Add default firewall rule to allow netbird traffic (#1056)

Add a default firewall rule to allow netbird traffic to be handled 
by the access control managers.

Userspace manager behavior:
- When running on Windows, a default rule is add on Windows firewall
- For Linux, we are using one of the Kernel managers to add a single rule
- This PR doesn't handle macOS

Kernel manager behavior:
- For NFtables, if there is a filter table, an INPUT rule is added
- Iptables follows the previous flow if running on kernel mode. If running 
on userspace mode, it adds a single rule for INPUT and OUTPUT chains

A new checkerFW package has been introduced to consolidate checks across
route and access control managers.
It supports a new environment variable to skip nftables and allow iptables tests

client/firewall/firewall.go

@@ -40,6 +40,9 @@ const (
 // It declares methods which handle actions required by the
 // Netbird client for ACL and routing functionality
 type Manager interface {
+	// AllowNetbird allows netbird interface traffic
+	AllowNetbird() error
+
 	// AddFiltering rule to the firewall
 	//
 	// If comment argument is empty firewall manager should set

client/firewall/iptables/manager_linux.go

@@ -44,6 +44,7 @@ type Manager struct {
 type iFaceMapper interface {
 	Name() string
 	Address() iface.WGAddress
+	IsUserspaceBind() bool
 }
 
 type ruleset struct {
@@ -52,7 +53,7 @@ type ruleset struct {
 }
 
 // Create iptables firewall manager
-func Create(wgIface iFaceMapper) (*Manager, error) {
+func Create(wgIface iFaceMapper, ipv6Supported bool) (*Manager, error) {
 	m := &Manager{
 		wgIface: wgIface,
 		inputDefaultRuleSpecs: []string{
@@ -62,26 +63,26 @@ func Create(wgIface iFaceMapper) (*Manager, error) {
 		rulesets: make(map[string]ruleset),
 	}
 
-	if err := ipset.Init(); err != nil {
+	err := ipset.Init()
+	if err != nil {
 		return nil, fmt.Errorf("init ipset: %w", err)
 	}
 
 	// init clients for booth ipv4 and ipv6
-	ipv4Client, err := iptables.NewWithProtocol(iptables.ProtocolIPv4)
+	m.ipv4Client, err = iptables.NewWithProtocol(iptables.ProtocolIPv4)
 	if err != nil {
 		return nil, fmt.Errorf("iptables is not installed in the system or not supported")
 	}
-	if isIptablesClientAvailable(ipv4Client) {
-		m.ipv4Client = ipv4Client
+
+	if ipv6Supported {
+		m.ipv6Client, err = iptables.NewWithProtocol(iptables.ProtocolIPv6)
+		if err != nil {
+			log.Warnf("ip6tables is not installed in the system or not supported: %v. Access rules for this protocol won't be applied.", err)
+		}
 	}
 
-	ipv6Client, err := iptables.NewWithProtocol(iptables.ProtocolIPv6)
-	if err != nil {
-		log.Errorf("ip6tables is not installed in the system or not supported: %v", err)
-	} else {
-		if isIptablesClientAvailable(ipv6Client) {
-			m.ipv6Client = ipv6Client
-		}
+	if m.ipv4Client == nil && m.ipv6Client == nil {
+		return nil, fmt.Errorf("iptables is not installed in the system or not enough permissions to use it")
 	}
 
 	if err := m.Reset(); err != nil {
@@ -90,11 +91,6 @@ func Create(wgIface iFaceMapper) (*Manager, error) {
 	return m, nil
 }
 
-func isIptablesClientAvailable(client *iptables.IPTables) bool {
-	_, err := client.ListChains("filter")
-	return err == nil
-}
-
 // AddFiltering rule to the firewall
 //
 // If comment is empty rule ID is used as comment
@@ -276,6 +272,38 @@ func (m *Manager) Reset() error {
 	return nil
 }
 
+// AllowNetbird allows netbird interface traffic
+func (m *Manager) AllowNetbird() error {
+	if m.wgIface.IsUserspaceBind() {
+		_, err := m.AddFiltering(
+			net.ParseIP("0.0.0.0"),
+			"all",
+			nil,
+			nil,
+			fw.RuleDirectionIN,
+			fw.ActionAccept,
+			"",
+			"allow netbird interface traffic",
+		)
+		if err != nil {
+			return fmt.Errorf("failed to allow netbird interface traffic: %w", err)
+		}
+		_, err = m.AddFiltering(
+			net.ParseIP("0.0.0.0"),
+			"all",
+			nil,
+			nil,
+			fw.RuleDirectionOUT,
+			fw.ActionAccept,
+			"",
+			"allow netbird interface traffic",
+		)
+		return err
+	}
+
+	return nil
+}
+
 // Flush doesn't need to be implemented for this manager
 func (m *Manager) Flush() error { return nil }
 
@@ -406,7 +434,7 @@ func (m *Manager) client(ip net.IP) (*iptables.IPTables, error) {
 			return nil, fmt.Errorf("failed to create default drop all in netbird input chain: %w", err)
 		}
 
-		if err := client.AppendUnique("filter", "INPUT", m.inputDefaultRuleSpecs...); err != nil {
+		if err := client.Insert("filter", "INPUT", 1, m.inputDefaultRuleSpecs...); err != nil {
 			return nil, fmt.Errorf("failed to create input chain jump rule: %w", err)
 		}
 

client/firewall/iptables/manager_linux_test.go

@@ -33,6 +33,8 @@ func (i *iFaceMock) Address() iface.WGAddress {
 	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)
@@ -53,7 +55,7 @@ func TestIptablesManager(t *testing.T) {
 	}
 
 	// just check on the local interface
-	manager, err := Create(mock)
+	manager, err := Create(mock, true)
 	require.NoError(t, err)
 
 	time.Sleep(time.Second)
@@ -141,7 +143,7 @@ func TestIptablesManagerIPSet(t *testing.T) {
 	}
 
 	// just check on the local interface
-	manager, err := Create(mock)
+	manager, err := Create(mock, true)
 	require.NoError(t, err)
 
 	time.Sleep(time.Second)
@@ -229,7 +231,7 @@ func TestIptablesCreatePerformance(t *testing.T) {
 	for _, testMax := range []int{10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 200, 300, 400, 500, 600, 700, 800, 900, 1000} {
 		t.Run(fmt.Sprintf("Testing %d rules", testMax), func(t *testing.T) {
 			// just check on the local interface
-			manager, err := Create(mock)
+			manager, err := Create(mock, true)
 			require.NoError(t, err)
 			time.Sleep(time.Second)
 

client/firewall/nftables/manager_linux.go

@@ -29,6 +29,8 @@ const (
 
 	// FilterOutputChainName is the name of the chain that is used for filtering outgoing packets
 	FilterOutputChainName = "netbird-acl-output-filter"
+
+	AllowNetbirdInputRuleID = "allow Netbird incoming traffic"
 )
 
 var anyIP = []byte{0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
@@ -379,7 +381,7 @@ func (m *Manager) chain(
 		if c != nil {
 			return c, nil
 		}
-		return m.createChainIfNotExists(tf, name, hook, priority, cType)
+		return m.createChainIfNotExists(tf, FilterTableName, name, hook, priority, cType)
 	}
 
 	if ip.To4() != nil {
@@ -399,13 +401,20 @@ func (m *Manager) chain(
 }
 
 // table returns the table for the given family of the IP address
-func (m *Manager) table(family nftables.TableFamily) (*nftables.Table, error) {
+func (m *Manager) table(
+	family nftables.TableFamily, tableName string,
+) (*nftables.Table, error) {
+	// we cache access to Netbird ACL table only
+	if tableName != FilterTableName {
+		return m.createTableIfNotExists(nftables.TableFamilyIPv4, tableName)
+	}
+
 	if family == nftables.TableFamilyIPv4 {
 		if m.tableIPv4 != nil {
 			return m.tableIPv4, nil
 		}
 
-		table, err := m.createTableIfNotExists(nftables.TableFamilyIPv4)
+		table, err := m.createTableIfNotExists(nftables.TableFamilyIPv4, tableName)
 		if err != nil {
 			return nil, err
 		}
@@ -417,7 +426,7 @@ func (m *Manager) table(family nftables.TableFamily) (*nftables.Table, error) {
 		return m.tableIPv6, nil
 	}
 
-	table, err := m.createTableIfNotExists(nftables.TableFamilyIPv6)
+	table, err := m.createTableIfNotExists(nftables.TableFamilyIPv6, tableName)
 	if err != nil {
 		return nil, err
 	}
@@ -425,19 +434,21 @@ func (m *Manager) table(family nftables.TableFamily) (*nftables.Table, error) {
 	return m.tableIPv6, nil
 }
 
-func (m *Manager) createTableIfNotExists(family nftables.TableFamily) (*nftables.Table, error) {
+func (m *Manager) createTableIfNotExists(
+	family nftables.TableFamily, tableName string,
+) (*nftables.Table, error) {
 	tables, err := m.rConn.ListTablesOfFamily(family)
 	if err != nil {
 		return nil, fmt.Errorf("list of tables: %w", err)
 	}
 
 	for _, t := range tables {
-		if t.Name == FilterTableName {
+		if t.Name == tableName {
 			return t, nil
 		}
 	}
 
-	table := m.rConn.AddTable(&nftables.Table{Name: FilterTableName, Family: nftables.TableFamilyIPv4})
+	table := m.rConn.AddTable(&nftables.Table{Name: tableName, Family: nftables.TableFamilyIPv4})
 	if err := m.rConn.Flush(); err != nil {
 		return nil, err
 	}
@@ -446,12 +457,13 @@ func (m *Manager) createTableIfNotExists(family nftables.TableFamily) (*nftables
 
 func (m *Manager) createChainIfNotExists(
 	family nftables.TableFamily,
+	tableName string,
 	name string,
 	hooknum nftables.ChainHook,
 	priority nftables.ChainPriority,
 	chainType nftables.ChainType,
 ) (*nftables.Chain, error) {
-	table, err := m.table(family)
+	table, err := m.table(family, tableName)
 	if err != nil {
 		return nil, err
 	}
@@ -638,6 +650,22 @@ func (m *Manager) Reset() error {
 		return fmt.Errorf("list of chains: %w", err)
 	}
 	for _, c := range chains {
+		// delete Netbird allow input traffic rule if it exists
+		if c.Table.Name == "filter" && c.Name == "INPUT" {
+			rules, err := m.rConn.GetRules(c.Table, c)
+			if err != nil {
+				log.Errorf("get rules for chain %q: %v", c.Name, err)
+				continue
+			}
+			for _, r := range rules {
+				if bytes.Equal(r.UserData, []byte(AllowNetbirdInputRuleID)) {
+					if err := m.rConn.DelRule(r); err != nil {
+						log.Errorf("delete rule: %v", err)
+					}
+				}
+			}
+		}
+
 		if c.Name == FilterInputChainName || c.Name == FilterOutputChainName {
 			m.rConn.DelChain(c)
 		}
@@ -702,6 +730,53 @@ func (m *Manager) Flush() error {
 	return nil
 }
 
+// AllowNetbird allows netbird interface traffic
+func (m *Manager) AllowNetbird() error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	tf := nftables.TableFamilyIPv4
+	if m.wgIface.Address().IP.To4() == nil {
+		tf = nftables.TableFamilyIPv6
+	}
+
+	chains, err := m.rConn.ListChainsOfTableFamily(tf)
+	if err != nil {
+		return fmt.Errorf("list of chains: %w", err)
+	}
+
+	var chain *nftables.Chain
+	for _, c := range chains {
+		if c.Table.Name == "filter" && c.Name == "INPUT" {
+			chain = c
+			break
+		}
+	}
+
+	if chain == nil {
+		log.Debugf("chain INPUT not found. Skiping add allow netbird rule")
+		return nil
+	}
+
+	rules, err := m.rConn.GetRules(chain.Table, chain)
+	if err != nil {
+		return fmt.Errorf("failed to get rules for the INPUT chain: %v", err)
+	}
+
+	if rule := m.detectAllowNetbirdRule(rules); rule != nil {
+		log.Debugf("allow netbird rule already exists: %v", rule)
+		return nil
+	}
+
+	m.applyAllowNetbirdRules(chain)
+
+	err = m.rConn.Flush()
+	if err != nil {
+		return fmt.Errorf("failed to flush allow input netbird rules: %v", err)
+	}
+	return nil
+}
+
 func (m *Manager) flushWithBackoff() (err error) {
 	backoff := 4
 	backoffTime := 1000 * time.Millisecond
@@ -745,6 +820,44 @@ func (m *Manager) refreshRuleHandles(table *nftables.Table, chain *nftables.Chai
 	return nil
 }
 
+func (m *Manager) applyAllowNetbirdRules(chain *nftables.Chain) {
+	rule := &nftables.Rule{
+		Table: chain.Table,
+		Chain: chain,
+		Exprs: []expr.Any{
+			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+			&expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     ifname(m.wgIface.Name()),
+			},
+			&expr.Verdict{
+				Kind: expr.VerdictAccept,
+			},
+		},
+		UserData: []byte(AllowNetbirdInputRuleID),
+	}
+	_ = m.rConn.InsertRule(rule)
+}
+
+func (m *Manager) detectAllowNetbirdRule(existedRules []*nftables.Rule) *nftables.Rule {
+	ifName := ifname(m.wgIface.Name())
+	for _, rule := range existedRules {
+		if rule.Table.Name == "filter" && rule.Chain.Name == "INPUT" {
+			if len(rule.Exprs) < 4 {
+				if e, ok := rule.Exprs[0].(*expr.Meta); !ok || e.Key != expr.MetaKeyIIFNAME {
+					continue
+				}
+				if e, ok := rule.Exprs[1].(*expr.Cmp); !ok || e.Op != expr.CmpOpEq || !bytes.Equal(e.Data, ifName) {
+					continue
+				}
+				return rule
+			}
+		}
+	}
+	return nil
+}
+
 func encodePort(port fw.Port) []byte {
 	bs := make([]byte, 2)
 	binary.BigEndian.PutUint16(bs, uint16(port.Values[0]))

client/firewall/uspfilter/allow_netbird.go

@@ -0,0 +1,19 @@
+//go:build !windows && !linux
+
+package uspfilter
+
+// Reset firewall to the default state
+func (m *Manager) Reset() error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	m.outgoingRules = make(map[string]RuleSet)
+	m.incomingRules = make(map[string]RuleSet)
+
+	return nil
+}
+
+// AllowNetbird allows netbird interface traffic
+func (m *Manager) AllowNetbird() error {
+	return nil
+}

client/firewall/uspfilter/allow_netbird_linux.go

@@ -0,0 +1,21 @@
+package uspfilter
+
+// AllowNetbird allows netbird interface traffic
+func (m *Manager) AllowNetbird() error {
+	return nil
+}
+
+// Reset firewall to the default state
+func (m *Manager) Reset() error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	m.outgoingRules = make(map[string]RuleSet)
+	m.incomingRules = make(map[string]RuleSet)
+
+	if m.resetHook != nil {
+		return m.resetHook()
+	}
+
+	return nil
+}

client/firewall/uspfilter/allow_netbird_windows.go

@@ -0,0 +1,91 @@
+package uspfilter
+
+import (
+	"errors"
+	"fmt"
+	"os/exec"
+	"strings"
+	"syscall"
+)
+
+type action string
+
+const (
+	addRule    action = "add"
+	deleteRule action = "delete"
+
+	firewallRuleName     = "Netbird"
+	noRulesMatchCriteria = "No rules match the specified criteria"
+)
+
+// Reset firewall to the default state
+func (m *Manager) Reset() error {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
+
+	m.outgoingRules = make(map[string]RuleSet)
+	m.incomingRules = make(map[string]RuleSet)
+
+	if err := manageFirewallRule(firewallRuleName, deleteRule); err != nil {
+		return fmt.Errorf("couldn't remove windows firewall: %w", err)
+	}
+
+	return nil
+}
+
+// AllowNetbird allows netbird interface traffic
+func (m *Manager) AllowNetbird() error {
+	return manageFirewallRule(firewallRuleName,
+		addRule,
+		"dir=in",
+		"enable=yes",
+		"action=allow",
+		"profile=any",
+		"localip="+m.wgIface.Address().IP.String(),
+	)
+}
+
+func manageFirewallRule(ruleName string, action action, args ...string) error {
+	active, err := isFirewallRuleActive(ruleName)
+	if err != nil {
+		return err
+	}
+
+	if (action == addRule && !active) || (action == deleteRule && active) {
+		baseArgs := []string{"advfirewall", "firewall", string(action), "rule", "name=" + ruleName}
+		args := append(baseArgs, args...)
+
+		cmd := exec.Command("netsh", args...)
+		cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+		return cmd.Run()
+	}
+
+	return nil
+}
+
+func isFirewallRuleActive(ruleName string) (bool, error) {
+	args := []string{"advfirewall", "firewall", "show", "rule", "name=" + ruleName}
+
+	cmd := exec.Command("netsh", args...)
+	cmd.SysProcAttr = &syscall.SysProcAttr{HideWindow: true}
+	output, err := cmd.Output()
+	if err != nil {
+		var exitError *exec.ExitError
+		if errors.As(err, &exitError) {
+			// if the firewall rule is not active, we expect last exit code to be 1
+			exitStatus := exitError.Sys().(syscall.WaitStatus).ExitStatus()
+			if exitStatus == 1 {
+				if strings.Contains(string(output), noRulesMatchCriteria) {
+					return false, nil
+				}
+			}
+		}
+		return false, err
+	}
+
+	if strings.Contains(string(output), noRulesMatchCriteria) {
+		return false, nil
+	}
+
+	return true, nil
+}

client/firewall/uspfilter/uspfilter.go

@@ -19,6 +19,7 @@ const layerTypeAll = 0
 // IFaceMapper defines subset methods of interface required for manager
 type IFaceMapper interface {
 	SetFilter(iface.PacketFilter) error
+	Address() iface.WGAddress
 }
 
 // RuleSet is a set of rules grouped by a string key
@@ -30,6 +31,8 @@ type Manager struct {
 	incomingRules map[string]RuleSet
 	wgNetwork     *net.IPNet
 	decoders      sync.Pool
+	wgIface       IFaceMapper
+	resetHook func() error
 
 	mutex sync.RWMutex
 }
@@ -65,6 +68,7 @@ func Create(iface IFaceMapper) (*Manager, error) {
 		},
 		outgoingRules: make(map[string]RuleSet),
 		incomingRules: make(map[string]RuleSet),
+		wgIface:       iface,
 	}
 
 	if err := iface.SetFilter(m); err != nil {
@@ -171,17 +175,6 @@ func (m *Manager) DeleteRule(rule fw.Rule) error {
 	return nil
 }
 
-// Reset firewall to the default state
-func (m *Manager) Reset() error {
-	m.mutex.Lock()
-	defer m.mutex.Unlock()
-
-	m.outgoingRules = make(map[string]RuleSet)
-	m.incomingRules = make(map[string]RuleSet)
-
-	return nil
-}
-
 // Flush doesn't need to be implemented for this manager
 func (m *Manager) Flush() error { return nil }
 
@@ -375,3 +368,8 @@ func (m *Manager) RemovePacketHook(hookID string) error {
 	}
 	return fmt.Errorf("hook with given id not found")
 }
+
+// SetResetHook which will be executed in the end of Reset method
+func (m *Manager) SetResetHook(hook func() error) {
+	m.resetHook = hook
+}

client/firewall/uspfilter/uspfilter_test.go

@@ -16,6 +16,7 @@ import (
 
 type IFaceMock struct {
 	SetFilterFunc func(iface.PacketFilter) error
+	AddressFunc   func() iface.WGAddress
 }
 
 func (i *IFaceMock) SetFilter(iface iface.PacketFilter) error {
@@ -25,6 +26,13 @@ func (i *IFaceMock) SetFilter(iface iface.PacketFilter) error {
 	return i.SetFilterFunc(iface)
 }
 
+func (i *IFaceMock) Address() iface.WGAddress {
+	if i.AddressFunc == nil {
+		return iface.WGAddress{}
+	}
+	return i.AddressFunc()
+}
+
 func TestManagerCreate(t *testing.T) {
 	ifaceMock := &IFaceMock{
 		SetFilterFunc: func(iface.PacketFilter) error { return nil },