty in the forwarding path because of some corner cases
like these ?
> 0:
> https://github.com/cilium/ebpf/commit/a38fb6b5a46ab3b5639ea4d421232a10013596c0
> Thanks
> Lorenz
next prev parent reply other threads:[~2022-10-14 16:55 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-07-15 11:55 [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid pkt_len Zhengchao Shao
2022-07-15 23:30 ` Stanislav Fomichev
2022-07-19 17:00 ` patchwork-bot+netdevbpf
2022-09-14 11:19 ` Lorenz Bauer
2022-09-17 15:46 ` Stanislav Fomichev
2022-09-19 10:55 ` shaozhengchao
2022-09-20 14:42 ` Lorenz Bauer
2022-09-21 8:48 ` shaozhengchao
2022-09-21 20:59 ` Stanislav Fomichev
2022-10-13 9:36 ` Lorenz Bauer
2022-10-13 10:44 ` shaozhengchao
2022-10-14 16:29 ` Lorenz Bauer
2022-10-14 16:55 ` sdf [this message]
2022-10-15 2:36 ` shaozhengchao
2022-11-03 21:07 ` Martin KaFai Lau
2022-11-03 21:36 ` Stanislav Fomichev
2022-11-03 22:42 ` Martin KaFai Lau
2022-11-03 22:58 ` Stanislav Fomichev
2022-11-09 21:43 ` Stanislav Fomichev
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