feat: add openVPN analyzer

analyzer/internal/openvpn.go

@@ -0,0 +1,44 @@
+package internal
+
+// Ref paper:
+// https://www.usenix.org/system/files/sec22fall_xue-diwen.pdf
+
+// OpenVPN Opcodes definitions from:
+// https://github.com/OpenVPN/openvpn/blob/master/src/openvpn/ssl_pkt.h
+const (
+	OpenVpnControlHardResetClientV1 = 1
+	OpenVpnControlHardResetServerV1 = 2
+	OpenVpnControlSoftResetV1       = 3
+	OpenVpnControlV1                = 4
+	OpenVpnAckV1                    = 5
+	OpenVpnDataV1                   = 6
+	OpenVpnControlHardResetClientV2 = 7
+	OpenVpnControlHardResetServerV2 = 8
+	OpenVpnDataV2                   = 9
+	OpenVpnControlHardResetClientV3 = 10
+	OpenVpnControlWkcV1             = 11
+)
+
+const (
+	OpenVpnMinPktLen          = 6
+	OpenVpnTcpPktDefaultLimit = 256
+	OpenVpnUdpPktDefaultLimit = 256
+)
+
+func OpenVpnCheckForValidOpcode(opcode byte) bool {
+	switch opcode {
+	case OpenVpnControlHardResetClientV1,
+		OpenVpnControlHardResetServerV1,
+		OpenVpnControlSoftResetV1,
+		OpenVpnControlV1,
+		OpenVpnAckV1,
+		OpenVpnDataV1,
+		OpenVpnControlHardResetClientV2,
+		OpenVpnControlHardResetServerV2,
+		OpenVpnDataV2,
+		OpenVpnControlHardResetClientV3,
+		OpenVpnControlWkcV1:
+		return true
+	}
+	return false
+}

analyzer/tcp/openvpn.go

@@ -0,0 +1,234 @@
+package tcp
+
+import (
+	"github.com/apernet/OpenGFW/analyzer"
+	"github.com/apernet/OpenGFW/analyzer/internal"
+	"github.com/apernet/OpenGFW/analyzer/utils"
+)
+
+var _ analyzer.TCPAnalyzer = (*OpenVpnAnalyzer)(nil)
+var _ analyzer.TCPStream = (*openVpnStream)(nil)
+
+type OpenVpnAnalyzer struct{}
+
+func (a *OpenVpnAnalyzer) Name() string {
+	return "openvpn_tcp"
+}
+
+func (a *OpenVpnAnalyzer) Limit() int {
+	return 0
+}
+
+func (a *OpenVpnAnalyzer) NewTCP(info analyzer.TCPInfo, logger analyzer.Logger) analyzer.TCPStream {
+	return newOpenVpnTCPStream(logger)
+}
+
+type openVpnStream struct {
+	logger analyzer.Logger
+
+	reqBuf     *utils.ByteBuffer
+	reqUpdated bool
+	reqLSM     *utils.LinearStateMachine
+	reqDone    bool
+
+	respBuf     *utils.ByteBuffer
+	respUpdated bool
+	respLSM     *utils.LinearStateMachine
+	respDone    bool
+
+	rxPktCnt int
+	txPktCnt int
+	pktLimit int
+
+	lastOpcode byte
+}
+
+type openVpnTcpPkt struct {
+	pktLen uint16
+	opcode byte // 5 bits
+	_keyId byte // 3 bits, not used
+
+	// We don't care about the rest of the packet
+	// payload []byte
+}
+
+func newOpenVpnTCPStream(logger analyzer.Logger) *openVpnStream {
+	s := &openVpnStream{
+		logger:   logger,
+		reqBuf:   &utils.ByteBuffer{},
+		respBuf:  &utils.ByteBuffer{},
+		pktLimit: internal.OpenVpnTcpPktDefaultLimit,
+	}
+	s.reqLSM = utils.NewLinearStateMachine(
+		s.parseCtlHardResetClient,
+		s.parseReq,
+	)
+	s.respLSM = utils.NewLinearStateMachine(
+		s.parseCtlHardResetServer,
+		s.parseResp,
+	)
+	return s
+}
+
+func (o *openVpnStream) Feed(rev, start, end bool, skip int, data []byte) (u *analyzer.PropUpdate, d bool) {
+	if skip != 0 {
+		return nil, true
+	}
+	if len(data) == 0 {
+		return nil, false
+	}
+	var update *analyzer.PropUpdate
+	var cancelled bool
+	if rev {
+		o.respBuf.Append(data)
+		o.respUpdated = false
+		cancelled, o.respDone = o.respLSM.Run()
+		if o.respUpdated {
+			update = &analyzer.PropUpdate{
+				Type: analyzer.PropUpdateMerge,
+				M:    analyzer.PropMap{"rx_pkt_cnt": o.rxPktCnt},
+			}
+			o.respUpdated = false
+		}
+	} else {
+		o.reqBuf.Append(data)
+		o.reqUpdated = false
+		cancelled, o.reqDone = o.reqLSM.Run()
+		if o.reqUpdated {
+			update = &analyzer.PropUpdate{
+				Type: analyzer.PropUpdateMerge,
+				M:    analyzer.PropMap{"tx_pkt_cnt": o.txPktCnt},
+			}
+			o.reqUpdated = false
+		}
+	}
+
+	return update, cancelled || (o.reqDone && o.respDone) || o.rxPktCnt+o.txPktCnt > o.pktLimit
+}
+
+func (o *openVpnStream) Close(limited bool) *analyzer.PropUpdate {
+	o.reqBuf.Reset()
+	o.respBuf.Reset()
+	return nil
+}
+
+func (o *openVpnStream) parseCtlHardResetClient() utils.LSMAction {
+	pkt, action := o.parsePkt(false)
+	if action != utils.LSMActionNext {
+		return action
+	}
+
+	if pkt.opcode != internal.OpenVpnControlHardResetClientV1 &&
+		pkt.opcode != internal.OpenVpnControlHardResetClientV2 &&
+		pkt.opcode != internal.OpenVpnControlHardResetClientV3 {
+		return utils.LSMActionCancel
+	}
+	o.lastOpcode = pkt.opcode
+
+	return utils.LSMActionNext
+}
+
+func (o *openVpnStream) parseCtlHardResetServer() utils.LSMAction {
+	if o.lastOpcode != internal.OpenVpnControlHardResetClientV1 &&
+		o.lastOpcode != internal.OpenVpnControlHardResetClientV2 &&
+		o.lastOpcode != internal.OpenVpnControlHardResetClientV3 {
+		return utils.LSMActionCancel
+	}
+
+	pkt, action := o.parsePkt(true)
+	if action != utils.LSMActionNext {
+		return action
+	}
+
+	if pkt.opcode != internal.OpenVpnControlHardResetServerV1 &&
+		pkt.opcode != internal.OpenVpnControlHardResetServerV2 {
+		return utils.LSMActionCancel
+	}
+	o.lastOpcode = pkt.opcode
+
+	return utils.LSMActionNext
+}
+
+func (o *openVpnStream) parseReq() utils.LSMAction {
+	pkt, action := o.parsePkt(false)
+	if action != utils.LSMActionNext {
+		return action
+	}
+
+	if pkt.opcode != internal.OpenVpnControlSoftResetV1 &&
+		pkt.opcode != internal.OpenVpnControlV1 &&
+		pkt.opcode != internal.OpenVpnAckV1 &&
+		pkt.opcode != internal.OpenVpnDataV1 &&
+		pkt.opcode != internal.OpenVpnDataV2 &&
+		pkt.opcode != internal.OpenVpnControlWkcV1 {
+		return utils.LSMActionCancel
+	}
+
+	o.txPktCnt += 1
+	o.reqUpdated = true
+
+	return utils.LSMActionPause
+}
+
+func (o *openVpnStream) parseResp() utils.LSMAction {
+	pkt, action := o.parsePkt(true)
+	if action != utils.LSMActionNext {
+		return action
+	}
+
+	if pkt.opcode != internal.OpenVpnControlSoftResetV1 &&
+		pkt.opcode != internal.OpenVpnControlV1 &&
+		pkt.opcode != internal.OpenVpnAckV1 &&
+		pkt.opcode != internal.OpenVpnDataV1 &&
+		pkt.opcode != internal.OpenVpnDataV2 &&
+		pkt.opcode != internal.OpenVpnControlWkcV1 {
+		return utils.LSMActionCancel
+	}
+
+	o.rxPktCnt += 1
+	o.respUpdated = true
+
+	return utils.LSMActionPause
+}
+
+// Parse OpenVpn packet header but not consume buffer.
+func (o *openVpnStream) parsePkt(rev bool) (p *openVpnTcpPkt, action utils.LSMAction) {
+	var buffer *utils.ByteBuffer
+	if rev {
+		buffer = o.respBuf
+	} else {
+		buffer = o.reqBuf
+	}
+
+	// Parse packet length
+	pktLen, ok := buffer.GetUint16(false, false)
+	if !ok {
+		return nil, utils.LSMActionPause
+	}
+
+	if pktLen < internal.OpenVpnMinPktLen {
+		return nil, utils.LSMActionCancel
+	}
+
+	pktOp, ok := buffer.Get(3, false)
+	if !ok {
+		return nil, utils.LSMActionPause
+	}
+	if !internal.OpenVpnCheckForValidOpcode(pktOp[2] >> 3) {
+		return nil, utils.LSMActionCancel
+	}
+
+	pkt, ok := buffer.Get(int(pktLen)+2, true)
+	if !ok {
+		return nil, utils.LSMActionPause
+	}
+	pkt = pkt[2:]
+
+	// Parse packet header
+	p = &openVpnTcpPkt{}
+	p.pktLen = pktLen
+	p.opcode = pkt[0] >> 3
+	p._keyId = pkt[0] & 0x07
+
+	return p, utils.LSMActionNext
+}