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

[Lorenz Bauer]

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