[PATCH] af_packet: Handle outgoing VLAN packets without hardware offloading

[Chengen Du]

In the outbound packet path, if hardware VLAN offloading is unavailable,
the VLAN tag is inserted into the payload but then cleared from the
metadata. Consequently, this could lead to a false negative result when
checking for the presence of a VLAN tag using skb_vlan_tag_present(),
causing the packet sniffing outcome to lack VLAN tag information. As a
result, the packet capturing tool may be unable to parse packets as
expected.

Signed-off-by: Chengen Du <chengen.du@xxxxxxxxxxxxx>
---
 net/packet/af_packet.c | 25 +++++++++++++++++++------
 1 file changed, 19 insertions(+), 6 deletions(-)

diff --git a/net/packet/af_packet.c b/net/packet/af_packet.c
index ea3ebc160e25..73e9acb1875b 100644
--- a/net/packet/af_packet.c
+++ b/net/packet/af_packet.c
@@ -1010,12 +1010,15 @@ static void prb_fill_vlan_info(struct tpacket_kbdq_core *pkc,
 	if (skb_vlan_tag_present(pkc->skb)) {
 		ppd->hv1.tp_vlan_tci = skb_vlan_tag_get(pkc->skb);
 		ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->vlan_proto);
-		ppd->tp_status = TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
+	} else if (eth_type_vlan(pkc->skb->protocol)) {
+		ppd->hv1.tp_vlan_tci = ntohs(vlan_eth_hdr(pkc->skb)->h_vlan_TCI);
+		ppd->hv1.tp_vlan_tpid = ntohs(pkc->skb->protocol);
 	} else {
 		ppd->hv1.tp_vlan_tci = 0;
 		ppd->hv1.tp_vlan_tpid = 0;
-		ppd->tp_status = TP_STATUS_AVAILABLE;
 	}
+	ppd->tp_status = (ppd->hv1.tp_vlan_tci || ppd->hv1.tp_vlan_tpid) ?
+		TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID : TP_STATUS_AVAILABLE;
 }
 
 static void prb_run_all_ft_ops(struct tpacket_kbdq_core *pkc,
@@ -2427,11 +2430,15 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 		if (skb_vlan_tag_present(skb)) {
 			h.h2->tp_vlan_tci = skb_vlan_tag_get(skb);
 			h.h2->tp_vlan_tpid = ntohs(skb->vlan_proto);
-			status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
+		} else if (eth_type_vlan(skb->protocol)) {
+			h.h2->tp_vlan_tci = ntohs(vlan_eth_hdr(skb)->h_vlan_TCI);
+			h.h2->tp_vlan_tpid = ntohs(skb->protocol);
 		} else {
 			h.h2->tp_vlan_tci = 0;
 			h.h2->tp_vlan_tpid = 0;
 		}
+		if (h.h2->tp_vlan_tci || h.h2->tp_vlan_tpid)
+			status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
 		memset(h.h2->tp_padding, 0, sizeof(h.h2->tp_padding));
 		hdrlen = sizeof(*h.h2);
 		break;
@@ -2457,7 +2464,8 @@ static int tpacket_rcv(struct sk_buff *skb, struct net_device *dev,
 	sll->sll_halen = dev_parse_header(skb, sll->sll_addr);
 	sll->sll_family = AF_PACKET;
 	sll->sll_hatype = dev->type;
-	sll->sll_protocol = skb->protocol;
+	sll->sll_protocol = eth_type_vlan(skb->protocol) ?
+		vlan_eth_hdr(skb)->h_vlan_encapsulated_proto : skb->protocol;
 	sll->sll_pkttype = skb->pkt_type;
 	if (unlikely(packet_sock_flag(po, PACKET_SOCK_ORIGDEV)))
 		sll->sll_ifindex = orig_dev->ifindex;
@@ -3482,7 +3490,8 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		/* Original length was stored in sockaddr_ll fields */
 		origlen = PACKET_SKB_CB(skb)->sa.origlen;
 		sll->sll_family = AF_PACKET;
-		sll->sll_protocol = skb->protocol;
+		sll->sll_protocol = eth_type_vlan(skb->protocol) ?
+			vlan_eth_hdr(skb)->h_vlan_encapsulated_proto : skb->protocol;
 	}
 
 	sock_recv_cmsgs(msg, sk, skb);
@@ -3538,11 +3547,15 @@ static int packet_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
 		if (skb_vlan_tag_present(skb)) {
 			aux.tp_vlan_tci = skb_vlan_tag_get(skb);
 			aux.tp_vlan_tpid = ntohs(skb->vlan_proto);
-			aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
+		} else if (eth_type_vlan(skb->protocol)) {
+			aux.tp_vlan_tci = ntohs(vlan_eth_hdr(skb)->h_vlan_TCI);
+			aux.tp_vlan_tpid = ntohs(skb->protocol);
 		} else {
 			aux.tp_vlan_tci = 0;
 			aux.tp_vlan_tpid = 0;
 		}
+		if (aux.tp_vlan_tci || aux.tp_vlan_tpid)
+			aux.tp_status |= TP_STATUS_VLAN_VALID | TP_STATUS_VLAN_TPID_VALID;
 		put_cmsg(msg, SOL_PACKET, PACKET_AUXDATA, sizeof(aux), &aux);
 	}
 
-- 
2.40.1