Merge pull request #212 from crosbymichael/veth-naming

Add more entropy to veth pair creation

netlink/netlink.go

@@ -11,8 +11,9 @@ import (
 )
 
 var (
-	ErrWrongSockType = errors.New("Wrong socket type")
-	ErrShortResponse = errors.New("Got short response from netlink")
+	ErrWrongSockType   = errors.New("Wrong socket type")
+	ErrShortResponse   = errors.New("Got short response from netlink")
+	ErrInterfaceExists = errors.New("Network interface already exists")
 )
 
 // A Route is a subnet associated with the interface to reach it.

netlink/netlink_linux.go

@@ -6,6 +6,7 @@ import (
 	"io"
 	"math/rand"
 	"net"
+	"os"
 	"sync/atomic"
 	"syscall"
 	"unsafe"
@@ -708,7 +709,16 @@ func NetworkCreateVethPair(name1, name2 string) error {
 	if err := s.Send(wb); err != nil {
 		return err
 	}
-	return s.HandleAck(wb.Seq)
+
+	if err := s.HandleAck(wb.Seq); err != nil {
+		if os.IsExist(err) {
+			return ErrInterfaceExists
+		}
+
+		return err
+	}
+
+	return nil
 }
 
 // Add a new VLAN interface with masterDev as its upper device

network/veth.go

@@ -5,6 +5,7 @@ package network
 import (
 	"fmt"
 
+	"github.com/docker/libcontainer/netlink"
 	"github.com/docker/libcontainer/utils"
 )
 
@@ -96,16 +97,25 @@ func (v *Veth) Initialize(config *Network, networkState *NetworkState) error {
 // createVethPair will automatically generage two random names for
 // the veth pair and ensure that they have been created
 func createVethPair(prefix string) (name1 string, name2 string, err error) {
-	name1, err = utils.GenerateRandomName(prefix, 4)
-	if err != nil {
-		return
-	}
-	name2, err = utils.GenerateRandomName(prefix, 4)
-	if err != nil {
-		return
-	}
-	if err = CreateVethPair(name1, name2); err != nil {
-		return
+	for i := 0; i < 10; i++ {
+		if name1, err = utils.GenerateRandomName(prefix, 7); err != nil {
+			return
+		}
+
+		if name2, err = utils.GenerateRandomName(prefix, 7); err != nil {
+			return
+		}
+
+		if err = CreateVethPair(name1, name2); err != nil {
+			if err == netlink.ErrInterfaceExists {
+				continue
+			}
+
+			return
+		}
+
+		break
 	}
+
 	return
 }

network/veth_test.go

@@ -0,0 +1,53 @@
+// +build linux
+
+package network
+
+import (
+	"testing"
+
+	"github.com/docker/libcontainer/netlink"
+)
+
+func TestGenerateVethNames(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+
+	prefix := "veth"
+
+	name1, name2, err := createVethPair(prefix)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if name1 == "" {
+		t.Fatal("name1 should not be empty")
+	}
+
+	if name2 == "" {
+		t.Fatal("name2 should not be empty")
+	}
+}
+
+func TestCreateDuplicateVethPair(t *testing.T) {
+	if testing.Short() {
+		return
+	}
+
+	prefix := "veth"
+
+	name1, name2, err := createVethPair(prefix)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// retry to create the name interfaces and make sure that we get the correct error
+	err = CreateVethPair(name1, name2)
+	if err == nil {
+		t.Fatal("expected error to not be nil with duplicate interface")
+	}
+
+	if err != netlink.ErrInterfaceExists {
+		t.Fatalf("expected error to be ErrInterfaceExists but received %q", err)
+	}
+}