From 01fdecc0480d916c799dbee584833a4a37e94d06 Mon Sep 17 00:00:00 2001 From: Wei Fang Date: Fri, 7 Aug 2026 14:34:04 +0800 Subject: [PATCH 1/2] net: packet: fix wrong transport_header when sending VLAN-tagged frame In packet_parse_headers(), when processing a VLAN-tagged frame, skb_set_network_header() is called to advance network_header past the VLAN tag to the inner protocol header. skb_probe_transport_header() is then called with skb->protocol still set to the outer VLAN EtherType (e.g. ETH_P_8021Q), while nhoff (derived from skb_network_offset()) already points past the VLAN tag to the inner protocol header. In __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff points past the VLAN tag. When the dissector hits case ETH_P_8021Q, it reads a struct vlan_hdr at nhoff via __skb_header_pointer(), but that offset contains the inner protocol header (e.g. an IP header). The bytes are misinterpreted as a VLAN header, yielding a garbage encapsulated EtherType that matches no known protocol. The dissector returns false, so skb_probe_transport_header() never calls skb_set_transport_header(), leaving transport_header at its uninitialized sentinel value (~0U). Move skb_probe_transport_header() to before skb_set_network_header(). At the time skb_probe_transport_header() is called, network_header still points to the VLAN header, so nhoff correctly points to the VLAN header. The flow dissector can then parse the VLAN header, extract the inner EtherType, and advance nhoff to the inner protocol header, allowing transport_header to be set correctly. Fixes: dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO") Assisted-by: WChat:claude-opus-4-8 Signed-off-by: Wei Fang Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260807063405.688780-2-wei.fang@oss.nxp.com Signed-off-by: Paolo Abeni --- net/packet/af_packet.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 435756877aba..213a8a3b7ee5 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1943,13 +1943,13 @@ static void packet_parse_headers(struct sk_buff *skb, struct socket *sock) sock->type == SOCK_RAW) skb->protocol = dev_parse_header_protocol(skb); + skb_probe_transport_header(skb); + /* Move network header to the right position for VLAN tagged packets */ if (likely(skb->dev->type == ARPHRD_ETHER) && eth_type_vlan(skb->protocol) && vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0) skb_set_network_header(skb, depth); - - skb_probe_transport_header(skb); } /* From cbb35cbe8db268fefe34c23df15348cf99025298 Mon Sep 17 00:00:00 2001 From: Wei Fang Date: Fri, 7 Aug 2026 14:34:05 +0800 Subject: [PATCH 2/2] net: tap: fix wrong transport_header when sending VLAN-tagged frame In tap_get_user_xdp(), when processing a VLAN-tagged frame (e.g. ETH_P_8021Q), skb_set_network_header() is called first to advance network_header past the VLAN tag to the inner protocol header. skb_probe_transport_header() is then called with skb->protocol still set to ETH_P_8021Q, while nhoff (derived from skb_network_offset()) already points past the VLAN tag to the inner protocol header. In __skb_flow_dissect(), proto is initialized to ETH_P_8021Q and nhoff points past the VLAN tag. When the dissector hits case ETH_P_8021Q, it reads a struct vlan_hdr at the current nhoff via __skb_header_pointer(), but that offset contains the inner protocol header (e.g. an IP header). The bytes are misinterpreted as a VLAN header, yielding a garbage encapsulated EtherType that matches no known protocol. The dissector returns false, so skb_probe_transport_header() never calls skb_set_transport_header(), leaving transport_header at its uninitialized sentinel value (~0U). Move skb_set_network_header() to after skb_probe_transport_header(). At the time skb_probe_transport_header() is called, network_header still points to the VLAN header (offset ETH_HLEN), so nhoff is correct and the flow dissector can parse the VLAN header, extract the inner EtherType, and advance nhoff to the inner protocol header, allowing transport_header to be set correctly. Fixes: 8c76e77f9069 ("tap: call skb_probe_transport_header after setting skb->dev") Assisted-by: WChat:claude-opus-4-8 Signed-off-by: Wei Fang Reviewed-by: Willem de Bruijn Link: https://patch.msgid.link/20260807063405.688780-3-wei.fang@oss.nxp.com Signed-off-by: Paolo Abeni --- drivers/net/tap.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/drivers/net/tap.c b/drivers/net/tap.c index 5d2d34d24ce8..9b5af08cdd47 100644 --- a/drivers/net/tap.c +++ b/drivers/net/tap.c @@ -1091,12 +1091,13 @@ static int tap_get_user_xdp(struct tap_queue *q, struct xdp_buff *xdp) } } + skb_probe_transport_header(skb); + /* Move network header to the right position for VLAN tagged packets */ if (eth_type_vlan(skb->protocol) && vlan_get_protocol_and_depth(skb, skb->protocol, &depth) != 0) skb_set_network_header(skb, depth); - skb_probe_transport_header(skb); dev_queue_xmit(skb); rcu_read_unlock();