Update

vendor/tailscale.com/feature/acme/certstore.go

@@ -0,0 +1,478 @@
+// Copyright (c) Tailscale Inc & contributors
+// SPDX-License-Identifier: BSD-3-Clause
+
+package acme
+
+import (
+	"bytes"
+	"crypto"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/tls"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"io"
+	"os"
+	"path/filepath"
+	"runtime"
+	"strings"
+	"time"
+
+	"tailscale.com/atomicfile"
+	"tailscale.com/envknob"
+	"tailscale.com/feature/buildfeatures"
+	"tailscale.com/hostinfo"
+	"tailscale.com/ipn"
+	"tailscale.com/ipn/ipnlocal"
+	"tailscale.com/ipn/store"
+	"tailscale.com/ipn/store/mem"
+	"tailscale.com/net/bakedroots"
+	xacme "tailscale.com/tempfork/acme"
+	"tailscale.com/util/testenv"
+	"tailscale.com/version"
+	"tailscale.com/version/distro"
+)
+
+// certStore provides a way to perist and retrieve TLS certificates.
+// As of 2023-02-01, we store certs in directories on disk everywhere
+// except on Kubernetes, where we use the state store.
+type certStore interface {
+	// Read returns the cert and key for domain, if they exist and are valid
+	// for now. If they're expired, it returns errCertExpired.
+	// If they don't exist, it returns ipn.ErrStateNotExist.
+	Read(domain string, now time.Time) (*ipnlocal.TLSCertKeyPair, error)
+	// ACMEKey returns the value previously stored via WriteACMEKey.
+	// It is a PEM encoded ECDSA key.
+	ACMEKey() ([]byte, error)
+	// WriteACMEKey stores the provided PEM encoded ECDSA key.
+	WriteACMEKey([]byte) error
+	// WriteTLSCertAndKey writes the cert and key for domain.
+	WriteTLSCertAndKey(domain string, cert, key []byte) error
+}
+
+var errCertExpired = errors.New("cert expired")
+
+var testX509Roots *x509.CertPool // set non-nil by tests
+
+// certDir returns (creating if needed) the directory in which cached
+// cert keypairs are stored.
+func certDir(b *ipnlocal.LocalBackend) (string, error) {
+	d := b.TailscaleVarRoot()
+
+	// As a workaround for Synology DSM6 not having a "var" directory, use the
+	// app's "etc" directory (on a small partition) to hold certs at least.
+	// See https://github.com/tailscale/tailscale/issues/4060#issuecomment-1186592251
+	if buildfeatures.HasSynology && d == "" && runtime.GOOS == "linux" && distro.Get() == distro.Synology && distro.DSMVersion() == 6 {
+		d = "/var/packages/Tailscale/etc" // base; we append "certs" below
+	}
+	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
+}
+
+func (e *extension) getCertStore(b *ipnlocal.LocalBackend) (certStore, error) {
+	st := b.Sys().StateStore.Get()
+	switch st.(type) {
+	case *store.FileStore:
+	case *mem.Store:
+	default:
+		if hostinfo.GetEnvType() == hostinfo.Kubernetes {
+			// We're running in Kubernetes with a custom StateStore,
+			// use that instead of the cert directory.
+			// TODO(maisem): expand this to other environments?
+			return certStateStore{StateStore: st}, nil
+		}
+	}
+	dir, err := certDir(b)
+	if err != nil {
+		return nil, err
+	}
+	if testX509Roots != nil && !testenv.InTest() {
+		panic("use of test hook outside of tests")
+	}
+	return certFileStore{dir: dir, testRoots: testX509Roots}, nil
+}
+
+// certFileStore implements certStore by storing the cert & key files in
+// the named directory.
+type certFileStore struct {
+	dir string
+
+	// This field allows a test to override the CA root(s) for certificate
+	// verification. If nil the default system pool is used.
+	testRoots *x509.CertPool
+}
+
+const acmePEMName = "acme-account.key.pem"
+
+func (f certFileStore) ACMEKey() ([]byte, error) {
+	pemName := filepath.Join(f.dir, acmePEMName)
+	v, err := os.ReadFile(pemName)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ipn.ErrStateNotExist
+		}
+		return nil, err
+	}
+	return v, nil
+}
+
+func (f certFileStore) WriteACMEKey(b []byte) error {
+	pemName := filepath.Join(f.dir, acmePEMName)
+	return atomicfile.WriteFile(pemName, b, 0600)
+}
+
+func (f certFileStore) Read(domain string, now time.Time) (*ipnlocal.TLSCertKeyPair, error) {
+	certPEM, err := os.ReadFile(certFile(f.dir, domain))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ipn.ErrStateNotExist
+		}
+		return nil, err
+	}
+	keyPEM, err := os.ReadFile(keyFile(f.dir, domain))
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, ipn.ErrStateNotExist
+		}
+		return nil, err
+	}
+	if !validCertPEM(domain, keyPEM, certPEM, f.testRoots, now) {
+		return nil, errCertExpired
+	}
+	return &ipnlocal.TLSCertKeyPair{CertPEM: certPEM, KeyPEM: keyPEM, Cached: true}, nil
+}
+
+func (f certFileStore) WriteCert(domain string, cert []byte) error {
+	return atomicfile.WriteFile(certFile(f.dir, domain), cert, 0644)
+}
+
+func (f certFileStore) WriteKey(domain string, key []byte) error {
+	return atomicfile.WriteFile(keyFile(f.dir, domain), key, 0600)
+}
+
+func (f certFileStore) WriteTLSCertAndKey(domain string, cert, key []byte) error {
+	if err := f.WriteKey(domain, key); err != nil {
+		return err
+	}
+	return f.WriteCert(domain, cert)
+}
+
+// certStateStore implements certStore by storing the cert & key files
+// in an ipn.StateStore.
+type certStateStore struct {
+	ipn.StateStore
+
+	// This field allows a test to override the CA root(s) for certificate
+	// verification. If nil the default system pool is used.
+	testRoots *x509.CertPool
+}
+
+// TLSCertKeyReader is an interface implemented by state stores where it
+// makes sense to read the TLS cert and key in a single operation that
+// can be distinguished from generic state value reads. Currently this
+// is only implemented by the kubestore.Store, which, in some cases,
+// needs to read cert and key from a non-cached TLS Secret.
+type TLSCertKeyReader interface {
+	ReadTLSCertAndKey(domain string) ([]byte, []byte, error)
+}
+
+// ARIReplacesAllower is optionally implemented by state stores to opt
+// out of the ARI "replaces" hint on a per-domain basis at renewal time.
+// When implemented and returning false, the renewal path submits a plain
+// newOrder instead of claiming renewal exemption via "replaces".
+//
+// Used by the k8s cert-share store to prevent submitting a "replaces"
+// claim that Let's Encrypt would reject because the current ACME
+// account did not issue the previous cert (which can happen when a
+// shared per-tailnet account key is adopted after a cert was already
+// issued by a per-pod account). See #18251.
+type ARIReplacesAllower interface {
+	// ShouldUseARIReplacesForRenewal reports whether the renewal order
+	// for domain should carry the ARI "replaces" hint. It is advisory:
+	// a non-nil error means eligibility could not be determined, not
+	// that the hint should be skipped, and callers fail open (use the
+	// hint) in that case.
+	ShouldUseARIReplacesForRenewal(domain string) (bool, error)
+}
+
+func (s certStateStore) Read(domain string, now time.Time) (*ipnlocal.TLSCertKeyPair, error) {
+	// If we're using a store that supports atomic reads, use that
+	if kr, ok := s.StateStore.(TLSCertKeyReader); ok {
+		cert, key, err := kr.ReadTLSCertAndKey(domain)
+		if err != nil {
+			return nil, err
+		}
+		if !validCertPEM(domain, key, cert, s.testRoots, now) {
+			return nil, errCertExpired
+		}
+		return &ipnlocal.TLSCertKeyPair{CertPEM: cert, KeyPEM: key, Cached: true}, nil
+	}
+
+	// Otherwise fall back to separate reads
+	certPEM, err := s.ReadState(ipn.StateKey(domain + ".crt"))
+	if err != nil {
+		return nil, err
+	}
+	keyPEM, err := s.ReadState(ipn.StateKey(domain + ".key"))
+	if err != nil {
+		return nil, err
+	}
+	if !validCertPEM(domain, keyPEM, certPEM, s.testRoots, now) {
+		return nil, errCertExpired
+	}
+	return &ipnlocal.TLSCertKeyPair{CertPEM: certPEM, KeyPEM: keyPEM, Cached: true}, nil
+}
+
+// ShouldUseARIReplacesForRenewal delegates to the underlying state store
+// if it implements [ARIReplacesAllower]. Stores that don't opt in default
+// to true (attempt "replaces"), preserving the pre-hook behaviour.
+func (s certStateStore) ShouldUseARIReplacesForRenewal(domain string) (bool, error) {
+	if a, ok := s.StateStore.(ARIReplacesAllower); ok {
+		return a.ShouldUseARIReplacesForRenewal(domain)
+	}
+	return true, nil
+}
+
+func (s certStateStore) WriteCert(domain string, cert []byte) error {
+	return ipn.WriteState(s.StateStore, ipn.StateKey(domain+".crt"), cert)
+}
+
+func (s certStateStore) WriteKey(domain string, key []byte) error {
+	return ipn.WriteState(s.StateStore, ipn.StateKey(domain+".key"), key)
+}
+
+func (s certStateStore) ACMEKey() ([]byte, error) {
+	return s.ReadState(ipn.StateKey(acmePEMName))
+}
+
+func (s certStateStore) WriteACMEKey(key []byte) error {
+	return ipn.WriteState(s.StateStore, ipn.StateKey(acmePEMName), key)
+}
+
+// TLSCertKeyWriter is an interface implemented by state stores that can
+// write the TLS cert and key in a single atomic operation. Currently
+// this is only implemented by the kubestore.StoreKube.
+type TLSCertKeyWriter interface {
+	WriteTLSCertAndKey(domain string, cert, key []byte) error
+}
+
+// WriteTLSCertAndKey writes the TLS cert and key for domain to the
+// current LocalBackend's StateStore.
+func (s certStateStore) WriteTLSCertAndKey(domain string, cert, key []byte) error {
+	// If we're using a store that supports atomic writes, use that.
+	if aw, ok := s.StateStore.(TLSCertKeyWriter); ok {
+		return aw.WriteTLSCertAndKey(domain, cert, key)
+	}
+	// Otherwise fall back to separate writes for cert and key.
+	if err := s.WriteKey(domain, key); err != nil {
+		return err
+	}
+	return s.WriteCert(domain, cert)
+}
+
+func keyFile(dir, domain string) string {
+	return filepath.Join(dir, strings.Replace(domain, "*.", "wildcard_.", 1)+".key")
+}
+func certFile(dir, domain string) string {
+	return filepath.Join(dir, strings.Replace(domain, "*.", "wildcard_.", 1)+".crt")
+}
+
+// getCertPEMCached returns a non-nil keyPair if a cached keypair for
+// domain exists in the certStore that is valid at the provided now time.
+//
+// If the keypair is expired, it returns errCertExpired.
+// If the keypair doesn't exist, it returns ipn.ErrStateNotExist.
+func getCertPEMCached(cs certStore, domain string, now time.Time) (p *ipnlocal.TLSCertKeyPair, err error) {
+	if !validLookingCertDomain(domain) {
+		// Before we read files from disk using it, validate it's halfway
+		// reasonable looking.
+		return nil, fmt.Errorf("invalid domain %q", domain)
+	}
+	return cs.Read(domain, now)
+}
+
+// certRequest generates a CSR for the given domain and optional SANs.
+func certRequest(key crypto.Signer, domain string, ext []pkix.Extension) ([]byte, error) {
+	dnsNames := []string{domain}
+	if base, ok := strings.CutPrefix(domain, "*."); ok {
+		// Wildcard cert must also include the base domain as a SAN.
+		// This is load-bearing: getCertPEMCached validates certs using
+		// the storage key (base domain), which only passes x509 verification
+		// if the base domain is in DNSNames.
+		dnsNames = append(dnsNames, base)
+	}
+	req := &x509.CertificateRequest{
+		Subject:         pkix.Name{CommonName: domain},
+		DNSNames:        dnsNames,
+		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 (e *extension) acmeKey(cs certStore) (crypto.Signer, error) {
+	// Lock so two callers don't both generate a key and race on the
+	// write.
+	e.accountMu.Lock()
+	defer e.accountMu.Unlock()
+
+	if v, err := cs.ACMEKey(); 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)
+	} else if !errors.Is(err, ipn.ErrStateNotExist) {
+		return nil, err
+	}
+
+	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 := cs.WriteACMEKey(pemBuf.Bytes()); err != nil {
+		return nil, err
+	}
+	return privKey, nil
+}
+
+func (e *extension) acmeClient(cs certStore) (*xacme.Client, error) {
+	key, err := e.acmeKey(cs)
+	if err != nil {
+		return nil, fmt.Errorf("acmeKey: %w", err)
+	}
+	// Note: if we add support for additional ACME providers (other than
+	// LetsEncrypt), we should make sure that they support ARI extension (see
+	// shouldStartDomainRenewalARI).
+	return &xacme.Client{
+		Key:          key,
+		UserAgent:    "tailscaled/" + version.Long(),
+		DirectoryURL: envknob.String("TS_DEBUG_ACME_DIRECTORY_URL"),
+	}, nil
+}
+
+// validCertPEM reports whether the given certificate is valid for
+// domain at now.
+//
+// If roots != nil, it is used instead of the system root pool. This is
+// meant to support testing; production code should pass roots == nil.
+func validCertPEM(domain string, keyPEM, certPEM []byte, roots *x509.CertPool, 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)
+		}
+	}
+	return validateLeaf(leaf, intermediates, domain, now, roots)
+}
+
+// validateLeaf is a helper for [validCertPEM].
+//
+// If called with roots == nil, it will use the system root pool as well
+// as the baked-in roots. If non-nil, only those roots are used.
+func validateLeaf(leaf *x509.Certificate, intermediates *x509.CertPool, domain string, now time.Time, roots *x509.CertPool) bool {
+	if leaf == nil {
+		return false
+	}
+	_, err := leaf.Verify(x509.VerifyOptions{
+		DNSName:       domain,
+		CurrentTime:   now,
+		Roots:         roots,
+		Intermediates: intermediates,
+	})
+	if err != nil && roots == nil {
+		// If validation failed and they specified nil for roots (meaning to use
+		// the system roots), then give it another chance to validate using the
+		// binary's baked-in roots (LetsEncrypt). See tailscale/tailscale#14690.
+		return validateLeaf(leaf, intermediates, domain, now, bakedroots.Get())
+	}
+
+	if err == nil {
+		return true
+	}
+
+	// When pointed at a non-prod ACME server, we don't expect to have the CA
+	// in our system or baked-in roots. Verify only throws UnknownAuthorityError
+	// after first checking the leaf cert's expiry, hostnames etc, so we know
+	// that the only reason for an error is to do with constructing a full chain.
+	// Allow this error so that cert caching still works in testing environments.
+	if errors.As(err, &x509.UnknownAuthorityError{}) {
+		acmeURL := envknob.String("TS_DEBUG_ACME_DIRECTORY_URL")
+		if !isDefaultDirectoryURL(acmeURL) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func isDefaultDirectoryURL(u string) bool {
+	return u == "" || u == xacme.LetsEncryptURL
+}