mirror of
https://github.com/tailscale/tailscale.git
synced 2024-11-27 03:55:36 +00:00
004dded0a8
It seems some security software or macOS itself might be MITMing TLS (for ScreenTime?), so don't warn unless it fails x509 validation against system roots. Updates #3198 Change-Id: I6ea381b5bb6385b3d51da4a1468c0d803236b7bf Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
309 lines
10 KiB
Go
309 lines
10 KiB
Go
// Copyright (c) Tailscale Inc & AUTHORS
|
|
// SPDX-License-Identifier: BSD-3-Clause
|
|
|
|
// Package tlsdial generates tls.Config values and does x509 validation of
|
|
// certs. It bakes in the LetsEncrypt roots so even if the user's machine
|
|
// doesn't have TLS roots, we can at least connect to Tailscale's LetsEncrypt
|
|
// services. It's the unified point where we can add shared policy on outgoing
|
|
// TLS connections from the three places in the client that connect to Tailscale
|
|
// (logs, control, DERP).
|
|
package tlsdial
|
|
|
|
import (
|
|
"bytes"
|
|
"context"
|
|
"crypto/tls"
|
|
"crypto/x509"
|
|
"errors"
|
|
"fmt"
|
|
"log"
|
|
"net"
|
|
"net/http"
|
|
"os"
|
|
"sync"
|
|
"sync/atomic"
|
|
"time"
|
|
|
|
"tailscale.com/envknob"
|
|
"tailscale.com/health"
|
|
)
|
|
|
|
var counterFallbackOK int32 // atomic
|
|
|
|
// If SSLKEYLOGFILE is set, it's a file to which we write our TLS private keys
|
|
// in a way that WireShark can read.
|
|
//
|
|
// See https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format
|
|
var sslKeyLogFile = os.Getenv("SSLKEYLOGFILE")
|
|
|
|
var debug = envknob.RegisterBool("TS_DEBUG_TLS_DIAL")
|
|
|
|
// tlsdialWarningPrinted tracks whether we've printed a warning about a given
|
|
// hostname already, to avoid log spam for users with custom DERP servers,
|
|
// Headscale, etc.
|
|
var tlsdialWarningPrinted sync.Map // map[string]bool
|
|
|
|
// Config returns a tls.Config for connecting to a server.
|
|
// If base is non-nil, it's cloned as the base config before
|
|
// being configured and returned.
|
|
// If ht is non-nil, it's used to report health errors.
|
|
func Config(host string, ht *health.Tracker, base *tls.Config) *tls.Config {
|
|
var conf *tls.Config
|
|
if base == nil {
|
|
conf = new(tls.Config)
|
|
} else {
|
|
conf = base.Clone()
|
|
}
|
|
conf.ServerName = host
|
|
|
|
if n := 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)
|
|
conf.KeyLogWriter = f
|
|
}
|
|
|
|
if conf.InsecureSkipVerify {
|
|
panic("unexpected base.InsecureSkipVerify")
|
|
}
|
|
if conf.VerifyConnection != nil {
|
|
panic("unexpected base.VerifyConnection")
|
|
}
|
|
|
|
// Set InsecureSkipVerify to prevent crypto/tls from doing its
|
|
// own cert verification, as do the same work that it'd do
|
|
// (with the baked-in fallback root) in the VerifyConnection hook.
|
|
conf.InsecureSkipVerify = true
|
|
conf.VerifyConnection = func(cs tls.ConnectionState) (retErr error) {
|
|
// Perform some health checks on this certificate before we do
|
|
// any verification.
|
|
var selfSignedIssuer string
|
|
if certs := cs.PeerCertificates; len(certs) > 0 && certIsSelfSigned(certs[0]) {
|
|
selfSignedIssuer = certs[0].Issuer.String()
|
|
}
|
|
if ht != nil {
|
|
defer func() {
|
|
if retErr != nil && selfSignedIssuer != "" {
|
|
// Self-signed certs are never valid.
|
|
//
|
|
// TODO(bradfitz): plumb down the selfSignedIssuer as a
|
|
// structured health warning argument.
|
|
ht.SetTLSConnectionError(cs.ServerName, fmt.Errorf("likely intercepted connection; certificate is self-signed by %v", selfSignedIssuer))
|
|
} else {
|
|
// Ensure we clear any error state for this ServerName.
|
|
ht.SetTLSConnectionError(cs.ServerName, nil)
|
|
if selfSignedIssuer != "" {
|
|
// Log the self-signed issuer, but don't treat it as an error.
|
|
log.Printf("tlsdial: warning: server cert for %q passed x509 validation but is self-signed by %q", host, selfSignedIssuer)
|
|
}
|
|
}
|
|
}()
|
|
}
|
|
|
|
// First try doing x509 verification with the system's
|
|
// root CA pool.
|
|
opts := x509.VerifyOptions{
|
|
DNSName: cs.ServerName,
|
|
Intermediates: x509.NewCertPool(),
|
|
}
|
|
for _, cert := range cs.PeerCertificates[1:] {
|
|
opts.Intermediates.AddCert(cert)
|
|
}
|
|
_, errSys := cs.PeerCertificates[0].Verify(opts)
|
|
if debug() {
|
|
log.Printf("tlsdial(sys %q): %v", host, errSys)
|
|
}
|
|
|
|
// Always verify with our baked-in Let's Encrypt certificate,
|
|
// so we can log an informational message. This is useful for
|
|
// detecting SSL MiTM.
|
|
opts.Roots = bakedInRoots()
|
|
_, bakedErr := cs.PeerCertificates[0].Verify(opts)
|
|
if debug() {
|
|
log.Printf("tlsdial(bake %q): %v", host, bakedErr)
|
|
} else if bakedErr != nil {
|
|
if _, loaded := tlsdialWarningPrinted.LoadOrStore(host, true); !loaded {
|
|
if errSys == nil {
|
|
log.Printf("tlsdial: warning: server cert for %q is not a Let's Encrypt cert", host)
|
|
} else {
|
|
log.Printf("tlsdial: error: server cert for %q failed to verify and is not a Let's Encrypt cert", host)
|
|
}
|
|
}
|
|
}
|
|
|
|
if errSys == nil {
|
|
return nil
|
|
} else if bakedErr == nil {
|
|
atomic.AddInt32(&counterFallbackOK, 1)
|
|
return nil
|
|
}
|
|
return errSys
|
|
}
|
|
return conf
|
|
}
|
|
|
|
func certIsSelfSigned(cert *x509.Certificate) bool {
|
|
// A certificate is determined to be self-signed if the certificate's
|
|
// subject is the same as its issuer.
|
|
return bytes.Equal(cert.RawSubject, cert.RawIssuer)
|
|
}
|
|
|
|
// SetConfigExpectedCert modifies c to expect and verify that the server returns
|
|
// a certificate for the provided certDNSName.
|
|
//
|
|
// This is for user-configurable client-side domain fronting support,
|
|
// where we send one SNI value but validate a different cert.
|
|
func SetConfigExpectedCert(c *tls.Config, certDNSName string) {
|
|
if c.ServerName == certDNSName {
|
|
return
|
|
}
|
|
if c.ServerName == "" {
|
|
c.ServerName = certDNSName
|
|
return
|
|
}
|
|
if c.VerifyPeerCertificate != nil {
|
|
panic("refusing to override tls.Config.VerifyPeerCertificate")
|
|
}
|
|
// Set InsecureSkipVerify to prevent crypto/tls from doing its
|
|
// own cert verification, but do the same work that it'd do
|
|
// (but using certDNSName) in the VerifyPeerCertificate hook.
|
|
c.InsecureSkipVerify = true
|
|
c.VerifyConnection = nil
|
|
c.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
|
|
if len(rawCerts) == 0 {
|
|
return errors.New("no certs presented")
|
|
}
|
|
certs := make([]*x509.Certificate, len(rawCerts))
|
|
for i, asn1Data := range rawCerts {
|
|
cert, err := x509.ParseCertificate(asn1Data)
|
|
if err != nil {
|
|
return err
|
|
}
|
|
certs[i] = cert
|
|
}
|
|
opts := x509.VerifyOptions{
|
|
CurrentTime: time.Now(),
|
|
DNSName: certDNSName,
|
|
Intermediates: x509.NewCertPool(),
|
|
}
|
|
for _, cert := range certs[1:] {
|
|
opts.Intermediates.AddCert(cert)
|
|
}
|
|
_, errSys := certs[0].Verify(opts)
|
|
if debug() {
|
|
log.Printf("tlsdial(sys %q/%q): %v", c.ServerName, certDNSName, errSys)
|
|
}
|
|
if errSys == nil {
|
|
return nil
|
|
}
|
|
opts.Roots = bakedInRoots()
|
|
_, err := certs[0].Verify(opts)
|
|
if debug() {
|
|
log.Printf("tlsdial(bake %q/%q): %v", c.ServerName, certDNSName, err)
|
|
}
|
|
if err == nil {
|
|
return nil
|
|
}
|
|
return errSys
|
|
}
|
|
}
|
|
|
|
// NewTransport returns a new HTTP transport that verifies TLS certs using this
|
|
// package, including its baked-in LetsEncrypt fallback roots.
|
|
func NewTransport() *http.Transport {
|
|
return &http.Transport{
|
|
DialTLSContext: func(ctx context.Context, network, addr string) (net.Conn, error) {
|
|
host, _, err := net.SplitHostPort(addr)
|
|
if err != nil {
|
|
return nil, err
|
|
}
|
|
var d tls.Dialer
|
|
d.Config = Config(host, nil, nil)
|
|
return d.DialContext(ctx, network, addr)
|
|
},
|
|
}
|
|
}
|
|
|
|
/*
|
|
letsEncryptX1 is the LetsEncrypt X1 root:
|
|
|
|
Certificate:
|
|
|
|
Data:
|
|
Version: 3 (0x2)
|
|
Serial Number:
|
|
82:10:cf:b0:d2:40:e3:59:44:63:e0:bb:63:82:8b:00
|
|
Signature Algorithm: sha256WithRSAEncryption
|
|
Issuer: C = US, O = Internet Security Research Group, CN = ISRG Root X1
|
|
Validity
|
|
Not Before: Jun 4 11:04:38 2015 GMT
|
|
Not After : Jun 4 11:04:38 2035 GMT
|
|
Subject: C = US, O = Internet Security Research Group, CN = ISRG Root X1
|
|
Subject Public Key Info:
|
|
Public Key Algorithm: rsaEncryption
|
|
RSA Public-Key: (4096 bit)
|
|
|
|
We bake it into the binary as a fallback verification root,
|
|
in case the system we're running on doesn't have it.
|
|
(Tailscale runs on some ancient devices.)
|
|
|
|
To test that this code is working on Debian/Ubuntu:
|
|
|
|
$ sudo mv /usr/share/ca-certificates/mozilla/ISRG_Root_X1.crt{,.old}
|
|
$ sudo update-ca-certificates
|
|
|
|
Then restart tailscaled. To also test dnsfallback's use of it, nuke
|
|
your /etc/resolv.conf and it should still start & run fine.
|
|
*/
|
|
const letsEncryptX1 = `
|
|
-----BEGIN CERTIFICATE-----
|
|
MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
|
|
TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
|
|
cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4
|
|
WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu
|
|
ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY
|
|
MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc
|
|
h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+
|
|
0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U
|
|
A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW
|
|
T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH
|
|
B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC
|
|
B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv
|
|
KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn
|
|
OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn
|
|
jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw
|
|
qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI
|
|
rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV
|
|
HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq
|
|
hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL
|
|
ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ
|
|
3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK
|
|
NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5
|
|
ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur
|
|
TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC
|
|
jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc
|
|
oyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq
|
|
4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA
|
|
mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d
|
|
emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc=
|
|
-----END CERTIFICATE-----
|
|
`
|
|
|
|
var bakedInRootsOnce struct {
|
|
sync.Once
|
|
p *x509.CertPool
|
|
}
|
|
|
|
func bakedInRoots() *x509.CertPool {
|
|
bakedInRootsOnce.Do(func() {
|
|
p := x509.NewCertPool()
|
|
if !p.AppendCertsFromPEM([]byte(letsEncryptX1)) {
|
|
panic("bogus PEM")
|
|
}
|
|
bakedInRootsOnce.p = p
|
|
})
|
|
return bakedInRootsOnce.p
|
|
}
|