cloudflared-mirror/ingress/icmp_darwin.go

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//go:build darwin
package ingress
import (
"context"
"fmt"
"math"
"net"
"net/netip"
"strconv"
"sync"
"github.com/google/gopacket/layers"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"golang.org/x/net/icmp"
"github.com/cloudflare/cloudflared/packet"
)
// TODO: TUN-6654 Extend support to IPv6
// On Darwin, a non-privileged ICMP socket can read messages from all echo IDs, so we use it for all sources.
type icmpProxy struct {
// TODO: TUN-6588 clean up flows
srcFlowTracker *packet.FlowTracker
echoIDTracker *echoIDTracker
conn *icmp.PacketConn
logger *zerolog.Logger
}
// echoIDTracker tracks which ID has been assigned. It first loops through assignment from lastAssignment to then end,
// then from the beginning to lastAssignment.
// ICMP echo are short lived. By the time an ID is revisited, it should have been released.
type echoIDTracker struct {
lock sync.RWMutex
// maps the source IP to an echo ID obtained from assignment
srcIPMapping map[netip.Addr]uint16
// assignment tracks if an ID is assigned using index as the ID
// The size of the array is math.MaxUint16 because echo ID is 2 bytes
assignment [math.MaxUint16]bool
// nextAssignment is the next number to check for assigment
nextAssignment uint16
}
func newEchoIDTracker() *echoIDTracker {
return &echoIDTracker{
srcIPMapping: make(map[netip.Addr]uint16),
}
}
func (eit *echoIDTracker) get(srcIP netip.Addr) (uint16, bool) {
eit.lock.RLock()
defer eit.lock.RUnlock()
id, ok := eit.srcIPMapping[srcIP]
return id, ok
}
func (eit *echoIDTracker) assign(srcIP netip.Addr) (uint16, bool) {
eit.lock.Lock()
defer eit.lock.Unlock()
if eit.nextAssignment == math.MaxUint16 {
eit.nextAssignment = 0
}
for i, assigned := range eit.assignment[eit.nextAssignment:] {
if !assigned {
echoID := uint16(i) + eit.nextAssignment
eit.set(srcIP, echoID)
return echoID, true
}
}
for i, assigned := range eit.assignment[0:eit.nextAssignment] {
if !assigned {
echoID := uint16(i)
eit.set(srcIP, echoID)
return echoID, true
}
}
return 0, false
}
// Caller should hold the lock
func (eit *echoIDTracker) set(srcIP netip.Addr, echoID uint16) {
eit.assignment[echoID] = true
eit.srcIPMapping[srcIP] = echoID
eit.nextAssignment = echoID + 1
}
func (eit *echoIDTracker) release(srcIP netip.Addr, id uint16) bool {
eit.lock.Lock()
defer eit.lock.Unlock()
currentID, ok := eit.srcIPMapping[srcIP]
if ok && id == currentID {
delete(eit.srcIPMapping, srcIP)
eit.assignment[id] = false
return true
}
return false
}
type echoFlowID uint16
func (snf echoFlowID) Type() string {
return "echoID"
}
func (snf echoFlowID) String() string {
return strconv.FormatUint(uint64(snf), 10)
}
func newICMPProxy(listenIP netip.Addr, logger *zerolog.Logger) (ICMPProxy, error) {
conn, err := newICMPConn(listenIP)
if err != nil {
return nil, err
}
return &icmpProxy{
srcFlowTracker: packet.NewFlowTracker(),
echoIDTracker: newEchoIDTracker(),
conn: conn,
logger: logger,
}, nil
}
func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FlowResponder) error {
if pk == nil {
return errPacketNil
}
switch body := pk.Message.Body.(type) {
case *icmp.Echo:
return ip.sendICMPEchoRequest(pk, body, responder)
default:
return fmt.Errorf("sending ICMP %s is not implemented", pk.Type)
}
}
// Serve listens for responses to the requests until context is done
func (ip *icmpProxy) Serve(ctx context.Context) error {
go func() {
<-ctx.Done()
ip.conn.Close()
}()
buf := make([]byte, mtu)
encoder := packet.NewEncoder()
for {
n, src, err := ip.conn.ReadFrom(buf)
if err != nil {
return err
}
// TODO: TUN-6654 Check for IPv6
msg, err := icmp.ParseMessage(int(layers.IPProtocolICMPv4), buf[:n])
if err != nil {
ip.logger.Error().Err(err).Str("src", src.String()).Msg("Failed to parse ICMP message")
continue
}
switch body := msg.Body.(type) {
case *icmp.Echo:
if err := ip.handleEchoResponse(encoder, msg, body); err != nil {
ip.logger.Error().Err(err).
Str("src", src.String()).
Str("flowID", echoFlowID(body.ID).String()).
Msg("Failed to handle ICMP response")
continue
}
default:
ip.logger.Warn().
Str("icmpType", fmt.Sprintf("%s", msg.Type)).
Msgf("Responding to this type of ICMP is not implemented")
continue
}
}
}
func (ip *icmpProxy) sendICMPEchoRequest(pk *packet.ICMP, echo *icmp.Echo, responder packet.FlowResponder) error {
echoID, ok := ip.echoIDTracker.get(pk.Src)
if !ok {
echoID, ok = ip.echoIDTracker.assign(pk.Src)
if !ok {
return fmt.Errorf("failed to assign unique echo ID")
}
flowID := echoFlowID(echoID)
flow := packet.Flow{
Src: pk.Src,
Dst: pk.Dst,
Responder: responder,
}
if replaced := ip.srcFlowTracker.Register(flowID, &flow, true); replaced {
ip.logger.Info().Str("src", flow.Src.String()).Str("dst", flow.Dst.String()).Msg("Replaced flow")
}
}
echo.ID = int(echoID)
var pseudoHeader []byte = nil
serializedMsg, err := pk.Marshal(pseudoHeader)
if err != nil {
return errors.Wrap(err, "Failed to encode ICMP message")
}
// The address needs to be of type UDPAddr when conn is created without priviledge
_, err = ip.conn.WriteTo(serializedMsg, &net.UDPAddr{
IP: pk.Dst.AsSlice(),
})
return err
}
func (ip *icmpProxy) handleEchoResponse(encoder *packet.Encoder, msg *icmp.Message, echo *icmp.Echo) error {
flowID := echoFlowID(echo.ID)
flow, ok := ip.srcFlowTracker.Get(flowID)
if !ok {
return fmt.Errorf("flow not found")
}
icmpPacket := packet.ICMP{
IP: &packet.IP{
Src: flow.Dst,
Dst: flow.Src,
Protocol: layers.IPProtocol(msg.Type.Protocol()),
},
Message: msg,
}
serializedPacket, err := encoder.Encode(&icmpPacket)
if err != nil {
return errors.Wrap(err, "Failed to encode ICMP message")
}
if err := flow.Responder.SendPacket(serializedPacket); err != nil {
return errors.Wrap(err, "Failed to send packet to the edge")
}
return nil
}