feat(firewall): auto-detect which iptables

- On `iptables` error, try to use `iptables-nft`
- On `ip6tables` error, try to use `ip6tables-nft`

cmd/gluetun/main.go

@@ -205,8 +205,12 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 	if *allSettings.Firewall.Debug { // To remove in v4
 		firewallLogger.PatchLevel(logging.LevelDebug)
 	}
-	firewallConf := firewall.NewConfig(firewallLogger, cmder,
+	firewallConf, err := firewall.NewConfig(ctx, firewallLogger, cmder,
 		defaultInterface, defaultGateway, localNetworks, defaultIP)
+	if err != nil {
+		return err
+	}
+
 	if *allSettings.Firewall.Enabled {
 		err = firewallConf.SetEnabled(ctx, true)
 		if err != nil {

internal/firewall/firewall.go

@@ -33,7 +33,8 @@ type Config struct { //nolint:maligned
 	localIP          net.IP
 
 	// Fixed state
-	ip6Tables       bool
+	ipTables        string
+	ip6Tables       string
 	customRulesPath string
 
 	// State
@@ -45,20 +46,28 @@ type Config struct { //nolint:maligned
 	stateMutex        sync.Mutex
 }
 
-// NewConfig creates a new Config instance.
-func NewConfig(logger Logger, runner command.Runner,
-	defaultInterface string, defaultGateway net.IP,
-	localNetworks []routing.LocalNetwork, localIP net.IP) *Config {
+// NewConfig creates a new Config instance and returns an error
+// if no iptables implementation is available.
+func NewConfig(ctx context.Context, logger Logger,
+	runner command.Runner, defaultInterface string,
+	defaultGateway net.IP, localNetworks []routing.LocalNetwork,
+	localIP net.IP) (config *Config, err error) {
+	iptables, err := findIptablesSupported(ctx, runner)
+	if err != nil {
+		return nil, err
+	}
+
 	return &Config{
 		runner:            runner,
 		logger:            logger,
 		allowedInputPorts: make(map[uint16]string),
-		ip6Tables:         ip6tablesSupported(context.Background(), runner),
+		ipTables:          iptables,
+		ip6Tables:         findIP6tablesSupported(ctx, runner),
 		customRulesPath:   "/iptables/post-rules.txt",
 		// Obtained from routing
 		defaultInterface: defaultInterface,
 		defaultGateway:   defaultGateway,
 		localNetworks:    localNetworks,
 		localIP:          localIP,
-	}
+	}, nil
 }

internal/firewall/ip6tables.go

@@ -10,16 +10,27 @@ import (
 	"github.com/qdm12/golibs/command"
 )
 
-var (
-	ErrIP6NotSupported = errors.New("ip6tables not supported")
-)
+// findIP6tablesSupported checks for multiple iptables implementations
+// and returns the iptables path that is supported. If none work, an
+// empty string path is returned.
+func findIP6tablesSupported(ctx context.Context, runner command.Runner) (
+	ip6tablesPath string) {
+	binsToTry := []string{"ip6tables", "ip6tables-nft"}
 
-func ip6tablesSupported(ctx context.Context, runner command.Runner) (supported bool) {
-	cmd := exec.CommandContext(ctx, "ip6tables", "-L")
-	if _, err := runner.Run(cmd); err != nil {
-		return false
+	var err error
+	for _, ip6tablesPath = range binsToTry {
+		cmd := exec.CommandContext(ctx, ip6tablesPath, "-L")
+		_, err = runner.Run(cmd)
+		if err == nil {
+			break
+		}
 	}
-	return true
+
+	if err != nil {
+		return ""
+	}
+
+	return ip6tablesPath
 }
 
 func (c *Config) runIP6tablesInstructions(ctx context.Context, instructions []string) error {
@@ -32,18 +43,19 @@ func (c *Config) runIP6tablesInstructions(ctx context.Context, instructions []st
 }
 
 func (c *Config) runIP6tablesInstruction(ctx context.Context, instruction string) error {
-	if !c.ip6Tables {
+	if c.ip6Tables == "" {
 		return nil
 	}
 	c.ip6tablesMutex.Lock() // only one ip6tables command at once
 	defer c.ip6tablesMutex.Unlock()
 
-	c.logger.Debug("ip6tables " + instruction)
+	c.logger.Debug(c.ip6Tables + " " + instruction)
 
 	flags := strings.Fields(instruction)
-	cmd := exec.CommandContext(ctx, "ip6tables", flags...)
+	cmd := exec.CommandContext(ctx, c.ip6Tables, flags...) // #nosec G204
 	if output, err := c.runner.Run(cmd); err != nil {
-		return fmt.Errorf("command failed: \"ip6tables %s\": %s: %w", instruction, output, err)
+		return fmt.Errorf("command failed: \"%s %s\": %s: %w",
+			c.ip6Tables, instruction, output, err)
 	}
 	return nil
 }

internal/firewall/iptables.go

@@ -15,11 +15,31 @@ import (
 )
 
 var (
+	ErrIPTablesNotSupported    = errors.New("no iptables supported found")
 	ErrIPTablesVersionTooShort = errors.New("iptables version string is too short")
 	ErrPolicyUnknown           = errors.New("unknown policy")
 	ErrNeedIP6Tables           = errors.New("ip6tables is required, please upgrade your kernel to support it")
 )
 
+func findIptablesSupported(ctx context.Context, runner command.Runner) (iptablesPath string, err error) {
+	binsToTry := []string{"iptables", "iptables-nft"}
+
+	for _, iptablesPath = range binsToTry {
+		cmd := exec.CommandContext(ctx, iptablesPath, "-L")
+		_, err = runner.Run(cmd)
+		if err == nil {
+			break
+		}
+	}
+
+	if err != nil {
+		return "", fmt.Errorf("%w: from %s: last error is %s",
+			ErrIPTablesNotSupported, strings.Join(binsToTry, ", "), err)
+	}
+
+	return iptablesPath, nil
+}
+
 func appendOrDelete(remove bool) string {
 	if remove {
 		return "--delete"
@@ -71,12 +91,13 @@ func (c *Config) runIptablesInstruction(ctx context.Context, instruction string)
 	c.iptablesMutex.Lock() // only one iptables command at once
 	defer c.iptablesMutex.Unlock()
 
-	c.logger.Debug("iptables " + instruction)
+	c.logger.Debug(c.ipTables + " " + instruction)
 
 	flags := strings.Fields(instruction)
-	cmd := exec.CommandContext(ctx, "iptables", flags...)
+	cmd := exec.CommandContext(ctx, c.ipTables, flags...) // #nosec G204
 	if output, err := c.runner.Run(cmd); err != nil {
-		return fmt.Errorf("command failed: \"iptables %s\": %s: %w", instruction, output, err)
+		return fmt.Errorf("command failed: \"%s %s\": %s: %w",
+			c.ipTables, instruction, output, err)
 	}
 	return nil
 }
@@ -124,7 +145,7 @@ func (c *Config) acceptInputToSubnet(ctx context.Context, intf string, destinati
 	if isIP4Subnet {
 		return c.runIptablesInstruction(ctx, instruction)
 	}
-	if !c.ip6Tables {
+	if c.ip6Tables == "" {
 		return fmt.Errorf("accept input to subnet %s: %w", destination, ErrNeedIP6Tables)
 	}
 	return c.runIP6tablesInstruction(ctx, instruction)
@@ -151,7 +172,7 @@ func (c *Config) acceptOutputTrafficToVPN(ctx context.Context,
 	isIPv4 := connection.IP.To4() != nil
 	if isIPv4 {
 		return c.runIptablesInstruction(ctx, instruction)
-	} else if !c.ip6Tables {
+	} else if c.ip6Tables == "" {
 		return fmt.Errorf("accept output to VPN server: %w", ErrNeedIP6Tables)
 	}
 	return c.runIP6tablesInstruction(ctx, instruction)
@@ -172,7 +193,7 @@ func (c *Config) acceptOutputFromIPToSubnet(ctx context.Context,
 
 	if doIPv4 {
 		return c.runIptablesInstruction(ctx, instruction)
-	} else if !c.ip6Tables {
+	} else if c.ip6Tables == "" {
 		return fmt.Errorf("accept output from %s to %s: %w", sourceIP, destinationSubnet, ErrNeedIP6Tables)
 	}
 	return c.runIP6tablesInstruction(ctx, instruction)
@@ -223,9 +244,15 @@ func (c *Config) runUserPostRules(ctx context.Context, filepath string, remove b
 		case strings.HasPrefix(line, "iptables "):
 			ipv4 = true
 			rule = strings.TrimPrefix(line, "iptables ")
+		case strings.HasPrefix(line, "iptables-nft "):
+			ipv4 = true
+			rule = strings.TrimPrefix(line, "iptables-nft ")
 		case strings.HasPrefix(line, "ip6tables "):
 			ipv4 = false
 			rule = strings.TrimPrefix(line, "ip6tables ")
+		case strings.HasPrefix(line, "ip6tables-nft "):
+			ipv4 = false
+			rule = strings.TrimPrefix(line, "ip6tables-nft ")
 		default:
 			continue
 		}
@@ -237,7 +264,7 @@ func (c *Config) runUserPostRules(ctx context.Context, filepath string, remove b
 		switch {
 		case ipv4:
 			err = c.runIptablesInstruction(ctx, rule)
-		case !c.ip6Tables:
+		case c.ip6Tables == "":
 			err = fmt.Errorf("cannot run user ip6tables rule: %w", ErrNeedIP6Tables)
 		default: // ipv6
 			err = c.runIP6tablesInstruction(ctx, rule)