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Date:   Wed, 21 Sep 2022 16:48:13 +0800
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Subject: Re: [PATCH v4,bpf-next] bpf: Don't redirect packets with invalid
 pkt_len
To:     Lorenz Bauer <oss@lmb.io>, Stanislav Fomichev <sdf@google.com>
CC:     <ast@kernel.org>, <daniel@iogearbox.net>, <bpf@vger.kernel.org>,
        <linux-kernel@vger.kernel.org>, <yuehaibing@huawei.com>
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From:   shaozhengchao <shaozhengchao@huawei.com>
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On 2022/9/20 22:42, Lorenz Bauer wrote:
> On Mon, 19 Sep 2022, at 11:55, shaozhengchao wrote:
>> Sorry for the delay. I'm busy testing the TC module recently. I'm very
>> sorry for the user-space breakage.
>>
>> The root cause of this problem is that eth_type_trans() is called when
>> the protocol type of the SKB is parsed. The len value of the SKB is
>> reduced to 0. If the user mode requires that the forwarding succeed, or
>>    if the MAC header is added again after the MAC header is subtracted,
>> is this appropriate?
> 
> We don't require forwarding to succeed with a 14 byte input buffer. We also don't look at the MAC header.
> 
> I think refusing to forward 0 length packets would be OK. Not 100% certain I understood you correctly, let me know if this helps.
> 
> Best
> Lorenz
Hi Lorenz
	Sorry. But how does the rejection of the 0 length affect the
test case? Is the return value abnormal, send packet failure or some
others?

Zhengchao Shao