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tailscale/derp/derphttp/derphttp_client.go

762 lines
20 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 derphttp implements DERP-over-HTTP.
//
// This makes DERP look exactly like WebSockets.
// A server can implement DERP over HTTPS and even if the TLS connection
// intercepted using a fake root CA, unless the interceptor knows how to
// detect DERP packets, it will look like a web socket.
package derphttp
import (
"bufio"
"context"
"crypto/tls"
"crypto/x509"
"errors"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"net/http"
"net/url"
"os"
"strings"
"sync"
"time"
"go4.org/mem"
"inet.af/netaddr"
"tailscale.com/derp"
"tailscale.com/net/dnscache"
"tailscale.com/net/netns"
"tailscale.com/net/tlsdial"
"tailscale.com/net/tshttpproxy"
"tailscale.com/tailcfg"
"tailscale.com/types/key"
"tailscale.com/types/logger"
)
// Client is a DERP-over-HTTP client.
//
// It automatically reconnects on error retry. That is, a failed Send or
// Recv will report the error and not retry, but subsequent calls to
// Send/Recv will completely re-establish the connection (unless Close
// has been called).
type Client struct {
TLSConfig *tls.Config // optional; nil means default
DNSCache *dnscache.Resolver // optional; nil means no caching
MeshKey string // optional; for trusted clients
privateKey key.Private
logf logger.Logf
// Either url or getRegion is non-nil:
url *url.URL
getRegion func() *tailcfg.DERPRegion
ctx context.Context // closed via cancelCtx in Client.Close
cancelCtx context.CancelFunc
mu sync.Mutex
preferred bool
closed bool
netConn io.Closer
client *derp.Client
connGen int // incremented once per new connection; valid values are >0
serverPubKey key.Public
}
// NewRegionClient returns a new DERP-over-HTTP client. It connects lazily.
// To trigger a connection, use Connect.
func NewRegionClient(privateKey key.Private, logf logger.Logf, getRegion func() *tailcfg.DERPRegion) *Client {
ctx, cancel := context.WithCancel(context.Background())
c := &Client{
privateKey: privateKey,
logf: logf,
getRegion: getRegion,
ctx: ctx,
cancelCtx: cancel,
}
return c
}
// NewNetcheckClient returns a Client that's only able to have its DialRegion method called.
// It's used by the netcheck package.
func NewNetcheckClient(logf logger.Logf) *Client {
return &Client{logf: logf}
}
// NewClient returns a new DERP-over-HTTP client. It connects lazily.
// To trigger a connection, use Connect.
func NewClient(privateKey key.Private, serverURL string, logf logger.Logf) (*Client, error) {
u, err := url.Parse(serverURL)
if err != nil {
return nil, fmt.Errorf("derphttp.NewClient: %v", err)
}
if urlPort(u) == "" {
return nil, fmt.Errorf("derphttp.NewClient: invalid URL scheme %q", u.Scheme)
}
ctx, cancel := context.WithCancel(context.Background())
c := &Client{
privateKey: privateKey,
logf: logf,
url: u,
ctx: ctx,
cancelCtx: cancel,
}
return c, nil
}
// Connect connects or reconnects to the server, unless already connected.
// It returns nil if there was already a good connection, or if one was made.
func (c *Client) Connect(ctx context.Context) error {
_, _, err := c.connect(ctx, "derphttp.Client.Connect")
return err
}
// ServerPublicKey returns the server's public key.
//
// It only returns a non-zero value once a connection has succeeded
// from an earlier call.
func (c *Client) ServerPublicKey() key.Public {
c.mu.Lock()
defer c.mu.Unlock()
return c.serverPubKey
}
func urlPort(u *url.URL) string {
if p := u.Port(); p != "" {
return p
}
switch u.Scheme {
case "https":
return "443"
case "http":
return "80"
}
return ""
}
func (c *Client) targetString(reg *tailcfg.DERPRegion) string {
if c.url != nil {
return c.url.String()
}
return fmt.Sprintf("region %d (%v)", reg.RegionID, reg.RegionCode)
}
func (c *Client) useHTTPS() bool {
if c.url != nil && c.url.Scheme == "http" {
return false
}
return true
}
// tlsServerName returns the tls.Config.ServerName value (for the TLS ClientHello).
func (c *Client) tlsServerName(node *tailcfg.DERPNode) string {
if c.url != nil {
return c.url.Host
}
return node.HostName
}
func (c *Client) urlString(node *tailcfg.DERPNode) string {
if c.url != nil {
return c.url.String()
}
return fmt.Sprintf("https://%s/derp", node.HostName)
}
func (c *Client) connect(ctx context.Context, caller string) (client *derp.Client, connGen int, err error) {
c.mu.Lock()
defer c.mu.Unlock()
if c.closed {
return nil, 0, ErrClientClosed
}
if c.client != nil {
return c.client, c.connGen, nil
}
// timeout is the fallback maximum time (if ctx doesn't limit
// it further) to do all of: DNS + TCP + TLS + HTTP Upgrade +
// DERP upgrade.
const timeout = 10 * time.Second
ctx, cancel := context.WithTimeout(ctx, timeout)
go func() {
select {
case <-ctx.Done():
// Either timeout fired (handled below), or
// we're returning via the defer cancel()
// below.
case <-c.ctx.Done():
// Propagate a Client.Close call into
// cancelling this context.
cancel()
}
}()
defer cancel()
var reg *tailcfg.DERPRegion // nil when using c.url to dial
if c.getRegion != nil {
reg = c.getRegion()
if reg == nil {
return nil, 0, errors.New("DERP region not available")
}
}
var tcpConn net.Conn
defer func() {
if err != nil {
if ctx.Err() != nil {
err = fmt.Errorf("%v: %v", ctx.Err(), err)
}
err = fmt.Errorf("%s connect to %v: %v", caller, c.targetString(reg), err)
if tcpConn != nil {
go tcpConn.Close()
}
}
}()
var node *tailcfg.DERPNode // nil when using c.url to dial
if c.url != nil {
c.logf("%s: connecting to %v", caller, c.url)
tcpConn, err = c.dialURL(ctx)
} else {
c.logf("%s: connecting to derp-%d (%v)", caller, reg.RegionID, reg.RegionCode)
tcpConn, node, err = c.dialRegion(ctx, reg)
}
if err != nil {
return nil, 0, err
}
// Now that we have a TCP connection, force close it if the
// TLS handshake + DERP setup takes too long.
done := make(chan struct{})
defer close(done)
go func() {
select {
case <-done:
// Normal path. Upgrade occurred in time.
case <-ctx.Done():
select {
case <-done:
// Normal path. Upgrade occurred in time.
// But the ctx.Done() is also done because
// the "defer cancel()" above scheduled
// before this goroutine.
default:
// The TLS or HTTP or DERP exchanges didn't complete
// in time. Force close the TCP connection to force
// them to fail quickly.
tcpConn.Close()
}
}
}()
var httpConn net.Conn // a TCP conn or a TLS conn; what we speak HTTP to
var serverPub key.Public // or zero if unknown (if not using TLS or TLS middlebox eats it)
var serverProtoVersion int
if c.useHTTPS() {
tlsConn := c.tlsClient(tcpConn, node)
httpConn = tlsConn
// Force a handshake now (instead of waiting for it to
// be done implicitly on read/write) so we can check
// the ConnectionState.
if err := tlsConn.Handshake(); err != nil {
return nil, 0, err
}
// We expect to be using TLS 1.3 to our own servers, and only
// starting at TLS 1.3 are the server's returned certificates
// encrypted, so only look for and use our "meta cert" if we're
// using TLS 1.3. If we're not using TLS 1.3, it might be a user
// running cmd/derper themselves with a different configuration,
// in which case we can avoid this fast-start optimization.
// (If a corporate proxy is MITM'ing TLS 1.3 connections with
// corp-mandated TLS root certs than all bets are off anyway.)
// Note that we're not specifically concerned about TLS downgrade
// attacks. TLS handles that fine:
// https://blog.gypsyengineer.com/en/security/how-does-tls-1-3-protect-against-downgrade-attacks.html
connState := tlsConn.ConnectionState()
if connState.Version >= tls.VersionTLS13 {
serverPub, serverProtoVersion = parseMetaCert(connState.PeerCertificates)
}
} else {
httpConn = tcpConn
}
brw := bufio.NewReadWriter(bufio.NewReader(httpConn), bufio.NewWriter(httpConn))
var derpClient *derp.Client
req, err := http.NewRequest("GET", c.urlString(node), nil)
if err != nil {
return nil, 0, err
}
req.Header.Set("Upgrade", "DERP")
req.Header.Set("Connection", "Upgrade")
if !serverPub.IsZero() && serverProtoVersion != 0 {
// parseMetaCert found the server's public key (no TLS
// middlebox was in the way), so skip the HTTP upgrade
// exchange. See https://github.com/tailscale/tailscale/issues/693
// for an overview. We still send the HTTP request
// just to get routed into the server's HTTP Handler so it
// can Hijack the request, but we signal with a special header
// that we don't want to deal with its HTTP response.
req.Header.Set(fastStartHeader, "1") // suppresses the server's HTTP response
if err := req.Write(brw); err != nil {
return nil, 0, err
}
// No need to flush the HTTP request. the derp.Client's initial
// client auth frame will flush it.
} else {
if err := req.Write(brw); err != nil {
return nil, 0, err
}
if err := brw.Flush(); err != nil {
return nil, 0, err
}
resp, err := http.ReadResponse(brw.Reader, req)
if err != nil {
return nil, 0, err
}
if resp.StatusCode != http.StatusSwitchingProtocols {
b, _ := ioutil.ReadAll(resp.Body)
resp.Body.Close()
return nil, 0, fmt.Errorf("GET failed: %v: %s", err, b)
}
}
derpClient, err = derp.NewClient(c.privateKey, httpConn, brw, c.logf, derp.MeshKey(c.MeshKey), derp.ServerPublicKey(serverPub))
if err != nil {
return nil, 0, err
}
if c.preferred {
if err := derpClient.NotePreferred(true); err != nil {
go httpConn.Close()
return nil, 0, err
}
}
c.serverPubKey = derpClient.ServerPublicKey()
c.client = derpClient
c.netConn = tcpConn
c.connGen++
return c.client, c.connGen, nil
}
func (c *Client) dialURL(ctx context.Context) (net.Conn, error) {
host := c.url.Hostname()
hostOrIP := host
dialer := netns.NewDialer()
if c.DNSCache != nil {
ip, err := c.DNSCache.LookupIP(ctx, host)
if err == nil {
hostOrIP = ip.String()
}
if err != nil && netns.IsSOCKSDialer(dialer) {
// Return an error if we're not using a dial
// proxy that can do DNS lookups for us.
return nil, err
}
}
tcpConn, err := dialer.DialContext(ctx, "tcp", net.JoinHostPort(hostOrIP, urlPort(c.url)))
if err != nil {
return nil, fmt.Errorf("dial of %v: %v", host, err)
}
return tcpConn, nil
}
// dialRegion returns a TCP connection to the provided region, trying
// each node in order (with dialNode) until one connects or ctx is
// done.
func (c *Client) dialRegion(ctx context.Context, reg *tailcfg.DERPRegion) (net.Conn, *tailcfg.DERPNode, error) {
if len(reg.Nodes) == 0 {
return nil, nil, fmt.Errorf("no nodes for %s", c.targetString(reg))
}
var firstErr error
for _, n := range reg.Nodes {
if n.STUNOnly {
if firstErr == nil {
firstErr = fmt.Errorf("no non-STUNOnly nodes for %s", c.targetString(reg))
}
continue
}
c, err := c.dialNode(ctx, n)
if err == nil {
return c, n, nil
}
if firstErr == nil {
firstErr = err
}
}
return nil, nil, firstErr
}
func (c *Client) tlsClient(nc net.Conn, node *tailcfg.DERPNode) *tls.Conn {
tlsConf := tlsdial.Config(c.tlsServerName(node), c.TLSConfig)
if node != nil {
if node.DERPTestPort != 0 {
tlsConf.InsecureSkipVerify = true
}
if node.CertName != "" {
tlsdial.SetConfigExpectedCert(tlsConf, node.CertName)
}
}
if n := os.Getenv("SSLKEYLOGFILE"); n != "" {
f, err := os.OpenFile(n, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
if err != nil {
log.Fatal(err)
}
log.Printf("WARNING: writing to SSLKEYLOGFILE %v", n)
tlsConf.KeyLogWriter = f
}
return tls.Client(nc, tlsConf)
}
func (c *Client) DialRegionTLS(ctx context.Context, reg *tailcfg.DERPRegion) (tlsConn *tls.Conn, connClose io.Closer, err error) {
tcpConn, node, err := c.dialRegion(ctx, reg)
if err != nil {
return nil, nil, err
}
done := make(chan bool) // unbufferd
defer close(done)
tlsConn = c.tlsClient(tcpConn, node)
go func() {
select {
case <-done:
case <-ctx.Done():
tcpConn.Close()
}
}()
err = tlsConn.Handshake()
if err != nil {
return nil, nil, err
}
select {
case done <- true:
return tlsConn, tcpConn, nil
case <-ctx.Done():
return nil, nil, ctx.Err()
}
}
func (c *Client) dialContext(ctx context.Context, proto, addr string) (net.Conn, error) {
return netns.NewDialer().DialContext(ctx, proto, addr)
}
// shouldDialProto reports whether an explicitly provided IPv4 or IPv6
// address (given in s) is valid. An empty value means to dial, but to
// use DNS. The predicate function reports whether the non-empty
// string s contained a valid IP address of the right family.
func shouldDialProto(s string, pred func(netaddr.IP) bool) bool {
if s == "" {
return true
}
ip, _ := netaddr.ParseIP(s)
return pred(ip)
}
const dialNodeTimeout = 1500 * time.Millisecond
// dialNode returns a TCP connection to node n, racing IPv4 and IPv6
// (both as applicable) against each other.
// A node is only given dialNodeTimeout to connect.
//
// TODO(bradfitz): longer if no options remain perhaps? ... Or longer
// overall but have dialRegion start overlapping races?
func (c *Client) dialNode(ctx context.Context, n *tailcfg.DERPNode) (net.Conn, error) {
// First see if we need to use an HTTP proxy.
proxyReq := &http.Request{
Method: "GET", // doesn't really matter
URL: &url.URL{
Scheme: "https",
Host: c.tlsServerName(n),
Path: "/", // unused
},
}
if proxyURL, err := tshttpproxy.ProxyFromEnvironment(proxyReq); err == nil && proxyURL != nil {
return c.dialNodeUsingProxy(ctx, n, proxyURL)
}
type res struct {
c net.Conn
err error
}
resc := make(chan res) // must be unbuffered
ctx, cancel := context.WithTimeout(ctx, dialNodeTimeout)
defer cancel()
nwait := 0
startDial := func(dstPrimary, proto string) {
nwait++
go func() {
dst := dstPrimary
if dst == "" {
dst = n.HostName
}
port := "443"
if n.DERPTestPort != 0 {
port = fmt.Sprint(n.DERPTestPort)
}
c, err := c.dialContext(ctx, proto, net.JoinHostPort(dst, port))
select {
case resc <- res{c, err}:
case <-ctx.Done():
if c != nil {
c.Close()
}
}
}()
}
if shouldDialProto(n.IPv4, netaddr.IP.Is4) {
startDial(n.IPv4, "tcp4")
}
if shouldDialProto(n.IPv6, netaddr.IP.Is6) {
startDial(n.IPv6, "tcp6")
}
if nwait == 0 {
return nil, errors.New("both IPv4 and IPv6 are explicitly disabled for node")
}
var firstErr error
for {
select {
case res := <-resc:
nwait--
if res.err == nil {
return res.c, nil
}
if firstErr == nil {
firstErr = res.err
}
if nwait == 0 {
return nil, firstErr
}
case <-ctx.Done():
return nil, ctx.Err()
}
}
}
func firstStr(a, b string) string {
if a != "" {
return a
}
return b
}
// dialNodeUsingProxy connects to n using a CONNECT to the HTTP(s) proxy in proxyURL.
func (c *Client) dialNodeUsingProxy(ctx context.Context, n *tailcfg.DERPNode, proxyURL *url.URL) (proxyConn net.Conn, err error) {
pu := proxyURL
if pu.Scheme == "https" {
var d tls.Dialer
proxyConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(pu.Hostname(), firstStr(pu.Port(), "443")))
} else {
var d net.Dialer
proxyConn, err = d.DialContext(ctx, "tcp", net.JoinHostPort(pu.Hostname(), firstStr(pu.Port(), "80")))
}
defer func() {
if err != nil && proxyConn != nil {
// In a goroutine in case it's a *tls.Conn (that can block on Close)
// TODO(bradfitz): track the underlying tcp.Conn and just close that instead.
go proxyConn.Close()
}
}()
if err != nil {
return nil, err
}
done := make(chan struct{})
defer close(done)
go func() {
select {
case <-done:
return
case <-ctx.Done():
proxyConn.Close()
}
}()
target := net.JoinHostPort(n.HostName, "443")
if _, err := fmt.Fprintf(proxyConn, "CONNECT %s HTTP/1.1\r\nHost: %s\r\n\r\n", target, pu.Hostname()); err != nil {
if ctx.Err() != nil {
return nil, ctx.Err()
}
return nil, err
}
br := bufio.NewReader(proxyConn)
res, err := http.ReadResponse(br, nil)
if err != nil {
if ctx.Err() != nil {
return nil, ctx.Err()
}
c.logf("derphttp: CONNECT dial to %s: %v", target, err)
return nil, err
}
c.logf("derphttp: CONNECT dial to %s: %v", target, res.Status)
if res.StatusCode != 200 {
return nil, fmt.Errorf("invalid response status from HTTP proxy %s on CONNECT to %s: %v", pu, target, res.Status)
}
return proxyConn, nil
}
func (c *Client) Send(dstKey key.Public, b []byte) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.Send")
if err != nil {
return err
}
if err := client.Send(dstKey, b); err != nil {
c.closeForReconnect(client)
}
return err
}
func (c *Client) ForwardPacket(from, to key.Public, b []byte) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.ForwardPacket")
if err != nil {
return err
}
if err := client.ForwardPacket(from, to, b); err != nil {
c.closeForReconnect(client)
}
return err
}
// NotePreferred notes whether this Client is the caller's preferred
// (home) DERP node. It's only used for stats.
func (c *Client) NotePreferred(v bool) {
c.mu.Lock()
if c.preferred == v {
c.mu.Unlock()
return
}
c.preferred = v
client := c.client
c.mu.Unlock()
if client != nil {
if err := client.NotePreferred(v); err != nil {
c.closeForReconnect(client)
}
}
}
// WatchConnectionChanges sends a request to subscribe to
// notifications about clients connecting & disconnecting.
//
// Only trusted connections (using MeshKey) are allowed to use this.
func (c *Client) WatchConnectionChanges() error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.WatchConnectionChanges")
if err != nil {
return err
}
err = client.WatchConnectionChanges()
if err != nil {
c.closeForReconnect(client)
}
return err
}
// ClosePeer asks the server to close target's TCP connection.
//
// Only trusted connections (using MeshKey) are allowed to use this.
func (c *Client) ClosePeer(target key.Public) error {
client, _, err := c.connect(context.TODO(), "derphttp.Client.ClosePeer")
if err != nil {
return err
}
err = client.ClosePeer(target)
if err != nil {
c.closeForReconnect(client)
}
return err
}
// Recv reads a message from c. The returned message may alias memory from Client.
// The message should only be used until the next Client call.
func (c *Client) Recv() (derp.ReceivedMessage, error) {
m, _, err := c.RecvDetail()
return m, err
}
// RecvDetail is like Recv, but additional returns the connection generation on each message.
// The connGen value is incremented every time the derphttp.Client reconnects to the server.
func (c *Client) RecvDetail() (m derp.ReceivedMessage, connGen int, err error) {
client, connGen, err := c.connect(context.TODO(), "derphttp.Client.Recv")
if err != nil {
return nil, 0, err
}
m, err = client.Recv()
if err != nil {
c.closeForReconnect(client)
}
return m, connGen, err
}
// Close closes the client. It will not automatically reconnect after
// being closed.
func (c *Client) Close() error {
c.cancelCtx() // not in lock, so it can cancel Connect, which holds mu
c.mu.Lock()
defer c.mu.Unlock()
if c.closed {
return ErrClientClosed
}
c.closed = true
if c.netConn != nil {
c.netConn.Close()
}
return nil
}
// closeForReconnect closes the underlying network connection and
// zeros out the client field so future calls to Connect will
// reconnect.
//
// The provided brokenClient is the client to forget. If current
// client is not brokenClient, closeForReconnect does nothing. (This
// prevents a send and receive goroutine from failing at the ~same
// time and both calling closeForReconnect and the caller goroutines
// forever calling closeForReconnect in lockstep endlessly;
// https://github.com/tailscale/tailscale/pull/264)
func (c *Client) closeForReconnect(brokenClient *derp.Client) {
c.mu.Lock()
defer c.mu.Unlock()
if c.client != brokenClient {
return
}
if c.netConn != nil {
c.netConn.Close()
c.netConn = nil
}
c.client = nil
}
var ErrClientClosed = errors.New("derphttp.Client closed")
func parseMetaCert(certs []*x509.Certificate) (serverPub key.Public, serverProtoVersion int) {
for _, cert := range certs {
if cn := cert.Subject.CommonName; strings.HasPrefix(cn, "derpkey") {
var err error
serverPub, err = key.NewPublicFromHexMem(mem.S(strings.TrimPrefix(cn, "derpkey")))
if err == nil && cert.SerialNumber.BitLen() <= 8 { // supports up to version 255
return serverPub, int(cert.SerialNumber.Int64())
}
}
}
return key.Public{}, 0
}