mirror of
https://github.com/tailscale/tailscale.git
synced 2024-11-26 19:45:35 +00:00
a61825c7b8
In particular, tests showing that #3824 works. But that test doesn't actually work yet; it only gets a DERP connection. (why?) Updates #13038 Change-Id: Ie1fd1b6a38d4e90fae7e72a0b9a142a95f0b2e8f Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
316 lines
10 KiB
Go
316 lines
10 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
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// SPDX-License-Identifier: BSD-3-Clause
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// Package tlsdial generates tls.Config values and does x509 validation of
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// certs. It bakes in the LetsEncrypt roots so even if the user's machine
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// doesn't have TLS roots, we can at least connect to Tailscale's LetsEncrypt
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// services. It's the unified point where we can add shared policy on outgoing
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// TLS connections from the three places in the client that connect to Tailscale
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// (logs, control, DERP).
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package tlsdial
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import (
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"bytes"
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"context"
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"crypto/tls"
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"crypto/x509"
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"errors"
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"fmt"
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"log"
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"net"
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"net/http"
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"os"
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"sync"
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"sync/atomic"
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"time"
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"tailscale.com/envknob"
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"tailscale.com/health"
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"tailscale.com/hostinfo"
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)
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var counterFallbackOK int32 // atomic
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// If SSLKEYLOGFILE is set, it's a file to which we write our TLS private keys
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// in a way that WireShark can read.
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//
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// See https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format
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var sslKeyLogFile = os.Getenv("SSLKEYLOGFILE")
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var debug = envknob.RegisterBool("TS_DEBUG_TLS_DIAL")
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// tlsdialWarningPrinted tracks whether we've printed a warning about a given
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// hostname already, to avoid log spam for users with custom DERP servers,
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// Headscale, etc.
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var tlsdialWarningPrinted sync.Map // map[string]bool
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// Config returns a tls.Config for connecting to a server.
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// If base is non-nil, it's cloned as the base config before
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// being configured and returned.
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// If ht is non-nil, it's used to report health errors.
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func Config(host string, ht *health.Tracker, base *tls.Config) *tls.Config {
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var conf *tls.Config
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if base == nil {
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conf = new(tls.Config)
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} else {
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conf = base.Clone()
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}
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conf.ServerName = host
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if n := sslKeyLogFile; n != "" {
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f, err := os.OpenFile(n, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
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if err != nil {
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log.Fatal(err)
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}
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log.Printf("WARNING: writing to SSLKEYLOGFILE %v", n)
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conf.KeyLogWriter = f
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}
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if conf.InsecureSkipVerify {
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panic("unexpected base.InsecureSkipVerify")
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}
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if conf.VerifyConnection != nil {
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panic("unexpected base.VerifyConnection")
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}
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// Set InsecureSkipVerify to prevent crypto/tls from doing its
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// own cert verification, as do the same work that it'd do
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// (with the baked-in fallback root) in the VerifyConnection hook.
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conf.InsecureSkipVerify = true
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conf.VerifyConnection = func(cs tls.ConnectionState) (retErr error) {
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if host == "log.tailscale.io" && hostinfo.IsNATLabGuestVM() {
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// Allow log.tailscale.io TLS MITM for integration tests when
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// the client's running within a NATLab VM.
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return nil
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}
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// Perform some health checks on this certificate before we do
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// any verification.
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var selfSignedIssuer string
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if certs := cs.PeerCertificates; len(certs) > 0 && certIsSelfSigned(certs[0]) {
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selfSignedIssuer = certs[0].Issuer.String()
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}
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if ht != nil {
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defer func() {
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if retErr != nil && selfSignedIssuer != "" {
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// Self-signed certs are never valid.
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//
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// TODO(bradfitz): plumb down the selfSignedIssuer as a
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// structured health warning argument.
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ht.SetTLSConnectionError(cs.ServerName, fmt.Errorf("likely intercepted connection; certificate is self-signed by %v", selfSignedIssuer))
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} else {
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// Ensure we clear any error state for this ServerName.
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ht.SetTLSConnectionError(cs.ServerName, nil)
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if selfSignedIssuer != "" {
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// Log the self-signed issuer, but don't treat it as an error.
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log.Printf("tlsdial: warning: server cert for %q passed x509 validation but is self-signed by %q", host, selfSignedIssuer)
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}
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}
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}()
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}
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// First try doing x509 verification with the system's
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// root CA pool.
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opts := x509.VerifyOptions{
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DNSName: cs.ServerName,
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Intermediates: x509.NewCertPool(),
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}
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for _, cert := range cs.PeerCertificates[1:] {
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opts.Intermediates.AddCert(cert)
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}
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_, errSys := cs.PeerCertificates[0].Verify(opts)
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if debug() {
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log.Printf("tlsdial(sys %q): %v", host, errSys)
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}
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// Always verify with our baked-in Let's Encrypt certificate,
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// so we can log an informational message. This is useful for
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// detecting SSL MiTM.
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opts.Roots = bakedInRoots()
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_, bakedErr := cs.PeerCertificates[0].Verify(opts)
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if debug() {
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log.Printf("tlsdial(bake %q): %v", host, bakedErr)
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} else if bakedErr != nil {
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if _, loaded := tlsdialWarningPrinted.LoadOrStore(host, true); !loaded {
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if errSys == nil {
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log.Printf("tlsdial: warning: server cert for %q is not a Let's Encrypt cert", host)
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} else {
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log.Printf("tlsdial: error: server cert for %q failed to verify and is not a Let's Encrypt cert", host)
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}
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}
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}
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if errSys == nil {
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return nil
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} else if bakedErr == nil {
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atomic.AddInt32(&counterFallbackOK, 1)
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return nil
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}
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return errSys
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}
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return conf
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}
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func certIsSelfSigned(cert *x509.Certificate) bool {
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// A certificate is determined to be self-signed if the certificate's
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// subject is the same as its issuer.
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return bytes.Equal(cert.RawSubject, cert.RawIssuer)
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}
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// SetConfigExpectedCert modifies c to expect and verify that the server returns
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// a certificate for the provided certDNSName.
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//
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// This is for user-configurable client-side domain fronting support,
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// where we send one SNI value but validate a different cert.
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func SetConfigExpectedCert(c *tls.Config, certDNSName string) {
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if c.ServerName == certDNSName {
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return
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}
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if c.ServerName == "" {
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c.ServerName = certDNSName
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return
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}
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if c.VerifyPeerCertificate != nil {
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panic("refusing to override tls.Config.VerifyPeerCertificate")
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}
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// Set InsecureSkipVerify to prevent crypto/tls from doing its
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// own cert verification, but do the same work that it'd do
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// (but using certDNSName) in the VerifyPeerCertificate hook.
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c.InsecureSkipVerify = true
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c.VerifyConnection = nil
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c.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
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if len(rawCerts) == 0 {
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return errors.New("no certs presented")
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}
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certs := make([]*x509.Certificate, len(rawCerts))
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for i, asn1Data := range rawCerts {
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cert, err := x509.ParseCertificate(asn1Data)
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if err != nil {
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return err
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}
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certs[i] = cert
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}
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opts := x509.VerifyOptions{
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CurrentTime: time.Now(),
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DNSName: certDNSName,
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Intermediates: x509.NewCertPool(),
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}
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for _, cert := range certs[1:] {
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opts.Intermediates.AddCert(cert)
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}
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_, errSys := certs[0].Verify(opts)
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if debug() {
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log.Printf("tlsdial(sys %q/%q): %v", c.ServerName, certDNSName, errSys)
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}
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if errSys == nil {
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return nil
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}
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opts.Roots = bakedInRoots()
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_, err := certs[0].Verify(opts)
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if debug() {
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log.Printf("tlsdial(bake %q/%q): %v", c.ServerName, certDNSName, err)
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}
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if err == nil {
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return nil
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}
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return errSys
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}
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}
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// NewTransport returns a new HTTP transport that verifies TLS certs using this
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// package, including its baked-in LetsEncrypt fallback roots.
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func NewTransport() *http.Transport {
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return &http.Transport{
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DialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
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host, _, err := net.SplitHostPort(addr)
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if err != nil {
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return nil, err
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}
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var d tls.Dialer
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d.Config = Config(host, nil, nil)
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return d.DialContext(ctx, network, addr)
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},
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}
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}
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/*
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letsEncryptX1 is the LetsEncrypt X1 root:
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Certificate:
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Data:
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Version: 3 (0x2)
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Serial Number:
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82:10:cf:b0:d2:40:e3:59:44:63:e0:bb:63:82:8b:00
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Signature Algorithm: sha256WithRSAEncryption
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Issuer: C = US, O = Internet Security Research Group, CN = ISRG Root X1
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Validity
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Not Before: Jun 4 11:04:38 2015 GMT
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Not After : Jun 4 11:04:38 2035 GMT
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Subject: C = US, O = Internet Security Research Group, CN = ISRG Root X1
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Subject Public Key Info:
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Public Key Algorithm: rsaEncryption
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RSA Public-Key: (4096 bit)
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We bake it into the binary as a fallback verification root,
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in case the system we're running on doesn't have it.
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(Tailscale runs on some ancient devices.)
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To test that this code is working on Debian/Ubuntu:
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$ sudo mv /usr/share/ca-certificates/mozilla/ISRG_Root_X1.crt{,.old}
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$ sudo update-ca-certificates
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Then restart tailscaled. To also test dnsfallback's use of it, nuke
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your /etc/resolv.conf and it should still start & run fine.
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*/
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const letsEncryptX1 = `
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-----BEGIN CERTIFICATE-----
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MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
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TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
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cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4
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WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu
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ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY
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MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc
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h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+
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0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U
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A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW
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T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH
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B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC
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B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv
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KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn
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OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn
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jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw
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qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI
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rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV
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HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq
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hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL
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ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ
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3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK
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NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5
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ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur
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TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC
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jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc
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oyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq
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4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA
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mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d
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emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc=
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-----END CERTIFICATE-----
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`
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var bakedInRootsOnce struct {
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sync.Once
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p *x509.CertPool
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}
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func bakedInRoots() *x509.CertPool {
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bakedInRootsOnce.Do(func() {
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p := x509.NewCertPool()
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if !p.AppendCertsFromPEM([]byte(letsEncryptX1)) {
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panic("bogus PEM")
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}
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bakedInRootsOnce.p = p
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})
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return bakedInRootsOnce.p
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}
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