Network: Rework IPv6 check. (#12905)

Signed-off-by: Massimiliano Giovagnoli <me@maxgio.it>

Author: maxgio92

internal/net/net.go

@@ -19,7 +19,8 @@ package net
 import (
 	"fmt"
 	_net "net"
-	"os/exec"
+	"os"
+	"strings"
 )
 
 // IsIPV6 checks if the input contains a valid IPV6 address
@@ -41,11 +42,25 @@ func IsPortAvailable(p int) bool {
 // IsIPv6Enabled checks if IPV6 is enabled or not and we have
 // at least one configured in the pod
 func IsIPv6Enabled() bool {
-	cmd := exec.Command("test", "-f", "/proc/net/if_inet6")
-	if cmd.Run() != nil {
+	// Skip interface checks if the IPv6 kernel feature is disabled.
+	disable, err := os.ReadFile("/proc/sys/net/ipv6/conf/all/disable_ipv6")
+	if err != nil {
+		return false
+	}
+	if strings.TrimSpace(string(disable)) == "1" {
+		return false
+	}
+
+	// Check that there are interfaces with IPv6 enabled.
+	ifaces, err := os.Stat("/proc/net/if_inet6")
+	if err != nil {
+		return false
+	}
+	if ifaces.IsDir() {
 		return false
 	}
 
+	// Check IPv6 addresses on interfaces.
 	addrs, err := _net.InterfaceAddrs()
 	if err != nil {
 		return false

internal/net/net_ipv6_test.go

@@ -0,0 +1,28 @@
+//go:build test_ipv6
+
+/*
+Copyright 2015 The Kubernetes Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License 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 net
+
+import "testing"
+
+func TestIsIPv6Enabled(t *testing.T) {
+	isEnabled := IsIPv6Enabled()
+	if !isEnabled {
+		t.Fatalf("expected IPV6 be enabled")
+	}
+}

internal/net/net_test.go

@@ -58,13 +58,3 @@ func TestIsPortAvailable(t *testing.T) {
 		t.Fatalf("expected port %v to not be available", p)
 	}
 }
-
-/*
-// TODO: this test should be optional or running behind a flag
-func TestIsIPv6Enabled(t *testing.T) {
-	isEnabled := IsIPv6Enabled()
-	if !isEnabled {
-		t.Fatalf("expected IPV6 be enabled")
-	}
-}
-*/