overflow_discovery/service/matcher/snmp/v2/snmpv2.go

package v2

import (
	"bytes"
	"encoding/binary"

	"git.loafle.net/overflow/overflow_discovery/service/matcher"
	"git.loafle.net/overflow/overflow_discovery/service/matcher/snmp"
)

type snmpv2VarBinding struct {
	VarBindindStart uint8
	VarBindLen      uint8
	ObjectStart     uint8
	ObjectLen       uint8
	ValueType       uint8
	ValueLen        uint8
	ObjectValue     uint64
	NullValue       uint8
	EndIndicator    uint8
}

type snmpv2Data struct {
	DataType        uint8
	DataLen         uint8
	RequestIdType   uint8
	RequestIdLen    uint8
	RequestId       uint8
	ErrorStatusType uint8
	ErrorStatusLen  uint8
	ErrorStatus     uint8
	ErrorIndexType  uint8
	ErrorIndexLen   uint8
	ErrorIndex      uint8

	VarBinding snmpv2VarBinding
}

type snmpv2 struct {
	StartSeq             uint8
	SeqLen               uint8
	SNMPVersionType      uint8
	SNMPVersionLen       uint8
	SNMPVersion          uint8
	CommunityVersionType uint8
	CommunityVersionLen  uint8
	Community            [6]byte

	Data snmpv2Data
}

type SNMPMatcher struct {
	matcher.Matchers
}

func (t *SNMPMatcher) ServiceName() string {
	return "SNMP"
}

func (t *SNMPMatcher) IsPrePacket() bool {
	return false
}

func (t *SNMPMatcher) HasResponse(index int) bool {
	return true
}

func (t *SNMPMatcher) IsError(info matcher.MatchInfo, index int, packet *matcher.Packet) bool {
	return false
}

func (t *SNMPMatcher) Match(info matcher.MatchInfo, index int, packet *matcher.Packet) bool {

	if packet == nil {
		return false
	}

	r := new(bytes.Buffer)
	r.Write(packet.Buffer)

	s := snmpv2{}
	if err := binary.Read(r, binary.BigEndian, &s); err != nil {
		return false
	}

	if s.StartSeq != snmp.SNMP_START_SEQUENCE {
		return false
	}

	var p uint8
	reader := new(bytes.Buffer)
	reader.Write(packet.Buffer)
	for idx := 0; idx < 5; idx++ {
		if err := binary.Read(reader, binary.BigEndian, &p); err != nil {
			return false
		}
		if p == snmp.SNMP_TYPE_INTEGER {
			break
		}
		p++
	}

	//finding protocol version type : 0x02 0x01 0x01
	if err := binary.Read(reader, binary.BigEndian, &p); err != nil {
		return false
	}

	if p == 0x01 {
		if err := binary.Read(reader, binary.BigEndian, &p); err != nil {
			return false
		}
		if p == 0x01 {
			return true
		}
	}

	return false

}

func (t *SNMPMatcher) IsSend(port int) bool {
	if 161 == port {
		return true
	}
	return false
}

func NewMatcher() matcher.UDPMatcher {

	m := &SNMPMatcher{}

	snmpTempBuf := new(bytes.Buffer)
	binary.Write(snmpTempBuf, binary.BigEndian, snmpv2{}) //For getting the struct size

	snmpDataTempBuf := new(bytes.Buffer)
	binary.Write(snmpDataTempBuf, binary.BigEndian, snmpv2Data{}) //For getting the struct size

	snmpVarTempBuf := new(bytes.Buffer)
	binary.Write(snmpVarTempBuf, binary.BigEndian, snmpv2VarBinding{}) //For getting the struct size

	q := snmpv2{}
	q.StartSeq = snmp.SNMP_START_SEQUENCE
	q.SeqLen = uint8(len(snmpTempBuf.Bytes())) - 2
	q.SNMPVersionType = snmp.SNMP_TYPE_INTEGER
	q.SNMPVersionLen = 0x01
	q.SNMPVersion = snmp.SNMP_PROTOCOL_VERSION_2c
	q.CommunityVersionType = snmp.SNMP_TYPE_STRING
	q.CommunityVersionLen = 0x06
	var community [6]byte
	copy(community[:], "public")
	q.Community = community
	q.Data.DataType = snmp.SNMP_GET_REQUEST
	q.Data.DataLen = uint8(len(snmpDataTempBuf.Bytes())) - 2
	q.Data.RequestIdType = snmp.SNMP_TYPE_INTEGER
	q.Data.RequestIdLen = 0x01
	q.Data.RequestId = 0x01
	q.Data.ErrorStatusType = snmp.SNMP_TYPE_INTEGER
	q.Data.ErrorStatusLen = 0x01
	q.Data.ErrorStatus = 0x00
	q.Data.ErrorIndexType = snmp.SNMP_TYPE_INTEGER
	q.Data.ErrorIndexLen = 0x01
	q.Data.ErrorIndex = 0x00
	q.Data.VarBinding.VarBindindStart = snmp.SNMP_START_SEQUENCE
	q.Data.VarBinding.VarBindLen = uint8(len(snmpVarTempBuf.Bytes())) - 2
	q.Data.VarBinding.ObjectStart = snmp.SNMP_START_SEQUENCE
	q.Data.VarBinding.ObjectLen = uint8(len(snmpVarTempBuf.Bytes())) - 4
	q.Data.VarBinding.ValueType = snmp.SNMP_TYPE_OBJECT
	q.Data.VarBinding.ValueLen = 0x08
	q.Data.VarBinding.ObjectValue = 0x000001010201062b
	q.Data.VarBinding.NullValue = snmp.SNMP_TYPE_NULL
	q.Data.VarBinding.EndIndicator = 0x00

	writer := new(bytes.Buffer)
	binary.Write(writer, binary.LittleEndian, q)

	m.AddPacket(matcher.NewPacket(writer.Bytes(), writer.Len()))

	return m
}