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"
"golang.org/x/net/icmp"
"github.com/cloudflare/cloudflared/packet"
)
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(pk *packet.ICMP, responder packet.FunnelUniPipe) error {
if pk == nil {
return errPacketNil
}
originalEcho, err := getICMPEcho(pk.Message)
if err != nil {
return err
}
newConnChan := make(chan *icmp.PacketConn, 1)
newFunnelFunc := func() (packet.Funnel, error) {
conn, err := newICMPConn(ip.listenIP, ip.ipv6Zone)
if err != nil {
return nil, errors.Wrap(err, "failed to open ICMP socket")
}
ip.logger.Debug().Msgf("Opened ICMP socket listen on %s", conn.LocalAddr())
newConnChan <- conn
localUDPAddr, ok := conn.LocalAddr().(*net.UDPAddr)
if !ok {
return nil, fmt.Errorf("ICMP listener address %s is not net.UDPAddr", conn.LocalAddr())
}
originSender := originSender{conn: conn}
echoID := localUDPAddr.Port
icmpFlow := newICMPEchoFlow(pk.Src, &originSender, 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, newFunnelFunc)
if err != nil {
return err
}
icmpFlow, err := toICMPEchoFlow(funnel)
if err != nil {
return err
}
if isNew {
ip.logger.Debug().
Str("src", pk.Src.String()).
Str("dst", pk.Dst.String()).
Int("originalEchoID", originalEcho.ID).
Msg("New flow")
conn := <-newConnChan
go func() {
defer ip.srcFunnelTracker.Unregister(funnelID, icmpFlow)
if err := ip.listenResponse(icmpFlow, conn); 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 {
return errors.Wrap(err, "failed to send ICMP echo request")
}
return nil
}
func (ip *icmpProxy) Serve(ctx context.Context) error {
ip.srcFunnelTracker.ScheduleCleanup(ctx, ip.idleTimeout)
return ctx.Err()
}
func (ip *icmpProxy) listenResponse(flow *icmpEchoFlow, conn *icmp.PacketConn) error {
buf := make([]byte, mtu)
for {
n, from, err := conn.ReadFrom(buf)
if err != nil {
return 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")
continue
}
if !isEchoReply(reply.msg) {
ip.logger.Debug().Str("dst", from.String()).Msgf("Drop ICMP %s from reply", reply.msg.Type)
continue
}
if err := flow.returnToSrc(reply); err != nil {
ip.logger.Err(err).Str("dst", from.String()).Msg("Failed to send ICMP reply")
continue
}
}
}
// originSender wraps icmp.PacketConn to implement packet.FunnelUniPipe interface
type originSender struct {
conn *icmp.PacketConn
}
func (os *originSender) SendPacket(dst netip.Addr, pk packet.RawPacket) error {
_, err := os.conn.WriteTo(pk.Data, &net.UDPAddr{
IP: dst.AsSlice(),
})
return err
}
func (os *originSender) Close() error {
return os.conn.Close()
}
// 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)
}