cloudflared-mirror/ingress/icmp_linux.go

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//go:build linux
package ingress
// This file implements ICMPProxy for Linux. Each (source IP, destination IP, echo ID) opens a non-privileged ICMP socket.
// The source IP of the requests are rewritten to the bind IP of the socket and echo ID rewritten to the port number of
// the socket. The kernel ensures the socket only reads replies whose echo ID matches the port number.
// For more information about the socket, see https://man7.org/linux/man-pages/man7/icmp.7.html and https://lwn.net/Articles/422330/
import (
"context"
"fmt"
"net"
"net/netip"
"os"
"regexp"
"strconv"
"time"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"go.opentelemetry.io/otel/attribute"
"github.com/cloudflare/cloudflared/packet"
"github.com/cloudflare/cloudflared/tracing"
)
const (
// https://lwn.net/Articles/550551/ IPv4 and IPv6 share the same path
pingGroupPath = "/proc/sys/net/ipv4/ping_group_range"
)
var (
findGroupIDRegex = regexp.MustCompile(`\d+`)
)
type icmpProxy struct {
srcFunnelTracker *packet.FunnelTracker
listenIP netip.Addr
ipv6Zone string
logger *zerolog.Logger
idleTimeout time.Duration
}
func newICMPProxy(listenIP netip.Addr, zone string, logger *zerolog.Logger, idleTimeout time.Duration) (*icmpProxy, error) {
if err := testPermission(listenIP, zone, logger); err != nil {
return nil, err
}
return &icmpProxy{
srcFunnelTracker: packet.NewFunnelTracker(),
listenIP: listenIP,
ipv6Zone: zone,
logger: logger,
idleTimeout: idleTimeout,
}, nil
}
func testPermission(listenIP netip.Addr, zone string, logger *zerolog.Logger) error {
// Opens a non-privileged ICMP socket. On Linux the group ID of the process needs to be in ping_group_range
// Only check ping_group_range once for IPv4
if listenIP.Is4() {
if err := checkInPingGroup(); err != nil {
logger.Warn().Err(err).Msgf("The user running cloudflared process has a GID (group ID) that is not within ping_group_range. You might need to add that user to a group within that range, or instead update the range to encompass a group the user is already in by modifying %s. Otherwise cloudflared will not be able to ping this network", pingGroupPath)
return err
}
}
conn, err := newICMPConn(listenIP, zone)
if err != nil {
return err
}
// This conn is only to test if cloudflared has permission to open this type of socket
conn.Close()
return nil
}
func checkInPingGroup() error {
file, err := os.ReadFile(pingGroupPath)
if err != nil {
return err
}
groupID := os.Getgid()
// Example content: 999 59999
found := findGroupIDRegex.FindAll(file, 2)
if len(found) == 2 {
groupMin, err := strconv.ParseInt(string(found[0]), 10, 32)
if err != nil {
return errors.Wrapf(err, "failed to determine minimum ping group ID")
}
groupMax, err := strconv.ParseInt(string(found[1]), 10, 32)
if err != nil {
return errors.Wrapf(err, "failed to determine minimum ping group ID")
}
if groupID < int(groupMin) || groupID > int(groupMax) {
return fmt.Errorf("Group ID %d is not between ping group %d to %d", groupID, groupMin, groupMax)
}
return nil
}
return fmt.Errorf("did not find group range in %s", pingGroupPath)
}
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),
)
shouldReplaceFunnelFunc := createShouldReplaceFunnelFunc(ip.logger, responder.datagramMuxer, pk, originalEcho.ID)
newFunnelFunc := func() (packet.Funnel, error) {
conn, err := newICMPConn(ip.listenIP, ip.ipv6Zone)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return nil, errors.Wrap(err, "failed to open ICMP socket")
}
ip.logger.Debug().Msgf("Opened ICMP socket listen on %s", conn.LocalAddr())
closeCallback := func() error {
return conn.Close()
}
localUDPAddr, ok := conn.LocalAddr().(*net.UDPAddr)
if !ok {
return nil, fmt.Errorf("ICMP listener address %s is not net.UDPAddr", conn.LocalAddr())
}
span.SetAttributes(attribute.Int("port", localUDPAddr.Port))
echoID := localUDPAddr.Port
icmpFlow := newICMPEchoFlow(pk.Src, closeCallback, conn, responder, echoID, originalEcho.ID, packet.NewEncoder())
return icmpFlow, nil
}
funnelID := flow3Tuple{
srcIP: pk.Src,
dstIP: pk.Dst,
originalEchoID: originalEcho.ID,
}
funnel, isNew, err := ip.srcFunnelTracker.GetOrRegister(funnelID, shouldReplaceFunnelFunc, newFunnelFunc)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return err
}
icmpFlow, err := toICMPEchoFlow(funnel)
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).
Msg("New flow")
go func() {
defer ip.srcFunnelTracker.Unregister(funnelID, icmpFlow)
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if err := ip.listenResponse(ctx, icmpFlow); err != nil {
ip.logger.Debug().Err(err).
Str("src", pk.Src.String()).
Str("dst", pk.Dst.String()).
Int("originalEchoID", originalEcho.ID).
Msg("Failed to listen for ICMP echo response")
}
}()
}
if err := icmpFlow.sendToDst(pk.Dst, pk.Message); err != nil {
tracing.EndWithErrorStatus(span, err)
return errors.Wrap(err, "failed to send ICMP echo request")
}
tracing.End(span)
return nil
}
func (ip *icmpProxy) Serve(ctx context.Context) error {
ip.srcFunnelTracker.ScheduleCleanup(ctx, ip.idleTimeout)
return ctx.Err()
}
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func (ip *icmpProxy) listenResponse(ctx context.Context, flow *icmpEchoFlow) error {
buf := make([]byte, mtu)
for {
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retryable, err := ip.handleResponse(ctx, flow, buf)
if err != nil && !retryable {
return err
}
}
}
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func (ip *icmpProxy) handleResponse(ctx context.Context, flow *icmpEchoFlow, buf []byte) (retryableErr bool, err error) {
_, span := flow.responder.replySpan(ctx, ip.logger)
defer flow.responder.exportSpan()
span.SetAttributes(
attribute.Int("originalEchoID", flow.originalEchoID),
)
n, from, err := flow.originConn.ReadFrom(buf)
if err != nil {
tracing.EndWithErrorStatus(span, err)
return false, err
}
reply, err := parseReply(from, buf[:n])
if err != nil {
ip.logger.Error().Err(err).Str("dst", from.String()).Msg("Failed to parse ICMP reply")
tracing.EndWithErrorStatus(span, err)
return true, err
}
if !isEchoReply(reply.msg) {
err := fmt.Errorf("Expect ICMP echo reply, got %s", reply.msg.Type)
ip.logger.Debug().Str("dst", from.String()).Msgf("Drop ICMP %s from reply", reply.msg.Type)
tracing.EndWithErrorStatus(span, err)
return true, err
}
span.SetAttributes(
attribute.String("dst", reply.from.String()),
attribute.Int("echoID", reply.echo.ID),
attribute.Int("seq", reply.echo.Seq),
)
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if err := flow.returnToSrc(reply); err != nil {
ip.logger.Debug().Err(err).Str("dst", from.String()).Msg("Failed to send ICMP reply")
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tracing.EndWithErrorStatus(span, err)
return true, err
}
tracing.End(span)
return true, nil
}
// Only linux uses flow3Tuple as FunnelID
func (ft flow3Tuple) Type() string {
return "srcIP_dstIP_echoID"
}
func (ft flow3Tuple) String() string {
return fmt.Sprintf("%s:%s:%d", ft.srcIP, ft.dstIP, ft.originalEchoID)
}