Set rule handle during flush (#299)

This change makes it possible to delete rules after inserting them,
without needing to query the rules first. Additionally, this allows
positioning a new rule next to an existing rule.

There are two ways to refer to a rule: Either by ID or by handle. The ID
is assigned by userspace, and is only valid within a transaction, so it
can only be used before the flush. The handle is assigned by the kernel
when the transaction is committed, and can thus only be used after the
flush. We thus need to set an ID on each newly created rule, and
retrieve the handle of the rule during the flush.

I extended the message struct with a pointer to the Rule which the
message creates. This allows calling the reply handler callback which
sets the handle.

I updated tests to add a handle to generated replies for the
NFT_MSG_NEWRULE messages.

chain.go

@@ -140,7 +140,7 @@ func (cc *Conn) AddChain(c *Chain) *Chain {
 			{Type: unix.NFTA_CHAIN_TYPE, Data: []byte(c.Type + "\x00")},
 		})...)
 	}
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWCHAIN),
 			Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -161,7 +161,7 @@ func (cc *Conn) DelChain(c *Chain) {
 		{Type: unix.NFTA_CHAIN_NAME, Data: []byte(c.Name + "\x00")},
 	})
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELCHAIN),
 			Flags: netlink.Request | netlink.Acknowledge,
@@ -179,7 +179,7 @@ func (cc *Conn) FlushChain(c *Chain) {
 		{Type: unix.NFTA_RULE_TABLE, Data: []byte(c.Table.Name + "\x00")},
 		{Type: unix.NFTA_RULE_CHAIN, Data: []byte(c.Name + "\x00")},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELRULE),
 			Flags: netlink.Request | netlink.Acknowledge,

conn.go

@@ -41,7 +41,7 @@ type Conn struct {
 
 	lasting      bool       // establish a lasting connection to be used across multiple netlink operations.
 	mu           sync.Mutex // protects the following state
-	messages     []netlink.Message
+	messages     []netlinkMessage
 	err          error
 	nlconn       *netlink.Conn // netlink socket using NETLINK_NETFILTER protocol.
 	sockOptions  []SockOption
@@ -49,6 +49,12 @@ type Conn struct {
 	allocatedIDs uint32
 }
 
+type netlinkMessage struct {
+	Header netlink.Header
+	Data   []byte
+	rule   *Rule
+}
+
 // ConnOption is an option to change the behavior of the nftables Conn returned by Open.
 type ConnOption func(*Conn)
 
@@ -268,6 +274,11 @@ func (cc *Conn) Flush() error {
 		} else if replyIndex < len(cc.messages) {
 			msg := messages[replyIndex+1]
 			if msg.Header.Sequence == reply.Header.Sequence && msg.Header.Type == reply.Header.Type {
+				// The only messages which set the echo flag are rule create messages.
+				err := cc.messages[replyIndex].rule.handleCreateReply(reply)
+				if err != nil {
+					errs = errors.Join(errs, err)
+				}
 				replyIndex++
 				for replyIndex < len(cc.messages) && cc.messages[replyIndex].Header.Flags&netlink.Echo == 0 {
 					replyIndex++
@@ -309,7 +320,7 @@ func (cc *Conn) Flush() error {
 func (cc *Conn) FlushRuleset() {
 	cc.mu.Lock()
 	defer cc.mu.Unlock()
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELTABLE),
 			Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -368,26 +379,30 @@ func (cc *Conn) marshalExpr(fam byte, e expr.Any) []byte {
 	return b
 }
 
-func batch(messages []netlink.Message) []netlink.Message {
+func batch(messages []netlinkMessage) []netlink.Message {
-	batch := []netlink.Message{
+	batch := make([]netlink.Message, len(messages)+2)
-		{
+	batch[0] = netlink.Message{
-			Header: netlink.Header{
+		Header: netlink.Header{
-				Type:  netlink.HeaderType(unix.NFNL_MSG_BATCH_BEGIN),
+			Type:  netlink.HeaderType(unix.NFNL_MSG_BATCH_BEGIN),
-				Flags: netlink.Request,
+			Flags: netlink.Request,
-			},
-			Data: extraHeader(0, unix.NFNL_SUBSYS_NFTABLES),
 		},
+		Data: extraHeader(0, unix.NFNL_SUBSYS_NFTABLES),
 	}
 
-	batch = append(batch, messages...)
+	for i, msg := range messages {
+		batch[i+1] = netlink.Message{
+			Header: msg.Header,
+			Data:   msg.Data,
+		}
+	}
 
-	batch = append(batch, netlink.Message{
+	batch[len(messages)+1] = netlink.Message{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType(unix.NFNL_MSG_BATCH_END),
 			Flags: netlink.Request,
 		},
 		Data: extraHeader(0, unix.NFNL_SUBSYS_NFTABLES),
-	})
+	}
 
 	return batch
 }

flowtable.go

@@ -142,7 +142,7 @@ func (cc *Conn) AddFlowtable(f *Flowtable) *Flowtable {
 		{Type: unix.NLA_F_NESTED | NFTA_FLOWTABLE_HOOK, Data: cc.marshalAttr(hookAttr)},
 	})...)
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | NFT_MSG_NEWFLOWTABLE),
 			Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -162,7 +162,7 @@ func (cc *Conn) DelFlowtable(f *Flowtable) {
 		{Type: NFTA_FLOWTABLE_NAME, Data: []byte(f.Name)},
 	})
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | NFT_MSG_DELFLOWTABLE),
 			Flags: netlink.Request | netlink.Acknowledge,

internal/nftest/nftest.go

@@ -8,7 +8,9 @@ import (
 	"testing"
 
 	"github.com/google/nftables"
+	"github.com/google/nftables/binaryutil"
 	"github.com/mdlayher/netlink"
+	"golang.org/x/sys/unix"
 )
 
 // Recorder provides an nftables connection that does not send to the Linux
@@ -21,6 +23,7 @@ type Recorder struct {
 // Conn opens an nftables connection that records netlink messages into the
 // Recorder.
 func (r *Recorder) Conn() (*nftables.Conn, error) {
+	nextHandle := uint64(1)
 	return nftables.New(nftables.WithTestDial(
 		func(req []netlink.Message) ([]netlink.Message, error) {
 			r.requests = append(r.requests, req...)
@@ -30,6 +33,14 @@ func (r *Recorder) Conn() (*nftables.Conn, error) {
 			for _, msg := range req {
 				if msg.Header.Flags&netlink.Echo != 0 {
 					data := append([]byte{}, msg.Data...)
+					switch msg.Header.Type {
+					case netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWRULE):
+						attrs, _ := netlink.MarshalAttributes([]netlink.Attribute{
+							{Type: unix.NFTA_RULE_HANDLE, Data: binaryutil.BigEndian.PutUint64(nextHandle)},
+						})
+						nextHandle++
+						data = append(data, attrs...)
+					}
 					replies = append(replies, netlink.Message{
 						Header: msg.Header,
 						Data:   data,

nftables_test.go

@@ -80,6 +80,7 @@ func linediff(a, b string) string {
 }
 
 func expectMessages(t *testing.T, want [][]byte) nftables.ConnOption {
+	nextHandle := uint64(1)
 	return nftables.WithTestDial(func(req []netlink.Message) ([]netlink.Message, error) {
 		var replies []netlink.Message
 		for idx, msg := range req {
@@ -103,6 +104,14 @@ func expectMessages(t *testing.T, want [][]byte) nftables.ConnOption {
 			// Generate replies.
 			if msg.Header.Flags&netlink.Echo != 0 {
 				data := append([]byte{}, msg.Data...)
+				switch msg.Header.Type {
+				case netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWRULE):
+					attrs, _ := netlink.MarshalAttributes([]netlink.Attribute{
+						{Type: unix.NFTA_RULE_HANDLE, Data: binaryutil.BigEndian.PutUint64(nextHandle)},
+					})
+					nextHandle++
+					data = append(data, attrs...)
+				}
 				replies = append(replies, netlink.Message{
 					Header: msg.Header,
 					Data:   data,
@@ -316,7 +325,7 @@ func TestRuleHandle(t *testing.T) {
 	}
 
 	for _, tt := range tests {
-		for _, afterFlush := range []bool{false} {
+		for _, afterFlush := range []bool{false, true} {
 			flushName := map[bool]string{
 				false: "-before-flush",
 				true:  "-after-flush",

obj.go

@@ -124,7 +124,7 @@ func (cc *Conn) AddObj(o Obj) Obj {
 		attrs = append(attrs, netlink.Attribute{Type: unix.NLA_F_NESTED | unix.NFTA_OBJ_DATA, Data: data})
 	}
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWOBJ),
 			Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -146,7 +146,7 @@ func (cc *Conn) DeleteObject(o Obj) {
 	data := cc.marshalAttr(attrs)
 	data = append(data, cc.marshalAttr([]netlink.Attribute{{Type: unix.NLA_F_NESTED | unix.NFTA_OBJ_DATA}})...)
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELOBJ),
 			Flags: netlink.Request | netlink.Acknowledge,

rule.go

@@ -48,10 +48,13 @@ const (
 type Rule struct {
 	Table *Table
 	Chain *Chain
-	// Handle identifies an existing Rule.
+	// Handle identifies an existing Rule. For a new Rule, this field is set
+	// during the Flush() in which the rule is committed. Make sure to not access
+	// this field concurrently with this Flush() to avoid data races.
 	Handle uint64
 	// ID is an identifier for a new Rule, which is assigned by
 	// AddRule/InsertRule, and only valid before the rule is committed by Flush().
+	// The field is set to 0 during Flush().
 	ID uint32
 	// Position can be set to the Handle of another Rule to insert the new Rule
 	// before (InsertRule) or after (AddRule) the existing rule.
@@ -171,11 +174,14 @@ func (cc *Conn) newRule(r *Rule, op ruleOperation) *Rule {
 	}
 
 	var flags netlink.HeaderFlags
+	var ruleRef *Rule
 	switch op {
 	case operationAdd:
 		flags = netlink.Request | netlink.Acknowledge | netlink.Create | netlink.Echo | netlink.Append
+		ruleRef = r
 	case operationInsert:
 		flags = netlink.Request | netlink.Acknowledge | netlink.Create | netlink.Echo
+		ruleRef = r
 	case operationReplace:
 		flags = netlink.Request | netlink.Acknowledge | netlink.Replace
 	}
@@ -190,17 +196,42 @@ func (cc *Conn) newRule(r *Rule, op ruleOperation) *Rule {
 		})...)
 	}
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  newRuleHeaderType,
 			Flags: flags,
 		},
 		Data: append(extraHeader(uint8(r.Table.Family), 0), msgData...),
+		rule: ruleRef,
 	})
 
 	return r
 }
 
+func (r *Rule) handleCreateReply(reply netlink.Message) error {
+	ad, err := netlink.NewAttributeDecoder(reply.Data[4:])
+	if err != nil {
+		return err
+	}
+	ad.ByteOrder = binary.BigEndian
+	var handle uint64
+	for ad.Next() {
+		switch ad.Type() {
+		case unix.NFTA_RULE_HANDLE:
+			handle = ad.Uint64()
+		}
+	}
+	if ad.Err() != nil {
+		return ad.Err()
+	}
+	if handle == 0 {
+		return fmt.Errorf("missing rule handle in create reply")
+	}
+	r.Handle = handle
+	r.ID = 0
+	return nil
+}
+
 func (cc *Conn) ReplaceRule(r *Rule) *Rule {
 	return cc.newRule(r, operationReplace)
 }
@@ -247,7 +278,7 @@ func (cc *Conn) DelRule(r *Rule) error {
 	}
 	flags := netlink.Request | netlink.Acknowledge
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  delRuleHeaderType,
 			Flags: flags,

set.go

@@ -506,7 +506,7 @@ func (cc *Conn) appendElemList(s *Set, vals []SetElement, hdrType uint16) error
 			{Type: unix.NFTA_SET_ELEM_LIST_ELEMENTS | unix.NLA_F_NESTED, Data: encodedElem},
 		}
 
-		cc.messages = append(cc.messages, netlink.Message{
+		cc.messages = append(cc.messages, netlinkMessage{
 			Header: netlink.Header{
 				Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | hdrType),
 				Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -680,7 +680,7 @@ func (cc *Conn) AddSet(s *Set, vals []SetElement) error {
 		tableInfo = append(tableInfo, netlink.Attribute{Type: unix.NLA_F_NESTED | NFTA_SET_ELEM_EXPRESSIONS, Data: data})
 	}
 
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWSET),
 			Flags: netlink.Request | netlink.Acknowledge | netlink.Create,
@@ -700,7 +700,7 @@ func (cc *Conn) DelSet(s *Set) {
 		{Type: unix.NFTA_SET_TABLE, Data: []byte(s.Table.Name + "\x00")},
 		{Type: unix.NFTA_SET_NAME, Data: []byte(s.Name + "\x00")},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELSET),
 			Flags: netlink.Request | netlink.Acknowledge,
@@ -717,7 +717,7 @@ func (cc *Conn) FlushSet(s *Set) {
 		{Type: unix.NFTA_SET_TABLE, Data: []byte(s.Table.Name + "\x00")},
 		{Type: unix.NFTA_SET_NAME, Data: []byte(s.Name + "\x00")},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELSETELEM),
 			Flags: netlink.Request | netlink.Acknowledge,

set_test.go

@@ -254,7 +254,10 @@ func TestMarshalSet(t *testing.T) {
 			}
 			msg := c.messages[connMsgSetIdx]
 
-			nset, err := setsFromMsg(msg)
+			nset, err := setsFromMsg(netlink.Message{
+				Header: msg.Header,
+				Data:   msg.Data,
+			})
 			if err != nil {
 				t.Fatalf("setsFromMsg() error: %+v", err)
 			}

table.go

@@ -57,7 +57,7 @@ func (cc *Conn) DelTable(t *Table) {
 		{Type: unix.NFTA_TABLE_NAME, Data: []byte(t.Name + "\x00")},
 		{Type: unix.NFTA_TABLE_FLAGS, Data: []byte{0, 0, 0, 0}},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELTABLE),
 			Flags: netlink.Request | netlink.Acknowledge,
@@ -73,7 +73,7 @@ func (cc *Conn) addTable(t *Table, flag netlink.HeaderFlags) *Table {
 		{Type: unix.NFTA_TABLE_NAME, Data: []byte(t.Name + "\x00")},
 		{Type: unix.NFTA_TABLE_FLAGS, Data: []byte{0, 0, 0, 0}},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_NEWTABLE),
 			Flags: netlink.Request | netlink.Acknowledge | flag,
@@ -103,7 +103,7 @@ func (cc *Conn) FlushTable(t *Table) {
 	data := cc.marshalAttr([]netlink.Attribute{
 		{Type: unix.NFTA_RULE_TABLE, Data: []byte(t.Name + "\x00")},
 	})
-	cc.messages = append(cc.messages, netlink.Message{
+	cc.messages = append(cc.messages, netlinkMessage{
 		Header: netlink.Header{
 			Type:  netlink.HeaderType((unix.NFNL_SUBSYS_NFTABLES << 8) | unix.NFT_MSG_DELRULE),
 			Flags: netlink.Request | netlink.Acknowledge,