ibmveth: Detect unsupported packets before sending to the hypervisor

Currently, when ibmveth receive a loopback packet, it reports an
ambiguous error message "tx: h_send_logical_lan failed with rc=-4"
because the hypervisor rejects those types of packets. This fix
detects loopback packet and assures the source packet's MAC address
matches the driver's MAC address before transmitting to the
hypervisor.
Signed-off-by: Cris Forno <cforno12@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/ibm/ibmveth.c

@@ -1011,6 +1011,29 @@ static int ibmveth_send(struct ibmveth_adapter *adapter,
 	return 0;
 }
 
+static int ibmveth_is_packet_unsupported(struct sk_buff *skb,
+					 struct net_device *netdev)
+{
+	struct ethhdr *ether_header;
+	int ret = 0;
+
+	ether_header = eth_hdr(skb);
+
+	if (ether_addr_equal(ether_header->h_dest, netdev->dev_addr)) {
+		netdev_dbg(netdev, "veth doesn't support loopback packets, dropping packet.\n");
+		netdev->stats.tx_dropped++;
+		ret = -EOPNOTSUPP;
+	}
+
+	if (!ether_addr_equal(ether_header->h_source, netdev->dev_addr)) {
+		netdev_dbg(netdev, "source packet MAC address does not match veth device's, dropping packet.\n");
+		netdev->stats.tx_dropped++;
+		ret = -EOPNOTSUPP;
+	}
+
+	return ret;
+}
+
 static netdev_tx_t ibmveth_start_xmit(struct sk_buff *skb,
 				      struct net_device *netdev)
 {
@@ -1022,6 +1045,9 @@ static netdev_tx_t ibmveth_start_xmit(struct sk_buff *skb,
 	dma_addr_t dma_addr;
 	unsigned long mss = 0;
 
+	if (ibmveth_is_packet_unsupported(skb, netdev))
+		goto out;
+
 	/* veth doesn't handle frag_list, so linearize the skb.
 	 * When GRO is enabled SKB's can have frag_list.
 	 */