cloudflared-mirror/ingress/icmp_linux.go

158 lines
4.5 KiB
Go

//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"
"time"
"github.com/pkg/errors"
"github.com/rs/zerolog"
"golang.org/x/net/icmp"
"github.com/cloudflare/cloudflared/packet"
)
type icmpProxy struct {
srcFunnelTracker *packet.FunnelTracker
listenIP netip.Addr
logger *zerolog.Logger
idleTimeout time.Duration
}
func newICMPProxy(listenIP netip.Addr, logger *zerolog.Logger, idleTimeout time.Duration) (ICMPProxy, error) {
if err := testPermission(listenIP); err != nil {
return nil, err
}
return &icmpProxy{
srcFunnelTracker: packet.NewFunnelTracker(),
listenIP: listenIP,
logger: logger,
idleTimeout: idleTimeout,
}, nil
}
func testPermission(listenIP netip.Addr) error {
// Opens a non-privileged ICMP socket. On Linux the group ID of the process needs to be in ping_group_range
conn, err := newICMPConn(listenIP)
if err != nil {
// TODO: TUN-6715 check if cloudflared is in ping_group_range if the check failed. If not log instruction to
// change the group ID
return err
}
// This conn is only to test if cloudflared has permission to open this type of socket
conn.Close()
return nil
}
func (ip *icmpProxy) Request(pk *packet.ICMP, responder packet.FunnelUniPipe) error {
if pk == nil {
return errPacketNil
}
funnelID := srcIPFunnelID(pk.Src)
funnel, exists := ip.srcFunnelTracker.Get(funnelID)
if !exists {
originalEcho, err := getICMPEcho(pk.Message)
if err != nil {
return err
}
conn, err := newICMPConn(ip.listenIP)
if err != nil {
return errors.Wrap(err, "failed to open ICMP socket")
}
localUDPAddr, ok := conn.LocalAddr().(*net.UDPAddr)
if !ok {
return 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())
if replaced := ip.srcFunnelTracker.Register(funnelID, icmpFlow); replaced {
ip.logger.Info().Str("src", pk.Src.String()).Msg("Replaced funnel")
}
if err := icmpFlow.sendToDst(pk.Dst, pk.Message); err != nil {
return errors.Wrap(err, "failed to send ICMP echo request")
}
go func() {
defer ip.srcFunnelTracker.Unregister(funnelID, icmpFlow)
if err := ip.listenResponse(icmpFlow, conn); err != nil {
ip.logger.Err(err).
Str("funnelID", funnelID.String()).
Int("echoID", echoID).
Msg("Failed to listen for ICMP echo response")
}
}()
return nil
}
icmpFlow, err := toICMPEchoFlow(funnel)
if err != nil {
return err
}
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()
}
type srcIPFunnelID netip.Addr
func (sifd srcIPFunnelID) Type() string {
return "srcIP"
}
func (sifd srcIPFunnelID) String() string {
return netip.Addr(sifd).String()
}