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Fri, 23 Oct 2026 11:17:17 -0700 (PDT) X-Received: by 2002:a05:600c:3b18:b0:4a1:78c5:79f5 with SMTP id 5b1f17b1804b1-4a211ed8fb3mr45466695e9.33.1792779436892; Fri, 23 Oct 2026 11:17:16 -0700 (PDT) Received: from aconole-thinkpadt14gen4.rmtusnh.csb ([216.212.39.190]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-4a35a046fefsm305055e9.5.2026.10.23.11.17.14 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 23 Oct 2026 11:17:16 -0700 (PDT) From: Aaron Conole To: Jamal Hadi Salim Cc: netdev@vger.kernel.org, Eelco Chaudron , Ilya Maximets , "David S . Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , Pravin B Shelar , Martin Varghese , Jiri Pirko , Victor Nogueira , dev@openvswitch.org, stable@vger.kernel.org Subject: Re: [PATCH net v2 5/6] net: openvswitch: ensure a linear inner Ethernet header on TEB pop In-Reply-To: (Jamal Hadi Salim's message of "Fri, 23 Oct 2026 07:59:20 -0400") References: Date: Fri, 23 Oct 2026 14:17:13 -0400 Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) X-Mailing-List: netdev@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Type: text/plain Jamal Hadi Salim writes: > The issue: > pop_mpls() restores MAC_PROTO_ETHERNET when the popped ethertype is > ETH_P_TEB, but skb_mpls_pop() only guarantees that the MPLS shim is in > the linear area. When the inner Ethernet header sits in a page > fragment, the datapath now claims an Ethernet header it cannot access > linearly. > > Output to an OVS internal vport then calls eth_type_trans(), which > pulls ETH_HLEN from an empty linear area and triggers the BUG in > __skb_pull(): > > kernel BUG at ./include/linux/skbuff.h:2830! > RIP: 0010:eth_type_trans+0x335/0x500 > internal_dev_recv > ovs_vport_send > do_output > do_execute_actions > ovs_execute_actions > ovs_dp_process_packet > ovs_vport_receive > internal_dev_xmit > > Conditions to recreate the bug: > On a system with 4 KiB pages and CONFIG_OPENVSWITCH and CONFIG_PACKET > enabled, use CAP_NET_ADMIN to create an OVS datapath and bring its local > internal port up with MTU 9000. Install a flow matching an Ethernet/MPLS > packet with one bottom-of-stack label and actions pop_eth, > pop_mpls(0x6558), output to the local port. With CAP_NET_RAW, send a > 4128-byte AF_PACKET/SOCK_RAW frame containing outer Ethernet, the MPLS > label, inner Ethernet and 4096 payload bytes. The two pops consume the > linear headers and expose the inner Ethernet header in page fragments. > > The Fix: > Pull the inner Ethernet header into the linear area before restoring > MAC_PROTO_ETHERNET. > > Fixes: f66b53fdbb22 ("openvswitch: New MPLS actions for layer 2 tunnelling") > Link: https://lore.kernel.org/netdev/e85fa16e-df3c-43dd-bb3a-9edca07200ea@kernel.org/ > Cc: stable@vger.kernel.org > Reviewed-by: Ilya Maximets > Reviewed-by: Eric Dumazet > Signed-off-by: Jamal Hadi Salim > --- Reviewed-by: Aaron Conole