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[35.245.46.111]) by smtp.gmail.com with ESMTPSA id 00721157ae682-8b19e5c7d50sm33374577b3.30.2026.10.28.11.48.32 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Oct 2026 11:48:33 -0700 (PDT) Date: Wed, 28 Oct 2026 14:48:32 -0400 From: Willem de Bruijn To: Eric Dumazet , "David S . Miller" , Jakub Kicinski , Paolo Abeni Cc: Willem de Bruijn , Simon Horman , netdev@vger.kernel.org, bpf@vger.kernel.org, Eric Dumazet , Andrew Lunn , Aaron Conole , Eelco Chaudron , Ilya Maximets , Jamal Hadi Salim , Jiri Pirko , dev@openvswitch.org, Willem de Bruijn , Ren Wei , Vega Message-ID: In-Reply-To: <20261028122703.2093730-3-edumazet@kernel.org> References: <20261028122703.2093730-1-edumazet@kernel.org> <20261028122703.2093730-3-edumazet@kernel.org> Subject: Re: [PATCH net v2 2/5] loopback: use eth_type_trans_careful() X-Mailing-List: bpf@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; charset=utf-8 Content-Transfer-Encoding: 7bit Eric Dumazet wrote: > tc egress actions can leave an skb with fewer than ETH_HLEN bytes in > its linear part. loopback_xmit() then crashes in eth_type_trans(): > > tc qdisc add dev lo clsact > tc filter add dev lo egress matchall action vlan pop_eth > # AF_PACKET SOCK_RAW: eth / eth / 8192 bytes of payload > > kernel BUG at include/linux/skbuff.h:2839! > RIP: 0010:eth_type_trans (include/linux/etherdevice.h:635 net/ethernet/eth.c:163) > Call Trace: > loopback_xmit (drivers/net/loopback.c:87) > dev_hard_start_xmit (include/linux/netdevice.h:5455 include/linux/netdevice.h:5464 net/core/dev.c:4057 net/core/dev.c:4073) > __dev_queue_xmit (net/core/dev.c:5066) > packet_sendmsg (net/packet/af_packet.c:3157 net/packet/af_packet.c:3189) > > The same happens with "action ife decode" on lo egress. > > Use eth_type_trans_careful(), and drop the packet if the Ethernet > header can not be pulled. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Reported-by: Vega > Link: https://lore.kernel.org/netdev/20261005052249.1914367-2-weir@nebusec.ai/ > Signed-off-by: Eric Dumazet > Reviewed-by: Jamal Hadi Salim > Tested-by: Jamal Hadi Salim Reviewed-by: Willem de Bruijn