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charset="utf-8" From: Wei Fang In packet_parse_headers(), when processing a VLAN-tagged frame on a SOCK_RAW AF_PACKET socket, skb_set_network_header() is called with the depth returned by vlan_get_protocol_and_depth() to advance network_header past the VLAN tag to the inner protocol header. However, skb->protocol was not updated to reflect the inner EtherType resolved by vlan_get_protocol_and_depth(), leaving it pointing to the outer VLAN EtherType (e.g. ETH_P_8021Q). This mismatch causes skb_probe_transport_header() to invoke the flow dissector with proto=3DETH_P_8021Q but nhoff already pointing past the VLAN tag to the inner header. The dissector interprets the inner header bytes as a VLAN header, fails to find a recognizable encapsulated protocol, and returns false. Consequently, transport_header is never set and remains at its uninitialized sentinel value (~0U =3D 0xFFFF). Any subsequent code that calls skb_transport_header() or udp_hdr() on such an skb will dereference a pointer 65535 bytes past skb->head, potentially corrupting arbitrary kernel memory. Save the return value of vlan_get_protocol_and_depth(), which already resolves the inner EtherType, and assign it to skb->protocol after skb_set_network_header(). This keeps skb->protocol and network_header consistent when skb_probe_transport_header() is called, allowing the flow dissector to correctly identify the transport layer header. Fixes: dfed913e8b55 ("net/af_packet: add VLAN support for AF_PACKET SOCK_RA= W GSO") Assisted-by: WChat:claude-opus-4-8 Signed-off-by: Wei Fang --- net/packet/af_packet.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c index 0e1355be89f6..a62d445047c0 100644 --- a/net/packet/af_packet.c +++ b/net/packet/af_packet.c @@ -1945,9 +1945,15 @@ static void packet_parse_headers(struct sk_buff *skb= , struct socket *sock) =20 /* Move network header to the right position for VLAN tagged packets */ if (likely(skb->dev->type =3D=3D ARPHRD_ETHER) && - eth_type_vlan(skb->protocol) && - vlan_get_protocol_and_depth(skb, skb->protocol, &depth) !=3D 0) - skb_set_network_header(skb, depth); + eth_type_vlan(skb->protocol)) { + __be16 proto =3D vlan_get_protocol_and_depth(skb, skb->protocol, + &depth); + + if (proto !=3D 0) { + skb_set_network_header(skb, depth); + skb->protocol =3D proto; + } + } =20 skb_probe_transport_header(skb); 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charset="utf-8" From: Wei Fang In tap_get_user_xdp(), when processing a VLAN-tagged frame, skb_set_network_header() is called with the depth returned by vlan_get_protocol_and_depth() to advance network_header past the VLAN tag to the inner protocol header. However, skb->protocol was not updated to reflect the inner EtherType, leaving it pointing to the outer VLAN EtherType (e.g. ETH_P_8021Q). This mismatch has two consequences. First, skb_probe_transport_header() is called after the VLAN adjustment with proto=3DETH_P_8021Q but nhoff already pointing past the VLAN tag to the inner header. The flow dissector interprets the inner header bytes as a VLAN header, fails to find a recognizable encapsulated protocol, and returns false. Consequently, transport_header is never set and remains at its uninitialized sentinel value (~0U), causing any subsequent skb_transport_header() or udp_hdr() call to dereference a pointer 65535 bytes past skb->head, potentially corrupting arbitrary kernel memory. Second, TC egress and eBPF programs that inspect skb->protocol directly (e.g. bpf_skb_net_base_len(), bpf_skb_net_grow(), __bpf_redirect_neigh()) will see ETH_P_8021Q instead of the inner protocol and behave incorrectly. Save the return value of vlan_get_protocol_and_depth(), which already resolves the inner EtherType, and assign it to skb->protocol after skb_set_network_header(). This keeps skb->protocol and network_header consistent for all subsequent processing. Fixes: 8c76e77f9069 ("tap: call skb_probe_transport_header after setting sk= b->dev") Assisted-by: WChat:claude-opus-4-8 Signed-off-by: Wei Fang --- drivers/net/tap.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/net/tap.c b/drivers/net/tap.c index fae115915c8e..afcc4919bd04 100644 --- a/drivers/net/tap.c +++ b/drivers/net/tap.c @@ -1081,9 +1081,15 @@ static int tap_get_user_xdp(struct tap_queue *q, str= uct xdp_buff *xdp) } =20 /* 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) !=3D 0) - skb_set_network_header(skb, depth); + if (eth_type_vlan(skb->protocol)) { + __be16 proto =3D vlan_get_protocol_and_depth(skb, skb->protocol, + &depth); + + if (proto !=3D 0) { + skb_set_network_header(skb, depth); + skb->protocol =3D proto; + } + } =20 rcu_read_lock(); tap =3D rcu_dereference(q->tap); --=20 2.34.1