Add ntp protocol sniffing

common/sniff/ntp.go

@@ -0,0 +1,58 @@
+package sniff
+
+import (
+	"context"
+	"encoding/binary"
+	"os"
+
+	"github.com/sagernet/sing-box/adapter"
+	C "github.com/sagernet/sing-box/constant"
+)
+
+func NTP(ctx context.Context, metadata *adapter.InboundContext, packet []byte) error {
+	// NTP packets must be at least 48 bytes long (standard NTP header size).
+	pLen := len(packet)
+	if pLen < 48 {
+		return os.ErrInvalid
+	}
+	// Check the LI (Leap Indicator) and Version Number (VN) in the first byte.
+	// We'll primarily focus on ensuring the version is valid for NTP.
+	// Many NTP versions are used, but let's check for generally accepted ones (3 & 4 for IPv4, plus potential extensions/customizations)
+	firstByte := packet[0]
+	li := (firstByte >> 6) & 0x03 // Extract LI
+	vn := (firstByte >> 3) & 0x07 // Extract VN
+	mode := firstByte & 0x07      // Extract Mode
+
+	// Leap Indicator should be a valid value (0-3).
+	if li > 3 {
+		return os.ErrInvalid
+	}
+
+	// Version Check (common NTP versions are 3 and 4)
+	if vn != 3 && vn != 4 {
+		return os.ErrInvalid
+	}
+
+	// Check the Mode field for a client request (Mode 3).  This validates it *is* a request.
+	if mode != 3 {
+		return os.ErrInvalid
+	}
+
+	// Check Root Delay and Root Dispersion. While not strictly *required* for a request,
+	// we can check if they appear to be reasonable values (not excessively large).
+	rootDelay := binary.BigEndian.Uint32(packet[4:8])
+	rootDispersion := binary.BigEndian.Uint32(packet[8:12])
+
+	// Check for unreasonably large root delay and dispersion.  NTP RFC specifies max values of approximately 16 seconds.
+	// Convert to milliseconds for easy comparison.  Each unit is 1/2^16 seconds.
+	if float64(rootDelay)/65536.0 > 16.0 {
+		return os.ErrInvalid
+	}
+	if float64(rootDispersion)/65536.0 > 16.0 {
+		return os.ErrInvalid
+	}
+
+	metadata.Protocol = C.ProtocolNTP
+
+	return nil
+}

common/sniff/ntp_test.go

@@ -0,0 +1,33 @@
+package sniff_test
+
+import (
+	"context"
+	"encoding/hex"
+	"os"
+	"testing"
+
+	"github.com/sagernet/sing-box/adapter"
+	"github.com/sagernet/sing-box/common/sniff"
+	C "github.com/sagernet/sing-box/constant"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestSniffNTP(t *testing.T) {
+	t.Parallel()
+	packet, err := hex.DecodeString("1b0006000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000")
+	require.NoError(t, err)
+	var metadata adapter.InboundContext
+	err = sniff.NTP(context.Background(), &metadata, packet)
+	require.NoError(t, err)
+	require.Equal(t, metadata.Protocol, C.ProtocolNTP)
+}
+
+func TestSniffNTPFailed(t *testing.T) {
+	t.Parallel()
+	packet, err := hex.DecodeString("400000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000")
+	require.NoError(t, err)
+	var metadata adapter.InboundContext
+	err = sniff.NTP(context.Background(), &metadata, packet)
+	require.ErrorIs(t, err, os.ErrInvalid)
+}

docs/configuration/route/sniff.md

@@ -22,6 +22,7 @@ If enabled in the inbound, the protocol and domain name (if present) of by the c
 |   UDP   |    `dtls`    |      /      |        /         |
 |   TCP   |    `ssh`     |      /      | SSH Client Name  |
 |   TCP   |    `rdp`     |      /      |        /         |
+|   UDP   |    `ntp`     |      /      |        /         |
 
 |       QUIC Client        |    Type    |
 |:------------------------:|:----------:|

docs/configuration/route/sniff.zh.md

@@ -22,6 +22,7 @@
 |   UDP   |    `dtls`    |      /      |     /      |
 |   TCP   |    `ssh`     |      /      | SSH 客户端名称  |
 |   TCP   |    `rdp`     |      /      |     /      |
+|   UDP   |    `ntp`     |      /      |     /      |
 
 |         QUIC 客户端         |     类型     |
 |:------------------------:|:----------:|

route/route.go

@@ -607,6 +607,7 @@ func (r *Router) actionSniff(
 							sniff.UTP,
 							sniff.UDPTracker,
 							sniff.DTLSRecord,
+							sniff.NTP,
 						}
 					}
 					err = sniff.PeekPacket(

route/rule/rule_action.go

@@ -368,6 +368,8 @@ func (r *RuleActionSniff) build() error {
 			r.StreamSniffers = append(r.StreamSniffers, sniff.SSH)
 		case C.ProtocolRDP:
 			r.StreamSniffers = append(r.StreamSniffers, sniff.RDP)
+		case C.ProtocolNTP:
+			r.PacketSniffers = append(r.PacketSniffers, sniff.NTP)
 		default:
 			return E.New("unknown sniffer: ", name)
 		}