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tailscale/derp/derp_client.go

540 lines
15 KiB
Go

// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package derp
import (
"bufio"
crand "crypto/rand"
"encoding/binary"
"encoding/json"
"errors"
"fmt"
"io"
"sync"
"time"
"golang.org/x/crypto/nacl/box"
"tailscale.com/types/key"
"tailscale.com/types/logger"
)
// Client is a DERP client.
type Client struct {
serverKey key.Public // of the DERP server; not a machine or node key
privateKey key.Private
publicKey key.Public // of privateKey
logf logger.Logf
nc Conn
br *bufio.Reader
meshKey string
canAckPings bool
isProber bool
wmu sync.Mutex // hold while writing to bw
bw *bufio.Writer
// Owned by Recv:
peeked int // bytes to discard on next Recv
readErr error // sticky read error
}
// ClientOpt is an option passed to NewClient.
type ClientOpt interface {
update(*clientOpt)
}
type clientOptFunc func(*clientOpt)
func (f clientOptFunc) update(o *clientOpt) { f(o) }
// clientOpt are the options passed to newClient.
type clientOpt struct {
MeshKey string
ServerPub key.Public
CanAckPings bool
IsProber bool
}
// MeshKey returns a ClientOpt to pass to the DERP server during connect to get
// access to join the mesh.
//
// An empty key means to not use a mesh key.
func MeshKey(key string) ClientOpt { return clientOptFunc(func(o *clientOpt) { o.MeshKey = key }) }
// IsProber returns a ClientOpt to pass to the DERP server during connect to
// declare that this client is a a prober.
func IsProber(v bool) ClientOpt { return clientOptFunc(func(o *clientOpt) { o.IsProber = v }) }
// ServerPublicKey returns a ClientOpt to declare that the server's DERP public key is known.
// If key is the zero value, the returned ClientOpt is a no-op.
func ServerPublicKey(key key.Public) ClientOpt {
return clientOptFunc(func(o *clientOpt) { o.ServerPub = key })
}
// CanAckPings returns a ClientOpt to set whether it advertises to the
// server that it's capable of acknowledging ping requests.
func CanAckPings(v bool) ClientOpt {
return clientOptFunc(func(o *clientOpt) { o.CanAckPings = v })
}
func NewClient(privateKey key.Private, nc Conn, brw *bufio.ReadWriter, logf logger.Logf, opts ...ClientOpt) (*Client, error) {
var opt clientOpt
for _, o := range opts {
if o == nil {
return nil, errors.New("nil ClientOpt")
}
o.update(&opt)
}
return newClient(privateKey, nc, brw, logf, opt)
}
func newClient(privateKey key.Private, nc Conn, brw *bufio.ReadWriter, logf logger.Logf, opt clientOpt) (*Client, error) {
c := &Client{
privateKey: privateKey,
publicKey: privateKey.Public(),
logf: logf,
nc: nc,
br: brw.Reader,
bw: brw.Writer,
meshKey: opt.MeshKey,
canAckPings: opt.CanAckPings,
isProber: opt.IsProber,
}
if opt.ServerPub.IsZero() {
if err := c.recvServerKey(); err != nil {
return nil, fmt.Errorf("derp.Client: failed to receive server key: %v", err)
}
} else {
c.serverKey = opt.ServerPub
}
if err := c.sendClientKey(); err != nil {
return nil, fmt.Errorf("derp.Client: failed to send client key: %v", err)
}
return c, nil
}
func (c *Client) recvServerKey() error {
var buf [40]byte
t, flen, err := readFrame(c.br, 1<<10, buf[:])
if err == io.ErrShortBuffer {
// For future-proofing, allow server to send more in its greeting.
err = nil
}
if err != nil {
return err
}
if flen < uint32(len(buf)) || t != frameServerKey || string(buf[:len(magic)]) != magic {
return errors.New("invalid server greeting")
}
copy(c.serverKey[:], buf[len(magic):])
return nil
}
func (c *Client) parseServerInfo(b []byte) (*serverInfo, error) {
const maxLength = nonceLen + maxInfoLen
fl := len(b)
if fl < nonceLen {
return nil, fmt.Errorf("short serverInfo frame")
}
if fl > maxLength {
return nil, fmt.Errorf("long serverInfo frame")
}
// TODO: add a read-nonce-and-box helper
var nonce [nonceLen]byte
copy(nonce[:], b)
msgbox := b[nonceLen:]
msg, ok := box.Open(nil, msgbox, &nonce, c.serverKey.B32(), c.privateKey.B32())
if !ok {
return nil, fmt.Errorf("failed to open naclbox from server key %x", c.serverKey[:])
}
info := new(serverInfo)
if err := json.Unmarshal(msg, info); err != nil {
return nil, fmt.Errorf("invalid JSON: %v", err)
}
return info, nil
}
type clientInfo struct {
Version int `json:"version,omitempty"`
// MeshKey optionally specifies a pre-shared key used by
// trusted clients. It's required to subscribe to the
// connection list & forward packets. It's empty for regular
// users.
MeshKey string `json:"meshKey,omitempty"`
// CanAckPings is whether the client declares it's able to ack
// pings.
CanAckPings bool
// IsProber is whether this client is a prober.
IsProber bool `json:",omitempty"`
}
func (c *Client) sendClientKey() error {
var nonce [nonceLen]byte
if _, err := crand.Read(nonce[:]); err != nil {
return err
}
msg, err := json.Marshal(clientInfo{
Version: ProtocolVersion,
MeshKey: c.meshKey,
CanAckPings: c.canAckPings,
IsProber: c.isProber,
})
if err != nil {
return err
}
msgbox := box.Seal(nil, msg, &nonce, c.serverKey.B32(), c.privateKey.B32())
buf := make([]byte, 0, nonceLen+keyLen+len(msgbox))
buf = append(buf, c.publicKey[:]...)
buf = append(buf, nonce[:]...)
buf = append(buf, msgbox...)
return writeFrame(c.bw, frameClientInfo, buf)
}
// ServerPublicKey returns the server's public key.
func (c *Client) ServerPublicKey() key.Public { return c.serverKey }
// Send sends a packet to the Tailscale node identified by dstKey.
//
// It is an error if the packet is larger than 64KB.
func (c *Client) Send(dstKey key.Public, pkt []byte) error { return c.send(dstKey, pkt) }
func (c *Client) send(dstKey key.Public, pkt []byte) (ret error) {
defer func() {
if ret != nil {
ret = fmt.Errorf("derp.Send: %w", ret)
}
}()
if len(pkt) > MaxPacketSize {
return fmt.Errorf("packet too big: %d", len(pkt))
}
c.wmu.Lock()
defer c.wmu.Unlock()
if err := writeFrameHeader(c.bw, frameSendPacket, uint32(len(dstKey)+len(pkt))); err != nil {
return err
}
if _, err := c.bw.Write(dstKey[:]); err != nil {
return err
}
if _, err := c.bw.Write(pkt); err != nil {
return err
}
return c.bw.Flush()
}
func (c *Client) ForwardPacket(srcKey, dstKey key.Public, pkt []byte) (err error) {
defer func() {
if err != nil {
err = fmt.Errorf("derp.ForwardPacket: %w", err)
}
}()
if len(pkt) > MaxPacketSize {
return fmt.Errorf("packet too big: %d", len(pkt))
}
c.wmu.Lock()
defer c.wmu.Unlock()
timer := time.AfterFunc(5*time.Second, c.writeTimeoutFired)
defer timer.Stop()
if err := writeFrameHeader(c.bw, frameForwardPacket, uint32(keyLen*2+len(pkt))); err != nil {
return err
}
if _, err := c.bw.Write(srcKey[:]); err != nil {
return err
}
if _, err := c.bw.Write(dstKey[:]); err != nil {
return err
}
if _, err := c.bw.Write(pkt); err != nil {
return err
}
return c.bw.Flush()
}
func (c *Client) writeTimeoutFired() { c.nc.Close() }
func (c *Client) SendPong(data [8]byte) error {
c.wmu.Lock()
defer c.wmu.Unlock()
if err := writeFrameHeader(c.bw, framePong, 8); err != nil {
return err
}
if _, err := c.bw.Write(data[:]); err != nil {
return err
}
return c.bw.Flush()
}
// NotePreferred sends a packet that tells the server whether this
// client is the user's preferred server. This is only used in the
// server for stats.
func (c *Client) NotePreferred(preferred bool) (err error) {
defer func() {
if err != nil {
err = fmt.Errorf("derp.NotePreferred: %v", err)
}
}()
c.wmu.Lock()
defer c.wmu.Unlock()
if err := writeFrameHeader(c.bw, frameNotePreferred, 1); err != nil {
return err
}
var b byte = 0x00
if preferred {
b = 0x01
}
if err := c.bw.WriteByte(b); err != nil {
return err
}
return c.bw.Flush()
}
// WatchConnectionChanges sends a request to subscribe to the peer's connection list.
// It's a fatal error if the client wasn't created using MeshKey.
func (c *Client) WatchConnectionChanges() error {
c.wmu.Lock()
defer c.wmu.Unlock()
if err := writeFrameHeader(c.bw, frameWatchConns, 0); err != nil {
return err
}
return c.bw.Flush()
}
// ClosePeer asks the server to close target's TCP connection.
// It's a fatal error if the client wasn't created using MeshKey.
func (c *Client) ClosePeer(target key.Public) error {
c.wmu.Lock()
defer c.wmu.Unlock()
return writeFrame(c.bw, frameClosePeer, target[:])
}
// ReceivedMessage represents a type returned by Client.Recv. Unless
// otherwise documented, the returned message aliases the byte slice
// provided to Recv and thus the message is only as good as that
// buffer, which is up to the caller.
type ReceivedMessage interface {
msg()
}
// ReceivedPacket is a ReceivedMessage representing an incoming packet.
type ReceivedPacket struct {
Source key.Public
// Data is the received packet bytes. It aliases the memory
// passed to Client.Recv.
Data []byte
}
func (ReceivedPacket) msg() {}
// PeerGoneMessage is a ReceivedMessage that indicates that the client
// identified by the underlying public key had previously sent you a
// packet but has now disconnected from the server.
type PeerGoneMessage key.Public
func (PeerGoneMessage) msg() {}
// PeerPresentMessage is a ReceivedMessage that indicates that the client
// is connected to the server. (Only used by trusted mesh clients)
type PeerPresentMessage key.Public
func (PeerPresentMessage) msg() {}
// ServerInfoMessage is sent by the server upon first connect.
type ServerInfoMessage struct{}
func (ServerInfoMessage) msg() {}
// PingMessage is a request from a client or server to reply to the
// other side with a PongMessage with the given payload.
type PingMessage [8]byte
func (PingMessage) msg() {}
// KeepAliveMessage is a one-way empty message from server to client, just to
// keep the connection alive. It's like a PingMessage, but doesn't solicit
// a reply from the client.
type KeepAliveMessage struct{}
func (KeepAliveMessage) msg() {}
// HealthMessage is a one-way message from server to client, declaring the
// connection health state.
type HealthMessage struct {
// Problem, if non-empty, is a description of why the connection
// is unhealthy.
//
// The empty string means the connection is healthy again.
//
// The default condition is healthy, so the server doesn't
// broadcast a HealthMessage until a problem exists.
Problem string
}
func (HealthMessage) msg() {}
// ServerRestartingMessage is a one-way message from server to client,
// advertising that the server is restarting.
type ServerRestartingMessage struct {
// ReconnectIn is an advisory duration that the client should wait
// before attempting to reconnect. It might be zero.
// It exists for the server to smear out the reconnects.
ReconnectIn time.Duration
// TryFor is an advisory duration for how long the client
// should attempt to reconnect before giving up and proceeding
// with its normal connection failure logic. The interval
// between retries is undefined for now.
// A server should not send a TryFor duration more than a few
// seconds.
TryFor time.Duration
}
func (ServerRestartingMessage) msg() {}
// Recv reads a message from the DERP server.
//
// The returned message may alias memory owned by the Client; it
// should only be accessed until the next call to Client.
//
// Once Recv returns an error, the Client is dead forever.
func (c *Client) Recv() (m ReceivedMessage, err error) {
return c.recvTimeout(120 * time.Second)
}
func (c *Client) recvTimeout(timeout time.Duration) (m ReceivedMessage, err error) {
if c.readErr != nil {
return nil, c.readErr
}
defer func() {
if err != nil {
err = fmt.Errorf("derp.Recv: %w", err)
c.readErr = err
}
}()
for {
c.nc.SetReadDeadline(time.Now().Add(timeout))
// Discard any peeked bytes from a previous Recv call.
if c.peeked != 0 {
if n, err := c.br.Discard(c.peeked); err != nil || n != c.peeked {
// Documented to never fail, but might as well check.
return nil, fmt.Errorf("bufio.Reader.Discard(%d bytes): got %v, %v", c.peeked, n, err)
}
c.peeked = 0
}
t, n, err := readFrameHeader(c.br)
if err != nil {
return nil, err
}
if n > 1<<20 {
return nil, fmt.Errorf("unexpectedly large frame of %d bytes returned", n)
}
var b []byte // frame payload (past the 5 byte header)
// If the frame fits in our bufio.Reader buffer, just use it.
// In practice it's 4KB (from derphttp.Client's bufio.NewReader(httpConn)) and
// in practive, WireGuard packets (and thus DERP frames) are under 1.5KB.
// So this is the common path.
if int(n) <= c.br.Size() {
b, err = c.br.Peek(int(n))
c.peeked = int(n)
} else {
// But if for some reason we read a large DERP message (which isn't necessarily
// a Wireguard packet), then just allocate memory for it.
// TODO(bradfitz): use a pool if large frames ever happen in practice.
b = make([]byte, n)
_, err = io.ReadFull(c.br, b)
}
if err != nil {
return nil, err
}
switch t {
default:
continue
case frameServerInfo:
// Server sends this at start-up. Currently unused.
// Just has a JSON message saying "version: 2",
// but the protocol seems extensible enough as-is without
// needing to wait an RTT to discover the version at startup.
// We'd prefer to give the connection to the client (magicsock)
// to start writing as soon as possible.
_, err := c.parseServerInfo(b)
if err != nil {
return nil, fmt.Errorf("invalid server info frame: %v", err)
}
// TODO: add the results of parseServerInfo to ServerInfoMessage if we ever need it.
return ServerInfoMessage{}, nil
case frameKeepAlive:
// A one-way keep-alive message that doesn't require an acknowledgement.
// This predated framePing/framePong.
return KeepAliveMessage{}, nil
case framePeerGone:
if n < keyLen {
c.logf("[unexpected] dropping short peerGone frame from DERP server")
continue
}
var pg PeerGoneMessage
copy(pg[:], b[:keyLen])
return pg, nil
case framePeerPresent:
if n < keyLen {
c.logf("[unexpected] dropping short peerPresent frame from DERP server")
continue
}
var pg PeerPresentMessage
copy(pg[:], b[:keyLen])
return pg, nil
case frameRecvPacket:
var rp ReceivedPacket
if n < keyLen {
c.logf("[unexpected] dropping short packet from DERP server")
continue
}
copy(rp.Source[:], b[:keyLen])
rp.Data = b[keyLen:n]
return rp, nil
case framePing:
var pm PingMessage
if n < 8 {
c.logf("[unexpected] dropping short ping frame")
continue
}
copy(pm[:], b[:])
return pm, nil
case frameHealth:
return HealthMessage{Problem: string(b[:])}, nil
case frameRestarting:
var m ServerRestartingMessage
if n < 8 {
c.logf("[unexpected] dropping short server restarting frame")
continue
}
m.ReconnectIn = time.Duration(binary.BigEndian.Uint32(b[0:4])) * time.Millisecond
m.TryFor = time.Duration(binary.BigEndian.Uint32(b[4:8])) * time.Millisecond
return m, nil
}
}
}