vnet: fix issues (#4771)

pkg/vnet/tun_linux.go

@@ -16,35 +16,44 @@ package vnet
 
 import (
 	"context"
+	"crypto/sha256"
+	"encoding/hex"
 	"fmt"
 	"net"
+	"strconv"
+	"strings"
 
 	"github.com/vishvananda/netlink"
 	"golang.zx2c4.com/wireguard/tun"
 )
 
 const (
-	defaultTunName = "utun"
-	defaultMTU     = 1420
+	baseTunName = "utun"
+	defaultMTU  = 1420
 )
 
 func openTun(_ context.Context, addr string) (tun.Device, error) {
-	dev, err := tun.CreateTUN(defaultTunName, defaultMTU)
+	name, err := findNextTunName(baseTunName)
+	if err != nil {
+		name = getFallbackTunName(baseTunName, addr)
+	}
+
+	tunDevice, err := tun.CreateTUN(name, defaultMTU)
+	if err != nil {
+		return nil, fmt.Errorf("failed to create TUN device '%s': %w", name, err)
+	}
+
+	actualName, err := tunDevice.Name()
 	if err != nil {
 		return nil, err
 	}
 
-	name, err := dev.Name()
+	ifn, err := net.InterfaceByName(actualName)
 	if err != nil {
 		return nil, err
 	}
 
-	ifn, err := net.InterfaceByName(name)
-	if err != nil {
-		return nil, err
-	}
-
-	link, err := netlink.LinkByName(name)
+	link, err := netlink.LinkByName(actualName)
 	if err != nil {
 		return nil, err
 	}
@@ -69,7 +78,34 @@ func openTun(_ context.Context, addr string) (tun.Device, error) {
 	if err = addRoutes(ifn, cidr); err != nil {
 		return nil, err
 	}
-	return dev, nil
+	return tunDevice, nil
+}
+
+func findNextTunName(basename string) (string, error) {
+	interfaces, err := net.Interfaces()
+	if err != nil {
+		return "", fmt.Errorf("failed to get network interfaces: %w", err)
+	}
+	maxSuffix := -1
+
+	for _, iface := range interfaces {
+		name := iface.Name
+		if strings.HasPrefix(name, basename) {
+			suffix := name[len(basename):]
+			if suffix == "" {
+				continue
+			}
+
+			numSuffix, err := strconv.Atoi(suffix)
+			if err == nil && numSuffix > maxSuffix {
+				maxSuffix = numSuffix
+			}
+		}
+	}
+
+	nextSuffix := maxSuffix + 1
+	name := fmt.Sprintf("%s%d", basename, nextSuffix)
+	return name, nil
 }
 
 func addRoutes(ifn *net.Interface, cidr *net.IPNet) error {
@@ -82,3 +118,14 @@ func addRoutes(ifn *net.Interface, cidr *net.IPNet) error {
 	}
 	return nil
 }
+
+// getFallbackTunName generates a deterministic fallback TUN device name
+// based on the base name and the provided address string using a hash.
+func getFallbackTunName(baseName, addr string) string {
+	hasher := sha256.New()
+	hasher.Write([]byte(addr))
+	hashBytes := hasher.Sum(nil)
+	// Use first 4 bytes -> 8 hex chars for brevity, respecting IFNAMSIZ limit.
+	shortHash := hex.EncodeToString(hashBytes[:4])
+	return fmt.Sprintf("%s%s", baseName, shortHash)
+}