Use ErrKernelModuleMissing when missing kernel module string is detected

.devcontainer/Dockerfile

@@ -1,2 +1,2 @@
 FROM ghcr.io/qdm12/godevcontainer:v0.21-alpine
-RUN apk add wireguard-tools htop openssl tcpdump iptables nftables
+RUN apk add wireguard-tools htop openssl tcpdump iptables

cmd/gluetun/main.go

@@ -227,7 +227,7 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 		firewallLogger.Patch(log.SetLevel(log.LevelDebug))
 	}
 	firewallConf, err := firewall.NewConfig(ctx, firewallLogger, cmder,
-		defaultRoutes, localNetworks)
+		netLinker, defaultRoutes, localNetworks)
 	if err != nil {
 		return err
 	}
@@ -237,10 +237,6 @@ func _main(ctx context.Context, buildInfo models.BuildInformation,
 		if err != nil {
 			return err
 		}
-		err = netLinker.FlushConntrack()
-		if err != nil {
-			logger.Warnf("flushing conntrack failed: %s", err)
-		}
 	}
 
 	// TODO run this in a loop or in openvpn to reload from file without restarting

go.mod

@@ -4,15 +4,14 @@ go 1.25.0
 
 require (
 	github.com/ProtonMail/go-srp v0.0.7
-	github.com/breml/rootcerts v0.3.4
+	github.com/breml/rootcerts v0.3.3
 	github.com/fatih/color v1.18.0
 	github.com/golang/mock v1.6.0
-	github.com/google/nftables v0.3.0
 	github.com/jsimonetti/rtnetlink v1.4.2
 	github.com/klauspost/compress v1.18.1
 	github.com/klauspost/pgzip v1.2.6
 	github.com/mdlayher/genetlink v1.3.2
-	github.com/mdlayher/netlink v1.7.3-0.20250113171957-fbb4dce95f42
+	github.com/mdlayher/netlink v1.7.2
 	github.com/pelletier/go-toml/v2 v2.2.4
 	github.com/qdm12/dns/v2 v2.0.0-rc9.0.20260216151239-36b3306f2205
 	github.com/qdm12/gosettings v0.4.4
@@ -43,6 +42,7 @@ require (
 	github.com/cronokirby/saferith v0.33.0 // indirect
 	github.com/davecgh/go-spew v1.1.1 // indirect
 	github.com/google/go-cmp v0.7.0 // indirect
+	github.com/josharian/native v1.1.0 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/mdlayher/socket v0.5.1 // indirect

go.sum

@@ -8,8 +8,8 @@ github.com/ProtonMail/go-srp v0.0.7 h1:Sos3Qk+th4tQR64vsxGIxYpN3rdnG9Wf9K4ZloC1J
 github.com/ProtonMail/go-srp v0.0.7/go.mod h1:giCp+7qRnMIcCvI6V6U3S1lDDXDQYx2ewJ6F/9wdlJk=
 github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
 github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
-github.com/breml/rootcerts v0.3.4 h1:9i7WNl/ctd9OEAOaTfLy//Wrlfxq/tRQ7v4okYFN9Ys=
+github.com/breml/rootcerts v0.3.3 h1://GnaRtQ/9BY2+GtMk2wtWxVdCRysiaPr5/xBwl7NKw=
-github.com/breml/rootcerts v0.3.4/go.mod h1:S/PKh+4d1HUn4HQovEB8hPJZO6pUZYrIhmXBhsegfXw=
+github.com/breml/rootcerts v0.3.3/go.mod h1:S/PKh+4d1HUn4HQovEB8hPJZO6pUZYrIhmXBhsegfXw=
 github.com/bwesterb/go-ristretto v1.2.0/go.mod h1:fUIoIZaG73pV5biE2Blr2xEzDoMj7NFEuV9ekS419A0=
 github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
 github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
@@ -30,8 +30,8 @@ github.com/google/btree v1.0.1 h1:gK4Kx5IaGY9CD5sPJ36FHiBJ6ZXl0kilRiiCj+jdYp4=
 github.com/google/btree v1.0.1/go.mod h1:xXMiIv4Fb/0kKde4SpL7qlzvu5cMJDRkFDxJfI9uaxA=
 github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
 github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
-github.com/google/nftables v0.3.0 h1:bkyZ0cbpVeMHXOrtlFc8ISmfVqq5gPJukoYieyVmITg=
+github.com/josharian/native v1.1.0 h1:uuaP0hAbW7Y4l0ZRQ6C9zfb7Mg1mbFKry/xzDAfmtLA=
-github.com/google/nftables v0.3.0/go.mod h1:BCp9FsrbF1Fn/Yu6CLUc9GGZFw/+hsxfluNXXmxBfRM=
+github.com/josharian/native v1.1.0/go.mod h1:7X/raswPFr05uY3HiLlYeyQntB6OO7E/d2Cu7qoaN2w=
 github.com/jsimonetti/rtnetlink v1.4.2 h1:Df9w9TZ3npHTyDn0Ev9e1uzmN2odmXd0QX+J5GTEn90=
 github.com/jsimonetti/rtnetlink v1.4.2/go.mod h1:92s6LJdE+1iOrw+F2/RO7LYI2Qd8pPpFNNUYW06gcoM=
 github.com/klauspost/compress v1.18.1 h1:bcSGx7UbpBqMChDtsF28Lw6v/G94LPrrbMbdC3JH2co=
@@ -49,8 +49,8 @@ github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWE
 github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
 github.com/mdlayher/genetlink v1.3.2 h1:KdrNKe+CTu+IbZnm/GVUMXSqBBLqcGpRDa0xkQy56gw=
 github.com/mdlayher/genetlink v1.3.2/go.mod h1:tcC3pkCrPUGIKKsCsp0B3AdaaKuHtaxoJRz3cc+528o=
-github.com/mdlayher/netlink v1.7.3-0.20250113171957-fbb4dce95f42 h1:A1Cq6Ysb0GM0tpKMbdCXCIfBclan4oHk1Jb+Hrejirg=
+github.com/mdlayher/netlink v1.7.2 h1:/UtM3ofJap7Vl4QWCPDGXY8d3GIY2UGSDbK+QWmY8/g=
-github.com/mdlayher/netlink v1.7.3-0.20250113171957-fbb4dce95f42/go.mod h1:BB4YCPDOzfy7FniQ/lxuYQ3dgmM2cZumHbK8RpTjN2o=
+github.com/mdlayher/netlink v1.7.2/go.mod h1:xraEF7uJbxLhc5fpHL4cPe221LI2bdttWlU+ZGLfQSw=
 github.com/mdlayher/socket v0.5.1 h1:VZaqt6RkGkt2OE9l3GcC6nZkqD3xKeQLyfleW/uBcos=
 github.com/mdlayher/socket v0.5.1/go.mod h1:TjPLHI1UgwEv5J1B5q0zTZq12A/6H7nKmtTanQE37IQ=
 github.com/miekg/dns v1.1.62 h1:cN8OuEF1/x5Rq6Np+h1epln8OiyPWV+lROx9LxcGgIQ=
@@ -99,8 +99,6 @@ github.com/ti-mo/netfilter v0.5.3 h1:ikzduvnaUMwre5bhbNwWOd6bjqLMVb33vv0XXbK0xGQ
 github.com/ti-mo/netfilter v0.5.3/go.mod h1:08SyBCg6hu1qyQk4s3DjjJKNrm3RTb32nm6AzyT972E=
 github.com/ulikunitz/xz v0.5.15 h1:9DNdB5s+SgV3bQ2ApL10xRc35ck0DuIX/isZvIk+ubY=
 github.com/ulikunitz/xz v0.5.15/go.mod h1:nbz6k7qbPmH4IRqmfOplQw/tblSgqTqBwxkY0oWt/14=
-github.com/vishvananda/netns v0.0.4 h1:Oeaw1EM2JMxD51g9uhtC0D7erkIjgmj8+JZc26m1YX8=
-github.com/vishvananda/netns v0.0.4/go.mod h1:SpkAiCQRtJ6TvvxPnOSyH3BMl6unz3xZlaprSwhNNJM=
 github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a h1:fZHgsYlfvtyqToslyjUt3VOPF4J7aK/3MPcK7xp3PDk=
 github.com/youmark/pkcs8 v0.0.0-20201027041543-1326539a0a0a/go.mod h1:ul22v+Nro/R083muKhosV54bj5niojjWZvU8xrevuH4=
 github.com/yuin/goldmark v1.3.5/go.mod h1:mwnBkeHKe2W/ZEtQ+71ViKU8L12m81fl3OWwC1Zlc8k=

internal/firewall/enable.go

@@ -45,16 +45,20 @@ func (c *Config) enable(ctx context.Context) (err error) {
 		return fmt.Errorf("saving firewall rules: %w", err)
 	}
 
+	if err = c.impl.SetIPv4AllPolicies(ctx, "DROP"); err != nil {
+		return err
+	}
+
+	if err = c.impl.SetIPv6AllPolicies(ctx, "DROP"); err != nil {
+		return err
+	}
+
 	defer func() {
 		if err != nil {
 			c.restore(context.Background())
 		}
 	}()
 
-	if err = c.impl.SetBaseChainsPolicy(ctx, "DROP"); err != nil {
-		return err
-	}
-
 	// Loopback traffic
 	if err = c.impl.AcceptInputThroughInterface(ctx, "lo"); err != nil {
 		return err
@@ -65,6 +69,11 @@ func (c *Config) enable(ctx context.Context) (err error) {
 		return err
 	}
 
+	err = c.flushExistingConnections(ctx)
+	if err != nil {
+		return fmt.Errorf("flushing existing connections: %w", err)
+	}
+
 	if err = c.impl.AcceptEstablishedRelatedTraffic(ctx); err != nil {
 		return err
 	}

internal/firewall/firewall.go

@@ -13,6 +13,7 @@ import (
 
 type Config struct {
 	runner        CmdRunner
+	netlinker     Netlinker
 	logger        Logger
 	defaultRoutes []routing.DefaultRoute
 	localNetworks []routing.LocalNetwork
@@ -35,8 +36,8 @@ type Config struct {
 // NewConfig creates a new Config instance and returns an error
 // if no iptables implementation is available.
 func NewConfig(ctx context.Context, logger Logger,
-	runner CmdRunner, defaultRoutes []routing.DefaultRoute,
+	runner CmdRunner, netlinker Netlinker,
-	localNetworks []routing.LocalNetwork,
+	defaultRoutes []routing.DefaultRoute, localNetworks []routing.LocalNetwork,
 ) (config *Config, err error) {
 	impl, err := iptables.New(ctx, runner, logger)
 	if err != nil {
@@ -45,6 +46,7 @@ func NewConfig(ctx context.Context, logger Logger,
 
 	return &Config{
 		runner:            runner,
+		netlinker:         netlinker,
 		logger:            logger,
 		allowedInputPorts: make(map[uint16]map[string]struct{}),
 		// Obtained from routing

internal/firewall/flush.go

@@ -0,0 +1,74 @@
+package firewall
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/qdm12/gluetun/internal/firewall/iptables"
+	"github.com/qdm12/gluetun/internal/netlink"
+)
+
+func (c *Config) flushExistingConnections(ctx context.Context) error {
+	tries := []struct {
+		name string
+		f    func(ctx context.Context) error
+	}{
+		{name: "flushing conntrack", f: func(_ context.Context) error {
+			return c.netlinker.FlushConntrack()
+		}},
+		{name: "marking and filtering unmarked packets", f: c.impl.AcceptOutputPublicOnlyNewTraffic},
+		{name: "rejecting connections for one second", f: c.rejectOutputTrafficTemporarily},
+		{name: "dropping connections for one second", f: c.dropOutputTrafficTemporarily},
+	}
+	errs := make([]error, 0, len(tries))
+	for i, try := range tries {
+		if i > 0 {
+			c.logger.Debugf("falling back to %s because %s failed: %s", try.name, tries[i-1].name, errs[i-1])
+		}
+		err := try.f(ctx)
+		if err == nil {
+			return nil
+		}
+		err = fmt.Errorf("%s: %w", try.name, err)
+		if !errors.Is(err, iptables.ErrKernelModuleMissing) && !errors.Is(err, netlink.ErrConntrackNetlinkNotSupported) {
+			return err
+		}
+		errs = append(errs, err)
+	}
+	return fmt.Errorf("all tries failed: %v", errs) //nolint:err113
+}
+
+func (c *Config) rejectOutputTrafficTemporarily(ctx context.Context) error {
+	return setupThenRevert(ctx, c.impl.RejectOutputPublicTraffic)
+}
+
+func (c *Config) dropOutputTrafficTemporarily(ctx context.Context) error {
+	return setupThenRevert(ctx, c.impl.DropOutputPublicTraffic)
+}
+
+// setupThenRevert is a helper function to run a setup function that takes a remove boolean argument,
+// and then run the same function with remove set to true after one second or when the context is canceled,
+// whichever comes first.
+func setupThenRevert(ctx context.Context, f func(ctx context.Context, remove bool) error) error {
+	remove := false
+	err := f(ctx, remove)
+	if err != nil {
+		return fmt.Errorf("setting up: %w", err)
+	}
+	timer := time.NewTimer(time.Second)
+	select {
+	case <-timer.C:
+	case <-ctx.Done():
+		timer.Stop()
+	}
+	remove = true
+	// Use [context.Background] to make sure this is removed, even if the context
+	// passed to this function is canceled.
+	err = f(context.Background(), remove)
+	if err != nil {
+		return fmt.Errorf("reverting: %w", err)
+	}
+	return nil
+}

internal/firewall/interfaces.go

@@ -14,15 +14,23 @@ type CmdRunner interface {
 
 type Logger interface {
 	Debug(s string)
+	Debugf(format string, args ...any)
 	Info(s string)
 	Warn(s string)
 	Error(s string)
 }
 
+type Netlinker interface {
+	FlushConntrack() error
+}
+
 type firewallImpl interface { //nolint:interfacebloat
 	SaveAndRestore(ctx context.Context) (restore func(context.Context), err error)
-	AcceptEstablishedRelatedTraffic(ctx context.Context) error
+	AcceptOutputPublicOnlyNewTraffic(ctx context.Context) error
+	RejectOutputPublicTraffic(ctx context.Context, remove bool) error
+	DropOutputPublicTraffic(ctx context.Context, remove bool) error
 	AcceptInputThroughInterface(ctx context.Context, intf string) error
+	AcceptEstablishedRelatedTraffic(ctx context.Context) error
 	AcceptInputToPort(ctx context.Context, intf string, port uint16, remove bool) error
 	AcceptInputToSubnet(ctx context.Context, intf string, subnet netip.Prefix) error
 	AcceptIpv6MulticastOutput(ctx context.Context, intf string) error
@@ -34,7 +42,8 @@ type firewallImpl interface { //nolint:interfacebloat
 	RedirectPort(ctx context.Context, intf string, sourcePort,
 		destinationPort uint16, remove bool) error
 	RunUserPostRules(ctx context.Context, customRulesPath string) error
-	SetBaseChainsPolicy(ctx context.Context, policy string) error
+	SetIPv4AllPolicies(ctx context.Context, policy string) error
+	SetIPv6AllPolicies(ctx context.Context, policy string) error
 	TempDropOutputTCPRST(ctx context.Context, src, dst netip.AddrPort, excludeMark int) (
 		revert func(ctx context.Context) error, err error)
 	Version(ctx context.Context) (version string, err error)

internal/firewall/iptables/firewall.go

@@ -2,11 +2,12 @@ package iptables
 
 import (
 	"context"
+	"errors"
 	"sync"
-
-	"github.com/qdm12/gluetun/internal/mod"
 )
 
+var ErrKernelModuleMissing = errors.New("kernel module is missing for this operation")
+
 type Config struct {
 	runner         CmdRunner
 	logger         Logger
@@ -16,8 +17,6 @@ type Config struct {
 	// Fixed state
 	ipTables  string
 	ip6Tables string
-	nftables  bool
-	xtMark    bool
 }
 
 func New(ctx context.Context, runner CmdRunner, logger Logger) (*Config, error) {
@@ -31,21 +30,10 @@ func New(ctx context.Context, runner CmdRunner, logger Logger) (*Config, error)
 		return nil, err
 	}
 
-	modules := map[string]bool{
-		"xt_mark":   false,
-		"nf_tables": false,
-	}
-	for module := range modules {
-		err := mod.Probe(module)
-		modules[module] = err == nil
-	}
-
 	return &Config{
 		runner:    runner,
 		logger:    logger,
 		ipTables:  iptables,
 		ip6Tables: ip6tables,
-		nftables:  modules["nf_tables"],
-		xtMark:    modules["xt_mark"],
 	}, nil
 }

internal/firewall/iptables/ip6tables.go

@@ -76,8 +76,26 @@ func (c *Config) runIP6tablesInstructionNoSave(ctx context.Context, instruction
 	cmd := exec.CommandContext(ctx, c.ip6Tables, flags...) // #nosec G204
 	c.logger.Debug(cmd.String())
 	if output, err := c.runner.Run(cmd); err != nil {
+		if strings.Contains(output, "missing kernel module") {
+			err = ErrKernelModuleMissing
+		}
 		return fmt.Errorf("command failed: \"%s %s\": %s: %w",
 			c.ip6Tables, instruction, output, err)
 	}
 	return nil
 }
+
+var ErrPolicyNotValid = errors.New("policy is not valid")
+
+func (c *Config) SetIPv6AllPolicies(ctx context.Context, policy string) error {
+	switch policy {
+	case "ACCEPT", "DROP":
+	default:
+		return fmt.Errorf("%w: %s", ErrPolicyNotValid, policy)
+	}
+	return c.runIP6tablesInstructions(ctx, []string{
+		"--policy INPUT " + policy,
+		"--policy OUTPUT " + policy,
+		"--policy FORWARD " + policy,
+	})
+}

internal/firewall/iptables/iptables.go

@@ -92,20 +92,22 @@ func (c *Config) runIptablesInstructionNoSave(ctx context.Context, instruction s
 	cmd := exec.CommandContext(ctx, c.ipTables, flags...) // #nosec G204
 	c.logger.Debug(cmd.String())
 	if output, err := c.runner.Run(cmd); err != nil {
+		if strings.Contains(output, "missing kernel module") {
+			err = ErrKernelModuleMissing
+		}
 		return fmt.Errorf("command failed: \"%s %s\": %s: %w",
 			c.ipTables, instruction, output, err)
 	}
 	return nil
 }
 
-func (c *Config) SetBaseChainsPolicy(ctx context.Context, policy string) error {
+func (c *Config) SetIPv4AllPolicies(ctx context.Context, policy string) error {
-	policy = strings.ToUpper(policy)
 	switch policy {
 	case "ACCEPT", "DROP":
 	default:
 		return fmt.Errorf("%w: %s", ErrPolicyUnknown, policy)
 	}
-	return c.runMixedIptablesInstructions(ctx, []string{
+	return c.runIptablesInstructions(ctx, []string{
 		"--policy INPUT " + policy,
 		"--policy OUTPUT " + policy,
 		"--policy FORWARD " + policy,
@@ -148,6 +150,136 @@ func (c *Config) AcceptEstablishedRelatedTraffic(ctx context.Context) error {
 	})
 }
 
+// AcceptOutputPublicOnlyNewTraffic adds rules to mark new output connections, and to accept
+// established or related packets with this mark only. This effectively forces
+// previously established or related traffic to be blocked.
+// If remove is true, the rules are removed instead of appended.
+// If the relevant kernel modules are not available, it returns an error indicating
+// which kernel module is missing.
+func (c *Config) AcceptOutputPublicOnlyNewTraffic(ctx context.Context) error {
+	ipv4Instructions, ipv6Instructions := makeCreatePublicIPChainInstructions()
+	appendToBoth := func(instruction string) {
+		ipv4Instructions = append(ipv4Instructions, instruction)
+		ipv6Instructions = append(ipv6Instructions, instruction)
+	}
+
+	// Mark new connections with mark 0x567
+	appendToBoth("-A PUBLIC_ONLY -m conntrack --ctstate NEW -j CONNMARK --set-mark 0x567")
+	// Drop related/established connections that made it through; marked connections would
+	// be directly accepted by the first rule in the OUTPUT chain (see below)
+	appendToBoth("-A PUBLIC_ONLY -m conntrack --ctstate RELATED,ESTABLISHED -j DROP")
+	// Set the PUBLIC_ONLY chain as the second rule in the OUTPUT chain, so that it is evaluated
+	// after the accept rule below, for performance reasons.
+	appendToBoth("-I OUTPUT -j PUBLIC_ONLY")
+	appendToBoth("-I OUTPUT -m conntrack --ctstate RELATED,ESTABLISHED -m connmark --mark 0x567 -j ACCEPT")
+
+	c.iptablesMutex.Lock()
+	c.ip6tablesMutex.Lock()
+	defer c.iptablesMutex.Unlock()
+	defer c.ip6tablesMutex.Unlock()
+
+	restore, err := c.saveAndRestore(ctx)
+	if err != nil {
+		return err
+	}
+
+	err = c.runIptablesInstructionsNoSave(ctx, ipv4Instructions)
+	if err != nil {
+		restore(ctx)
+		return err
+	}
+	err = c.runIP6tablesInstructionsNoSave(ctx, ipv6Instructions)
+	if err != nil {
+		restore(ctx)
+		return err
+	}
+
+	return nil
+}
+
+func (c *Config) RejectOutputPublicTraffic(ctx context.Context, remove bool) error {
+	return c.targetOutputPublicTraffic(ctx, "REJECT", remove)
+}
+
+func (c *Config) DropOutputPublicTraffic(ctx context.Context, remove bool) error {
+	return c.targetOutputPublicTraffic(ctx, "DROP", remove)
+}
+
+func (c *Config) targetOutputPublicTraffic(ctx context.Context, target string, remove bool) error {
+	removeInstructions := []string{
+		"-D OUTPUT -j PUBLIC_ONLY",
+		"-F PUBLIC_ONLY",
+		"-X PUBLIC_ONLY",
+	}
+	if remove {
+		return c.runMixedIptablesInstructions(ctx, removeInstructions)
+	}
+
+	ipv4Instructions, ipv6Instructions := makeCreatePublicIPChainInstructions()
+	appendToBoth := func(instruction string) {
+		ipv4Instructions = append(ipv4Instructions, instruction)
+		ipv6Instructions = append(ipv6Instructions, instruction)
+	}
+
+	if target == "REJECT" {
+		// Block TCP by sending back TCP RST packets.
+		appendToBoth("-A PUBLIC_ONLY -p tcp -m conntrack --ctstate RELATED,ESTABLISHED " +
+			"-j REJECT --reject-with tcp-reset")
+		// Block UDP and ICMP, sending back ICMP port unreachable.
+		appendToBoth("-A PUBLIC_ONLY -m conntrack --ctstate RELATED,ESTABLISHED -j REJECT")
+	} else {
+		appendToBoth("-A PUBLIC_ONLY -m conntrack --ctstate RELATED,ESTABLISHED -j " + target)
+	}
+	appendToBoth("-I OUTPUT -j PUBLIC_ONLY")
+
+	err := c.runIptablesInstructions(ctx, ipv4Instructions)
+	if err != nil {
+		if strings.Contains(err.Error(), " support") {
+			return fmt.Errorf("%w: %w", ErrKernelModuleMissing, err)
+		}
+	}
+
+	err = c.runIP6tablesInstructions(ctx, ipv6Instructions)
+	if err != nil {
+		_ = c.runIptablesInstructions(ctx, removeInstructions)
+		if strings.Contains(err.Error(), " support") {
+			return fmt.Errorf("%w: %w", ErrKernelModuleMissing, err)
+		}
+		return err
+	}
+
+	return nil
+}
+
+func makeCreatePublicIPChainInstructions() (ipv4Instructions, ipv6Instructions []string) {
+	ipv4PrivatePrefixes := []netip.Prefix{
+		netip.MustParsePrefix("10.0.0.0/8"),
+		netip.MustParsePrefix("172.16.0.0/12"),
+		netip.MustParsePrefix("192.168.0.0/16"),
+		netip.MustParsePrefix("127.0.0.0/8"),
+	}
+	ipv6PrivatePrefixes := []netip.Prefix{
+		netip.MustParsePrefix("fc00::/7"),
+		netip.MustParsePrefix("fe80::/10"),
+		netip.MustParsePrefix("::1/128"),
+	}
+
+	ipv4Instructions = append(ipv4Instructions, "-N PUBLIC_ONLY")
+	ipv6Instructions = append(ipv6Instructions, "-N PUBLIC_ONLY")
+
+	for _, prefix := range ipv4PrivatePrefixes {
+		ipv4Instructions = append(ipv4Instructions, fmt.Sprintf(
+			"-A PUBLIC_ONLY -d %s -j RETURN", prefix))
+	}
+
+	for _, prefix := range ipv6PrivatePrefixes {
+		ipv6Instructions = append(ipv6Instructions, fmt.Sprintf(
+			"-A PUBLIC_ONLY -d %s -j RETURN", prefix))
+	}
+
+	return ipv4Instructions, ipv6Instructions
+}
+
 func (c *Config) AcceptOutputTrafficToVPN(ctx context.Context,
 	defaultInterface string, connection models.Connection, remove bool,
 ) error {
@@ -338,11 +470,11 @@ func (c *Config) RunUserPostRules(ctx context.Context, filepath string) error {
 
 		switch {
 		case ipv4:
-			err = c.runIptablesInstructionNoSave(ctx, rule)
+			err = c.runIptablesInstruction(ctx, rule)
 		case c.ip6Tables == "":
 			err = fmt.Errorf("running user ip6tables rule: %w", ErrNeedIP6Tables)
 		default: // ipv6
-			err = c.runIP6tablesInstructionNoSave(ctx, rule)
+			err = c.runIP6tablesInstruction(ctx, rule)
 		}
 		if err != nil {
 			restore(ctx)

internal/firewall/iptables/iptablesmix.go

@@ -34,7 +34,7 @@ func (c *Config) runMixedIptablesInstruction(ctx context.Context, instruction st
 	if err != nil {
 		return err
 	}
-	err = c.runMixedIptablesInstructionNoSave(ctx, instruction)
+	err = c.runIptablesInstructionNoSave(ctx, instruction)
 	if err != nil {
 		restore(ctx)
 	}

internal/firewall/iptables/list.go

@@ -33,6 +33,9 @@ type chainRule struct {
 	ctstate         []string     // for example ["RELATED","ESTABLISHED"]. Can be empty.
 	tcpFlags        tcpFlags
 	mark            mark
+	connMark        mark
+	setMark         uint
+	rejectWith      string // for example "tcp-reset", only used for REJECT targets
 }
 
 type mark struct {
@@ -219,10 +222,6 @@ func parseChainRuleField(fieldIndex int, field string, rule *chainRule) (err err
 			return fmt.Errorf("parsing bytes: %w", err)
 		}
 	case targetIndex:
-		err = checkTarget(field)
-		if err != nil {
-			return fmt.Errorf("checking target: %w", err)
-		}
 		rule.target = field
 	case protocolIndex:
 		rule.protocol, err = parseProtocol(field)
@@ -293,6 +292,33 @@ func parseChainRuleOptionalFields(optionalFields []string, rule *chainRule) (err
 			}
 			rule.mark = mark
 			i += consumed
+		case "reject-with":
+			i++
+			rule.rejectWith = optionalFields[i] // for example "tcp-reset"
+			i++
+		case "connmark":
+			i++
+			connMark, consumed, err := parseMark(optionalFields[i:])
+			if err != nil {
+				return fmt.Errorf("parsing connmark: %w", err)
+			}
+			rule.connMark = connMark
+			i += consumed
+		case "CONNMARK":
+			i++
+			switch optionalFields[i] {
+			case "set":
+				i++
+				value, err := parseAny32bNumber(optionalFields[i])
+				if err != nil {
+					return fmt.Errorf("parsing CONNMARK set value: %w", err)
+				}
+				rule.setMark = value
+				i++
+			default:
+				return fmt.Errorf("%w: unexpected %q after CONNMARK",
+					ErrChainRuleMalformed, optionalFields[i])
+			}
 		default:
 			return fmt.Errorf("%w: unexpected optional field: %s",
 				ErrChainRuleMalformed, optionalFields[i])
@@ -422,8 +448,6 @@ func parsePortsCSV(s string) (ports []uint16, err error) {
 	return ports, nil
 }
 
-var errMarkValueMalformed = errors.New("mark value is malformed")
-
 func parseMark(optionalFields []string) (m mark, consumed int, err error) {
 	switch optionalFields[consumed] {
 	case "match":
@@ -433,13 +457,11 @@ func parseMark(optionalFields []string) (m mark, consumed int, err error) {
 			consumed++
 		}
 
-		const base = 0 // auto-detect
+		value, err := parseAny32bNumber(optionalFields[consumed])
-		const bits = 32
-		value, err := strconv.ParseUint(optionalFields[consumed], base, bits)
 		if err != nil {
-			return mark{}, 0, fmt.Errorf("%w: %s", errMarkValueMalformed, optionalFields[consumed])
+			return mark{}, 0, fmt.Errorf("value malformed: %w", err)
 		}
-		m.value = uint(value)
+		m.value = value
 		consumed++
 	default:
 		return mark{}, 0, fmt.Errorf("%w: unexpected mark mode field: %s",

internal/firewall/iptables/parse.go

@@ -9,9 +9,19 @@ import (
 	"strings"
 )
 
+type operation uint8
+
+const (
+	opNone operation = iota
+	opAppend
+	opDelete
+	opInsert
+	opReplace
+)
+
 type iptablesInstruction struct {
 	table           string // defaults to "filter", and can be "nat" for example.
-	append          bool
+	operation       operation
 	chain           string       // for example INPUT, PREROUTING. Cannot be empty.
 	target          string       // for example ACCEPT. Can be empty.
 	protocol        string       // "tcp" or "udp" or "" for all protocols.
@@ -25,6 +35,9 @@ type iptablesInstruction struct {
 	ctstate         []string     // if empty, there is no ctstate
 	tcpFlags        tcpFlags
 	mark            mark
+	connMark        mark
+	setMark         uint   // only used for jump CONNMARK --set-mark
+	rejectWith      string // only used for REJECT targets
 }
 
 func (i *iptablesInstruction) setDefaults() {
@@ -65,6 +78,12 @@ func (i *iptablesInstruction) equalToRule(table, chain string, rule chainRule) (
 		return false
 	case i.mark != rule.mark:
 		return false
+	case i.connMark != rule.connMark:
+		return false
+	case i.setMark != rule.setMark:
+		return false
+	case i.rejectWith != rule.rejectWith:
+		return false
 	default:
 		return true
 	}
@@ -113,13 +132,20 @@ func parseInstructionFlag(fields []string, instruction *iptablesInstruction) (co
 	case "-t", "--table":
 		instruction.table = value
 	case "-D", "--delete":
-		instruction.append = false
+		instruction.operation = opDelete
 		instruction.chain = value
 	case "-A", "--append":
-		instruction.append = true
+		instruction.operation = opAppend
+		instruction.chain = value
+	case "-I", "--insert":
+		instruction.operation = opInsert
 		instruction.chain = value
 	case "-j", "--jump":
-		instruction.target = value
+		subConsumed, err := parseJumpFlag(fields[1:], instruction)
+		if err != nil {
+			return 0, fmt.Errorf("parsing jump flag: %w", err)
+		}
+		consumed += subConsumed
 	case "-p", "--protocol":
 		instruction.protocol = value
 	case "-m", "--match":
@@ -128,13 +154,11 @@ func parseInstructionFlag(fields []string, instruction *iptablesInstruction) (co
 			return 0, fmt.Errorf("parsing match module: %w", err)
 		}
 	case "--mark":
-		const base = 0 // auto-detect
+		n, err := parseAny32bNumber(value)
-		const bits = 32
-		value, err := strconv.ParseUint(value, base, bits)
 		if err != nil {
-			return 0, fmt.Errorf("parsing mark value %q: %w", fields[2], err)
+			return 0, fmt.Errorf("parsing mark value %q: %w", value, err)
 		}
-		instruction.mark.value = uint(value)
+		instruction.mark.value = n
 	case "-i", "--in-interface":
 		instruction.inputInterface = value
 	case "-o", "--out-interface":
@@ -172,6 +196,8 @@ func parseInstructionFlag(fields []string, instruction *iptablesInstruction) (co
 		if err != nil {
 			return 0, fmt.Errorf("parsing TCP flags: %w", err)
 		}
+	case "--reject-with":
+		instruction.rejectWith = value // for example "tcp-reset"
 	default:
 		return 0, fmt.Errorf("%w: unknown key %q", ErrIptablesCommandMalformed, flag)
 	}
@@ -182,7 +208,7 @@ func preCheckInstructionFields(fields []string) (consumed int, err error) {
 	flag := fields[0]
 	// All flags use one value after the flag, except the following:
 	switch flag {
-	case "--tcp-flags": // -m can have 1 or 2 values
+	case "--tcp-flags":
 		const expected = 3
 		if len(fields) < expected {
 			return 0, fmt.Errorf("%w: flag %q requires at least 2 values, but got %s",
@@ -199,6 +225,34 @@ func preCheckInstructionFields(fields []string) (consumed int, err error) {
 	}
 }
 
+func parseJumpFlag(fields []string, instruction *iptablesInstruction) (consumed int, err error) {
+	instruction.target = fields[0]
+	// consumed in the caller already takes fields[0] into account
+	if instruction.target != "CONNMARK" {
+		return consumed, nil
+	}
+	// consumed already accounts for the "CONNMARK" value
+	const expectedFields = 3
+	if len(fields) < expectedFields {
+		return 0, fmt.Errorf("%w: jump CONNMARK requires at least two additional values",
+			ErrIptablesCommandMalformed)
+	}
+	switch fields[1] {
+	case "--set-mark":
+		n, err := parseAny32bNumber(fields[2])
+		if err != nil {
+			return 0, fmt.Errorf("parsing connmark mark value %q: %w", fields[2], err)
+		}
+		consumed++
+		instruction.setMark = n
+	default:
+		return consumed, fmt.Errorf("%w: unsupported jump CONNMARK with value: %s",
+			ErrIptablesCommandMalformed, fields[1])
+	}
+	consumed++
+	return consumed, nil
+}
+
 func parseIPPrefix(value string) (prefix netip.Prefix, err error) {
 	slashIndex := strings.Index(value, "/")
 	if slashIndex >= 0 {
@@ -221,6 +275,13 @@ func parsePort(value string) (port uint16, err error) {
 	return uint16(portValue), nil
 }
 
+func parseAny32bNumber(mark string) (value uint, err error) {
+	const base = 0 // auto-detect
+	const bits = 32
+	n, err := strconv.ParseUint(mark, base, bits)
+	return uint(n), err
+}
+
 func parseMatchModule(fields []string, instruction *iptablesInstruction) (
 	consumed int, err error,
 ) {
@@ -234,14 +295,30 @@ func parseMatchModule(fields []string, instruction *iptablesInstruction) (
 		// parse it twice.
 	case "mark":
 		consumed++
-		switch fields[consumed] {
+		switch {
-		case "!":
+		case len(fields[consumed:]) == 0 || strings.HasPrefix(fields[consumed], "-"):
+			// end or another flag
+			return consumed, nil
+		case fields[consumed] == "!":
 			consumed++
 			instruction.mark.invert = true
 		default:
 			return consumed, fmt.Errorf("%w: unsupported match mark with value: %s",
 				ErrIptablesCommandMalformed, fields[2])
 		}
+	case "connmark":
+		consumed++
+		switch {
+		case len(fields[consumed:]) == 0 || strings.HasPrefix(fields[consumed], "-"):
+			// end or another flag
+			return consumed, nil
+		case fields[consumed] == "!":
+			consumed++
+			instruction.connMark.invert = true
+		default:
+			return consumed, fmt.Errorf("%w: unsupported match connmark with value: %s",
+				ErrIptablesCommandMalformed, fields[2])
+		}
 	default:
 		return 0, fmt.Errorf("%w: unknown match value: %s",
 			ErrIptablesCommandMalformed, fields[consumed])

internal/firewall/iptables/parse_test.go

@@ -33,9 +33,9 @@ func Test_parseIptablesInstruction(t *testing.T) {
 		"one_pair": {
 			s: "-A INPUT",
 			instruction: iptablesInstruction{
-				table:  "filter",
+				table:     "filter",
-				chain:  "INPUT",
+				chain:     "INPUT",
-				append: true,
+				operation: opAppend,
 			},
 		},
 		"instruction_A": {
@@ -43,7 +43,7 @@ func Test_parseIptablesInstruction(t *testing.T) {
 			instruction: iptablesInstruction{
 				table:           "filter",
 				chain:           "INPUT",
-				append:          true,
+				operation:       opAppend,
 				inputInterface:  "tun0",
 				protocol:        "tcp",
 				source:          netip.MustParsePrefix("1.2.3.4/32"),
@@ -57,7 +57,7 @@ func Test_parseIptablesInstruction(t *testing.T) {
 			instruction: iptablesInstruction{
 				table:           "nat",
 				chain:           "PREROUTING",
-				append:          false,
+				operation:       opDelete,
 				inputInterface:  "tun0",
 				protocol:        "tcp",
 				destinationPort: 43716,

internal/firewall/iptables/tcp.go

@@ -5,6 +5,7 @@ import (
 	"errors"
 	"fmt"
 	"net/netip"
+	"os"
 )
 
 type tcpFlags struct {
@@ -63,7 +64,7 @@ func parseTCPFlag(s string) (tcpFlag, error) {
 	return 0, fmt.Errorf("%w: %s", errTCPFlagUnknown, s)
 }
 
-var ErrMarkMatchModuleMissing = errors.New("kernel is missing the mark module libxt_mark.so")
+var ErrMarkMatchModuleMissing = errors.New("libxt_mark.so module is missing")
 
 // TempDropOutputTCPRST temporarily drops outgoing TCP RST packets to the specified address and port,
 // for any TCP packets not marked with the excludeMark given.
@@ -73,7 +74,8 @@ func (c *Config) TempDropOutputTCPRST(ctx context.Context,
 	src, dst netip.AddrPort, excludeMark int) (
 	revert func(ctx context.Context) error, err error,
 ) {
-	if !c.nftables && !c.xtMark {
+	_, err = os.Stat("/usr/lib/xtables/libxt_mark.so")
+	if err != nil && errors.Is(err, os.ErrNotExist) {
 		return nil, fmt.Errorf("%w", ErrMarkMatchModuleMissing)
 	}
 

internal/firewall/nftables/atomic.go

@@ -1,99 +0,0 @@
-package nftables
-
-import (
-	"context"
-	"fmt"
-
-	"github.com/google/nftables"
-)
-
-// SaveAndRestore saves the current nftables tree and returns a restore function that
-// can be called to restore the saved tree.
-func (f *Firewall) SaveAndRestore(_ context.Context) (restore func(context.Context), err error) {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return nil, fmt.Errorf("creating nftables connection: %w", err)
-	}
-	tables, err := saveTables(conn)
-	if err != nil {
-		return nil, fmt.Errorf("saving nftables state: %w", err)
-	}
-	return func(_ context.Context) {
-		conn, err := nftables.New()
-		if err != nil {
-			f.logger.Warnf("creating nftables connection for restore: %s", err)
-			return
-		}
-		err = restoreTables(conn, tables)
-		if err != nil {
-			f.logger.Warnf("restoring nftables state: %s", err)
-		}
-	}, nil
-}
-
-type savedTable struct {
-	table  *nftables.Table
-	chains []savedChain
-}
-
-type savedChain struct {
-	chain *nftables.Chain
-	rules []*nftables.Rule
-}
-
-func saveTables(conn *nftables.Conn) ([]savedTable, error) {
-	tables, err := conn.ListTables()
-	if err != nil {
-		return nil, err
-	}
-
-	savedTables := make([]savedTable, len(tables))
-	for i, table := range tables {
-		savedTables[i].table = table
-
-		chains, err := conn.ListChains()
-		if err != nil {
-			return nil, err
-		}
-
-		for _, chain := range chains {
-			if chain.Table.Name != table.Name ||
-				chain.Table.Family != table.Family {
-				continue
-			}
-			rules, err := conn.GetRules(table, chain)
-			if err != nil {
-				return nil, fmt.Errorf("getting rules for chain %s in table %s: %w", chain.Name, table.Name, err)
-			}
-			savedChain := savedChain{chain: chain, rules: rules}
-			savedTables[i].chains = append(savedTables[i].chains, savedChain)
-		}
-	}
-
-	return savedTables, nil
-}
-
-func restoreTables(conn *nftables.Conn, savedTables []savedTable) error {
-	conn.FlushRuleset()
-
-	for _, savedTable := range savedTables {
-		table := conn.AddTable(savedTable.table)
-		for _, savedChain := range savedTable.chains {
-			// Make the [nftables.Chain.Table] points to the new [nftables.Table]
-			// created in this connection.
-			savedChain.chain.Table = table
-			savedChain.chain = conn.AddChain(savedChain.chain)
-
-			for _, rule := range savedChain.rules {
-				rule.Table = table
-				rule.Chain = savedChain.chain
-				conn.AddRule(rule)
-			}
-		}
-	}
-
-	return conn.Flush()
-}

internal/firewall/nftables/basechains.go

@@ -1,50 +0,0 @@
-package nftables
-
-import (
-	"context"
-	"errors"
-	"fmt"
-	"strings"
-
-	"github.com/google/nftables"
-)
-
-var ErrPolicyUnknown = errors.New("unknown policy")
-
-// SetBaseChainsPolicy sets the policy of all the base chains (INPUT, FORWARD, or OUTPUT)
-// for the filter table to the given policy (accept or drop).
-func (f *Firewall) SetBaseChainsPolicy(_ context.Context, policy string) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	var chainPolicy nftables.ChainPolicy
-	switch strings.ToLower(policy) {
-	case "accept":
-		chainPolicy = nftables.ChainPolicyAccept
-	case "drop":
-		chainPolicy = nftables.ChainPolicyDrop
-	default:
-		return fmt.Errorf("%w: %s", ErrPolicyUnknown, policy)
-	}
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	_, inputChain, forwardChain, outputChain := setupFilterWithBaseChains(conn)
-	inputChain.Policy = &chainPolicy
-	forwardChain.Policy = &chainPolicy
-	outputChain.Policy = &chainPolicy
-
-	conn.AddChain(inputChain)
-	conn.AddChain(forwardChain)
-	conn.AddChain(outputChain)
-
-	err = conn.Flush()
-	if err != nil {
-		return fmt.Errorf("flushing nftables changes: %w", err)
-	}
-
-	return nil
-}

internal/firewall/nftables/conntrack.go

@@ -1,61 +0,0 @@
-package nftables
-
-import (
-	"context"
-	"fmt"
-
-	"github.com/google/nftables"
-	"github.com/google/nftables/expr"
-)
-
-func (f *Firewall) AcceptEstablishedRelatedTraffic(_ context.Context) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	table, inputChain, _, outputChain := setupFilterWithBaseChains(conn)
-
-	ctStateExprs := []expr.Any{
-		&expr.Ct{
-			Key:      expr.CtKeySTATE,
-			Register: 1,
-		},
-		&expr.Bitwise{
-			SourceRegister: 1,
-			DestRegister:   1,
-			Len:            4, //nolint:mnd
-			Mask:           []byte{byte(expr.CtStateBitESTABLISHED | expr.CtStateBitRELATED), 0x00, 0x00, 0x00},
-			Xor:            []byte{0x00, 0x00, 0x00, 0x00},
-		},
-		&expr.Cmp{
-			Op:       expr.CmpOpNeq,
-			Register: 1,
-			Data:     []byte{0x00, 0x00, 0x00, 0x00},
-		},
-		&expr.Verdict{
-			Kind: expr.VerdictAccept,
-		},
-	}
-
-	conn.AddRule(&nftables.Rule{
-		Table: table,
-		Chain: inputChain,
-		Exprs: ctStateExprs,
-	})
-
-	conn.AddRule(&nftables.Rule{
-		Table: table,
-		Chain: outputChain,
-		Exprs: ctStateExprs,
-	})
-
-	if err := conn.Flush(); err != nil {
-		return fmt.Errorf("flushing: %w", err)
-	}
-
-	return nil
-}

internal/firewall/nftables/delete.go

@@ -1,27 +0,0 @@
-package nftables
-
-import (
-	"errors"
-	"fmt"
-	"reflect"
-
-	"github.com/google/nftables"
-)
-
-var errRuleToDeleteNotFound = errors.New("rule not found for removal")
-
-func (f *Firewall) deleteRule(conn *nftables.Conn, rule *nftables.Rule) error {
-	for i, existing := range f.rules {
-		if !reflect.DeepEqual(existing, rule) {
-			continue
-		}
-		err := conn.DelRule(existing)
-		if err != nil {
-			return fmt.Errorf("deleting rule: %w", err)
-		}
-		f.rules[i], f.rules[len(f.rules)-1] = f.rules[len(f.rules)-1], f.rules[i]
-		f.rules = f.rules[:len(f.rules)-1]
-		return nil
-	}
-	return fmt.Errorf("%w: %#v", errRuleToDeleteNotFound, rule)
-}

internal/firewall/nftables/filter.go

@@ -1,38 +0,0 @@
-package nftables
-
-import "github.com/google/nftables"
-
-func setupFilterWithBaseChains(conn *nftables.Conn) (table *nftables.Table,
-	inputChain, forwardChain, outputChain *nftables.Chain,
-) {
-	table = conn.AddTable(&nftables.Table{
-		Family: nftables.TableFamilyINet,
-		Name:   "filter",
-	})
-
-	inputChain = conn.AddChain(&nftables.Chain{
-		Name:     "input",
-		Table:    table,
-		Type:     nftables.ChainTypeFilter,
-		Hooknum:  nftables.ChainHookInput,
-		Priority: nftables.ChainPriorityFilter,
-	})
-
-	forwardChain = conn.AddChain(&nftables.Chain{
-		Name:     "forward",
-		Table:    table,
-		Type:     nftables.ChainTypeFilter,
-		Hooknum:  nftables.ChainHookForward,
-		Priority: nftables.ChainPriorityFilter,
-	})
-
-	outputChain = conn.AddChain(&nftables.Chain{
-		Name:     "output",
-		Table:    table,
-		Type:     nftables.ChainTypeFilter,
-		Hooknum:  nftables.ChainHookOutput,
-		Priority: nftables.ChainPriorityFilter,
-	})
-
-	return table, inputChain, forwardChain, outputChain
-}

internal/firewall/nftables/firewall.go

@@ -1,22 +0,0 @@
-package nftables
-
-import (
-	"sync"
-
-	"github.com/google/nftables"
-)
-
-type Firewall struct {
-	logger Logger
-
-	// rules are only rules added and tracked for later removal.
-	// Not all rules added are tracked for removal.
-	rules []*nftables.Rule
-	mutex sync.Mutex
-}
-
-func New(logger Logger) *Firewall {
-	return &Firewall{
-		logger: logger,
-	}
-}

internal/firewall/nftables/input.go

@@ -1,170 +0,0 @@
-package nftables
-
-import (
-	"context"
-	"fmt"
-	"net/netip"
-
-	"github.com/google/nftables"
-	"github.com/google/nftables/expr"
-)
-
-func (f *Firewall) AcceptInputThroughInterface(_ context.Context, intf string) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
-
-	rule := &nftables.Rule{
-		Table: table,
-		Chain: inputChain,
-		Exprs: []expr.Any{
-			&expr.Meta{
-				Key:      expr.MetaKeyIIFNAME,
-				Register: 1,
-			},
-			&expr.Cmp{
-				Op:       expr.CmpOpEq,
-				Register: 1,
-				Data:     []byte(intf + "\x00"),
-			},
-			&expr.Verdict{
-				Kind: expr.VerdictAccept,
-			},
-		},
-	}
-
-	conn.AddRule(rule)
-
-	err = conn.Flush()
-	if err != nil {
-		return fmt.Errorf("flushing: %w", err)
-	}
-
-	return nil
-}
-
-// AcceptInputToPort accepts incoming traffic on the specified port, for both TCP and UDP
-// protocols, on the interface intf. If intf is empty or "*", the interface is not used as a filter.
-// If remove is true, the rule is removed instead of added. This is used for port forwarding, with
-// intf set to the VPN tunnel interface.
-func (f *Firewall) AcceptInputToPort(_ context.Context, intf string, port uint16, remove bool) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
-	portBytes := []byte{byte(port >> 8), byte(port)} //nolint:mnd
-	const tcp, udp uint8 = 6, 17
-	protocols := []uint8{tcp, udp}
-
-	for _, protocol := range protocols {
-		const maxExprsLen = 7
-		exprs := make([]expr.Any, 0, maxExprsLen)
-		if intf != "" && intf != "*" {
-			exprs = append(exprs,
-				&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
-				&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte(intf + "\x00")},
-			)
-		}
-		exprs = append(exprs,
-			&expr.Payload{DestRegister: 1, Base: expr.PayloadBaseNetworkHeader, Offset: 9, Len: 1}, //nolint:mnd
-			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte{protocol}},
-			&expr.Payload{DestRegister: 1, Base: expr.PayloadBaseTransportHeader, Offset: 2, Len: 2}, //nolint:mnd
-			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: portBytes},
-			&expr.Verdict{Kind: expr.VerdictAccept},
-		)
-
-		rule := &nftables.Rule{
-			Table: table,
-			Chain: inputChain,
-			Exprs: exprs,
-		}
-
-		if !remove {
-			conn.AddRule(rule)
-			f.rules = append(f.rules, rule)
-			continue
-		}
-		err = f.deleteRule(conn, rule)
-		if err != nil {
-			return fmt.Errorf("deleting rule: %w", err)
-		}
-	}
-
-	err = conn.Flush()
-	if err != nil {
-		f.rules = f.rules[:len(f.rules)-len(protocols)]
-		return fmt.Errorf("flushing: %w", err)
-	}
-
-	return nil
-}
-
-func (f *Firewall) AcceptInputToSubnet(_ context.Context, intf string, subnet netip.Prefix) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	table, inputChain, _, _ := setupFilterWithBaseChains(conn)
-
-	const maxExprsLen = 5
-	exprs := make([]expr.Any, 0, maxExprsLen)
-
-	if intf != "" && intf != "*" {
-		exprs = append(exprs,
-			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
-			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte(intf + "\x00")},
-		)
-	}
-
-	var payloadOffset uint32
-	if subnet.Addr().Is4() {
-		payloadOffset = 16
-	} else {
-		payloadOffset = 24
-	}
-
-	exprs = append(exprs,
-		&expr.Payload{
-			DestRegister: 1,
-			Base:         expr.PayloadBaseNetworkHeader,
-			Offset:       payloadOffset,
-			Len:          uint32(len(subnet.Addr().AsSlice())), //nolint:gosec
-		},
-		&expr.Cmp{
-			Op:       expr.CmpOpEq,
-			Register: 1,
-			Data:     subnet.Addr().AsSlice(),
-		},
-		&expr.Verdict{Kind: expr.VerdictAccept},
-	)
-
-	rule := &nftables.Rule{
-		Table: table,
-		Chain: inputChain,
-		Exprs: exprs,
-	}
-
-	conn.AddRule(rule)
-
-	err = conn.Flush()
-	if err != nil {
-		return fmt.Errorf("flushing: %w", err)
-	}
-
-	return nil
-}

internal/firewall/nftables/interfaces.go

@@ -1,5 +0,0 @@
-package nftables
-
-type Logger interface {
-	Warnf(format string, args ...any)
-}

internal/firewall/nftables/output.go

@@ -1,78 +0,0 @@
-package nftables
-
-import (
-	"context"
-	"fmt"
-
-	"github.com/google/nftables"
-	"github.com/google/nftables/expr"
-)
-
-func (f *Firewall) AcceptIpv6MulticastOutput(_ context.Context, intf string) error {
-	f.mutex.Lock()
-	defer f.mutex.Unlock()
-
-	conn, err := nftables.New()
-	if err != nil {
-		return fmt.Errorf("creating nftables connection: %w", err)
-	}
-
-	table, _, _, outputChain := setupFilterWithBaseChains(conn)
-
-	const maxExprsLen = 6
-	exprs := make([]expr.Any, 0, maxExprsLen)
-
-	if intf != "" && intf != "*" {
-		exprs = append(exprs,
-			&expr.Meta{Key: expr.MetaKeyOIFNAME, Register: 1},
-			&expr.Cmp{Op: expr.CmpOpEq, Register: 1, Data: []byte(intf + "\x00")},
-		)
-	}
-
-	// ff02::1:ff00:0/104 mask is 13 bytes of 0xff
-	mask := []byte{
-		0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
-		0xff, 0xff, 0xff, 0xff, 0xff, 0x00, 0x00, 0x00,
-	} //nolint:mnd
-	addr := []byte{
-		0xff, 0x02, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
-		0x00, 0x00, 0x00, 0x01, 0xff, 0x00, 0x00, 0x00,
-	} //nolint:mnd
-
-	exprs = append(exprs,
-		&expr.Payload{
-			DestRegister: 1,
-			Base:         expr.PayloadBaseNetworkHeader,
-			Offset:       24, // IPv6 Destination Address offset //nolint:mnd
-			Len:          16, //nolint:mnd
-		},
-		&expr.Bitwise{
-			SourceRegister: 1,
-			DestRegister:   1,
-			Len:            16, //nolint:mnd
-			Mask:           mask,
-			Xor:            []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}, //nolint:mnd
-		},
-		&expr.Cmp{
-			Op:       expr.CmpOpEq,
-			Register: 1,
-			Data:     addr,
-		},
-		&expr.Verdict{Kind: expr.VerdictAccept},
-	)
-
-	rule := &nftables.Rule{
-		Table: table,
-		Chain: outputChain,
-		Exprs: exprs,
-	}
-
-	conn.AddRule(rule)
-
-	err = conn.Flush()
-	if err != nil {
-		return fmt.Errorf("flushing: %w", err)
-	}
-
-	return nil
-}

internal/firewall/nftables/support.go

@@ -1,12 +0,0 @@
-package nftables
-
-import "github.com/google/nftables"
-
-func IsSupported() bool {
-	conn, err := nftables.New()
-	if err != nil {
-		return false
-	}
-	_, err = conn.ListTable("filter")
-	return err == nil
-}

internal/netlink/conntrack_linux.go

@@ -1,38 +1,44 @@
 package netlink
 
 import (
+	"errors"
 	"fmt"
 
 	"github.com/mdlayher/netlink"
 	"github.com/ti-mo/netfilter"
+	"golang.org/x/sys/unix"
 )
 
+var ErrConntrackNetlinkNotSupported = errors.New("nf_conntrack_netlink is not supported by the kernel")
+
 func (n *NetLink) FlushConntrack() error {
 	conn, err := netfilter.Dial(nil)
 	if err != nil {
+		if !n.conntrackNetlink {
+			err = fmt.Errorf("%w: %w", err, ErrConntrackNetlinkNotSupported)
+		}
 		return fmt.Errorf("dialing netfilter: %w", err)
 	}
 	defer conn.Close()
 
-	families := [...]netfilter.ProtoFamily{netfilter.ProtoIPv4, netfilter.ProtoIPv6}
+	const ipCtnlMsgCtDelete = netfilter.MessageType(2)
-	for _, family := range families {
+	header := netfilter.Header{
-		const IPCtnlMsgCtDelete = 2
+		SubsystemID: netfilter.NFSubsysCTNetlink,
-		request, err := netfilter.MarshalNetlink(
+		MessageType: ipCtnlMsgCtDelete,
-			netfilter.Header{
+		Family:      unix.AF_UNSPEC,
-				SubsystemID: netfilter.NFSubsysCTNetlink,
+		Flags:       netlink.Request | netlink.Acknowledge,
-				MessageType: netfilter.MessageType(IPCtnlMsgCtDelete),
+	}
-				Family:      family,
+	request, err := netfilter.MarshalNetlink(header, nil)
-				Flags:       netlink.Request | netlink.Acknowledge,
+	if err != nil {
-			},
+		return fmt.Errorf("encoding netlink request: %w", err)
-			nil)
+	}
-		if err != nil {
-			return fmt.Errorf("encoding netlink request: %w", err)
-		}
 
-		_, err = conn.Query(request)
+	_, err = conn.Query(request)
-		if err != nil {
+	if err != nil {
-			return fmt.Errorf("querying netlink request: %w", err)
+		if !n.conntrackNetlink {
+			err = fmt.Errorf("%w: %w", err, ErrConntrackNetlinkNotSupported)
 		}
+		return fmt.Errorf("querying netlink request: %w", err)
 	}
 	return nil
 }

internal/netlink/conntrack_unspecified.go

@@ -2,6 +2,10 @@
 
 package netlink
 
+import "errors"
+
+var ErrConntrackNetlinkNotSupported = errors.New("error not implemented")
+
 func (n *NetLink) FlushConntrack() error {
 	panic("not implemented")
 }

internal/netlink/netlink.go

@@ -1,14 +1,22 @@
 package netlink
 
-import "github.com/qdm12/log"
+import (
+	"github.com/qdm12/gluetun/internal/mod"
+	"github.com/qdm12/log"
+)
 
 type NetLink struct {
 	debugLogger DebugLogger
+
+	// Fixed state
+	conntrackNetlink bool
 }
 
 func New(debugLogger DebugLogger) *NetLink {
+	conntrackNetlink := mod.Probe("nf_conntrack_netlink") == nil
 	return &NetLink{
-		debugLogger: debugLogger,
+		debugLogger:      debugLogger,
+		conntrackNetlink: conntrackNetlink,
 	}
 }
 

internal/pmtud/pmtud.go

@@ -74,7 +74,7 @@ func PathMTUDiscover(ctx context.Context, icmpAddrs []netip.Addr, tcpAddrs []net
 	}
 	mtu, err = tcp.PathMTUDiscover(ctx, tcpAddrs, minMTU, maxPossibleMTU, tryTimeout, fw, logger)
 	if err != nil {
-		if errors.Is(err, iptables.ErrMarkMatchModuleMissing) {
+		if errors.Is(err, iptables.ErrKernelModuleMissing) {
 			logger.Debugf("aborting TCP path MTU discovery: %s", err)
 			if icmpSuccess {
 				return maxPossibleMTU, nil // only rely on ICMP PMTUD results

internal/pmtud/tcp/helpers_test.go

@@ -35,7 +35,7 @@ func getFirewall(t *testing.T) *firewall.Config {
 		noopLogger := &noopLogger{}
 		cmder := command.New()
 		var err error
-		testFirewall, err = firewall.NewConfig(t.Context(), noopLogger, cmder, nil, nil)
+		testFirewall, err = firewall.NewConfig(t.Context(), noopLogger, cmder, nil, nil, nil)
 		if errors.Is(err, iptables.ErrNotSupported) {
 			t.Skip("iptables not installed, skipping TCP PMTUD tests")
 		}

internal/pmtud/tcp/mss.go

@@ -43,7 +43,7 @@ func findHighestMSSDestination(ctx context.Context, familyToFD map[int]fileDescr
 		if result.err != nil {
 			switch {
 			case err != nil: // error already occurred for another findMSS goroutine
-			case errors.Is(result.err, iptables.ErrMarkMatchModuleMissing):
+			case errors.Is(result.err, iptables.ErrKernelModuleMissing):
 				err = fmt.Errorf("finding MSS for %s: %w", result.dst, result.err)
 			case dst.Addr().Is6() && errors.Is(result.err, ip.ErrNetworkUnreachable):
 				// silently discard IPv6 network unreachable errors since they are common