drivers_nftables.go

package drivers

import (
	"encoding/hex"
	"encoding/json"
	"fmt"
	"net"
	"os/exec"
	"strconv"
	"strings"
	"text/template"

	"github.com/pkg/errors"

	deviceConfig "github.com/lxc/lxd/lxd/device/config"
	"github.com/lxc/lxd/lxd/project"
	"github.com/lxc/lxd/shared"
	"github.com/lxc/lxd/shared/logger"
	"github.com/lxc/lxd/shared/version"
)

const nftablesNamespace = "lxd"
const nftablesContentTemplate = "nftablesContent"

// nftablesChainSeparator The "." character is specifically chosen here so as to prevent the ability for collisions
// between project prefix (which is empty if project is default) and device name combinations that both are allowed
// to contain underscores (where as instance name is not).
const nftablesChainSeparator = "."

// nftablesMinVersion We need at least 0.9.1 as this was when the arp ether saddr filters were added.
const nftablesMinVersion = "0.9.1"

// Nftables is an implmentation of LXD firewall using nftables.
type Nftables struct{}

// String returns the driver name.
func (d Nftables) String() string {
	return "nftables"
}

// Compat returns whether the host is compatible with this driver and whether the driver backend is in use.
func (d Nftables) Compat() (bool, bool) {
	// Get the kernel version.
	uname, err := shared.Uname()
	if err != nil {
		return false, false
	}

	// We require a 5.x kernel to avoid weird conflicts with xtables.
	if len(uname.Release) > 1 {
		verInt, err := strconv.Atoi(uname.Release[0:1])
		if err != nil {
			return false, false
		}

		if verInt < 5 {
			return false, false
		}
	}

	// Check if nftables nft command exists, if not use xtables.
	_, err = exec.LookPath("nft")
	if err != nil {
		return false, false
	}

	// Get nftables version.
	nftVersion, err := d.hostVersion()
	if err != nil {
		logger.Debugf("Firewall nftables failed detecting nft version: %v", err)
		return false, false
	}

	// Check nft version meets minimum required.
	minVer, _ := version.NewDottedVersion(nftablesMinVersion)
	if nftVersion.Compare(minVer) < 0 {
		logger.Debugf("Firewall nftables detected nft version %q is too low, need %q or above", nftVersion, nftablesMinVersion)
		return false, false
	}

	// Check whether in use by parsing ruleset and looking for existing rules.
	ruleset, err := d.nftParseRuleset()
	if err != nil {
		logger.Errorf("Firewall nftables unable to parse existing ruleset: %v", err)
		return false, false
	}

	for _, item := range ruleset {
		if item.Type == "rule" {
			return true, true // At least one rule found indicates in use.
		}
	}

	return true, false
}

// nftGenericItem represents some common fields amongst the different nftables types.
type nftGenericItem struct {
	Type   string // Type of item (table, chain or rule).
	Family string `json:"family"` // Family of item (ip, ip6, bridge etc).
	Table  string `json:"table"`  // Table the item belongs to (for chains and rules).
	Chain  string `json:"chain"`  // Chain the item belongs to (for rules).
	Name   string `json:"name"`   // Name of item (for tables and chains).
}

// nftParseRuleset parses the ruleset and returns the generic parts as a slice of items.
func (d Nftables) nftParseRuleset() ([]nftGenericItem, error) {
	// Dump ruleset as JSON. Use -nn flags to avoid doing DNS lookups of IPs mentioned in any rules.
	cmd := exec.Command("nft", "list", "ruleset", "--json", "-nn")
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, err
	}
	err = cmd.Start()
	if err != nil {
		return nil, err
	}
	defer cmd.Wait()

	// This only extracts certain generic parts of the ruleset, see man libnftables-json for more info.
	v := &struct {
		Nftables []map[string]nftGenericItem `json:"nftables"`
	}{}

	err = json.NewDecoder(stdout).Decode(v)
	if err != nil {
		return nil, err
	}

	items := []nftGenericItem{}
	for _, item := range v.Nftables {
		if rule, found := item["rule"]; found {
			rule.Type = "rule"
			items = append(items, rule)
		} else if chain, found := item["chain"]; found {
			chain.Type = "chain"
			items = append(items, chain)
		} else if table, found := item["table"]; found {
			table.Type = "table"
			items = append(items, table)
		}
	}

	err = cmd.Wait()
	if err != nil {
		return nil, err
	}

	return items, nil
}

// GetVersion returns the version of dnsmasq.
func (d Nftables) hostVersion() (*version.DottedVersion, error) {
	output, err := shared.RunCommandCLocale("nft", "--version")
	if err != nil {
		return nil, errors.Wrap(err, "Failed to check nftables version")
	}

	lines := strings.Split(string(output), " ")
	return version.NewDottedVersion(strings.TrimPrefix(lines[1], "v"))
}

// NetworkSetupForwardingPolicy allows forwarding dependent on boolean argument
func (d Nftables) NetworkSetupForwardingPolicy(networkName string, ipVersion uint, allow bool) error {
	action := "reject"
	if allow {
		action = "accept"
	}

	family, err := d.getIPFamily(ipVersion)
	if err != nil {
		return err
	}

	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"networkName":    networkName,
		"family":         family,
		"action":         action,
	}

	err = d.applyNftConfig(nftablesNetForwardingPolicy, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding forwarding policy rules for network %q (%s)", networkName, tplFields["family"])
	}

	return nil
}

// NetworkSetupOutboundNAT configures outbound NAT.
// If srcIP is non-nil then SNAT is used with the specified address, otherwise MASQUERADE mode is used.
// Append mode is always on and so the append argument is ignored.
func (d Nftables) NetworkSetupOutboundNAT(networkName string, subnet *net.IPNet, srcIP net.IP, _ bool) error {
	family := "ip"
	if subnet.IP.To4() == nil {
		family = "ip6"
	}

	// If SNAT IP not supplied then use the IP of the outbound interface (MASQUERADE).
	srcIPStr := ""
	if srcIP != nil {
		srcIPStr = srcIP.String()
	}

	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"networkName":    networkName,
		"family":         family,
		"subnet":         subnet.String(),
		"srcIP":          srcIPStr,
	}

	err := d.applyNftConfig(nftablesNetOutboundNAT, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding outbound NAT rules for network %q (%s)", networkName, tplFields["family"])
	}

	return nil
}

// NetworkSetupDHCPDNSAccess sets up basic nftables overrides for DHCP/DNS.
func (d Nftables) NetworkSetupDHCPDNSAccess(networkName string, ipVersion uint) error {
	family, err := d.getIPFamily(ipVersion)
	if err != nil {
		return err
	}

	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"networkName":    networkName,
		"family":         family,
	}

	err = d.applyNftConfig(nftablesNetDHCPDNS, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding DHCP/DNS access rules for network %q (%s)", networkName, tplFields["family"])
	}

	return nil
}

// NetworkSetupDHCPv4Checksum attempts a workaround for broken DHCP clients. No-op as not supported by nftables.
// See https://wiki.nftables.org/wiki-nftables/index.php/Supported_features_compared_to_xtables#CHECKSUM.
func (d Nftables) NetworkSetupDHCPv4Checksum(networkName string) error {
	return nil
}

// NetworkClear removes the LXD network related chains.
func (d Nftables) NetworkClear(networkName string, ipVersion uint) error {
	family, err := d.getIPFamily(ipVersion)
	if err != nil {
		return err
	}

	// Remove chains created by network rules.
	err = d.removeChains([]string{family}, networkName, "fwd", "pstrt", "in", "out")
	if err != nil {
		return errors.Wrapf(err, "Failed clearing nftables rules for network %q", networkName)
	}

	return nil
}

//instanceDeviceLabel returns the unique label used for instance device chains.
func (d Nftables) instanceDeviceLabel(projectName, instanceName, deviceName string) string {
	return fmt.Sprintf("%s%s%s", project.Instance(projectName, instanceName), nftablesChainSeparator, deviceName)
}

// InstanceSetupBridgeFilter sets up the filter rules to apply bridged device IP filtering.
func (d Nftables) InstanceSetupBridgeFilter(projectName string, instanceName string, deviceName string, parentName string, hostName string, hwAddr string, IPv4 net.IP, IPv6 net.IP) error {
	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)

	mac, err := net.ParseMAC(hwAddr)
	if err != nil {
		return err
	}

	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"family":         "bridge",
		"deviceLabel":    deviceLabel,
		"parentName":     parentName,
		"hostName":       hostName,
		"hwAddr":         hwAddr,
		"hwAddrHex":      fmt.Sprintf("0x%s", hex.EncodeToString(mac)),
	}

	if IPv4 != nil {
		if IPv4.String() == FilterIPv4All {
			tplFields["ipv4FilterAll"] = true
		} else {
			tplFields["ipv4Addr"] = IPv4.String()
		}
	}

	if IPv6 != nil {
		if IPv6.String() == FilterIPv6All {
			tplFields["ipv6FilterAll"] = true
		} else {
			tplFields["ipv6Addr"] = IPv6.String()
			tplFields["ipv6AddrHex"] = fmt.Sprintf("0x%s", hex.EncodeToString(IPv6))
		}
	}

	err = d.applyNftConfig(nftablesInstanceBridgeFilter, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding bridge filter rules for instance device %q (%s)", deviceLabel, tplFields["family"])
	}

	return nil
}

// InstanceClearBridgeFilter removes any filter rules that were added to apply bridged device IP filtering.
func (d Nftables) InstanceClearBridgeFilter(projectName string, instanceName string, deviceName string, parentName string, hostName string, hwAddr string, _ net.IP, _ net.IP) error {
	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)

	// Remove chains created by bridge filter rules.
	err := d.removeChains([]string{"bridge"}, deviceLabel, "in", "fwd")
	if err != nil {
		return errors.Wrapf(err, "Failed clearing bridge filter rules for instance device %q", deviceLabel)
	}

	return nil
}

// InstanceSetupProxyNAT creates DNAT rules for proxy devices.
func (d Nftables) InstanceSetupProxyNAT(projectName string, instanceName string, deviceName string, listen, connect *deviceConfig.ProxyAddress) error {
	connectAddrCount := len(connect.Addr)
	if connectAddrCount < 1 {
		return fmt.Errorf("At least 1 connect address must be supplied")
	}

	if len(listen.Addr) < 1 {
		return fmt.Errorf("At least 1 listen address must be supplied")
	}

	if connectAddrCount > 1 && len(listen.Addr) != connectAddrCount {
		return fmt.Errorf("More than 1 connect addresses have been supplied, but insufficient for listen addresses")
	}

	// Generate a slice of rules to add.
	var rules []map[string]interface{}
	for i, lAddr := range listen.Addr {
		listenHost, listenPort, err := net.SplitHostPort(lAddr)
		if err != nil {
			return err
		}

		// Use the connect address that corresponds to the listen address (unless only 1 is specified).
		connectIndex := 0
		if connectAddrCount > 1 {
			connectIndex = i
		}

		connectHost, connectPort, err := net.SplitHostPort(connect.Addr[connectIndex])
		if err != nil {
			return err
		}

		// Figure out which IP family we are using and format the destination host/port as appropriate.
		family := "ip"
		connectDest := fmt.Sprintf("%s:%s", connectHost, connectPort)
		connectIP := net.ParseIP(connectHost)
		if connectIP.To4() == nil {
			family = "ip6"
			connectDest = fmt.Sprintf("[%s]:%s", connectHost, connectPort)
		}

		rules = append(rules, map[string]interface{}{
			"family":      family,
			"connType":    listen.ConnType,
			"listenHost":  listenHost,
			"listenPort":  listenPort,
			"connectDest": connectDest,
			"connectHost": connectHost,
			"connectPort": connectPort,
		})
	}

	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)
	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"family":         rules[0]["family"], // Family should be same for all rules, so use 1st as global.
		"deviceLabel":    deviceLabel,
		"rules":          rules,
	}

	err := d.applyNftConfig(nftablesNetProxyNAT, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding proxy rules for instance device %q", deviceLabel)
	}

	return nil
}

// InstanceClearProxyNAT remove DNAT rules for proxy devices.
func (d Nftables) InstanceClearProxyNAT(projectName string, instanceName string, deviceName string) error {
	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)
	err := d.removeChains([]string{"ip", "ip6"}, deviceLabel, "out", "prert", "pstrt")
	if err != nil {
		return errors.Wrapf(err, "Failed clearing proxy rules for instance device %q", deviceLabel)
	}

	return nil
}

// getIPFamily converts IP version number into family name used by nftables.
func (d Nftables) getIPFamily(ipVersion uint) (string, error) {
	if ipVersion == 4 {
		return "ip", nil
	} else if ipVersion == 6 {
		return "ip6", nil
	}

	return "", fmt.Errorf("Invalid IP version")
}

// applyNftConfig loads the specified config template and then applies it to the common template before sending to
// the nft command to be atomically applied to the system.
func (d Nftables) applyNftConfig(tpl *template.Template, tplFields map[string]interface{}) error {
	// Load the specified template into the common template's parse tree under the nftableContentTemplate
	// name so that the nftableContentTemplate template can use it with the generic name.
	_, err := nftablesCommonTable.AddParseTree(nftablesContentTemplate, tpl.Tree)
	if err != nil {
		return errors.Wrapf(err, "Failed loading %q template", tpl.Name())
	}

	config := &strings.Builder{}
	err = nftablesCommonTable.Execute(config, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed running %q template", tpl.Name())
	}

	_, err = shared.RunCommand("nft", config.String())
	if err != nil {
		return errors.Wrapf(err, "Failed apply nftables config")
	}

	return nil
}

// removeChains removes the specified chains from the specified families.
// If not empty, chain suffix is appended to each chain name, separated with "_".
func (d Nftables) removeChains(families []string, chainSuffix string, chains ...string) error {
	ruleset, err := d.nftParseRuleset()
	if err != nil {
		return err
	}

	fullChains := chains
	if chainSuffix != "" {
		fullChains = make([]string, 0, len(chains))
		for _, chain := range chains {
			fullChains = append(fullChains, fmt.Sprintf("%s%s%s", chain, nftablesChainSeparator, chainSuffix))
		}
	}

	for _, family := range families {
		for _, item := range ruleset {
			if item.Type == "chain" && item.Family == family && item.Table == nftablesNamespace && shared.StringInSlice(item.Name, fullChains) {
				_, err = shared.RunCommand("nft", "flush", "chain", family, nftablesNamespace, item.Name, ";", "delete", "chain", family, nftablesNamespace, item.Name)
				if err != nil {
					return errors.Wrapf(err, "Failed deleting nftables chain %q (%s)", item.Name, family)
				}
			}
		}
	}

	return nil
}

// InstanceSetupRPFilter activates reverse path filtering for the specified instance device on the host interface.
func (d Nftables) InstanceSetupRPFilter(projectName string, instanceName string, deviceName string, hostName string) error {
	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)
	tplFields := map[string]interface{}{
		"namespace":      nftablesNamespace,
		"chainSeparator": nftablesChainSeparator,
		"deviceLabel":    deviceLabel,
		"hostName":       hostName,
	}

	// IPv4 filter.
	tplFields["family"] = "ip"
	err := d.applyNftConfig(nftablesInstanceRPFilter, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding reverse path filter rules for instance device %q (%s)", deviceLabel, tplFields["family"])
	}

	// IPv46filter.
	tplFields["family"] = "ip6"
	err = d.applyNftConfig(nftablesInstanceRPFilter, tplFields)
	if err != nil {
		return errors.Wrapf(err, "Failed adding reverse path filter rules for instance device %q (%s)", deviceLabel, tplFields["family"])
	}

	return nil
}

// InstanceClearRPFilter removes reverse path filtering for the specified instance device on the host interface.
func (d Nftables) InstanceClearRPFilter(projectName string, instanceName string, deviceName string) error {
	deviceLabel := d.instanceDeviceLabel(projectName, instanceName, deviceName)
	err := d.removeChains([]string{"ip", "ip6"}, deviceLabel, "prert")
	if err != nil {
		return errors.Wrapf(err, "Failed clearing reverse path filter rules for instance device %q", deviceLabel)
	}

	return nil
}