tailscale/ipn/localapi/cert.go

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// Copyright (c) 2021 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.
//go:build !ios && !android
// +build !ios,!android
package localapi
import (
"bytes"
"context"
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/rsa"
"crypto/tls"
"crypto/x509"
"crypto/x509/pkix"
"encoding/json"
"encoding/pem"
"errors"
"fmt"
"io"
"io/ioutil"
"log"
"net"
"net/http"
"os"
"path/filepath"
"strconv"
"strings"
"sync"
"time"
"golang.org/x/crypto/acme"
"tailscale.com/ipn/ipnstate"
"tailscale.com/types/logger"
)
// Process-wide cache. (A new *Handler is created per connection,
// effectively per request)
var (
// acmeMu guards all ACME operations, so concurrent requests
// for certs don't slam ACME. The first will go through and
// populate the on-disk cache and the rest should use that.
acmeMu sync.Mutex
renewMu sync.Mutex // lock order: don't hold acmeMu and renewMu at the same time
lastRenewCheck = map[string]time.Time{}
)
func (h *Handler) certDir() (string, error) {
d := h.b.TailscaleVarRoot()
if d == "" {
return "", errors.New("no TailscaleVarRoot")
}
full := filepath.Join(d, "certs")
if err := os.MkdirAll(full, 0700); err != nil {
return "", err
}
return full, nil
}
var acmeDebug, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_ACME"))
func (h *Handler) serveCert(w http.ResponseWriter, r *http.Request) {
if !h.PermitWrite {
http.Error(w, "cert access denied", http.StatusForbidden)
return
}
dir, err := h.certDir()
if err != nil {
h.logf("certDir: %v", err)
http.Error(w, "failed to get cert dir", 500)
return
}
domain := strings.TrimPrefix(r.URL.Path, "/localapi/v0/cert/")
if domain == r.URL.Path {
http.Error(w, "internal handler config wired wrong", 500)
return
}
now := time.Now()
logf := logger.WithPrefix(h.logf, fmt.Sprintf("cert(%q): ", domain))
traceACME := func(v interface{}) {
if !acmeDebug {
return
}
j, _ := json.MarshalIndent(v, "", "\t")
log.Printf("acme %T: %s", v, j)
}
if pair, ok := h.getCertPEMCached(dir, domain, now); ok {
future := now.AddDate(0, 0, 14)
if h.shouldStartDomainRenewal(dir, domain, future) {
logf("starting async renewal")
// Start renewal in the background.
go h.getCertPEM(context.Background(), logf, traceACME, dir, domain, future)
}
serveKeyPair(w, r, pair)
return
}
pair, err := h.getCertPEM(r.Context(), logf, traceACME, dir, domain, now)
if err != nil {
logf("getCertPEM: %v", err)
http.Error(w, fmt.Sprint(err), 500)
return
}
serveKeyPair(w, r, pair)
}
func (h *Handler) shouldStartDomainRenewal(dir, domain string, future time.Time) bool {
renewMu.Lock()
defer renewMu.Unlock()
now := time.Now()
if last, ok := lastRenewCheck[domain]; ok && now.Sub(last) < time.Minute {
// We checked very recently. Don't bother reparsing &
// validating the x509 cert.
return false
}
lastRenewCheck[domain] = now
_, ok := h.getCertPEMCached(dir, domain, future)
return !ok
}
func serveKeyPair(w http.ResponseWriter, r *http.Request, p *keyPair) {
w.Header().Set("Content-Type", "text/plain")
switch r.URL.Query().Get("type") {
case "", "crt", "cert":
w.Write(p.certPEM)
case "key":
w.Write(p.keyPEM)
case "pair":
w.Write(p.keyPEM)
w.Write(p.certPEM)
default:
http.Error(w, `invalid type; want "cert" (default), "key", or "pair"`, 400)
}
}
type keyPair struct {
certPEM []byte
keyPEM []byte
cached bool
}
func keyFile(dir, domain string) string { return filepath.Join(dir, domain+".key") }
func certFile(dir, domain string) string { return filepath.Join(dir, domain+".crt") }
// getCertPEMCached returns a non-nil keyPair and true if a cached
// keypair for domain exists on disk in dir that is valid at the
// provided now time.
func (h *Handler) getCertPEMCached(dir, domain string, now time.Time) (p *keyPair, ok bool) {
if keyPEM, err := os.ReadFile(keyFile(dir, domain)); err == nil {
certPEM, _ := os.ReadFile(certFile(dir, domain))
if validCertPEM(domain, keyPEM, certPEM, now) {
return &keyPair{certPEM: certPEM, keyPEM: keyPEM, cached: true}, true
}
}
return nil, false
}
func (h *Handler) getCertPEM(ctx context.Context, logf logger.Logf, traceACME func(interface{}), dir, domain string, now time.Time) (*keyPair, error) {
acmeMu.Lock()
defer acmeMu.Unlock()
if p, ok := h.getCertPEMCached(dir, domain, now); ok {
return p, nil
}
key, err := acmeKey(dir)
if err != nil {
return nil, fmt.Errorf("acmeKey: %w", err)
}
ac := &acme.Client{Key: key}
a, err := ac.GetReg(ctx, "" /* pre-RFC param */)
switch {
case err == nil:
// Great, already registered.
logf("already had ACME account.")
case err == acme.ErrNoAccount:
a, err = ac.Register(ctx, new(acme.Account), acme.AcceptTOS)
if err == acme.ErrAccountAlreadyExists {
// Potential race. Double check.
a, err = ac.GetReg(ctx, "" /* pre-RFC param */)
}
if err != nil {
return nil, fmt.Errorf("acme.Register: %w", err)
}
logf("registered ACME account.")
traceACME(a)
default:
return nil, fmt.Errorf("acme.GetReg: %w", err)
}
if a.Status != acme.StatusValid {
return nil, fmt.Errorf("unexpected ACME account status %q", a.Status)
}
// Before hitting LetsEncrypt, see if this is a domain that Tailscale will do DNS challenges for.
st := h.b.StatusWithoutPeers()
if err := checkCertDomain(st, domain); err != nil {
return nil, err
}
order, err := ac.AuthorizeOrder(ctx, []acme.AuthzID{{Type: "dns", Value: domain}})
if err != nil {
return nil, err
}
traceACME(order)
for _, aurl := range order.AuthzURLs {
az, err := ac.GetAuthorization(ctx, aurl)
if err != nil {
return nil, err
}
traceACME(az)
for _, ch := range az.Challenges {
if ch.Type == "dns-01" {
rec, err := ac.DNS01ChallengeRecord(ch.Token)
if err != nil {
return nil, err
}
key := "_acme-challenge." + domain
var resolver net.Resolver
var ok bool
txts, _ := resolver.LookupTXT(ctx, key)
for _, txt := range txts {
if txt == rec {
ok = true
logf("TXT record already existed")
break
}
}
if !ok {
err = h.b.SetDNS(ctx, key, rec)
if err != nil {
return nil, fmt.Errorf("SetDNS %q => %q: %w", key, rec, err)
}
logf("did SetDNS")
}
chal, err := ac.Accept(ctx, ch)
if err != nil {
return nil, fmt.Errorf("Accept: %v", err)
}
traceACME(chal)
break
}
}
}
wait0 := time.Now()
orderURI := order.URI
for {
order, err = ac.WaitOrder(ctx, orderURI)
if err == nil {
break
}
if oe, ok := err.(*acme.OrderError); ok && oe.Status == acme.StatusInvalid {
if time.Since(wait0) > 2*time.Minute {
return nil, errors.New("timeout waiting for order to not be invalid")
}
log.Printf("order invalid; waiting...")
select {
case <-time.After(5 * time.Second):
continue
case <-ctx.Done():
return nil, ctx.Err()
}
}
return nil, fmt.Errorf("WaitOrder: %v", err)
}
traceACME(order)
certPrivKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, err
}
var privPEM bytes.Buffer
if err := encodeECDSAKey(&privPEM, certPrivKey); err != nil {
return nil, err
}
if err := ioutil.WriteFile(keyFile(dir, domain), privPEM.Bytes(), 0600); err != nil {
return nil, err
}
csr, err := certRequest(certPrivKey, domain, nil)
if err != nil {
return nil, err
}
der, _, err := ac.CreateOrderCert(ctx, order.FinalizeURL, csr, true)
if err != nil {
return nil, fmt.Errorf("CreateOrder: %v", err)
}
var certPEM bytes.Buffer
for _, b := range der {
pb := &pem.Block{Type: "CERTIFICATE", Bytes: b}
if err := pem.Encode(&certPEM, pb); err != nil {
return nil, err
}
}
if err := ioutil.WriteFile(certFile(dir, domain), certPEM.Bytes(), 0644); err != nil {
return nil, err
}
return &keyPair{certPEM: certPEM.Bytes(), keyPEM: privPEM.Bytes()}, nil
}
// certRequest generates a CSR for the given common name cn and optional SANs.
func certRequest(key crypto.Signer, cn string, ext []pkix.Extension, san ...string) ([]byte, error) {
req := &x509.CertificateRequest{
Subject: pkix.Name{CommonName: cn},
DNSNames: san,
ExtraExtensions: ext,
}
return x509.CreateCertificateRequest(rand.Reader, req, key)
}
func encodeECDSAKey(w io.Writer, key *ecdsa.PrivateKey) error {
b, err := x509.MarshalECPrivateKey(key)
if err != nil {
return err
}
pb := &pem.Block{Type: "EC PRIVATE KEY", Bytes: b}
return pem.Encode(w, pb)
}
// parsePrivateKey is a copy of x/crypto/acme's parsePrivateKey.
//
// Attempt to parse the given private key DER block. OpenSSL 0.9.8 generates
// PKCS#1 private keys by default, while OpenSSL 1.0.0 generates PKCS#8 keys.
// OpenSSL ecparam generates SEC1 EC private keys for ECDSA. We try all three.
//
// Inspired by parsePrivateKey in crypto/tls/tls.go.
func parsePrivateKey(der []byte) (crypto.Signer, error) {
if key, err := x509.ParsePKCS1PrivateKey(der); err == nil {
return key, nil
}
if key, err := x509.ParsePKCS8PrivateKey(der); err == nil {
switch key := key.(type) {
case *rsa.PrivateKey:
return key, nil
case *ecdsa.PrivateKey:
return key, nil
default:
return nil, errors.New("acme/autocert: unknown private key type in PKCS#8 wrapping")
}
}
if key, err := x509.ParseECPrivateKey(der); err == nil {
return key, nil
}
return nil, errors.New("acme/autocert: failed to parse private key")
}
func acmeKey(dir string) (crypto.Signer, error) {
pemName := filepath.Join(dir, "acme-account.key.pem")
if v, err := ioutil.ReadFile(pemName); err == nil {
priv, _ := pem.Decode(v)
if priv == nil || !strings.Contains(priv.Type, "PRIVATE") {
return nil, errors.New("acme/autocert: invalid account key found in cache")
}
return parsePrivateKey(priv.Bytes)
}
privKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, err
}
var pemBuf bytes.Buffer
if err := encodeECDSAKey(&pemBuf, privKey); err != nil {
return nil, err
}
if err := ioutil.WriteFile(pemName, pemBuf.Bytes(), 0600); err != nil {
return nil, err
}
return privKey, nil
}
func validCertPEM(domain string, keyPEM, certPEM []byte, now time.Time) bool {
if len(keyPEM) == 0 || len(certPEM) == 0 {
return false
}
tlsCert, err := tls.X509KeyPair(certPEM, keyPEM)
if err != nil {
return false
}
var leaf *x509.Certificate
intermediates := x509.NewCertPool()
for i, certDER := range tlsCert.Certificate {
cert, err := x509.ParseCertificate(certDER)
if err != nil {
return false
}
if i == 0 {
leaf = cert
} else {
intermediates.AddCert(cert)
}
}
if leaf == nil {
return false
}
_, err = leaf.Verify(x509.VerifyOptions{
DNSName: domain,
CurrentTime: now,
Intermediates: intermediates,
})
return err == nil
}
func checkCertDomain(st *ipnstate.Status, domain string) error {
if domain == "" {
return errors.New("missing domain name")
}
for _, d := range st.CertDomains {
if d == domain {
return nil
}
}
// Transitional way while server doesn't yet populate CertDomains: also permit the client
// attempting Self.DNSName.
okay := st.CertDomains[:len(st.CertDomains):len(st.CertDomains)]
if st.Self != nil {
if v := strings.Trim(st.Self.DNSName, "."); v != "" {
if v == domain {
return nil
}
okay = append(okay, v)
}
}
switch len(okay) {
case 0:
return errors.New("your Tailscale account does not support getting TLS certs")
case 1:
return fmt.Errorf("invalid domain %q; only %q is permitted", domain, okay[0])
default:
return fmt.Errorf("invalid domain %q; must be one of %q", domain, okay)
}
}