Add PortKnocking interface and implementation to manage port-knocking rules and sequences

internal/daemon/firewall/chain/chains.go

@@ -44,6 +44,7 @@ type Chains interface {
 	NewBlockListIP(name string) (block.ListIP, error)
 	NewBlockListIPWithPort(name string) (block.ListIPWithPort, error)
 	NewBlocklist(name string) (block.Blocklist, error)
+	NewPortKnocking(name string) (PortKnocking, error)
 }
 
 type chains struct {
@@ -255,6 +256,15 @@ func (c *chains) NewBlocklist(name string) (block.Blocklist, error) {
 	return blockList, nil
 }
 
+func (c *chains) NewPortKnocking(name string) (PortKnocking, error) {
+	portKnocking, err := newPortKnocking(c.nft, c.family, c.table, name)
+	if err != nil {
+		return nil, err
+	}
+
+	return portKnocking, nil
+}
+
 func clearRules(nft nft.NFT, family nftFamily.Type, table string) error {
 	if err := nft.Table().Delete(family, table); err != nil {
 		if !strings.Contains(string(err.Error()), "delete table "+family.String()+" "+table) {

internal/daemon/firewall/chain/port_knocking.go

@@ -0,0 +1,91 @@
+package chain
+
+import (
+	"strconv"
+
+	nft "git.kor-elf.net/kor-elf-shield/go-nftables-client"
+	nftChain "git.kor-elf.net/kor-elf-shield/go-nftables-client/chain"
+	"git.kor-elf.net/kor-elf-shield/go-nftables-client/family"
+	"git.kor-elf.net/kor-elf-shield/kor-elf-shield/internal/daemon/firewall/chain/block"
+	"git.kor-elf.net/kor-elf-shield/kor-elf-shield/internal/daemon/firewall/types"
+	"git.kor-elf.net/kor-elf-shield/kor-elf-shield/internal/pkg/ip"
+)
+
+type PortKnocking interface {
+	AddFirstStageRule(
+		name string,
+		ipVersion ip.Version,
+		l4Port types.L4Port,
+		timeout uint32,
+		action types.KnockAction,
+	) error
+	AddNextStageRule(
+		prevName, nextName string,
+		ipVersion ip.Version,
+		l4Port types.L4Port,
+		timeout uint32,
+		action types.KnockAction,
+	) error
+	AddRuleIn(AddRuleFunc func(expr ...string) error) error
+}
+
+type portKnocking struct {
+	nft    nft.NFT
+	family family.Type
+	table  string
+	chain  string
+}
+
+func newPortKnocking(nft nft.NFT, family family.Type, table string, chain string) (PortKnocking, error) {
+	if err := nft.Chain().Add(family, table, chain, nftChain.TypeNone); err != nil {
+		return nil, err
+	}
+
+	return &portKnocking{
+		nft:    nft,
+		family: family,
+		table:  table,
+		chain:  chain,
+	}, nil
+}
+
+func (k *portKnocking) AddRuleIn(AddRuleFunc func(expr ...string) error) error {
+	return AddRuleFunc("iifname != \"lo\" counter jump " + k.chain)
+}
+
+func (k *portKnocking) AddFirstStageRule(
+	name string,
+	ipVersion ip.Version,
+	l4Port types.L4Port,
+	timeout uint32,
+	action types.KnockAction,
+) error {
+	if err := block.NewPortKnocking(k.nft, k.family, k.table, name, ipVersion, timeout); err != nil {
+		return err
+	}
+
+	expr := []string{
+		l4Port.ProtocolString(), "dport", l4Port.NumberString(), "add", "@" + name,
+		"{", ipVersion.ToNft(), "saddr timeout", strconv.Itoa(int(timeout)) + "s", "}", action.String(),
+	}
+	return k.nft.Rule().Add(k.family, k.table, k.chain, expr...)
+}
+
+func (k *portKnocking) AddNextStageRule(
+	prevName, nextName string,
+	ipVersion ip.Version,
+	l4Port types.L4Port,
+	timeout uint32,
+	action types.KnockAction,
+) error {
+	if err := block.NewPortKnocking(k.nft, k.family, k.table, nextName, ipVersion, timeout); err != nil {
+		return err
+	}
+
+	expr := []string{
+		ipVersion.ToNft(), "saddr", "@" + prevName,
+		l4Port.ProtocolString(), "dport", l4Port.NumberString(), "add", "@" + nextName,
+		"{", ipVersion.ToNft(), "saddr}", action.String(),
+	}
+	return k.nft.Rule().Add(k.family, k.table, k.chain, expr...)
+}