Re: [PATCH net-next] net: xdp: don't assume an Ethernet header in generic XDP

["Toke Høiland-Jørgensen" <toke@redhat.com>]

Alexander Lobakin <aleksander.lobakin@intel.com> writes:

> From: Jiayuan Chen <jiayuan.chen@linux.dev>
> Date: Thu, 13 Aug 2026 19:32:24 +0800
>
>> Kenneth Lee reported a bug [1]:
>> 
>>   skb_vlan_push got skb with skb->data not at mac header (offset 14)
>>   WARNING: net/core/skbuff.c:6474 at skb_vlan_push+0x5ec/0x8a0
>>    ____bpf_skb_vlan_push net/core/filter.c:3239 [inline]
>>    bpf_skb_vlan_push+0x216/0x8b0 net/core/filter.c:3229
>>    bpf_prog_run_data_pointers+0x17c/0x240 include/linux/filter.h:917
>>    tcf_bpf_act+0x31c/0x940 net/sched/act_bpf.c:50
>>    tcf_action_exec+0x2c1/0x720 net/sched/act_api.c:1147
>>    tcf_classify+0x6e4/0x1080 net/sched/cls_api.c:1860
>>    tc_run+0x31c/0x5d0 net/core/dev.c:4411
>>    sch_handle_ingress net/core/dev.c:4486 [inline]
>>    __netif_receive_skb_core+0x141b/0x2ec0 net/core/dev.c:6054
>> 
>> bpf_prog_run_generic_xdp() just assumes xdp->data is an Ethernet header:
> Most XDP programs expect Ethernet header at the beginning of a frame.
> Unless you write a custom one which doesn't.
> But then you may face that XDP_TX, XDP_REDIRECT won't work properly --
> cpumap Rx, each .ndo_xdp_xmit() implementation -- all expect Ethernet
> header at the beginning.

Yeah, I don't think we should start messing with the "XDP is Ethernet
only" assumption at this point...

-Toke