[client] Use native firewall for peer ACLs in userspace WireGuard mode

client/firewall/create_linux.go

@@ -6,6 +6,7 @@ import (
 	"errors"
 	"fmt"
 	"os"
+	"strconv"
 
 	"github.com/coreos/go-iptables/iptables"
 	"github.com/google/nftables"
@@ -35,20 +36,27 @@ const SKIP_NFTABLES_ENV = "NB_SKIP_NFTABLES_CHECK"
 type FWType int
 
 func NewFirewall(iface IFaceMapper, stateManager *statemanager.Manager, flowLogger nftypes.FlowLogger, disableServerRoutes bool, mtu uint16) (firewall.Manager, error) {
-	// on the linux system we try to user nftables or iptables
-	// in any case, because we need to allow netbird interface traffic
-	// so we use AllowNetbird traffic from these firewall managers
-	// for the userspace packet filtering firewall
+	// We run in userspace mode and force userspace firewall was requested. We don't attempt native firewall.
+	if iface.IsUserspaceBind() && forceUserspaceFirewall() {
+		log.Info("forcing userspace firewall")
+		return createUserspaceFirewall(iface, nil, disableServerRoutes, flowLogger, mtu)
+	}
+
+	// Use native firewall for either kernel or userspace, the interface appears identical to netfilter
 	fm, err := createNativeFirewall(iface, stateManager, disableServerRoutes, mtu)
 
+	// Kernel cannot fall back to anything else, need to return error
 	if !iface.IsUserspaceBind() {
 		return fm, err
 	}
 
+	// Fall back to the userspace packet filter if native is unavailable
 	if err != nil {
 		log.Warnf("failed to create native firewall: %v. Proceeding with userspace", err)
+		return createUserspaceFirewall(iface, nil, disableServerRoutes, flowLogger, mtu)
 	}
-	return createUserspaceFirewall(iface, fm, disableServerRoutes, flowLogger, mtu)
+
+	return fm, nil
 }
 
 func createNativeFirewall(iface IFaceMapper, stateManager *statemanager.Manager, routes bool, mtu uint16) (firewall.Manager, error) {
@@ -160,3 +168,17 @@ func isIptablesClientAvailable(client *iptables.IPTables) bool {
 	_, err := client.ListChains("filter")
 	return err == nil
 }
+
+func forceUserspaceFirewall() bool {
+	val := os.Getenv(EnvForceUserspaceFirewall)
+	if val == "" {
+		return false
+	}
+
+	force, err := strconv.ParseBool(val)
+	if err != nil {
+		log.Warnf("failed to parse %s: %v", EnvForceUserspaceFirewall, err)
+		return false
+	}
+	return force
+}

client/firewall/iface.go

@@ -7,6 +7,12 @@ import (
 	"github.com/netbirdio/netbird/client/iface/wgaddr"
 )
 
+// EnvForceUserspaceFirewall forces the use of the userspace packet filter even when
+// native iptables/nftables is available. This only applies when the WireGuard interface
+// runs in userspace mode. When set, peer ACLs are handled by USPFilter instead of
+// kernel netfilter rules.
+const EnvForceUserspaceFirewall = "NB_FORCE_USERSPACE_FIREWALL"
+
 // IFaceMapper defines subset methods of interface required for manager
 type IFaceMapper interface {
 	Name() string

client/firewall/iptables/manager_linux.go

@@ -33,7 +33,6 @@ type Manager struct {
 type iFaceMapper interface {
 	Name() string
 	Address() wgaddr.Address
-	IsUserspaceBind() bool
 }
 
 // Create iptables firewall manager
@@ -64,10 +63,9 @@ func Create(wgIface iFaceMapper, mtu uint16) (*Manager, error) {
 func (m *Manager) Init(stateManager *statemanager.Manager) error {
 	state := &ShutdownState{
 		InterfaceState: &InterfaceState{
-			NameStr:       m.wgIface.Name(),
-			WGAddress:     m.wgIface.Address(),
-			UserspaceBind: m.wgIface.IsUserspaceBind(),
-			MTU:           m.router.mtu,
+			NameStr:   m.wgIface.Name(),
+			WGAddress: m.wgIface.Address(),
+			MTU:       m.router.mtu,
 		},
 	}
 	stateManager.RegisterState(state)
@@ -203,12 +201,10 @@ func (m *Manager) Close(stateManager *statemanager.Manager) error {
 	return nberrors.FormatErrorOrNil(merr)
 }
 
-// AllowNetbird allows netbird interface traffic
+// AllowNetbird allows netbird interface traffic.
+// This is called when USPFilter wraps the native firewall, adding blanket accept
+// rules so that packet filtering is handled in userspace instead of by netfilter.
 func (m *Manager) AllowNetbird() error {
-	if !m.wgIface.IsUserspaceBind() {
-		return nil
-	}
-
 	_, err := m.AddPeerFiltering(
 		nil,
 		net.IP{0, 0, 0, 0},

client/firewall/iptables/manager_linux_test.go

@@ -47,8 +47,6 @@ func (i *iFaceMock) Address() wgaddr.Address {
 	panic("AddressFunc is not set")
 }
 
-func (i *iFaceMock) IsUserspaceBind() bool { return false }
-
 func TestIptablesManager(t *testing.T) {
 	ipv4Client, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	require.NoError(t, err)

client/firewall/iptables/state_linux.go

@@ -9,10 +9,9 @@ import (
 )
 
 type InterfaceState struct {
-	NameStr       string         `json:"name"`
-	WGAddress     wgaddr.Address `json:"wg_address"`
-	UserspaceBind bool           `json:"userspace_bind"`
-	MTU           uint16         `json:"mtu"`
+	NameStr   string         `json:"name"`
+	WGAddress wgaddr.Address `json:"wg_address"`
+	MTU       uint16         `json:"mtu"`
 }
 
 func (i *InterfaceState) Name() string {
@@ -23,10 +22,6 @@ func (i *InterfaceState) Address() wgaddr.Address {
 	return i.WGAddress
 }
 
-func (i *InterfaceState) IsUserspaceBind() bool {
-	return i.UserspaceBind
-}
-
 type ShutdownState struct {
 	sync.Mutex
 

client/firewall/nftables/manager_linux.go

@@ -40,7 +40,6 @@ func getTableName() string {
 type iFaceMapper interface {
 	Name() string
 	Address() wgaddr.Address
-	IsUserspaceBind() bool
 }
 
 // Manager of iptables firewall
@@ -106,10 +105,9 @@ func (m *Manager) Init(stateManager *statemanager.Manager) error {
 	// cleanup using Close() without needing to store specific rules.
 	if err := stateManager.UpdateState(&ShutdownState{
 		InterfaceState: &InterfaceState{
-			NameStr:       m.wgIface.Name(),
-			WGAddress:     m.wgIface.Address(),
-			UserspaceBind: m.wgIface.IsUserspaceBind(),
-			MTU:           m.router.mtu,
+			NameStr:   m.wgIface.Name(),
+			WGAddress: m.wgIface.Address(),
+			MTU:       m.router.mtu,
 		},
 	}); err != nil {
 		log.Errorf("failed to update state: %v", err)
@@ -205,12 +203,10 @@ func (m *Manager) RemoveNatRule(pair firewall.RouterPair) error {
 	return m.router.RemoveNatRule(pair)
 }
 
-// AllowNetbird allows netbird interface traffic
+// AllowNetbird allows netbird interface traffic.
+// This is called when USPFilter wraps the native firewall, adding blanket accept
+// rules so that packet filtering is handled in userspace instead of by netfilter.
 func (m *Manager) AllowNetbird() error {
-	if !m.wgIface.IsUserspaceBind() {
-		return nil
-	}
-
 	m.mutex.Lock()
 	defer m.mutex.Unlock()
 

client/firewall/nftables/manager_linux_test.go

@@ -52,8 +52,6 @@ func (i *iFaceMock) Address() wgaddr.Address {
 	panic("AddressFunc is not set")
 }
 
-func (i *iFaceMock) IsUserspaceBind() bool { return false }
-
 func TestNftablesManager(t *testing.T) {
 
 	// just check on the local interface

client/firewall/nftables/state_linux.go

@@ -8,10 +8,9 @@ import (
 )
 
 type InterfaceState struct {
-	NameStr       string         `json:"name"`
-	WGAddress     wgaddr.Address `json:"wg_address"`
-	UserspaceBind bool           `json:"userspace_bind"`
-	MTU           uint16         `json:"mtu"`
+	NameStr   string         `json:"name"`
+	WGAddress wgaddr.Address `json:"wg_address"`
+	MTU       uint16         `json:"mtu"`
 }
 
 func (i *InterfaceState) Name() string {
@@ -22,10 +21,6 @@ func (i *InterfaceState) Address() wgaddr.Address {
 	return i.WGAddress
 }
 
-func (i *InterfaceState) IsUserspaceBind() bool {
-	return i.UserspaceBind
-}
-
 type ShutdownState struct {
 	InterfaceState *InterfaceState `json:"interface_state,omitempty"`
 }

client/internal/acl/manager_test.go

@@ -19,6 +19,9 @@ import (
 var flowLogger = netflow.NewManager(nil, []byte{}, nil).GetLogger()
 
 func TestDefaultManager(t *testing.T) {
+	t.Setenv("NB_WG_KERNEL_DISABLED", "true")
+	t.Setenv(firewall.EnvForceUserspaceFirewall, "true")
+
 	networkMap := &mgmProto.NetworkMap{
 		FirewallRules: []*mgmProto.FirewallRule{
 			{
@@ -135,6 +138,7 @@ func TestDefaultManager(t *testing.T) {
 func TestDefaultManagerStateless(t *testing.T) {
 	// stateless currently only in userspace, so we have to disable kernel
 	t.Setenv("NB_WG_KERNEL_DISABLED", "true")
+	t.Setenv(firewall.EnvForceUserspaceFirewall, "true")
 	t.Setenv("NB_DISABLE_CONNTRACK", "true")
 
 	networkMap := &mgmProto.NetworkMap{
@@ -194,6 +198,7 @@ func TestDefaultManagerStateless(t *testing.T) {
 // This tests the full ACL manager -> uspfilter integration.
 func TestDenyRulesNotAccumulatedOnRepeatedApply(t *testing.T) {
 	t.Setenv("NB_WG_KERNEL_DISABLED", "true")
+	t.Setenv(firewall.EnvForceUserspaceFirewall, "true")
 
 	networkMap := &mgmProto.NetworkMap{
 		FirewallRules: []*mgmProto.FirewallRule{
@@ -258,6 +263,7 @@ func TestDenyRulesNotAccumulatedOnRepeatedApply(t *testing.T) {
 // up when they're removed from the network map in a subsequent update.
 func TestDenyRulesCleanedUpOnRemoval(t *testing.T) {
 	t.Setenv("NB_WG_KERNEL_DISABLED", "true")
+	t.Setenv(firewall.EnvForceUserspaceFirewall, "true")
 
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()
@@ -339,6 +345,7 @@ func TestDenyRulesCleanedUpOnRemoval(t *testing.T) {
 // one added without leaking.
 func TestRuleUpdateChangingAction(t *testing.T) {
 	t.Setenv("NB_WG_KERNEL_DISABLED", "true")
+	t.Setenv(firewall.EnvForceUserspaceFirewall, "true")
 
 	ctrl := gomock.NewController(t)
 	defer ctrl.Finish()