ebtables.go

/*
Copyright 2016 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 ebtables allows to control the ebtables Linux-based bridging firewall.
// Both chains and rules can be added, deleted and modified.
// For ebtables specific documentation see: http://ebtables.netfilter.org/
package ebtables

import (
	"fmt"
	"regexp"
	"strings"

	utilexec "k8s.io/utils/exec"
)

const (
	cmdebtables = "ebtables"

	// Flag to show full mac in output. The default representation omits leading zeroes.
	fullMac = "--Lmac2"
)

// RulePosition is the rule position within a table
type RulePosition string

// Relative position for a new rule
const (
	Prepend RulePosition = "-I"
	Append  RulePosition = "-A"
)

// Table is an Ebtables table type
type Table string

// Tables available in ebtables by default
const (
	TableNAT    Table = "nat"
	TableFilter Table = "filter"
	TableBroute Table = "broute"
)

// Chain is an Ebtables chain type
type Chain string

// Chains that are built-in in ebtables
const (
	ChainPostrouting Chain = "POSTROUTING"
	ChainPrerouting  Chain = "PREROUTING"
	ChainOutput      Chain = "OUTPUT"
	ChainInput       Chain = "INPUT"
	ChainBrouting    Chain = "BROUTING"
)

type operation string

const (
	opCreateChain operation = "-N"
	opFlushChain  operation = "-F"
	opDeleteChain operation = "-X"
	opListChain   operation = "-L"
	opAppendRule  operation = "-A"
	opPrependRule operation = "-I"
	opDeleteRule  operation = "-D"
)

// Interface for running ebtables commands.  Implementations must be goroutine-safe.
type Interface interface {
	// GetVersion returns the "X.Y.Z" semver string for ebtables.
	GetVersion() (string, error)
	// EnsureRule checks if the specified rule is present and, if not, creates it.  If the rule existed, return true.
	// WARNING: ebtables does not provide check operation like iptables do. Hence we have to do a string match of args.
	// Input args must follow the format and sequence of ebtables list output. Otherwise, EnsureRule will always create
	// new rules and causing duplicates.
	EnsureRule(position RulePosition, table Table, chain Chain, args ...string) (bool, error)
	// DeleteRule checks if the specified rule is present and, if so, deletes it.
	DeleteRule(table Table, chain Chain, args ...string) error
	// EnsureChain checks if the specified chain is present and, if not, creates it.  If the rule existed, return true.
	EnsureChain(table Table, chain Chain) (bool, error)
	// DeleteChain deletes the specified chain.  If the chain did not exist, return error.
	DeleteChain(table Table, chain Chain) error
	// FlushChain flush the specified chain.  If the chain did not exist, return error.
	FlushChain(table Table, chain Chain) error
}

// runner implements Interface in terms of exec("ebtables").
type runner struct {
	exec utilexec.Interface
}

// New returns a new Interface which will exec ebtables.
func New(exec utilexec.Interface) Interface {
	runner := &runner{
		exec: exec,
	}
	return runner
}

func makeFullArgs(table Table, op operation, chain Chain, args ...string) []string {
	return append([]string{"-t", string(table), string(op), string(chain)}, args...)
}

// getEbtablesVersionString runs "ebtables --version" to get the version string
// in the form "X.X.X"
func getEbtablesVersionString(exec utilexec.Interface) (string, error) {
	// this doesn't access mutable state so we don't need to use the interface / runner
	bytes, err := exec.Command(cmdebtables, "--version").CombinedOutput()
	if err != nil {
		return "", err
	}
	return parseVersion(string(bytes))
}

func parseVersion(version string) (string, error) {
	// the regular expression contains `v?` at the beginning because
	// different OS distros have different version format output i.e
	// either starts with `v` or it doesn't
	versionMatcher := regexp.MustCompile(`v?([0-9]+\.[0-9]+\.[0-9]+)`)
	match := versionMatcher.FindStringSubmatch(version)
	if match == nil {
		return "", fmt.Errorf("no ebtables version found in string: %s", version)
	}
	return match[1], nil
}

func (runner *runner) GetVersion() (string, error) {
	return getEbtablesVersionString(runner.exec)
}

func (runner *runner) EnsureRule(position RulePosition, table Table, chain Chain, args ...string) (bool, error) {
	var exist bool
	fullArgs := makeFullArgs(table, opListChain, chain, fullMac)
	out, err := runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
	if err != nil {
		exist = false
	} else {
		exist = checkIfRuleExists(string(out), args...)
	}
	if !exist {
		fullArgs = makeFullArgs(table, operation(position), chain, args...)
		out, err := runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
		if err != nil {
			return exist, fmt.Errorf("Failed to ensure rule: %v, output: %v", err, string(out))
		}
	}
	return exist, nil
}

func (runner *runner) DeleteRule(table Table, chain Chain, args ...string) error {
	var exist bool
	fullArgs := makeFullArgs(table, opListChain, chain, fullMac)
	out, err := runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
	if err != nil {
		exist = false
	} else {
		exist = checkIfRuleExists(string(out), args...)
	}

	if !exist {
		return nil
	}
	fullArgs = makeFullArgs(table, opDeleteRule, chain, args...)
	out, err = runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
	if err != nil {
		return fmt.Errorf("Failed to delete rule: %v, output: %s", err, out)
	}
	return nil
}

func (runner *runner) EnsureChain(table Table, chain Chain) (bool, error) {
	exist := true

	args := makeFullArgs(table, opListChain, chain)
	_, err := runner.exec.Command(cmdebtables, args...).CombinedOutput()
	if err != nil {
		exist = false
	}
	if !exist {
		args = makeFullArgs(table, opCreateChain, chain)
		out, err := runner.exec.Command(cmdebtables, args...).CombinedOutput()
		if err != nil {
			return exist, fmt.Errorf("Failed to ensure %v chain: %v, output: %v", chain, err, string(out))
		}
	}
	return exist, nil
}

// checkIfRuleExists takes the output of ebtables list chain and checks if the input rules exists
// WARNING: checkIfRuleExists expects the input args matches the format and sequence of ebtables list output
func checkIfRuleExists(listChainOutput string, args ...string) bool {
	rule := strings.Join(args, " ")
	for _, line := range strings.Split(listChainOutput, "\n") {
		if strings.TrimSpace(line) == rule {
			return true
		}
	}
	return false
}

func (runner *runner) DeleteChain(table Table, chain Chain) error {
	fullArgs := makeFullArgs(table, opDeleteChain, chain)
	out, err := runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
	if err != nil {
		return fmt.Errorf("Failed to delete %v chain %v: %v, output: %v", string(table), string(chain), err, string(out))
	}
	return nil
}

func (runner *runner) FlushChain(table Table, chain Chain) error {
	fullArgs := makeFullArgs(table, opFlushChain, chain)
	out, err := runner.exec.Command(cmdebtables, fullArgs...).CombinedOutput()
	if err != nil {
		return fmt.Errorf("Failed to flush %v chain %v: %v, output: %v", string(table), string(chain), err, string(out))
	}
	return nil
}