iptables.go

// Copyright 2015 CoreOS, Inc.
//
// 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 iptables

import (
	"bytes"
	"fmt"
	"io"
	"net"
	"os/exec"
	"regexp"
	"strconv"
	"strings"
	"syscall"
)

// Adds the output of stderr to exec.ExitError
type Error struct {
	exec.ExitError
	cmd        exec.Cmd
	msg        string
	exitStatus *int //for overriding
}

func (e *Error) ExitStatus() int {
	if e.exitStatus != nil {
		return *e.exitStatus
	}
	return e.Sys().(syscall.WaitStatus).ExitStatus()
}

func (e *Error) Error() string {
	return fmt.Sprintf("running %v: exit status %v: %v", e.cmd.Args, e.ExitStatus(), e.msg)
}

// IsNotExist returns true if the error is due to the chain or rule not existing
func (e *Error) IsNotExist() bool {
	return e.ExitStatus() == 1 &&
		(e.msg == "iptables: Bad rule (does a matching rule exist in that chain?).\n" ||
			e.msg == "iptables: No chain/target/match by that name.\n")
}

// Protocol to differentiate between IPv4 and IPv6
type Protocol byte

const (
	ProtocolIPv4 Protocol = iota
	ProtocolIPv6
)

type IPTables struct {
	path           string
	proto          Protocol
	hasCheck       bool
	hasWait        bool
	hasRandomFully bool
	v1             int
	v2             int
	v3             int
	mode           string // the underlying iptables operating mode, e.g. nf_tables
}

// New creates a new IPTables.
// For backwards compatibility, this always uses IPv4, i.e. "iptables".
func New() (*IPTables, error) {
	return NewWithProtocol(ProtocolIPv4)
}

// New creates a new IPTables for the given proto.
// The proto will determine which command is used, either "iptables" or "ip6tables".
func NewWithProtocol(proto Protocol) (*IPTables, error) {
	path, err := exec.LookPath(getIptablesCommand(proto))
	if err != nil {
		return nil, err
	}
	vstring, err := getIptablesVersionString(path)
	v1, v2, v3, mode, err := extractIptablesVersion(vstring)

	checkPresent, waitPresent, randomFullyPresent := getIptablesCommandSupport(v1, v2, v3)

	ipt := IPTables{
		path:           path,
		proto:          proto,
		hasCheck:       checkPresent,
		hasWait:        waitPresent,
		hasRandomFully: randomFullyPresent,
		v1:             v1,
		v2:             v2,
		v3:             v3,
		mode:           mode,
	}
	return &ipt, nil
}

// Proto returns the protocol used by this IPTables.
func (ipt *IPTables) Proto() Protocol {
	return ipt.proto
}

// Exists checks if given rulespec in specified table/chain exists
func (ipt *IPTables) Exists(table, chain string, rulespec ...string) (bool, error) {
	if !ipt.hasCheck {
		return ipt.existsForOldIptables(table, chain, rulespec)

	}
	cmd := append([]string{"-t", table, "-C", chain}, rulespec...)
	err := ipt.run(cmd...)
	eerr, eok := err.(*Error)
	switch {
	case err == nil:
		return true, nil
	case eok && eerr.ExitStatus() == 1:
		return false, nil
	default:
		return false, err
	}
}

// Insert inserts rulespec to specified table/chain (in specified pos)
func (ipt *IPTables) Insert(table, chain string, pos int, rulespec ...string) error {
	cmd := append([]string{"-t", table, "-I", chain, strconv.Itoa(pos)}, rulespec...)
	return ipt.run(cmd...)
}

// Append appends rulespec to specified table/chain
func (ipt *IPTables) Append(table, chain string, rulespec ...string) error {
	cmd := append([]string{"-t", table, "-A", chain}, rulespec...)
	return ipt.run(cmd...)
}

// AppendUnique acts like Append except that it won't add a duplicate
func (ipt *IPTables) AppendUnique(table, chain string, rulespec ...string) error {
	exists, err := ipt.Exists(table, chain, rulespec...)
	if err != nil {
		return err
	}

	if !exists {
		return ipt.Append(table, chain, rulespec...)
	}

	return nil
}

// Delete removes rulespec in specified table/chain
func (ipt *IPTables) Delete(table, chain string, rulespec ...string) error {
	cmd := append([]string{"-t", table, "-D", chain}, rulespec...)
	return ipt.run(cmd...)
}

// List rules in specified table/chain
func (ipt *IPTables) List(table, chain string) ([]string, error) {
	args := []string{"-t", table, "-S", chain}
	return ipt.executeList(args)
}

// List rules (with counters) in specified table/chain
func (ipt *IPTables) ListWithCounters(table, chain string) ([]string, error) {
	args := []string{"-t", table, "-v", "-S", chain}
	return ipt.executeList(args)
}

// ListChains returns a slice containing the name of each chain in the specified table.
func (ipt *IPTables) ListChains(table string) ([]string, error) {
	args := []string{"-t", table, "-S"}

	result, err := ipt.executeList(args)
	if err != nil {
		return nil, err
	}

	// Iterate over rules to find all default (-P) and user-specified (-N) chains.
	// Chains definition always come before rules.
	// Format is the following:
	// -P OUTPUT ACCEPT
	// -N Custom
	var chains []string
	for _, val := range result {
		if strings.HasPrefix(val, "-P") || strings.HasPrefix(val, "-N") {
			chains = append(chains, strings.Fields(val)[1])
		} else {
			break
		}
	}
	return chains, nil
}

// Stats lists rules including the byte and packet counts
func (ipt *IPTables) Stats(table, chain string) ([][]string, error) {
	args := []string{"-t", table, "-L", chain, "-n", "-v", "-x"}
	lines, err := ipt.executeList(args)
	if err != nil {
		return nil, err
	}

	appendSubnet := func(addr string) string {
		if strings.IndexByte(addr, byte('/')) < 0 {
			if strings.IndexByte(addr, '.') < 0 {
				return addr + "/128"
			}
			return addr + "/32"
		}
		return addr
	}

	ipv6 := ipt.proto == ProtocolIPv6

	rows := [][]string{}
	for i, line := range lines {
		// Skip over chain name and field header
		if i < 2 {
			continue
		}

		// Fields:
		// 0=pkts 1=bytes 2=target 3=prot 4=opt 5=in 6=out 7=source 8=destination 9=options
		line = strings.TrimSpace(line)
		fields := strings.Fields(line)

		// The ip6tables verbose output cannot be naively split due to the default "opt"
		// field containing 2 single spaces.
		if ipv6 {
			// Check if field 6 is "opt" or "source" address
			dest := fields[6]
			ip, _, _ := net.ParseCIDR(dest)
			if ip == nil {
				ip = net.ParseIP(dest)
			}

			// If we detected a CIDR or IP, the "opt" field is empty.. insert it.
			if ip != nil {
				f := []string{}
				f = append(f, fields[:4]...)
				f = append(f, "  ") // Empty "opt" field for ip6tables
				f = append(f, fields[4:]...)
				fields = f
			}
		}

		// Adjust "source" and "destination" to include netmask, to match regular
		// List output
		fields[7] = appendSubnet(fields[7])
		fields[8] = appendSubnet(fields[8])

		// Combine "options" fields 9... into a single space-delimited field.
		options := fields[9:]
		fields = fields[:9]
		fields = append(fields, strings.Join(options, " "))
		rows = append(rows, fields)
	}
	return rows, nil
}

func (ipt *IPTables) executeList(args []string) ([]string, error) {
	var stdout bytes.Buffer
	if err := ipt.runWithOutput(args, &stdout); err != nil {
		return nil, err
	}

	rules := strings.Split(stdout.String(), "\n")

	// strip trailing newline
	if len(rules) > 0 && rules[len(rules)-1] == "" {
		rules = rules[:len(rules)-1]
	}

	// nftables mode doesn't return an error code when listing a non-existent
	// chain. Patch that up.
	if len(rules) == 0 && ipt.mode == "nf_tables" {
		v := 1
		return nil, &Error{
			cmd:        exec.Cmd{Args: args},
			msg:        "iptables: No chain/target/match by that name.",
			exitStatus: &v,
		}
	}

	for i, rule := range rules {
		rules[i] = filterRuleOutput(rule)
	}

	return rules, nil
}

// NewChain creates a new chain in the specified table.
// If the chain already exists, it will result in an error.
func (ipt *IPTables) NewChain(table, chain string) error {
	return ipt.run("-t", table, "-N", chain)
}

// ClearChain flushed (deletes all rules) in the specified table/chain.
// If the chain does not exist, a new one will be created
func (ipt *IPTables) ClearChain(table, chain string) error {
	err := ipt.NewChain(table, chain)

	// the exit code for "this table already exists" is different for
	// different iptables modes
	existsErr := 1
	if ipt.mode == "nf_tables" {
		existsErr = 4
	}

	eerr, eok := err.(*Error)
	switch {
	case err == nil:
		return nil
	case eok && eerr.ExitStatus() == existsErr:
		// chain already exists. Flush (clear) it.
		return ipt.run("-t", table, "-F", chain)
	default:
		return err
	}
}

// RenameChain renames the old chain to the new one.
func (ipt *IPTables) RenameChain(table, oldChain, newChain string) error {
	return ipt.run("-t", table, "-E", oldChain, newChain)
}

// DeleteChain deletes the chain in the specified table.
// The chain must be empty
func (ipt *IPTables) DeleteChain(table, chain string) error {
	return ipt.run("-t", table, "-X", chain)
}

// ChangePolicy changes policy on chain to target
func (ipt *IPTables) ChangePolicy(table, chain, target string) error {
	return ipt.run("-t", table, "-P", chain, target)
}

// Check if the underlying iptables command supports the --random-fully flag
func (ipt *IPTables) HasRandomFully() bool {
	return ipt.hasRandomFully
}

// Return version components of the underlying iptables command
func (ipt *IPTables) GetIptablesVersion() (int, int, int) {
	return ipt.v1, ipt.v2, ipt.v3
}

// run runs an iptables command with the given arguments, ignoring
// any stdout output
func (ipt *IPTables) run(args ...string) error {
	return ipt.runWithOutput(args, nil)
}

// runWithOutput runs an iptables command with the given arguments,
// writing any stdout output to the given writer
func (ipt *IPTables) runWithOutput(args []string, stdout io.Writer) error {
	args = append([]string{ipt.path}, args...)
	if ipt.hasWait {
		args = append(args, "--wait")
	} else {
		fmu, err := newXtablesFileLock()
		if err != nil {
			return err
		}
		ul, err := fmu.tryLock()
		if err != nil {
			return err
		}
		defer ul.Unlock()
	}

	var stderr bytes.Buffer
	cmd := exec.Cmd{
		Path:   ipt.path,
		Args:   args,
		Stdout: stdout,
		Stderr: &stderr,
	}

	if err := cmd.Run(); err != nil {
		switch e := err.(type) {
		case *exec.ExitError:
			return &Error{*e, cmd, stderr.String(), nil}
		default:
			return err
		}
	}

	return nil
}

// getIptablesCommand returns the correct command for the given protocol, either "iptables" or "ip6tables".
func getIptablesCommand(proto Protocol) string {
	if proto == ProtocolIPv6 {
		return "ip6tables"
	} else {
		return "iptables"
	}
}

// Checks if iptables has the "-C" and "--wait" flag
func getIptablesCommandSupport(v1 int, v2 int, v3 int) (bool, bool, bool) {
	return iptablesHasCheckCommand(v1, v2, v3), iptablesHasWaitCommand(v1, v2, v3), iptablesHasRandomFully(v1, v2, v3)
}

// getIptablesVersion returns the first three components of the iptables version
// and the operating mode (e.g. nf_tables or legacy)
// e.g. "iptables v1.3.66" would return (1, 3, 66, legacy, nil)
func extractIptablesVersion(str string) (int, int, int, string, error) {
	versionMatcher := regexp.MustCompile(`v([0-9]+)\.([0-9]+)\.([0-9]+)(?:\s+\((\w+))?`)
	result := versionMatcher.FindStringSubmatch(str)
	if result == nil {
		return 0, 0, 0, "", fmt.Errorf("no iptables version found in string: %s", str)
	}

	v1, err := strconv.Atoi(result[1])
	if err != nil {
		return 0, 0, 0, "", err
	}

	v2, err := strconv.Atoi(result[2])
	if err != nil {
		return 0, 0, 0, "", err
	}

	v3, err := strconv.Atoi(result[3])
	if err != nil {
		return 0, 0, 0, "", err
	}

	mode := "legacy"
	if result[4] != "" {
		mode = result[4]
	}
	return v1, v2, v3, mode, nil
}

// Runs "iptables --version" to get the version string
func getIptablesVersionString(path string) (string, error) {
	cmd := exec.Command(path, "--version")
	var out bytes.Buffer
	cmd.Stdout = &out
	err := cmd.Run()
	if err != nil {
		return "", err
	}
	return out.String(), nil
}

// Checks if an iptables version is after 1.4.11, when --check was added
func iptablesHasCheckCommand(v1 int, v2 int, v3 int) bool {
	if v1 > 1 {
		return true
	}
	if v1 == 1 && v2 > 4 {
		return true
	}
	if v1 == 1 && v2 == 4 && v3 >= 11 {
		return true
	}
	return false
}

// Checks if an iptables version is after 1.4.20, when --wait was added
func iptablesHasWaitCommand(v1 int, v2 int, v3 int) bool {
	if v1 > 1 {
		return true
	}
	if v1 == 1 && v2 > 4 {
		return true
	}
	if v1 == 1 && v2 == 4 && v3 >= 20 {
		return true
	}
	return false
}

// Checks if an iptables version is after 1.6.2, when --random-fully was added
func iptablesHasRandomFully(v1 int, v2 int, v3 int) bool {
	if v1 > 1 {
		return true
	}
	if v1 == 1 && v2 > 6 {
		return true
	}
	if v1 == 1 && v2 == 6 && v3 >= 2 {
		return true
	}
	return false
}

// Checks if a rule specification exists for a table
func (ipt *IPTables) existsForOldIptables(table, chain string, rulespec []string) (bool, error) {
	rs := strings.Join(append([]string{"-A", chain}, rulespec...), " ")
	args := []string{"-t", table, "-S"}
	var stdout bytes.Buffer
	err := ipt.runWithOutput(args, &stdout)
	if err != nil {
		return false, err
	}
	return strings.Contains(stdout.String(), rs), nil
}

// counterRegex is the regex used to detect nftables counter format
var counterRegex = regexp.MustCompile(`^\[([0-9]+):([0-9]+)\] `)

// filterRuleOutput works around some inconsistencies in output.
// For example, when iptables is in legacy vs. nftables mode, it produces
// different results.
func filterRuleOutput(rule string) string {
	out := rule

	// work around an output difference in nftables mode where counters
	// are output in iptables-save format, rather than iptables -S format
	// The string begins with "[0:0]"
	//
	// Fixes #49
	if groups := counterRegex.FindStringSubmatch(out); groups != nil {
		// drop the brackets
		out = out[len(groups[0]):]
		out = fmt.Sprintf("%s -c %s %s", out, groups[1], groups[2])
	}

	return out
}