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Date: Thu, 8 Oct 2020 10:25:51 +0200 From: Daniel Borkmann <daniel@...earbox.net> To: Jesper Dangaard Brouer <brouer@...hat.com>, John Fastabend <john.fastabend@...il.com> Cc: Maciej Żenczykowski <maze@...gle.com>, bpf <bpf@...r.kernel.org>, Linux NetDev <netdev@...r.kernel.org>, Daniel Borkmann <borkmann@...earbox.net>, Alexei Starovoitov <alexei.starovoitov@...il.com>, Lorenz Bauer <lmb@...udflare.com>, Shaun Crampton <shaun@...era.io>, Lorenzo Bianconi <lorenzo@...nel.org>, Marek Majkowski <marek@...udflare.com>, Jakub Kicinski <kuba@...nel.org>, Eyal Birger <eyal.birger@...il.com> Subject: Re: [PATCH bpf-next V2 5/6] bpf: Add MTU check for TC-BPF packets after egress hook On 10/8/20 10:07 AM, Jesper Dangaard Brouer wrote: [...] >>> However, due to both gso and vlan offload, even this is not trivial to do... >>> The mtu is L3, but drivers/hardware/the wire usually care about L2... > > If net_device->mtu is L3 (1500) and XDP (and TC, right?) operate at L2, > that likely means that the "strict" bpf_mtu_check (in my BPF-helper) is > wrong, as XDP (and TC) length at this point include the 14 bytes > Ethernet header. I will check and fix. Yes, both at L2 layer. > Is this accounted for via net_device->hard_header_len ? It is, see also ether_setup().
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