netlink/conntrack_linux.go

package netlink

import (
	"bytes"
	"encoding/binary"
	"errors"
	"fmt"
	"net"
	"syscall"

	"github.com/vishvananda/netlink/nl"
)

// ConntrackTableType Conntrack table for the netlink operation
type ConntrackTableType uint8

const (
	// ConntrackTable Conntrack table
	// https://github.com/torvalds/linux/blob/master/include/uapi/linux/netfilter/nfnetlink.h -> #define NFNL_SUBSYS_CTNETLINK		 1
	ConntrackTable = 1
	// ConntrackExpectTable Conntrack expect table
	// https://github.com/torvalds/linux/blob/master/include/uapi/linux/netfilter/nfnetlink.h -> #define NFNL_SUBSYS_CTNETLINK_EXP 2
	ConntrackExpectTable = 2
)

const (
	// backward compatibility with golang 1.6 which does not have io.SeekCurrent
	seekCurrent = 1
)

// InetFamily Family type
type InetFamily uint8

//  -L [table] [options]          List conntrack or expectation table
//  -G [table] parameters         Get conntrack or expectation

//  -I [table] parameters         Create a conntrack or expectation
//  -U [table] parameters         Update a conntrack
//  -E [table] [options]          Show events

//  -C [table]                    Show counter
//  -S                            Show statistics

// ConntrackTableList returns the flow list of a table of a specific family
// conntrack -L [table] [options]          List conntrack or expectation table
func ConntrackTableList(table ConntrackTableType, family InetFamily) ([]*ConntrackFlow, error) {
	return pkgHandle.ConntrackTableList(table, family)
}

// ConntrackTableFlush flushes all the flows of a specified table
// conntrack -F [table]            Flush table
// The flush operation applies to all the family types
func ConntrackTableFlush(table ConntrackTableType) error {
	return pkgHandle.ConntrackTableFlush(table)
}

// ConntrackDeleteFilter deletes entries on the specified table on the base of the filter
// conntrack -D [table] parameters         Delete conntrack or expectation
func ConntrackDeleteFilter(table ConntrackTableType, family InetFamily, filter *ConntrackFilter) (uint, error) {
	return pkgHandle.ConntrackDeleteFilter(table, family, filter)
}

// ConntrackTableList returns the flow list of a table of a specific family using the netlink handle passed
// conntrack -L [table] [options]          List conntrack or expectation table
func (h *Handle) ConntrackTableList(table ConntrackTableType, family InetFamily) ([]*ConntrackFlow, error) {
	res, err := h.dumpConntrackTable(table, family)
	if err != nil {
		return nil, err
	}

	// Deserialize all the flows
	var result []*ConntrackFlow
	for _, dataRaw := range res {
		result = append(result, parseRawData(dataRaw))
	}

	return result, nil
}

// ConntrackTableFlush flushes all the flows of a specified table using the netlink handle passed
// conntrack -F [table]            Flush table
// The flush operation applies to all the family types
func (h *Handle) ConntrackTableFlush(table ConntrackTableType) error {
	req := h.newConntrackRequest(table, syscall.AF_INET, nl.IPCTNL_MSG_CT_DELETE, syscall.NLM_F_ACK)
	_, err := req.Execute(syscall.NETLINK_NETFILTER, 0)
	return err
}

// ConntrackDeleteFilter deletes entries on the specified table on the base of the filter using the netlink handle passed
// conntrack -D [table] parameters         Delete conntrack or expectation
func (h *Handle) ConntrackDeleteFilter(table ConntrackTableType, family InetFamily, filter *ConntrackFilter) (uint, error) {
	res, err := h.dumpConntrackTable(table, family)
	if err != nil {
		return 0, err
	}

	var matched uint
	for _, dataRaw := range res {
		flow := parseRawData(dataRaw)
		if match := filter.MatchConntrackFlow(flow); match {
			req2 := h.newConntrackRequest(table, family, nl.IPCTNL_MSG_CT_DELETE, syscall.NLM_F_ACK)
			// skip the first 4 byte that are the netfilter header, the newConntrackRequest is adding it already
			req2.AddRawData(dataRaw[4:])
			req2.Execute(syscall.NETLINK_NETFILTER, 0)
			matched++
		}
	}

	return matched, nil
}

func (h *Handle) newConntrackRequest(table ConntrackTableType, family InetFamily, operation, flags int) *nl.NetlinkRequest {
	// Create the Netlink request object
	req := h.newNetlinkRequest((int(table)<<8)|operation, flags)
	// Add the netfilter header
	msg := &nl.Nfgenmsg{
		NfgenFamily: uint8(family),
		Version:     nl.NFNETLINK_V0,
		ResId:       0,
	}
	req.AddData(msg)
	return req
}

func (h *Handle) dumpConntrackTable(table ConntrackTableType, family InetFamily) ([][]byte, error) {
	req := h.newConntrackRequest(table, family, nl.IPCTNL_MSG_CT_GET, syscall.NLM_F_DUMP)
	return req.Execute(syscall.NETLINK_NETFILTER, 0)
}

// The full conntrack flow structure is very complicated and can be found in the file:
// http://git.netfilter.org/libnetfilter_conntrack/tree/include/internal/object.h
// For the time being, the structure below allows to parse and extract the base information of a flow
type ipTuple struct {
	SrcIP    net.IP
	DstIP    net.IP
	Protocol uint8
	SrcPort  uint16
	DstPort  uint16
}

type ConntrackFlow struct {
	FamilyType uint8
	Forward    ipTuple
	Reverse    ipTuple
}

func (s *ConntrackFlow) String() string {
	// conntrack cmd output:
	// udp      17 src=127.0.0.1 dst=127.0.0.1 sport=4001 dport=1234 [UNREPLIED] src=127.0.0.1 dst=127.0.0.1 sport=1234 dport=4001
	return fmt.Sprintf("%s\t%d src=%s dst=%s sport=%d dport=%d\tsrc=%s dst=%s sport=%d dport=%d",
		nl.L4ProtoMap[s.Forward.Protocol], s.Forward.Protocol,
		s.Forward.SrcIP.String(), s.Forward.DstIP.String(), s.Forward.SrcPort, s.Forward.DstPort,
		s.Reverse.SrcIP.String(), s.Reverse.DstIP.String(), s.Reverse.SrcPort, s.Reverse.DstPort)
}

// This method parse the ip tuple structure
// The message structure is the following:
// <len, [CTA_IP_V4_SRC|CTA_IP_V6_SRC], 16 bytes for the IP>
// <len, [CTA_IP_V4_DST|CTA_IP_V6_DST], 16 bytes for the IP>
// <len, NLA_F_NESTED|nl.CTA_TUPLE_PROTO, 1 byte for the protocol, 3 bytes of padding>
// <len, CTA_PROTO_SRC_PORT, 2 bytes for the source port, 2 bytes of padding>
// <len, CTA_PROTO_DST_PORT, 2 bytes for the source port, 2 bytes of padding>
func parseIpTuple(reader *bytes.Reader, tpl *ipTuple) {
	for i := 0; i < 2; i++ {
		_, t, _, v := parseNfAttrTLV(reader)
		switch t {
		case nl.CTA_IP_V4_SRC, nl.CTA_IP_V6_SRC:
			tpl.SrcIP = v
		case nl.CTA_IP_V4_DST, nl.CTA_IP_V6_DST:
			tpl.DstIP = v
		}
	}
	// Skip the next 4 bytes  nl.NLA_F_NESTED|nl.CTA_TUPLE_PROTO
	reader.Seek(4, seekCurrent)
	_, t, _, v := parseNfAttrTLV(reader)
	if t == nl.CTA_PROTO_NUM {
		tpl.Protocol = uint8(v[0])
	}
	// Skip some padding 3 bytes
	reader.Seek(3, seekCurrent)
	for i := 0; i < 2; i++ {
		_, t, _ := parseNfAttrTL(reader)
		switch t {
		case nl.CTA_PROTO_SRC_PORT:
			parseBERaw16(reader, &tpl.SrcPort)
		case nl.CTA_PROTO_DST_PORT:
			parseBERaw16(reader, &tpl.DstPort)
		}
		// Skip some padding 2 byte
		reader.Seek(2, seekCurrent)
	}
}

func parseNfAttrTLV(r *bytes.Reader) (isNested bool, attrType, len uint16, value []byte) {
	isNested, attrType, len = parseNfAttrTL(r)

	value = make([]byte, len)
	binary.Read(r, binary.BigEndian, &value)
	return isNested, attrType, len, value
}

func parseNfAttrTL(r *bytes.Reader) (isNested bool, attrType, len uint16) {
	binary.Read(r, nl.NativeEndian(), &len)
	len -= nl.SizeofNfattr

	binary.Read(r, nl.NativeEndian(), &attrType)
	isNested = (attrType & nl.NLA_F_NESTED) == nl.NLA_F_NESTED
	attrType = attrType & (nl.NLA_F_NESTED - 1)

	return isNested, attrType, len
}

func parseBERaw16(r *bytes.Reader, v *uint16) {
	binary.Read(r, binary.BigEndian, v)
}

func parseRawData(data []byte) *ConntrackFlow {
	s := &ConntrackFlow{}
	// First there is the Nfgenmsg header
	// consume only the family field
	reader := bytes.NewReader(data)
	binary.Read(reader, nl.NativeEndian(), &s.FamilyType)

	// skip rest of the Netfilter header
	reader.Seek(3, seekCurrent)
	// The message structure is the following:
	// <len, NLA_F_NESTED|CTA_TUPLE_ORIG> 4 bytes
	// <len, NLA_F_NESTED|CTA_TUPLE_IP> 4 bytes
	// flow information of the forward flow
	// <len, NLA_F_NESTED|CTA_TUPLE_REPLY> 4 bytes
	// <len, NLA_F_NESTED|CTA_TUPLE_IP> 4 bytes
	// flow information of the reverse flow
	for reader.Len() > 0 {
		nested, t, l := parseNfAttrTL(reader)
		if nested && t == nl.CTA_TUPLE_ORIG {
			if nested, t, _ = parseNfAttrTL(reader); nested && t == nl.CTA_TUPLE_IP {
				parseIpTuple(reader, &s.Forward)
			}
		} else if nested && t == nl.CTA_TUPLE_REPLY {
			if nested, t, _ = parseNfAttrTL(reader); nested && t == nl.CTA_TUPLE_IP {
				parseIpTuple(reader, &s.Reverse)

				// Got all the useful information stop parsing
				break
			} else {
				// Header not recognized skip it
				reader.Seek(int64(l), seekCurrent)
			}
		}
	}

	return s
}

// Conntrack parameters and options:
//   -n, --src-nat ip                      source NAT ip
//   -g, --dst-nat ip                      destination NAT ip
//   -j, --any-nat ip                      source or destination NAT ip
//   -m, --mark mark                       Set mark
//   -c, --secmark secmark                 Set selinux secmark
//   -e, --event-mask eventmask            Event mask, eg. NEW,DESTROY
//   -z, --zero                            Zero counters while listing
//   -o, --output type[,...]               Output format, eg. xml
//   -l, --label label[,...]               conntrack labels

// Common parameters and options:
//   -s, --src, --orig-src ip              Source address from original direction
//   -d, --dst, --orig-dst ip              Destination address from original direction
//   -r, --reply-src ip            Source addres from reply direction
//   -q, --reply-dst ip            Destination address from reply direction
//   -p, --protonum proto          Layer 4 Protocol, eg. 'tcp'
//   -f, --family proto            Layer 3 Protocol, eg. 'ipv6'
//   -t, --timeout timeout         Set timeout
//   -u, --status status           Set status, eg. ASSURED
//   -w, --zone value              Set conntrack zone
//   --orig-zone value             Set zone for original direction
//   --reply-zone value            Set zone for reply direction
//   -b, --buffer-size             Netlink socket buffer size
//   --mask-src ip                 Source mask address
//   --mask-dst ip                 Destination mask address

// Filter types
type ConntrackFilterType uint8

const (
	ConntrackOrigSrcIP = iota // -orig-src ip   Source address from original direction
	ConntrackOrigDstIP        // -orig-dst ip   Destination address from original direction
	ConntrackNatSrcIP         // -src-nat ip    Source NAT ip
	ConntrackNatDstIP         // -dst-nat ip    Destination NAT ip
	ConntrackNatAnyIP         // -any-nat ip    Source or destination NAT ip
)

type ConntrackFilter struct {
	ipFilter map[ConntrackFilterType]net.IP
}

// AddIP adds an IP to the conntrack filter
func (f *ConntrackFilter) AddIP(tp ConntrackFilterType, ip net.IP) error {
	if f.ipFilter == nil {
		f.ipFilter = make(map[ConntrackFilterType]net.IP)
	}
	if _, ok := f.ipFilter[tp]; ok {
		return errors.New("Filter attribute already present")
	}
	f.ipFilter[tp] = ip
	return nil
}

// MatchConntrackFlow applies the filter to the flow and returns true if the flow matches the filter
// false otherwise
func (f *ConntrackFilter) MatchConntrackFlow(flow *ConntrackFlow) bool {
	if len(f.ipFilter) == 0 {
		// empty filter always not match
		return false
	}

	match := true
	// -orig-src ip   Source address from original direction
	if elem, found := f.ipFilter[ConntrackOrigSrcIP]; found {
		match = match && elem.Equal(flow.Forward.SrcIP)
	}

	// -orig-dst ip   Destination address from original direction
	if elem, found := f.ipFilter[ConntrackOrigDstIP]; match && found {
		match = match && elem.Equal(flow.Forward.DstIP)
	}

	// -src-nat ip    Source NAT ip
	if elem, found := f.ipFilter[ConntrackNatSrcIP]; match && found {
		match = match && elem.Equal(flow.Reverse.SrcIP)
	}

	// -dst-nat ip    Destination NAT ip
	if elem, found := f.ipFilter[ConntrackNatDstIP]; match && found {
		match = match && elem.Equal(flow.Reverse.DstIP)
	}

	// -any-nat ip    Source or destination NAT ip
	if elem, found := f.ipFilter[ConntrackNatAnyIP]; match && found {
		match = match && (elem.Equal(flow.Reverse.SrcIP) || elem.Equal(flow.Reverse.DstIP))
	}

	return match
}