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