[management, client] Add access control support to network routes (#2100)

client/firewall/nftables/router_linux.go

@@ -0,0 +1,798 @@
+package nftables
+
+import (
+	"bytes"
+	"context"
+	"encoding/binary"
+	"errors"
+	"fmt"
+	"net"
+	"net/netip"
+	"strings"
+
+	"github.com/google/nftables"
+	"github.com/google/nftables/binaryutil"
+	"github.com/google/nftables/expr"
+	"github.com/hashicorp/go-multierror"
+	log "github.com/sirupsen/logrus"
+
+	nberrors "github.com/netbirdio/netbird/client/errors"
+	firewall "github.com/netbirdio/netbird/client/firewall/manager"
+	"github.com/netbirdio/netbird/client/internal/acl/id"
+	"github.com/netbirdio/netbird/client/internal/routemanager/refcounter"
+)
+
+const (
+	chainNameRoutingFw  = "netbird-rt-fwd"
+	chainNameRoutingNat = "netbird-rt-nat"
+	chainNameForward    = "FORWARD"
+
+	userDataAcceptForwardRuleIif = "frwacceptiif"
+	userDataAcceptForwardRuleOif = "frwacceptoif"
+)
+
+const refreshRulesMapError = "refresh rules map: %w"
+
+var (
+	errFilterTableNotFound = fmt.Errorf("nftables: 'filter' table not found")
+)
+
+type router struct {
+	ctx         context.Context
+	stop        context.CancelFunc
+	conn        *nftables.Conn
+	workTable   *nftables.Table
+	filterTable *nftables.Table
+	chains      map[string]*nftables.Chain
+	// rules is useful to avoid duplicates and to get missing attributes that we don't have when adding new rules
+	rules        map[string]*nftables.Rule
+	ipsetCounter *refcounter.Counter[string, []netip.Prefix, *nftables.Set]
+
+	wgIface          iFaceMapper
+	legacyManagement bool
+}
+
+func newRouter(parentCtx context.Context, workTable *nftables.Table, wgIface iFaceMapper) (*router, error) {
+	ctx, cancel := context.WithCancel(parentCtx)
+
+	r := &router{
+		ctx:       ctx,
+		stop:      cancel,
+		conn:      &nftables.Conn{},
+		workTable: workTable,
+		chains:    make(map[string]*nftables.Chain),
+		rules:     make(map[string]*nftables.Rule),
+		wgIface:   wgIface,
+	}
+
+	r.ipsetCounter = refcounter.New(
+		r.createIpSet,
+		r.deleteIpSet,
+	)
+
+	var err error
+	r.filterTable, err = r.loadFilterTable()
+	if err != nil {
+		if errors.Is(err, errFilterTableNotFound) {
+			log.Warnf("table 'filter' not found for forward rules")
+		} else {
+			return nil, err
+		}
+	}
+
+	err = r.cleanUpDefaultForwardRules()
+	if err != nil {
+		log.Errorf("failed to clean up rules from FORWARD chain: %s", err)
+	}
+
+	err = r.createContainers()
+	if err != nil {
+		log.Errorf("failed to create containers for route: %s", err)
+	}
+	return r, err
+}
+
+// Reset cleans existing nftables default forward rules from the system
+func (r *router) Reset() error {
+	// clear without deleting the ipsets, the nf table will be deleted by the caller
+	r.ipsetCounter.Clear()
+
+	return r.cleanUpDefaultForwardRules()
+}
+
+func (r *router) cleanUpDefaultForwardRules() error {
+	if r.filterTable == nil {
+		return nil
+	}
+
+	chains, err := r.conn.ListChainsOfTableFamily(nftables.TableFamilyIPv4)
+	if err != nil {
+		return fmt.Errorf("list chains: %v", err)
+	}
+
+	for _, chain := range chains {
+		if chain.Table.Name != r.filterTable.Name || chain.Name != chainNameForward {
+			continue
+		}
+
+		rules, err := r.conn.GetRules(r.filterTable, chain)
+		if err != nil {
+			return fmt.Errorf("get rules: %v", err)
+		}
+
+		for _, rule := range rules {
+			if bytes.Equal(rule.UserData, []byte(userDataAcceptForwardRuleIif)) ||
+				bytes.Equal(rule.UserData, []byte(userDataAcceptForwardRuleOif)) {
+				if err := r.conn.DelRule(rule); err != nil {
+					return fmt.Errorf("delete rule: %v", err)
+				}
+			}
+		}
+	}
+
+	return r.conn.Flush()
+}
+
+func (r *router) loadFilterTable() (*nftables.Table, error) {
+	tables, err := r.conn.ListTablesOfFamily(nftables.TableFamilyIPv4)
+	if err != nil {
+		return nil, fmt.Errorf("nftables: unable to list tables: %v", err)
+	}
+
+	for _, table := range tables {
+		if table.Name == "filter" {
+			return table, nil
+		}
+	}
+
+	return nil, errFilterTableNotFound
+}
+
+func (r *router) createContainers() error {
+
+	r.chains[chainNameRoutingFw] = r.conn.AddChain(&nftables.Chain{
+		Name:  chainNameRoutingFw,
+		Table: r.workTable,
+	})
+
+	insertReturnTrafficRule(r.conn, r.workTable, r.chains[chainNameRoutingFw])
+
+	r.chains[chainNameRoutingNat] = r.conn.AddChain(&nftables.Chain{
+		Name:     chainNameRoutingNat,
+		Table:    r.workTable,
+		Hooknum:  nftables.ChainHookPostrouting,
+		Priority: nftables.ChainPriorityNATSource - 1,
+		Type:     nftables.ChainTypeNAT,
+	})
+
+	r.acceptForwardRules()
+
+	err := r.refreshRulesMap()
+	if err != nil {
+		log.Errorf("failed to clean up rules from FORWARD chain: %s", err)
+	}
+
+	err = r.conn.Flush()
+	if err != nil {
+		return fmt.Errorf("nftables: unable to initialize table: %v", err)
+	}
+	return nil
+}
+
+// AddRouteFiltering appends a nftables rule to the routing chain
+func (r *router) AddRouteFiltering(
+	sources []netip.Prefix,
+	destination netip.Prefix,
+	proto firewall.Protocol,
+	sPort *firewall.Port,
+	dPort *firewall.Port,
+	action firewall.Action,
+) (firewall.Rule, error) {
+	ruleKey := id.GenerateRouteRuleKey(sources, destination, proto, sPort, dPort, action)
+	if _, ok := r.rules[string(ruleKey)]; ok {
+		return ruleKey, nil
+	}
+
+	chain := r.chains[chainNameRoutingFw]
+	var exprs []expr.Any
+
+	switch {
+	case len(sources) == 1 && sources[0].Bits() == 0:
+		// If it's 0.0.0.0/0, we don't need to add any source matching
+	case len(sources) == 1:
+		// If there's only one source, we can use it directly
+		exprs = append(exprs, generateCIDRMatcherExpressions(true, sources[0])...)
+	default:
+		// If there are multiple sources, create or get an ipset
+		var err error
+		exprs, err = r.getIpSetExprs(sources, exprs)
+		if err != nil {
+			return nil, fmt.Errorf("get ipset expressions: %w", err)
+		}
+	}
+
+	// Handle destination
+	exprs = append(exprs, generateCIDRMatcherExpressions(false, destination)...)
+
+	// Handle protocol
+	if proto != firewall.ProtocolALL {
+		protoNum, err := protoToInt(proto)
+		if err != nil {
+			return nil, fmt.Errorf("convert protocol to number: %w", err)
+		}
+		exprs = append(exprs, &expr.Meta{Key: expr.MetaKeyL4PROTO, Register: 1})
+		exprs = append(exprs, &expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     []byte{protoNum},
+		})
+
+		exprs = append(exprs, applyPort(sPort, true)...)
+		exprs = append(exprs, applyPort(dPort, false)...)
+	}
+
+	exprs = append(exprs, &expr.Counter{})
+
+	var verdict expr.VerdictKind
+	if action == firewall.ActionAccept {
+		verdict = expr.VerdictAccept
+	} else {
+		verdict = expr.VerdictDrop
+	}
+	exprs = append(exprs, &expr.Verdict{Kind: verdict})
+
+	rule := &nftables.Rule{
+		Table:    r.workTable,
+		Chain:    chain,
+		Exprs:    exprs,
+		UserData: []byte(ruleKey),
+	}
+
+	r.rules[string(ruleKey)] = r.conn.AddRule(rule)
+
+	return ruleKey, r.conn.Flush()
+}
+
+func (r *router) getIpSetExprs(sources []netip.Prefix, exprs []expr.Any) ([]expr.Any, error) {
+	setName := firewall.GenerateSetName(sources)
+	ref, err := r.ipsetCounter.Increment(setName, sources)
+	if err != nil {
+		return nil, fmt.Errorf("create or get ipset for sources: %w", err)
+	}
+
+	exprs = append(exprs,
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseNetworkHeader,
+			Offset:       12,
+			Len:          4,
+		},
+		&expr.Lookup{
+			SourceRegister: 1,
+			SetName:        ref.Out.Name,
+			SetID:          ref.Out.ID,
+		},
+	)
+	return exprs, nil
+}
+
+func (r *router) DeleteRouteRule(rule firewall.Rule) error {
+	if err := r.refreshRulesMap(); err != nil {
+		return fmt.Errorf(refreshRulesMapError, err)
+	}
+
+	ruleKey := rule.GetRuleID()
+	nftRule, exists := r.rules[ruleKey]
+	if !exists {
+		log.Debugf("route rule %s not found", ruleKey)
+		return nil
+	}
+
+	setName := r.findSetNameInRule(nftRule)
+
+	if err := r.deleteNftRule(nftRule, ruleKey); err != nil {
+		return fmt.Errorf("delete: %w", err)
+	}
+
+	if setName != "" {
+		if _, err := r.ipsetCounter.Decrement(setName); err != nil {
+			return fmt.Errorf("decrement ipset reference: %w", err)
+		}
+	}
+
+	if err := r.conn.Flush(); err != nil {
+		return fmt.Errorf(flushError, err)
+	}
+
+	return nil
+}
+
+func (r *router) createIpSet(setName string, sources []netip.Prefix) (*nftables.Set, error) {
+	// overlapping prefixes will result in an error, so we need to merge them
+	sources = firewall.MergeIPRanges(sources)
+
+	set := &nftables.Set{
+		Name:  setName,
+		Table: r.workTable,
+		// required for prefixes
+		Interval: true,
+		KeyType:  nftables.TypeIPAddr,
+	}
+
+	var elements []nftables.SetElement
+	for _, prefix := range sources {
+		// TODO: Implement IPv6 support
+		if prefix.Addr().Is6() {
+			log.Printf("Skipping IPv6 prefix %s: IPv6 support not yet implemented", prefix)
+			continue
+		}
+
+		// nftables needs half-open intervals [firstIP, lastIP) for prefixes
+		// e.g. 10.0.0.0/24 becomes [10.0.0.0, 10.0.1.0), 10.1.1.1/32 becomes [10.1.1.1, 10.1.1.2) etc
+		firstIP := prefix.Addr()
+		lastIP := calculateLastIP(prefix).Next()
+
+		elements = append(elements,
+			// the nft tool also adds a line like this, see https://github.com/google/nftables/issues/247
+			// nftables.SetElement{Key: []byte{0, 0, 0, 0}, IntervalEnd: true},
+			nftables.SetElement{Key: firstIP.AsSlice()},
+			nftables.SetElement{Key: lastIP.AsSlice(), IntervalEnd: true},
+		)
+	}
+
+	if err := r.conn.AddSet(set, elements); err != nil {
+		return nil, fmt.Errorf("error adding elements to set %s: %w", setName, err)
+	}
+
+	if err := r.conn.Flush(); err != nil {
+		return nil, fmt.Errorf("flush error: %w", err)
+	}
+
+	log.Printf("Created new ipset: %s with %d elements", setName, len(elements)/2)
+
+	return set, nil
+}
+
+// calculateLastIP determines the last IP in a given prefix.
+func calculateLastIP(prefix netip.Prefix) netip.Addr {
+	hostMask := ^uint32(0) >> prefix.Masked().Bits()
+	lastIP := uint32FromNetipAddr(prefix.Addr()) | hostMask
+
+	return netip.AddrFrom4(uint32ToBytes(lastIP))
+}
+
+// Utility function to convert netip.Addr to uint32.
+func uint32FromNetipAddr(addr netip.Addr) uint32 {
+	b := addr.As4()
+	return binary.BigEndian.Uint32(b[:])
+}
+
+// Utility function to convert uint32 to a netip-compatible byte slice.
+func uint32ToBytes(ip uint32) [4]byte {
+	var b [4]byte
+	binary.BigEndian.PutUint32(b[:], ip)
+	return b
+}
+
+func (r *router) deleteIpSet(setName string, set *nftables.Set) error {
+	r.conn.DelSet(set)
+	if err := r.conn.Flush(); err != nil {
+		return fmt.Errorf(flushError, err)
+	}
+
+	log.Debugf("Deleted unused ipset %s", setName)
+	return nil
+}
+
+func (r *router) findSetNameInRule(rule *nftables.Rule) string {
+	for _, e := range rule.Exprs {
+		if lookup, ok := e.(*expr.Lookup); ok {
+			return lookup.SetName
+		}
+	}
+	return ""
+}
+
+func (r *router) deleteNftRule(rule *nftables.Rule, ruleKey string) error {
+	if err := r.conn.DelRule(rule); err != nil {
+		return fmt.Errorf("delete rule %s: %w", ruleKey, err)
+	}
+	delete(r.rules, ruleKey)
+
+	log.Debugf("removed route rule %s", ruleKey)
+
+	return nil
+}
+
+// AddNatRule appends a nftables rule pair to the nat chain
+func (r *router) AddNatRule(pair firewall.RouterPair) error {
+	if err := r.refreshRulesMap(); err != nil {
+		return fmt.Errorf(refreshRulesMapError, err)
+	}
+
+	if r.legacyManagement {
+		log.Warnf("This peer is connected to a NetBird Management service with an older version. Allowing all traffic for %s", pair.Destination)
+		if err := r.addLegacyRouteRule(pair); err != nil {
+			return fmt.Errorf("add legacy routing rule: %w", err)
+		}
+	}
+
+	if pair.Masquerade {
+		if err := r.addNatRule(pair); err != nil {
+			return fmt.Errorf("add nat rule: %w", err)
+		}
+
+		if err := r.addNatRule(firewall.GetInversePair(pair)); err != nil {
+			return fmt.Errorf("add inverse nat rule: %w", err)
+		}
+	}
+
+	if err := r.conn.Flush(); err != nil {
+		return fmt.Errorf("nftables: insert rules for %s: %v", pair.Destination, err)
+	}
+
+	return nil
+}
+
+// addNatRule inserts a nftables rule to the conn client flush queue
+func (r *router) addNatRule(pair firewall.RouterPair) error {
+	sourceExp := generateCIDRMatcherExpressions(true, pair.Source)
+	destExp := generateCIDRMatcherExpressions(false, pair.Destination)
+
+	dir := expr.MetaKeyIIFNAME
+	if pair.Inverse {
+		dir = expr.MetaKeyOIFNAME
+	}
+
+	intf := ifname(r.wgIface.Name())
+	exprs := []expr.Any{
+		&expr.Meta{
+			Key:      dir,
+			Register: 1,
+		},
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     intf,
+		},
+	}
+
+	exprs = append(exprs, sourceExp...)
+	exprs = append(exprs, destExp...)
+	exprs = append(exprs,
+		&expr.Counter{}, &expr.Masq{},
+	)
+
+	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
+
+	if _, exists := r.rules[ruleKey]; exists {
+		if err := r.removeNatRule(pair); err != nil {
+			return fmt.Errorf("remove routing rule: %w", err)
+		}
+	}
+
+	r.rules[ruleKey] = r.conn.AddRule(&nftables.Rule{
+		Table:    r.workTable,
+		Chain:    r.chains[chainNameRoutingNat],
+		Exprs:    exprs,
+		UserData: []byte(ruleKey),
+	})
+	return nil
+}
+
+// addLegacyRouteRule adds a legacy routing rule for mgmt servers pre route acls
+func (r *router) addLegacyRouteRule(pair firewall.RouterPair) error {
+	sourceExp := generateCIDRMatcherExpressions(true, pair.Source)
+	destExp := generateCIDRMatcherExpressions(false, pair.Destination)
+
+	exprs := []expr.Any{
+		&expr.Counter{},
+		&expr.Verdict{
+			Kind: expr.VerdictAccept,
+		},
+	}
+
+	expression := append(sourceExp, append(destExp, exprs...)...) // nolint:gocritic
+
+	ruleKey := firewall.GenKey(firewall.ForwardingFormat, pair)
+
+	if _, exists := r.rules[ruleKey]; exists {
+		if err := r.removeLegacyRouteRule(pair); err != nil {
+			return fmt.Errorf("remove legacy routing rule: %w", err)
+		}
+	}
+
+	r.rules[ruleKey] = r.conn.AddRule(&nftables.Rule{
+		Table:    r.workTable,
+		Chain:    r.chains[chainNameRoutingFw],
+		Exprs:    expression,
+		UserData: []byte(ruleKey),
+	})
+	return nil
+}
+
+// removeLegacyRouteRule removes a legacy routing rule for mgmt servers pre route acls
+func (r *router) removeLegacyRouteRule(pair firewall.RouterPair) error {
+	ruleKey := firewall.GenKey(firewall.ForwardingFormat, pair)
+
+	if rule, exists := r.rules[ruleKey]; exists {
+		if err := r.conn.DelRule(rule); err != nil {
+			return fmt.Errorf("remove legacy forwarding rule %s -> %s: %v", pair.Source, pair.Destination, err)
+		}
+
+		log.Debugf("nftables: removed legacy forwarding rule %s -> %s", pair.Source, pair.Destination)
+
+		delete(r.rules, ruleKey)
+	} else {
+		log.Debugf("nftables: legacy forwarding rule %s not found", ruleKey)
+	}
+
+	return nil
+}
+
+// GetLegacyManagement returns the route manager's legacy management mode
+func (r *router) GetLegacyManagement() bool {
+	return r.legacyManagement
+}
+
+// SetLegacyManagement sets the route manager to use legacy management mode
+func (r *router) SetLegacyManagement(isLegacy bool) {
+	r.legacyManagement = isLegacy
+}
+
+// RemoveAllLegacyRouteRules removes all legacy routing rules for mgmt servers pre route acls
+func (r *router) RemoveAllLegacyRouteRules() error {
+	if err := r.refreshRulesMap(); err != nil {
+		return fmt.Errorf(refreshRulesMapError, err)
+	}
+
+	var merr *multierror.Error
+	for k, rule := range r.rules {
+		if !strings.HasPrefix(k, firewall.ForwardingFormatPrefix) {
+			continue
+		}
+		if err := r.conn.DelRule(rule); err != nil {
+			merr = multierror.Append(merr, fmt.Errorf("remove legacy forwarding rule: %v", err))
+		}
+	}
+	return nberrors.FormatErrorOrNil(merr)
+}
+
+// acceptForwardRules adds iif/oif rules in the filter table/forward chain to make sure
+// that our traffic is not dropped by existing rules there.
+// The existing FORWARD rules/policies decide outbound traffic towards our interface.
+// In case the FORWARD policy is set to "drop", we add an established/related rule to allow return traffic for the inbound rule.
+func (r *router) acceptForwardRules() {
+	if r.filterTable == nil {
+		log.Debugf("table 'filter' not found for forward rules, skipping accept rules")
+		return
+	}
+
+	intf := ifname(r.wgIface.Name())
+
+	// Rule for incoming interface (iif) with counter
+	iifRule := &nftables.Rule{
+		Table: r.filterTable,
+		Chain: &nftables.Chain{
+			Name:     "FORWARD",
+			Table:    r.filterTable,
+			Type:     nftables.ChainTypeFilter,
+			Hooknum:  nftables.ChainHookForward,
+			Priority: nftables.ChainPriorityFilter,
+		},
+		Exprs: []expr.Any{
+			&expr.Meta{Key: expr.MetaKeyIIFNAME, Register: 1},
+			&expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     intf,
+			},
+			&expr.Counter{},
+			&expr.Verdict{Kind: expr.VerdictAccept},
+		},
+		UserData: []byte(userDataAcceptForwardRuleIif),
+	}
+	r.conn.InsertRule(iifRule)
+
+	// Rule for outgoing interface (oif) with counter
+	oifRule := &nftables.Rule{
+		Table: r.filterTable,
+		Chain: &nftables.Chain{
+			Name:     "FORWARD",
+			Table:    r.filterTable,
+			Type:     nftables.ChainTypeFilter,
+			Hooknum:  nftables.ChainHookForward,
+			Priority: nftables.ChainPriorityFilter,
+		},
+		Exprs: []expr.Any{
+			&expr.Meta{Key: expr.MetaKeyOIFNAME, Register: 1},
+			&expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     intf,
+			},
+			&expr.Ct{
+				Key:      expr.CtKeySTATE,
+				Register: 2,
+			},
+			&expr.Bitwise{
+				SourceRegister: 2,
+				DestRegister:   2,
+				Len:            4,
+				Mask:           binaryutil.NativeEndian.PutUint32(expr.CtStateBitESTABLISHED | expr.CtStateBitRELATED),
+				Xor:            binaryutil.NativeEndian.PutUint32(0),
+			},
+			&expr.Cmp{
+				Op:       expr.CmpOpNeq,
+				Register: 2,
+				Data:     []byte{0, 0, 0, 0},
+			},
+			&expr.Counter{},
+			&expr.Verdict{Kind: expr.VerdictAccept},
+		},
+		UserData: []byte(userDataAcceptForwardRuleOif),
+	}
+
+	r.conn.InsertRule(oifRule)
+}
+
+// RemoveNatRule removes a nftables rule pair from nat chains
+func (r *router) RemoveNatRule(pair firewall.RouterPair) error {
+	if err := r.refreshRulesMap(); err != nil {
+		return fmt.Errorf(refreshRulesMapError, err)
+	}
+
+	if err := r.removeNatRule(pair); err != nil {
+		return fmt.Errorf("remove nat rule: %w", err)
+	}
+
+	if err := r.removeNatRule(firewall.GetInversePair(pair)); err != nil {
+		return fmt.Errorf("remove inverse nat rule: %w", err)
+	}
+
+	if err := r.removeLegacyRouteRule(pair); err != nil {
+		return fmt.Errorf("remove legacy routing rule: %w", err)
+	}
+
+	if err := r.conn.Flush(); err != nil {
+		return fmt.Errorf("nftables: received error while applying rule removal for %s: %v", pair.Destination, err)
+	}
+
+	log.Debugf("nftables: removed rules for %s", pair.Destination)
+	return nil
+}
+
+// removeNatRule adds a nftables rule to the removal queue and deletes it from the rules map
+func (r *router) removeNatRule(pair firewall.RouterPair) error {
+	ruleKey := firewall.GenKey(firewall.NatFormat, pair)
+
+	if rule, exists := r.rules[ruleKey]; exists {
+		err := r.conn.DelRule(rule)
+		if err != nil {
+			return fmt.Errorf("remove nat rule %s -> %s: %v", pair.Source, pair.Destination, err)
+		}
+
+		log.Debugf("nftables: removed nat rule %s -> %s", pair.Source, pair.Destination)
+
+		delete(r.rules, ruleKey)
+	} else {
+		log.Debugf("nftables: nat rule %s not found", ruleKey)
+	}
+
+	return nil
+}
+
+// refreshRulesMap refreshes the rule map with the latest rules. this is useful to avoid
+// duplicates and to get missing attributes that we don't have when adding new rules
+func (r *router) refreshRulesMap() error {
+	for _, chain := range r.chains {
+		rules, err := r.conn.GetRules(chain.Table, chain)
+		if err != nil {
+			return fmt.Errorf("nftables: unable to list rules: %v", err)
+		}
+		for _, rule := range rules {
+			if len(rule.UserData) > 0 {
+				r.rules[string(rule.UserData)] = rule
+			}
+		}
+	}
+	return nil
+}
+
+// generateCIDRMatcherExpressions generates nftables expressions that matches a CIDR
+func generateCIDRMatcherExpressions(source bool, prefix netip.Prefix) []expr.Any {
+	var offset uint32
+	if source {
+		offset = 12 // src offset
+	} else {
+		offset = 16 // dst offset
+	}
+
+	ones := prefix.Bits()
+	// 0.0.0.0/0 doesn't need extra expressions
+	if ones == 0 {
+		return nil
+	}
+
+	mask := net.CIDRMask(ones, 32)
+
+	return []expr.Any{
+		&expr.Payload{
+			DestRegister: 1,
+			Base:         expr.PayloadBaseNetworkHeader,
+			Offset:       offset,
+			Len:          4,
+		},
+		// netmask
+		&expr.Bitwise{
+			DestRegister:   1,
+			SourceRegister: 1,
+			Len:            4,
+			Mask:           mask,
+			Xor:            []byte{0, 0, 0, 0},
+		},
+		// net address
+		&expr.Cmp{
+			Op:       expr.CmpOpEq,
+			Register: 1,
+			Data:     prefix.Masked().Addr().AsSlice(),
+		},
+	}
+}
+
+func applyPort(port *firewall.Port, isSource bool) []expr.Any {
+	if port == nil {
+		return nil
+	}
+
+	var exprs []expr.Any
+
+	offset := uint32(2) // Default offset for destination port
+	if isSource {
+		offset = 0 // Offset for source port
+	}
+
+	exprs = append(exprs, &expr.Payload{
+		DestRegister: 1,
+		Base:         expr.PayloadBaseTransportHeader,
+		Offset:       offset,
+		Len:          2,
+	})
+
+	if port.IsRange && len(port.Values) == 2 {
+		// Handle port range
+		exprs = append(exprs,
+			&expr.Cmp{
+				Op:       expr.CmpOpGte,
+				Register: 1,
+				Data:     binaryutil.BigEndian.PutUint16(uint16(port.Values[0])),
+			},
+			&expr.Cmp{
+				Op:       expr.CmpOpLte,
+				Register: 1,
+				Data:     binaryutil.BigEndian.PutUint16(uint16(port.Values[1])),
+			},
+		)
+	} else {
+		// Handle single port or multiple ports
+		for i, p := range port.Values {
+			if i > 0 {
+				// Add a bitwise OR operation between port checks
+				exprs = append(exprs, &expr.Bitwise{
+					SourceRegister: 1,
+					DestRegister:   1,
+					Len:            4,
+					Mask:           []byte{0x00, 0x00, 0xff, 0xff},
+					Xor:            []byte{0x00, 0x00, 0x00, 0x00},
+				})
+			}
+			exprs = append(exprs, &expr.Cmp{
+				Op:       expr.CmpOpEq,
+				Register: 1,
+				Data:     binaryutil.BigEndian.PutUint16(uint16(p)),
+			})
+		}
+	}
+
+	return exprs
+}