Update dependencies

vendor/tailscale.com/util/linuxfw/iptables.go

@@ -0,0 +1,73 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+// TODO(#8502): add support for more architectures
+//go:build linux && (arm64 || amd64)
+
+package linuxfw
+
+import (
+	"fmt"
+	"os/exec"
+	"strings"
+	"unicode"
+
+	"tailscale.com/types/logger"
+	"tailscale.com/util/multierr"
+)
+
+// DebugNetfilter prints debug information about iptables rules to the
+// provided log function.
+func DebugIptables(logf logger.Logf) error {
+	// unused.
+	return nil
+}
+
+// detectIptables returns the number of iptables rules that are present in the
+// system, ignoring the default "ACCEPT" rule present in the standard iptables
+// chains.
+//
+// It only returns an error when there is no iptables binary, or when iptables -S
+// fails. In all other cases, it returns the number of non-default rules.
+//
+// If the iptables binary is not found, it returns an underlying exec.ErrNotFound
+// error.
+func detectIptables() (int, error) {
+	// run "iptables -S" to get the list of rules using iptables
+	// exec.Command returns an error if the binary is not found
+	cmd := exec.Command("iptables", "-S")
+	output, err := cmd.Output()
+	ip6cmd := exec.Command("ip6tables", "-S")
+	ip6output, ip6err := ip6cmd.Output()
+	var allLines []string
+	outputStr := string(output)
+	lines := strings.Split(outputStr, "\n")
+	ip6outputStr := string(ip6output)
+	ip6lines := strings.Split(ip6outputStr, "\n")
+	switch {
+	case err == nil && ip6err == nil:
+		allLines = append(lines, ip6lines...)
+	case err == nil && ip6err != nil:
+		allLines = lines
+	case err != nil && ip6err == nil:
+		allLines = ip6lines
+	default:
+		return 0, FWModeNotSupportedError{
+			Mode: FirewallModeIPTables,
+			Err:  fmt.Errorf("iptables command run fail: %w", multierr.New(err, ip6err)),
+		}
+	}
+
+	// count the number of non-default rules
+	count := 0
+	for _, line := range allLines {
+		trimmedLine := strings.TrimLeftFunc(line, unicode.IsSpace)
+		if line != "" && strings.HasPrefix(trimmedLine, "-A") {
+			// if the line is not empty and starts with "-A", it is a rule appended not default
+			count++
+		}
+	}
+
+	// return the count of non-default rules
+	return count, nil
+}