mirror of
https://github.com/tailscale/tailscale.git
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41fd4eab5c
A new package can also later record/report which knobs are checked and set. It also makes the code cleaner & easier to grep for env knobs. Change-Id: Id8a123ab7539f1fadbd27e0cbeac79c2e4f09751 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
243 lines
7.8 KiB
Go
243 lines
7.8 KiB
Go
// Copyright (c) 2020 Tailscale Inc & AUTHORS All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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// Package tlsdial originally existed to set up a tls.Config for x509
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// validation, using a memory-optimized path for iOS, but then we
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// moved that to the tailscale/go tree instead, so now this package
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// does very little. But for now we keep it as a unified point where
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// we might want to add shared policy on outgoing TLS connections from
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// the 3 places in the client that connect to Tailscale (logs,
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// control, DERP).
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package tlsdial
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import (
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"crypto/tls"
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"crypto/x509"
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"errors"
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"log"
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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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)
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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.Bool("TS_DEBUG_TLS_DIAL")
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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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func Config(host string, 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) error {
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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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if errSys == nil {
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return nil
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}
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// If that failed, because the system's CA roots are old
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// or broken, fall back to trying LetsEncrypt at least.
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opts.Roots = bakedInRoots()
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_, err := cs.PeerCertificates[0].Verify(opts)
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if debug {
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log.Printf("tlsdial(bake %q): %v", host, err)
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}
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if err == 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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// 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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/*
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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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