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Miller" , Jakub Kicinski , Paolo Abeni Cc: Willem de Bruijn , Simon Horman , netdev@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 Subject: [PATCH net 3/5] net: use eth_type_trans_careful() in __dev_forward_skb2() Date: Tue, 27 Oct 2026 09:26:02 +0100 Message-ID: <20261027082604.1485903-4-edumazet@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20261027082604.1485903-1-edumazet@kernel.org> References: <20261027082604.1485903-1-edumazet@kernel.org> 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-Transfer-Encoding: 8bit A tc egress BPF program can push a tiny link-layer header with bpf_skb_change_head() on an skb whose head is almost empty, then redirect it to an Ethernet device ingress. __bpf_redirect_common() only checks mac_header < network_header, and __dev_forward_skb2() crashes in eth_type_trans(): tc filter add dev lo egress pref 1 matchall action vlan pop_eth continue tc filter add dev lo egress pref 2 bpf da obj prog.o # prog: bpf_skb_change_head(skb, 1, 0); # return bpf_redirect(veth1_ifindex, BPF_F_INGRESS); # AF_PACKET SOCK_RAW on lo: 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: __dev_forward_skb2 (net/core/dev.c:2507) dev_forward_skb_nomtu (net/core/dev.c:2546) __dev_queue_xmit (net/core/dev.c:4738 net/core/dev.c:4998) packet_sendmsg (net/packet/af_packet.c:3157 net/packet/af_packet.c:3189) Use eth_type_trans_careful(), and drop the packet if the Ethernet header can not be pulled. This also covers other dev_forward_skb() users (veth, macvlan, ipvlan, netdevsim, l2tp_eth). Fixes: 3a0af8fd61f9 ("bpf: BPF for lightweight tunnel infrastructure") Signed-off-by: Eric Dumazet --- net/core/dev.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) diff --git a/net/core/dev.c b/net/core/dev.c index 1a09e7869118059e92b53e00ed873dfc7485ffc3..ac784310a69c1d9ceecf68909334196b555871c5 100644 --- a/net/core/dev.c +++ b/net/core/dev.c @@ -2501,14 +2501,22 @@ EXPORT_SYMBOL_GPL(is_skb_forwardable); static int __dev_forward_skb2(struct net_device *dev, struct sk_buff *skb, bool check_mtu) { - int ret = ____dev_forward_skb(dev, skb, check_mtu); + enum skb_drop_reason reason; + int ret; + + ret = ____dev_forward_skb(dev, skb, check_mtu); + if (unlikely(ret)) + return ret; - if (likely(!ret)) { - skb->protocol = eth_type_trans(skb, dev); - skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN); + reason = eth_type_trans_careful(skb, dev); + if (unlikely(reason)) { + dev_core_stats_rx_dropped_inc(dev); + kfree_skb_reason(skb, reason); + return NET_RX_DROP; } + skb_postpull_rcsum(skb, eth_hdr(skb), ETH_HLEN); - return ret; + return 0; } int __dev_forward_skb(struct net_device *dev, struct sk_buff *skb) -- 2.53.0