net/af_packet: add VLAN support for AF_PACKET SOCK_RAW GSO

Currently, the kernel drops GSO VLAN tagged packet if it's created with
socket(AF_PACKET, SOCK_RAW, 0) plus virtio_net_hdr.

The reason is AF_PACKET doesn't adjust the skb network header if there is
a VLAN tag. Then after virtio_net_hdr_set_proto() called, the skb->protocol
will be set to ETH_P_IP/IPv6. And in later inet/ipv6_gso_segment() the skb
is dropped as network header position is invalid.

Let's handle VLAN packets by adjusting network header position in
packet_parse_headers(). The adjustment is safe and does not affect the
later xmit as tap device also did that.

In packet_snd(), packet_parse_headers() need to be moved before calling
virtio_net_hdr_set_proto(), so we can set correct skb->protocol and
network header first.

There is no need to update tpacket_snd() as it calls packet_parse_headers()
in tpacket_fill_skb(), which is already before calling virtio_net_hdr_*
functions.

skb->no_fcs setting is also moved upper to make all skb settings together
and keep consistency with function packet_sendmsg_spkt().
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Link: https://lore.kernel.org/r/20220425014502.985464-1-liuhangbin@gmail.comSigned-off-by: Paolo Abeni <pabeni@redhat.com>

net/packet/af_packet.c

@@ -1924,12 +1924,20 @@ static int packet_rcv_spkt(struct sk_buff *skb, struct net_device *dev,
 
 static void packet_parse_headers(struct sk_buff *skb, struct socket *sock)
 {
+	int depth;
+
 	if ((!skb->protocol || skb->protocol == htons(ETH_P_ALL)) &&
 	    sock->type == SOCK_RAW) {
 		skb_reset_mac_header(skb);
 		skb->protocol = dev_parse_header_protocol(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(skb, skb->protocol, &depth) != 0)
+		skb_set_network_header(skb, depth);
+
 	skb_probe_transport_header(skb);
 }
 
@@ -3047,6 +3055,11 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	skb->mark = sockc.mark;
 	skb->tstamp = sockc.transmit_time;
 
+	if (unlikely(extra_len == 4))
+		skb->no_fcs = 1;
+
+	packet_parse_headers(skb, sock);
+
 	if (has_vnet_hdr) {
 		err = virtio_net_hdr_to_skb(skb, &vnet_hdr, vio_le());
 		if (err)
@@ -3055,11 +3068,6 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 		virtio_net_hdr_set_proto(skb, &vnet_hdr);
 	}
 
-	packet_parse_headers(skb, sock);
-
-	if (unlikely(extra_len == 4))
-		skb->no_fcs = 1;
-
 	err = po->xmit(skb);
 	if (unlikely(err != 0)) {
 		if (err > 0)