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tailscale/control/controlhttp/client.go

526 lines
16 KiB
Go

// Copyright (c) Tailscale Inc & AUTHORS
// SPDX-License-Identifier: BSD-3-Clause
//go:build !js
// Package controlhttp implements the Tailscale 2021 control protocol
// base transport over HTTP.
//
// This tunnels the protocol in control/controlbase over HTTP with a
// variety of compatibility fallbacks for handling picky or deep
// inspecting proxies.
//
// In the happy path, a client makes a single cleartext HTTP request
// to the server, the server responds with 101 Switching Protocols,
// and the control base protocol takes place over plain TCP.
//
// In the compatibility path, the client does the above over HTTPS,
// resulting in double encryption (once for the control transport, and
// once for the outer TLS layer).
package controlhttp
import (
"context"
"crypto/tls"
"encoding/base64"
"errors"
"fmt"
"io"
"math"
"net"
"net/http"
"net/http/httptrace"
"net/netip"
"net/url"
"sort"
"sync/atomic"
"time"
"tailscale.com/control/controlbase"
"tailscale.com/envknob"
"tailscale.com/net/dnscache"
"tailscale.com/net/dnsfallback"
"tailscale.com/net/netutil"
"tailscale.com/net/sockstats"
"tailscale.com/net/tlsdial"
"tailscale.com/net/tshttpproxy"
"tailscale.com/tailcfg"
"tailscale.com/util/multierr"
)
var stdDialer net.Dialer
// Dial connects to the HTTP server at this Dialer's Host:HTTPPort, requests to
// switch to the Tailscale control protocol, and returns an established control
// protocol connection.
//
// If Dial fails to connect using HTTP, it also tries to tunnel over TLS to the
// Dialer's Host:HTTPSPort as a compatibility fallback.
//
// The provided ctx is only used for the initial connection, until
// Dial returns. It does not affect the connection once established.
func (a *Dialer) Dial(ctx context.Context) (*ClientConn, error) {
if a.Hostname == "" {
return nil, errors.New("required Dialer.Hostname empty")
}
return a.dial(ctx)
}
func (a *Dialer) logf(format string, args ...any) {
if a.Logf != nil {
a.Logf(format, args...)
}
}
func (a *Dialer) getProxyFunc() func(*http.Request) (*url.URL, error) {
if a.proxyFunc != nil {
return a.proxyFunc
}
return tshttpproxy.ProxyFromEnvironment
}
// httpsFallbackDelay is how long we'll wait for a.HTTPPort to work before
// starting to try a.HTTPSPort.
func (a *Dialer) httpsFallbackDelay() time.Duration {
if forceNoise443() {
return time.Nanosecond
}
if v := a.testFallbackDelay; v != 0 {
return v
}
return 500 * time.Millisecond
}
var _ = envknob.RegisterBool("TS_USE_CONTROL_DIAL_PLAN") // to record at init time whether it's in use
func (a *Dialer) dial(ctx context.Context) (*ClientConn, error) {
// If we don't have a dial plan, just fall back to dialing the single
// host we know about.
useDialPlan := envknob.BoolDefaultTrue("TS_USE_CONTROL_DIAL_PLAN")
if !useDialPlan || a.DialPlan == nil || len(a.DialPlan.Candidates) == 0 {
return a.dialHost(ctx, netip.Addr{})
}
candidates := a.DialPlan.Candidates
// Otherwise, we try dialing per the plan. Store the highest priority
// in the list, so that if we get a connection to one of those
// candidates we can return quickly.
var highestPriority int = math.MinInt
for _, c := range candidates {
if c.Priority > highestPriority {
highestPriority = c.Priority
}
}
// This context allows us to cancel in-flight connections if we get a
// highest-priority connection before we're all done.
ctx, cancel := context.WithCancel(ctx)
defer cancel()
// Now, for each candidate, kick off a dial in parallel.
type dialResult struct {
conn *ClientConn
err error
addr netip.Addr
priority int
}
resultsCh := make(chan dialResult, len(candidates))
var pending atomic.Int32
pending.Store(int32(len(candidates)))
for _, c := range candidates {
go func(ctx context.Context, c tailcfg.ControlIPCandidate) {
var (
conn *ClientConn
err error
)
// Always send results back to our channel.
defer func() {
resultsCh <- dialResult{conn, err, c.IP, c.Priority}
if pending.Add(-1) == 0 {
close(resultsCh)
}
}()
// If non-zero, wait the configured start timeout
// before we do anything.
if c.DialStartDelaySec > 0 {
a.logf("[v2] controlhttp: waiting %.2f seconds before dialing %q @ %v", c.DialStartDelaySec, a.Hostname, c.IP)
tmr := time.NewTimer(time.Duration(c.DialStartDelaySec * float64(time.Second)))
defer tmr.Stop()
select {
case <-ctx.Done():
err = ctx.Err()
return
case <-tmr.C:
}
}
// Now, create a sub-context with the given timeout and
// try dialing the provided host.
ctx, cancel := context.WithTimeout(ctx, time.Duration(c.DialTimeoutSec*float64(time.Second)))
defer cancel()
// This will dial, and the defer above sends it back to our parent.
a.logf("[v2] controlhttp: trying to dial %q @ %v", a.Hostname, c.IP)
conn, err = a.dialHost(ctx, c.IP)
}(ctx, c)
}
var results []dialResult
for res := range resultsCh {
// If we get a response that has the highest priority, we don't
// need to wait for any of the other connections to finish; we
// can just return this connection.
//
// TODO(andrew): we could make this better by keeping track of
// the highest remaining priority dynamically, instead of just
// checking for the highest total
if res.priority == highestPriority && res.conn != nil {
a.logf("[v1] controlhttp: high-priority success dialing %q @ %v from dial plan", a.Hostname, res.addr)
// Drain the channel and any existing connections in
// the background.
go func() {
for _, res := range results {
if res.conn != nil {
res.conn.Close()
}
}
for res := range resultsCh {
if res.conn != nil {
res.conn.Close()
}
}
if a.drainFinished != nil {
close(a.drainFinished)
}
}()
return res.conn, nil
}
// This isn't a highest-priority result, so just store it until
// we're done.
results = append(results, res)
}
// After we finish this function, close any remaining open connections.
defer func() {
for _, result := range results {
// Note: below, we nil out the returned connection (if
// any) in the slice so we don't close it.
if result.conn != nil {
result.conn.Close()
}
}
// We don't drain asynchronously after this point, so notify our
// channel when we return.
if a.drainFinished != nil {
close(a.drainFinished)
}
}()
// Sort by priority, then take the first non-error response.
sort.Slice(results, func(i, j int) bool {
// NOTE: intentionally inverted so that the highest priority
// item comes first
return results[i].priority > results[j].priority
})
var (
conn *ClientConn
errs []error
)
for i, result := range results {
if result.err != nil {
errs = append(errs, result.err)
continue
}
a.logf("[v1] controlhttp: succeeded dialing %q @ %v from dial plan", a.Hostname, result.addr)
conn = result.conn
results[i].conn = nil // so we don't close it in the defer
return conn, nil
}
merr := multierr.New(errs...)
// If we get here, then we didn't get anywhere with our dial plan; fall back to just using DNS.
a.logf("controlhttp: failed dialing using DialPlan, falling back to DNS; errs=%s", merr.Error())
return a.dialHost(ctx, netip.Addr{})
}
// The TS_FORCE_NOISE_443 envknob forces the controlclient noise dialer to
// always use port 443 HTTPS connections to the controlplane and not try the
// port 80 HTTP fast path.
//
// This is currently (2023-01-17) needed for Docker Desktop's "VPNKit" proxy
// that breaks port 80 for us post-Noise-handshake, causing us to never try port
// 443. Until one of Docker's proxy and/or this package's port 443 fallback is
// fixed, this is a workaround. It might also be useful for future debugging.
var forceNoise443 = envknob.RegisterBool("TS_FORCE_NOISE_443")
var debugNoiseDial = envknob.RegisterBool("TS_DEBUG_NOISE_DIAL")
// dialHost connects to the configured Dialer.Hostname and upgrades the
// connection into a controlbase.Conn. If addr is valid, then no DNS is used
// and the connection will be made to the provided address.
func (a *Dialer) dialHost(ctx context.Context, addr netip.Addr) (*ClientConn, error) {
// Create one shared context used by both port 80 and port 443 dials.
// If port 80 is still in flight when 443 returns, this deferred cancel
// will stop the port 80 dial.
ctx, cancel := context.WithCancel(ctx)
defer cancel()
ctx = sockstats.WithSockStats(ctx, sockstats.LabelControlClientDialer, a.logf)
// u80 and u443 are the URLs we'll try to hit over HTTP or HTTPS,
// respectively, in order to do the HTTP upgrade to a net.Conn over which
// we'll speak Noise.
u80 := &url.URL{
Scheme: "http",
Host: net.JoinHostPort(a.Hostname, strDef(a.HTTPPort, "80")),
Path: serverUpgradePath,
}
u443 := &url.URL{
Scheme: "https",
Host: net.JoinHostPort(a.Hostname, strDef(a.HTTPSPort, "443")),
Path: serverUpgradePath,
}
type tryURLRes struct {
u *url.URL // input (the URL conn+err are for/from)
conn *ClientConn // result (mutually exclusive with err)
err error
}
ch := make(chan tryURLRes) // must be unbuffered
try := func(u *url.URL) {
if debugNoiseDial() {
a.logf("trying noise dial (%v, %v) ...", u, addr)
}
cbConn, err := a.dialURL(ctx, u, addr)
if debugNoiseDial() {
a.logf("noise dial (%v, %v) = (%v, %v)", u, addr, cbConn, err)
}
select {
case ch <- tryURLRes{u, cbConn, err}:
case <-ctx.Done():
if cbConn != nil {
cbConn.Close()
}
}
}
// Start the plaintext HTTP attempt first, unless disabled by the envknob.
if !forceNoise443() {
go try(u80)
}
// In case outbound port 80 blocked or MITM'ed poorly, start a backup timer
// to dial port 443 if port 80 doesn't either succeed or fail quickly.
try443Timer := time.AfterFunc(a.httpsFallbackDelay(), func() { try(u443) })
defer try443Timer.Stop()
var err80, err443 error
for {
select {
case <-ctx.Done():
return nil, fmt.Errorf("connection attempts aborted by context: %w", ctx.Err())
case res := <-ch:
if res.err == nil {
return res.conn, nil
}
switch res.u {
case u80:
// Connecting over plain HTTP failed; assume it's an HTTP proxy
// being difficult and see if we can get through over HTTPS.
err80 = res.err
// Stop the fallback timer and run it immediately. We don't use
// Timer.Reset(0) here because on AfterFuncs, that can run it
// again.
if try443Timer.Stop() {
go try(u443)
} // else we lost the race and it started already which is what we want
case u443:
err443 = res.err
default:
panic("invalid")
}
if err80 != nil && err443 != nil {
return nil, fmt.Errorf("all connection attempts failed (HTTP: %v, HTTPS: %v)", err80, err443)
}
}
}
}
// dialURL attempts to connect to the given URL.
func (a *Dialer) dialURL(ctx context.Context, u *url.URL, addr netip.Addr) (*ClientConn, error) {
init, cont, err := controlbase.ClientDeferred(a.MachineKey, a.ControlKey, a.ProtocolVersion)
if err != nil {
return nil, err
}
netConn, err := a.tryURLUpgrade(ctx, u, addr, init)
if err != nil {
return nil, err
}
cbConn, err := cont(ctx, netConn)
if err != nil {
netConn.Close()
return nil, err
}
return &ClientConn{
Conn: cbConn,
}, nil
}
// resolver returns a.DNSCache if non-nil or a new *dnscache.Resolver
// otherwise.
func (a *Dialer) resolver() *dnscache.Resolver {
if a.DNSCache != nil {
return a.DNSCache
}
return &dnscache.Resolver{
Forward: dnscache.Get().Forward,
LookupIPFallback: dnsfallback.MakeLookupFunc(a.logf, a.NetMon),
UseLastGood: true,
Logf: a.Logf, // not a.logf method; we want to propagate nil-ness
NetMon: a.NetMon,
}
}
// tryURLUpgrade connects to u, and tries to upgrade it to a net.Conn. If addr
// is valid, then no DNS is used and the connection will be made to the
// provided address.
//
// Only the provided ctx is used, not a.ctx.
func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr, init []byte) (net.Conn, error) {
var dns *dnscache.Resolver
// If we were provided an address to dial, then create a resolver that just
// returns that value; otherwise, fall back to DNS.
if addr.IsValid() {
dns = &dnscache.Resolver{
SingleHostStaticResult: []netip.Addr{addr},
SingleHost: u.Hostname(),
Logf: a.Logf, // not a.logf method; we want to propagate nil-ness
NetMon: a.NetMon,
}
} else {
dns = a.resolver()
}
var dialer dnscache.DialContextFunc
if a.Dialer != nil {
dialer = a.Dialer
} else {
dialer = stdDialer.DialContext
}
tr := http.DefaultTransport.(*http.Transport).Clone()
defer tr.CloseIdleConnections()
tr.Proxy = a.getProxyFunc()
tshttpproxy.SetTransportGetProxyConnectHeader(tr)
tr.DialContext = dnscache.Dialer(dialer, dns)
// Disable HTTP2, since h2 can't do protocol switching.
tr.TLSClientConfig.NextProtos = []string{}
tr.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{}
tr.TLSClientConfig = tlsdial.Config(a.Hostname, tr.TLSClientConfig)
if !tr.TLSClientConfig.InsecureSkipVerify {
panic("unexpected") // should be set by tlsdial.Config
}
verify := tr.TLSClientConfig.VerifyConnection
if verify == nil {
panic("unexpected") // should be set by tlsdial.Config
}
// Demote all cert verification errors to log messages. We don't actually
// care about the TLS security (because we just do the Noise crypto atop whatever
// connection we get, including HTTP port 80 plaintext) so this permits
// middleboxes to MITM their users. All they'll see is some Noise.
tr.TLSClientConfig.VerifyConnection = func(cs tls.ConnectionState) error {
if err := verify(cs); err != nil && a.Logf != nil && !a.omitCertErrorLogging {
a.Logf("warning: TLS cert verificication for %q failed: %v", a.Hostname, err)
}
return nil // regardless
}
tr.DialTLSContext = dnscache.TLSDialer(dialer, dns, tr.TLSClientConfig)
tr.DisableCompression = true
// (mis)use httptrace to extract the underlying net.Conn from the
// transport. We make exactly 1 request using this transport, so
// there will be exactly 1 GotConn call. Additionally, the
// transport handles 101 Switching Protocols correctly, such that
// the Conn will not be reused or kept alive by the transport once
// the response has been handed back from RoundTrip.
//
// In theory, the machinery of net/http should make it such that
// the trace callback happens-before we get the response, but
// there's no promise of that. So, to make sure, we use a buffered
// channel as a synchronization step to avoid data races.
//
// Note that even though we're able to extract a net.Conn via this
// mechanism, we must still keep using the eventual resp.Body to
// read from, because it includes a buffer we can't get rid of. If
// the server never sends any data after sending the HTTP
// response, we could get away with it, but violating this
// assumption leads to very mysterious transport errors (lockups,
// unexpected EOFs...), and we're bound to forget someday and
// introduce a protocol optimization at a higher level that starts
// eagerly transmitting from the server.
connCh := make(chan net.Conn, 1)
trace := httptrace.ClientTrace{
GotConn: func(info httptrace.GotConnInfo) {
connCh <- info.Conn
},
}
ctx = httptrace.WithClientTrace(ctx, &trace)
req := &http.Request{
Method: "POST",
URL: u,
Header: http.Header{
"Upgrade": []string{upgradeHeaderValue},
"Connection": []string{"upgrade"},
handshakeHeaderName: []string{base64.StdEncoding.EncodeToString(init)},
},
}
req = req.WithContext(ctx)
resp, err := tr.RoundTrip(req)
if err != nil {
return nil, err
}
if resp.StatusCode != http.StatusSwitchingProtocols {
return nil, fmt.Errorf("unexpected HTTP response: %s", resp.Status)
}
// From here on, the underlying net.Conn is ours to use, but there
// is still a read buffer attached to it within resp.Body. So, we
// must direct I/O through resp.Body, but we can still use the
// underlying net.Conn for stuff like deadlines.
var switchedConn net.Conn
select {
case switchedConn = <-connCh:
default:
}
if switchedConn == nil {
resp.Body.Close()
return nil, fmt.Errorf("httptrace didn't provide a connection")
}
if next := resp.Header.Get("Upgrade"); next != upgradeHeaderValue {
resp.Body.Close()
return nil, fmt.Errorf("server switched to unexpected protocol %q", next)
}
rwc, ok := resp.Body.(io.ReadWriteCloser)
if !ok {
resp.Body.Close()
return nil, errors.New("http Transport did not provide a writable body")
}
return netutil.NewAltReadWriteCloserConn(rwc, switchedConn), nil
}