ipn/ipnlocal: also store ACME keys in the certStore

We were not storing the ACME keys in the state store, they would always
be stored on disk.

Updates #7588

Signed-off-by: Maisem Ali <maisem@tailscale.com>

ipn/ipnlocal/cert.go

@@ -82,11 +82,6 @@ func (b *LocalBackend) GetCertPEM(ctx context.Context, domain string) (*TLSCertK
 		return nil, errors.New("invalid domain")
 	}
 	logf := logger.WithPrefix(b.logf, fmt.Sprintf("cert(%q): ", domain))
-	dir, err := b.certDir()
-	if err != nil {
-		logf("failed to get certDir: %v", err)
-		return nil, err
-	}
 	now := time.Now()
 	traceACME := func(v any) {
 		if !acmeDebug() {
@@ -96,17 +91,22 @@ func (b *LocalBackend) GetCertPEM(ctx context.Context, domain string) (*TLSCertK
 		log.Printf("acme %T: %s", v, j)
 	}
 
-	if pair, err := b.getCertPEMCached(dir, domain, now); err == nil {
+	cs, err := b.getCertStore()
+	if err != nil {
+		return nil, err
+	}
+
+	if pair, err := getCertPEMCached(cs, domain, now); err == nil {
 		future := now.AddDate(0, 0, 14)
-		if b.shouldStartDomainRenewal(dir, domain, future) {
+		if b.shouldStartDomainRenewal(cs, domain, future) {
 			logf("starting async renewal")
 			// Start renewal in the background.
-			go b.getCertPEM(context.Background(), logf, traceACME, dir, domain, future)
+			go b.getCertPEM(context.Background(), cs, logf, traceACME, domain, future)
 		}
 		return pair, nil
 	}
 
-	pair, err := b.getCertPEM(ctx, logf, traceACME, dir, domain, now)
+	pair, err := b.getCertPEM(ctx, cs, logf, traceACME, domain, now)
 	if err != nil {
 		logf("getCertPEM: %v", err)
 		return nil, err
@@ -114,7 +114,7 @@ func (b *LocalBackend) GetCertPEM(ctx context.Context, domain string) (*TLSCertK
 	return pair, nil
 }
 
-func (b *LocalBackend) shouldStartDomainRenewal(dir, domain string, future time.Time) bool {
+func (b *LocalBackend) shouldStartDomainRenewal(cs certStore, domain string, future time.Time) bool {
 	renewMu.Lock()
 	defer renewMu.Unlock()
 	now := time.Now()
@@ -124,7 +124,7 @@ func (b *LocalBackend) shouldStartDomainRenewal(dir, domain string, future time.
 		return false
 	}
 	lastRenewCheck[domain] = now
-	_, err := b.getCertPEMCached(dir, domain, future)
+	_, err := getCertPEMCached(cs, domain, future)
 	return errors.Is(err, errCertExpired)
 }
 
@@ -140,15 +140,24 @@ type certStore interface {
 	WriteCert(domain string, cert []byte) error
 	// WriteKey writes the key for domain.
 	WriteKey(domain string, key []byte) 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
 }
 
 var errCertExpired = errors.New("cert expired")
 
-func (b *LocalBackend) getCertStore(dir string) certStore {
+func (b *LocalBackend) getCertStore() (certStore, error) {
+	dir, err := b.certDir()
+	if err != nil {
+		return nil, err
+	}
 	if hostinfo.GetEnvType() == hostinfo.Kubernetes && dir == "/tmp" {
-		return certStateStore{StateStore: b.store}
+		return certStateStore{StateStore: b.store}, nil
 	}
-	return certFileStore{dir: dir}
+	return certFileStore{dir: dir}, nil
 }
 
 // certFileStore implements certStore by storing the cert & key files in the named directory.
@@ -160,6 +169,25 @@ type certFileStore struct {
 	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 os.WriteFile(pemName, b, 0600)
+}
+
 func (f certFileStore) Read(domain string, now time.Time) (*TLSCertKeyPair, error) {
 	certPEM, err := os.ReadFile(certFile(f.dir, domain))
 	if err != nil {
@@ -221,6 +249,14 @@ func (s certStateStore) WriteKey(domain string, key []byte) error {
 	return s.WriteState(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 s.WriteState(ipn.StateKey(acmePEMName), key)
+}
+
 // TLSCertKeyPair is a TLS public and private key, and whether they were obtained
 // from cache or freshly obtained.
 type TLSCertKeyPair struct {
@@ -236,26 +272,26 @@ func certFile(dir, domain string) string { return filepath.Join(dir, domain+".cr
 // domain exists on disk in dir 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 (b *LocalBackend) getCertPEMCached(dir, domain string, now time.Time) (p *TLSCertKeyPair, err error) {
+func getCertPEMCached(cs certStore, domain string, now time.Time) (p *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 b.getCertStore(dir).Read(domain, now)
+	return cs.Read(domain, now)
 }
 
-func (b *LocalBackend) getCertPEM(ctx context.Context, logf logger.Logf, traceACME func(any), dir, domain string, now time.Time) (*TLSCertKeyPair, error) {
+func (b *LocalBackend) getCertPEM(ctx context.Context, cs certStore, logf logger.Logf, traceACME func(any), domain string, now time.Time) (*TLSCertKeyPair, error) {
 	acmeMu.Lock()
 	defer acmeMu.Unlock()
 
-	if p, err := b.getCertPEMCached(dir, domain, now); err == nil {
+	if p, err := getCertPEMCached(cs, domain, now); err == nil {
 		return p, nil
 	} else if !errors.Is(err, ipn.ErrStateNotExist) && !errors.Is(err, errCertExpired) {
 		return nil, err
 	}
 
-	key, err := acmeKey(dir)
+	key, err := acmeKey(cs)
 	if err != nil {
 		return nil, fmt.Errorf("acmeKey: %w", err)
 	}
@@ -366,8 +402,7 @@ func (b *LocalBackend) getCertPEM(ctx context.Context, logf logger.Logf, traceAC
 	if err := encodeECDSAKey(&privPEM, certPrivKey); err != nil {
 		return nil, err
 	}
-	certStore := b.getCertStore(dir)
+	if err := cs.WriteKey(domain, privPEM.Bytes()); err != nil {
-	if err := certStore.WriteKey(domain, privPEM.Bytes()); err != nil {
 		return nil, err
 	}
 
@@ -390,7 +425,7 @@ func (b *LocalBackend) getCertPEM(ctx context.Context, logf logger.Logf, traceAC
 			return nil, err
 		}
 	}
-	if err := certStore.WriteCert(domain, certPEM.Bytes()); err != nil {
+	if err := cs.WriteCert(domain, certPEM.Bytes()); err != nil {
 		return nil, err
 	}
 
@@ -444,14 +479,15 @@ func parsePrivateKey(der []byte) (crypto.Signer, error) {
 	return nil, errors.New("acme/autocert: failed to parse private key")
 }
 
-func acmeKey(dir string) (crypto.Signer, error) {
+func acmeKey(cs certStore) (crypto.Signer, error) {
-	pemName := filepath.Join(dir, "acme-account.key.pem")
+	if v, err := cs.ACMEKey(); err == nil {
-	if v, err := os.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)
+	} else if err != nil && !errors.Is(err, ipn.ErrStateNotExist) {
+		return nil, err
 	}
 
 	privKey, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
@@ -462,7 +498,7 @@ func acmeKey(dir string) (crypto.Signer, error) {
 	if err := encodeECDSAKey(&pemBuf, privKey); err != nil {
 		return nil, err
 	}
-	if err := os.WriteFile(pemName, pemBuf.Bytes(), 0600); err != nil {
+	if err := cs.WriteACMEKey(pemBuf.Bytes()); err != nil {
 		return nil, err
 	}
 	return privKey, nil