macvtap: restore vlan header on user read

Ethernet vlan header is not on the packet and kept in the skb->vlan_tci
when it comes from lower dev. This patch inserts vlan header in user
buffer during skb copy on user read.
Signed-off-by: Basil Gor <basil.gor@gmail.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/macvtap.c

 #include <linux/etherdevice.h>
 #include <linux/if_macvlan.h>
+#include <linux/if_vlan.h>
 #include <linux/interrupt.h>
 #include <linux/nsproxy.h>
 #include <linux/compat.h>
@@ -759,6 +760,8 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
 	struct macvlan_dev *vlan;
 	int ret;
 	int vnet_hdr_len = 0;
+	int vlan_offset = 0;
+	int copied;
 
 	if (q->flags & IFF_VNET_HDR) {
 		struct virtio_net_hdr vnet_hdr;
@@ -773,18 +776,48 @@ static ssize_t macvtap_put_user(struct macvtap_queue *q,
 		if (memcpy_toiovecend(iv, (void *)&vnet_hdr, 0, sizeof(vnet_hdr)))
 			return -EFAULT;
 	}
+	copied = vnet_hdr_len;
 
+	if (!vlan_tx_tag_present(skb))
 		len = min_t(int, skb->len, len);
+	else {
+		int copy;
+		struct {
+			__be16 h_vlan_proto;
+			__be16 h_vlan_TCI;
+		} veth;
+		veth.h_vlan_proto = htons(ETH_P_8021Q);
+		veth.h_vlan_TCI = htons(vlan_tx_tag_get(skb));
+
+		vlan_offset = offsetof(struct vlan_ethhdr, h_vlan_proto);
+		len = min_t(int, skb->len + VLAN_HLEN, len);
+
+		copy = min_t(int, vlan_offset, len);
+		ret = skb_copy_datagram_const_iovec(skb, 0, iv, copied, copy);
+		len -= copy;
+		copied += copy;
+		if (ret || !len)
+			goto done;
+
+		copy = min_t(int, sizeof(veth), len);
+		ret = memcpy_toiovecend(iv, (void *)&veth, copied, copy);
+		len -= copy;
+		copied += copy;
+		if (ret || !len)
+			goto done;
+	}
 
-	ret = skb_copy_datagram_const_iovec(skb, 0, iv, vnet_hdr_len, len);
+	ret = skb_copy_datagram_const_iovec(skb, vlan_offset, iv, copied, len);
+	copied += len;
 
+done:
 	rcu_read_lock_bh();
 	vlan = rcu_dereference_bh(q->vlan);
 	if (vlan)
-		macvlan_count_rx(vlan, len, ret == 0, 0);
+		macvlan_count_rx(vlan, copied - vnet_hdr_len, ret == 0, 0);
 	rcu_read_unlock_bh();
 
-	return ret ? ret : (len + vnet_hdr_len);
+	return ret ? ret : copied;
 }
 
 static ssize_t macvtap_do_read(struct macvtap_queue *q, struct kiocb *iocb,