Fix a race condition in getting the trunk name via its mac.

During setting up a branch interface, it can have the same mac address as the trunk for a short period of time, and we may end up picking the branch's name when trying to get the trunk name by mac. Fixing it by picking the shortest name available since branch name is strictly longer than trunk.

network/eni/eni.go

@@ -82,12 +82,7 @@ func (eni *ENI) AttachToLink() error {
 			return err
 		}
 
-		for _, i := range interfaces {
-			if vpc.CompareMACAddress(i.HardwareAddr, eni.macAddress) {
-				iface = &i
-				break
-			}
-		}
+		iface = getInterfaceByMACAddress(eni.macAddress, interfaces)
 
 		if iface == nil {
 			log.Errorf("Failed to find interface with MAC address %s: %v", eni.macAddress, err)
@@ -107,3 +102,20 @@ func (eni *ENI) DetachFromLink() error {
 	eni.linkIndex = 0
 	return nil
 }
+
+// getInterfaceByMACAddress returns the interface with the specified MAC address.
+func getInterfaceByMACAddress(macAddress net.HardwareAddr, interfaces []net.Interface) *net.Interface {
+	var chosenInterface *net.Interface
+
+	// If there are multiple matches, pick the one with the shortest name.
+	for i := 0; i < len(interfaces); i++ {
+		iface := &interfaces[i]
+		if vpc.CompareMACAddress(iface.HardwareAddr, macAddress) {
+			if chosenInterface == nil || len(chosenInterface.Name) > len(iface.Name) {
+				chosenInterface = iface
+			}
+		}
+	}
+
+	return chosenInterface
+}

network/eni/eni_test.go

@@ -0,0 +1,53 @@
+// Copyright 2019 Amazon.com, Inc. or its affiliates. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License"). You may
+// not use this file except in compliance with the License. A copy of the
+// License is located at
+//
+//     http://aws.amazon.com/apache2.0/
+//
+// or in the "license" file accompanying this file. This file is distributed
+// on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either
+// express or implied. See the License for the specific language governing
+// permissions and limitations under the License.
+
+package eni
+
+import (
+	"net"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestGetInterfaceByMacAddress(t *testing.T) {
+	mac1, _ := net.ParseMAC("12:34:56:78:9a:bc")
+	mac2, _ := net.ParseMAC("cb:a9:87:65:43:21")
+
+	interfaces := []net.Interface{
+		{
+			Index: 1,
+			Name: "eth1.1",
+			HardwareAddr: mac1,
+		},
+		{
+			Index: 2,
+			Name: "eth1",
+			HardwareAddr: mac1,
+		},
+		{
+			Index: 3,
+			Name: "eth1.1.1",
+			HardwareAddr: mac1,
+		},
+		{
+			Index: 4,
+			Name: "eth",
+			HardwareAddr: mac2,
+		},
+	}
+
+	chosenInterface := getInterfaceByMACAddress(mac1, interfaces)
+	assert.NotNil(t, chosenInterface)
+	assert.Equal(t, "eth1", chosenInterface.Name)
+}