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tailscale/prober/derp.go

413 lines
11 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
package prober
import (
"bytes"
"context"
crand "crypto/rand"
"encoding/json"
"errors"
"fmt"
"log"
"net"
"net/http"
"strconv"
"strings"
"sync"
"time"
"tailscale.com/derp"
"tailscale.com/derp/derphttp"
"tailscale.com/net/stun"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
"tailscale.com/types/logger"
)
// derpProber dynamically manages several probes for each DERP server
// based on the current DERPMap.
type derpProber struct {
p *Prober
derpMapURL string
udpInterval time.Duration
meshInterval time.Duration
tlsInterval time.Duration
// Probe functions that can be overridden for testing.
tlsProbeFn func(string) ProbeFunc
udpProbeFn func(string, int) ProbeFunc
meshProbeFn func(string, string) ProbeFunc
sync.Mutex
lastDERPMap *tailcfg.DERPMap
lastDERPMapAt time.Time
nodes map[string]*tailcfg.DERPNode
probes map[string]*Probe
}
// DERP creates a new derpProber.
func DERP(p *Prober, derpMapURL string, udpInterval, meshInterval, tlsInterval time.Duration) (*derpProber, error) {
d := &derpProber{
p: p,
derpMapURL: derpMapURL,
udpInterval: udpInterval,
meshInterval: meshInterval,
tlsInterval: tlsInterval,
tlsProbeFn: TLS,
nodes: make(map[string]*tailcfg.DERPNode),
probes: make(map[string]*Probe),
}
d.udpProbeFn = d.ProbeUDP
d.meshProbeFn = d.probeMesh
return d, nil
}
// ProbeMap fetches the DERPMap and creates/destroys probes for each
// DERP server as necessary. It should get regularly executed as a
// probe function itself.
func (d *derpProber) ProbeMap(ctx context.Context) error {
if err := d.updateMap(ctx); err != nil {
return err
}
wantProbes := map[string]bool{}
d.Lock()
defer d.Unlock()
for _, region := range d.lastDERPMap.Regions {
for _, server := range region.Nodes {
labels := map[string]string{
"region": region.RegionCode,
"region_id": strconv.Itoa(region.RegionID),
"hostname": server.HostName,
}
n := fmt.Sprintf("derp/%s/%s/tls", region.RegionCode, server.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP TLS probe for %s (%s)", server.Name, region.RegionName)
d.probes[n] = d.p.Run(n, d.tlsInterval, labels, d.tlsProbeFn(server.HostName+":443"))
}
for idx, ipStr := range []string{server.IPv6, server.IPv4} {
n = fmt.Sprintf("derp/%s/%s/udp", region.RegionCode, server.Name)
if idx == 0 {
n = n + "6"
}
if ipStr == "" || server.STUNPort == -1 {
continue
}
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP UDP probe for %s (%s)", server.Name, n)
d.probes[n] = d.p.Run(n, d.udpInterval, labels, d.udpProbeFn(ipStr, server.STUNPort))
}
}
for _, to := range region.Nodes {
n = fmt.Sprintf("derp/%s/%s/%s/mesh", region.RegionCode, server.Name, to.Name)
wantProbes[n] = true
if d.probes[n] == nil {
log.Printf("adding DERP mesh probe for %s->%s (%s)", server.Name, to.Name, region.RegionName)
d.probes[n] = d.p.Run(n, d.meshInterval, labels, d.meshProbeFn(server.HostName, to.HostName))
}
}
}
}
for n, probe := range d.probes {
if !wantProbes[n] {
log.Printf("removing DERP probe %s", n)
probe.Close()
delete(d.probes, n)
}
}
return nil
}
func (d *derpProber) probeMesh(from, to string) ProbeFunc {
return func(ctx context.Context) error {
d.Lock()
dm := d.lastDERPMap
fromN, ok := d.nodes[from]
if !ok {
d.Unlock()
return fmt.Errorf("could not find derp node %s", from)
}
toN, ok := d.nodes[to]
if !ok {
d.Unlock()
return fmt.Errorf("could not find derp node %s", to)
}
d.Unlock()
// TODO: instead of ignoring latency, export it as a separate metric.
_, err := derpProbeNodePair(ctx, dm, fromN, toN)
return err
}
}
func (d *derpProber) updateMap(ctx context.Context) error {
req, err := http.NewRequestWithContext(ctx, "GET", d.derpMapURL, nil)
if err != nil {
return nil
}
res, err := httpOrFileClient.Do(req)
if err != nil {
d.Lock()
defer d.Unlock()
if d.lastDERPMap != nil && time.Since(d.lastDERPMapAt) < 10*time.Minute {
log.Printf("Error while fetching DERP map, using cached one: %s", err)
// Assume that control is restarting and use
// the same one for a bit.
return nil
}
return err
}
defer res.Body.Close()
if res.StatusCode != 200 {
return fmt.Errorf("fetching %s: %s", d.derpMapURL, res.Status)
}
dm := new(tailcfg.DERPMap)
if err := json.NewDecoder(res.Body).Decode(dm); err != nil {
return fmt.Errorf("decoding %s JSON: %v", d.derpMapURL, err)
}
d.Lock()
defer d.Unlock()
d.lastDERPMap = dm
d.lastDERPMapAt = time.Now()
d.nodes = make(map[string]*tailcfg.DERPNode)
for _, reg := range d.lastDERPMap.Regions {
for _, n := range reg.Nodes {
if existing, ok := d.nodes[n.HostName]; ok {
return fmt.Errorf("derpmap has duplicate nodes: %+v and %+v", existing, n)
}
d.nodes[n.HostName] = n
}
}
return nil
}
func (d *derpProber) ProbeUDP(ipaddr string, port int) ProbeFunc {
return func(ctx context.Context) error {
_, err := derpProbeUDP(ctx, ipaddr, port)
return err
}
}
func derpProbeUDP(ctx context.Context, ipStr string, port int) (latency time.Duration, err error) {
pc, err := net.ListenPacket("udp", ":0")
if err != nil {
return 0, err
}
defer pc.Close()
uc := pc.(*net.UDPConn)
tx := stun.NewTxID()
req := stun.Request(tx)
if port == 0 {
port = 3478
}
for {
ip := net.ParseIP(ipStr)
_, err := uc.WriteToUDP(req, &net.UDPAddr{IP: ip, Port: port})
if err != nil {
return 0, err
}
// Binding requests and responses are fairly small (~40 bytes),
// but in practice a STUN response can be up to the size of the
// path MTU, so we use a jumbo frame size buffer here.
buf := make([]byte, 9000)
uc.SetReadDeadline(time.Now().Add(2 * time.Second))
t0 := time.Now()
n, _, err := uc.ReadFromUDP(buf)
d := time.Since(t0)
if err != nil {
if ctx.Err() != nil {
return 0, fmt.Errorf("timeout reading from %v: %v", ip, err)
}
if d < time.Second {
return 0, fmt.Errorf("error reading from %v: %v", ip, err)
}
time.Sleep(100 * time.Millisecond)
continue
}
txBack, _, err := stun.ParseResponse(buf[:n])
if err != nil {
return 0, fmt.Errorf("parsing STUN response from %v: %v", ip, err)
}
if txBack != tx {
return 0, fmt.Errorf("read wrong tx back from %v", ip)
}
if latency == 0 || d < latency {
latency = d
}
break
}
return latency, nil
}
func derpProbeNodePair(ctx context.Context, dm *tailcfg.DERPMap, from, to *tailcfg.DERPNode) (latency time.Duration, err error) {
fromc, err := newConn(ctx, dm, from)
if err != nil {
return 0, err
}
defer fromc.Close()
toc, err := newConn(ctx, dm, to)
if err != nil {
return 0, err
}
defer toc.Close()
// Wait a bit for from's node to hear about to existing on the
// other node in the region, in the case where the two nodes
// are different.
if from.Name != to.Name {
time.Sleep(100 * time.Millisecond) // pretty arbitrary
}
latency, err = runDerpProbeNodePair(ctx, from, to, fromc, toc)
if err != nil {
// Record pubkeys on failed probes to aid investigation.
err = fmt.Errorf("%s -> %s: %w",
fromc.SelfPublicKey().ShortString(),
toc.SelfPublicKey().ShortString(), err)
}
return latency, err
}
func runDerpProbeNodePair(ctx context.Context, from, to *tailcfg.DERPNode, fromc, toc *derphttp.Client) (latency time.Duration, err error) {
// Make a random packet
pkt := make([]byte, 8)
crand.Read(pkt)
t0 := time.Now()
// Send the random packet.
sendc := make(chan error, 1)
go func() {
sendc <- fromc.Send(toc.SelfPublicKey(), pkt)
}()
select {
case <-ctx.Done():
return 0, fmt.Errorf("timeout sending via %q: %w", from.Name, ctx.Err())
case err := <-sendc:
if err != nil {
return 0, fmt.Errorf("error sending via %q: %w", from.Name, err)
}
}
// Receive the random packet.
recvc := make(chan any, 1) // either derp.ReceivedPacket or error
go func() {
for {
m, err := toc.Recv()
if err != nil {
recvc <- err
return
}
switch v := m.(type) {
case derp.ReceivedPacket:
recvc <- v
default:
log.Printf("%v: ignoring Recv frame type %T", to.Name, v)
// Loop.
}
}
}()
select {
case <-ctx.Done():
return 0, fmt.Errorf("timeout receiving from %q: %w", to.Name, ctx.Err())
case v := <-recvc:
if err, ok := v.(error); ok {
return 0, fmt.Errorf("error receiving from %q: %w", to.Name, err)
}
p := v.(derp.ReceivedPacket)
if p.Source != fromc.SelfPublicKey() {
return 0, fmt.Errorf("got data packet from unexpected source, %v", p.Source)
}
if !bytes.Equal(p.Data, pkt) {
return 0, fmt.Errorf("unexpected data packet %q", p.Data)
}
}
return time.Since(t0), nil
}
func newConn(ctx context.Context, dm *tailcfg.DERPMap, n *tailcfg.DERPNode) (*derphttp.Client, error) {
// To avoid spamming the log with regular connection messages.
l := logger.Filtered(log.Printf, func(s string) bool {
return !strings.Contains(s, "derphttp.Client.Connect: connecting to")
})
priv := key.NewNode()
dc := derphttp.NewRegionClient(priv, l, nil /* no netMon */, func() *tailcfg.DERPRegion {
rid := n.RegionID
// Allow the prober to monitor nodes marked as STUN only in the default map
n.STUNOnly = false
return &tailcfg.DERPRegion{
RegionID: rid,
RegionCode: fmt.Sprintf("%s-%s", dm.Regions[rid].RegionCode, n.Name),
RegionName: dm.Regions[rid].RegionName,
Nodes: []*tailcfg.DERPNode{n},
}
})
dc.IsProber = true
err := dc.Connect(ctx)
if err != nil {
return nil, err
}
cs, ok := dc.TLSConnectionState()
if !ok {
dc.Close()
return nil, errors.New("no TLS state")
}
if len(cs.PeerCertificates) == 0 {
dc.Close()
return nil, errors.New("no peer certificates")
}
if cs.ServerName != n.HostName {
dc.Close()
return nil, fmt.Errorf("TLS server name %q != derp hostname %q", cs.ServerName, n.HostName)
}
errc := make(chan error, 1)
go func() {
m, err := dc.Recv()
if err != nil {
errc <- err
return
}
switch m.(type) {
case derp.ServerInfoMessage:
errc <- nil
default:
errc <- fmt.Errorf("unexpected first message type %T", errc)
}
}()
select {
case err := <-errc:
if err != nil {
go dc.Close()
return nil, err
}
case <-ctx.Done():
go dc.Close()
return nil, fmt.Errorf("timeout waiting for ServerInfoMessage: %w", ctx.Err())
}
return dc, nil
}
var httpOrFileClient = &http.Client{Transport: httpOrFileTransport()}
func httpOrFileTransport() http.RoundTripper {
tr := http.DefaultTransport.(*http.Transport).Clone()
tr.RegisterProtocol("file", http.NewFileTransport(http.Dir("/")))
return tr
}