cloudflared-mirror/ingress/icmp_darwin.go

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//go:build darwin
package ingress
// This file implements ICMPProxy for Darwin. It uses a non-privileged ICMP socket to send echo requests and listen for
// echo replies. The source IP of the requests are rewritten to the bind IP of the socket and the socket reads all
// messages, so we use echo ID to distinguish the replies. Each (source IP, destination IP, echo ID) is assigned a
// unique echo ID.
import (
"context"
"fmt"
"math"
"net/netip"
"strconv"
"sync"
"time"
"github.com/rs/zerolog"
"go.opentelemetry.io/otel/attribute"
"golang.org/x/net/icmp"
"github.com/cloudflare/cloudflared/packet"
"github.com/cloudflare/cloudflared/tracing"
)
type icmpProxy struct {
srcFunnelTracker *packet.FunnelTracker
echoIDTracker *echoIDTracker
conn *icmp.PacketConn
// Response is handled in one-by-one, so encoder can be shared between funnels
encoder *packet.Encoder
logger *zerolog.Logger
idleTimeout time.Duration
}
// 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.Mutex
// maps the source IP, destination IP and original echo ID to a unique echo ID obtained from assignment
mapping map[flow3Tuple]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{
mapping: make(map[flow3Tuple]uint16),
}
}
// Get assignment or assign a new ID.
func (eit *echoIDTracker) getOrAssign(key flow3Tuple) (id uint16, success bool) {
eit.lock.Lock()
defer eit.lock.Unlock()
id, exists := eit.mapping[key]
if exists {
return id, true
}
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(key, echoID)
return echoID, true
}
}
for i, assigned := range eit.assignment[0:eit.nextAssignment] {
if !assigned {
echoID := uint16(i)
eit.set(key, echoID)
return echoID, true
}
}
return 0, false
}
// Caller should hold the lock
func (eit *echoIDTracker) set(key flow3Tuple, assignedEchoID uint16) {
eit.assignment[assignedEchoID] = true
eit.mapping[key] = assignedEchoID
eit.nextAssignment = assignedEchoID + 1
}
func (eit *echoIDTracker) release(key flow3Tuple, assigned uint16) bool {
eit.lock.Lock()
defer eit.lock.Unlock()
currentEchoID, exists := eit.mapping[key]
if exists && assigned == currentEchoID {
delete(eit.mapping, key)
eit.assignment[assigned] = false
return true
}
return false
}
type echoFunnelID uint16
func (snf echoFunnelID) Type() string {
return "echoID"
}
func (snf echoFunnelID) String() string {
return strconv.FormatUint(uint64(snf), 10)
}
func newICMPProxy(listenIP netip.Addr, zone string, logger *zerolog.Logger, idleTimeout time.Duration) (*icmpProxy, error) {
conn, err := newICMPConn(listenIP, zone)
if err != nil {
return nil, err
}
logger.Info().Msgf("Created ICMP proxy listening on %s", conn.LocalAddr())
return &icmpProxy{
srcFunnelTracker: packet.NewFunnelTracker(),
echoIDTracker: newEchoIDTracker(),
encoder: packet.NewEncoder(),
conn: conn,
logger: logger,
idleTimeout: idleTimeout,
}, nil
}
func (ip *icmpProxy) Request(ctx context.Context, pk *packet.ICMP, responder *packetResponder) error {
ctx, span := responder.requestSpan(ctx, pk)
defer responder.exportSpan()
originalEcho, err := getICMPEcho(pk.Message)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return err
}
span.SetAttributes(
attribute.Int("originalEchoID", originalEcho.ID),
attribute.Int("seq", originalEcho.Seq),
)
echoIDTrackerKey := flow3Tuple{
srcIP: pk.Src,
dstIP: pk.Dst,
originalEchoID: originalEcho.ID,
}
assignedEchoID, success := ip.echoIDTracker.getOrAssign(echoIDTrackerKey)
if !success {
err := fmt.Errorf("failed to assign unique echo ID")
tracing.EndWithErrorStatus(span, err)
return err
}
span.SetAttributes(attribute.Int("assignedEchoID", int(assignedEchoID)))
shouldReplaceFunnelFunc := createShouldReplaceFunnelFunc(ip.logger, responder.datagramMuxer, pk, originalEcho.ID)
newFunnelFunc := func() (packet.Funnel, error) {
originalEcho, err := getICMPEcho(pk.Message)
if err != nil {
return nil, err
}
closeCallback := func() error {
ip.echoIDTracker.release(echoIDTrackerKey, assignedEchoID)
return nil
}
icmpFlow := newICMPEchoFlow(pk.Src, closeCallback, ip.conn, responder, int(assignedEchoID), originalEcho.ID, ip.encoder)
return icmpFlow, nil
}
funnelID := echoFunnelID(assignedEchoID)
funnel, isNew, err := ip.srcFunnelTracker.GetOrRegister(funnelID, shouldReplaceFunnelFunc, newFunnelFunc)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return err
}
if isNew {
span.SetAttributes(attribute.Bool("newFlow", true))
ip.logger.Debug().
Str("src", pk.Src.String()).
Str("dst", pk.Dst.String()).
Int("originalEchoID", originalEcho.ID).
Int("assignedEchoID", int(assignedEchoID)).
Msg("New flow")
}
icmpFlow, err := toICMPEchoFlow(funnel)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return err
}
err = icmpFlow.sendToDst(pk.Dst, pk.Message)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return err
}
tracing.End(span)
return nil
}
// 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()
}()
go func() {
ip.srcFunnelTracker.ScheduleCleanup(ctx, ip.idleTimeout)
}()
buf := make([]byte, mtu)
icmpDecoder := packet.NewICMPDecoder()
for {
n, from, err := ip.conn.ReadFrom(buf)
if err != nil {
return err
}
reply, err := parseReply(from, buf[:n])
if err != nil {
ip.logger.Debug().Err(err).Str("dst", from.String()).Msg("Failed to parse ICMP reply, continue to parse as full packet")
// In unit test, we found out when the listener listens on 0.0.0.0, the socket reads the full packet after
// the second reply
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if err := ip.handleFullPacket(ctx, icmpDecoder, buf[:n]); err != nil {
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ip.logger.Debug().Err(err).Str("dst", from.String()).Msg("Failed to parse ICMP reply as full packet")
}
continue
}
if !isEchoReply(reply.msg) {
ip.logger.Debug().Str("dst", from.String()).Msgf("Drop ICMP %s from reply", reply.msg.Type)
continue
}
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if err := ip.sendReply(ctx, reply); err != nil {
ip.logger.Debug().Err(err).Str("dst", from.String()).Msg("Failed to send ICMP reply")
continue
}
}
}
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func (ip *icmpProxy) handleFullPacket(ctx context.Context, decoder *packet.ICMPDecoder, rawPacket []byte) error {
icmpPacket, err := decoder.Decode(packet.RawPacket{Data: rawPacket})
if err != nil {
return err
}
echo, err := getICMPEcho(icmpPacket.Message)
if err != nil {
return err
}
reply := echoReply{
from: icmpPacket.Src,
msg: icmpPacket.Message,
echo: echo,
}
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if ip.sendReply(ctx, &reply); err != nil {
return err
}
return nil
}
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func (ip *icmpProxy) sendReply(ctx context.Context, reply *echoReply) error {
funnelID := echoFunnelID(reply.echo.ID)
funnel, ok := ip.srcFunnelTracker.Get(funnelID)
if !ok {
return packet.ErrFunnelNotFound
}
icmpFlow, err := toICMPEchoFlow(funnel)
if err != nil {
return err
}
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_, span := icmpFlow.responder.replySpan(ctx, ip.logger)
defer icmpFlow.responder.exportSpan()
span.SetAttributes(
attribute.String("dst", reply.from.String()),
attribute.Int("echoID", reply.echo.ID),
attribute.Int("seq", reply.echo.Seq),
attribute.Int("originalEchoID", icmpFlow.originalEchoID),
)
if err := icmpFlow.returnToSrc(reply); err != nil {
tracing.EndWithErrorStatus(span, err)
}
tracing.End(span)
return nil
}