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Tue, 18 Aug 2026 11:09:36 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([45.145.92.2]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-482a5a7c603sm14758633f8f.21.2026.08.18.11.09.35 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 18 Aug 2026 11:09:35 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 57C3591AE2A; Tue, 18 Aug 2026 20:09:34 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Alexander Lobakin , Jiayuan Chen Cc: netdev@vger.kernel.org, Kenneth Lee , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Alexei Starovoitov , Daniel Borkmann , Jesper Dangaard Brouer , John Fastabend , Stanislav Fomichev , Kuniyuki Iwashima , Hangbin Liu , Krishna Kumar , Martin Karsten , Martin Willi , linux-kernel@vger.kernel.org, bpf@vger.kernel.org Subject: Re: [PATCH net-next] net: xdp: don't assume an Ethernet header in generic XDP In-Reply-To: References: <20260813113229.381136-1-jiayuan.chen@linux.dev> X-Clacks-Overhead: GNU Terry Pratchett Date: Tue, 18 Aug 2026 20:09:34 +0200 Message-ID: <875x179u75.fsf@toke.dk> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain Alexander Lobakin writes: > From: Jiayuan Chen > 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