fix: generate a per-installation root CA

2026-08-18 03:57:06 +08:00 · 2026-08-12 20:04:29 +08:00
parent 7a67e76617
commit 2b8d1c9e3d
14 changed files with 454 additions and 89 deletions
@@ -0,0 +1,191 @@
+package certs
+
+import (
+	"crypto/rand"
+	"crypto/rsa"
+	"crypto/sha256"
+	"crypto/x509"
+	"crypto/x509/pkix"
+	"encoding/hex"
+	"encoding/pem"
+	"errors"
+	"fmt"
+	"math/big"
+	"os"
+	"path/filepath"
+	"strings"
+	"time"
+)
+
+const legacySharedCASHA256 = "836E6BB84F6C3E63316DBB4EC257223AF09F7490E7AAE09030B8515ED61EE9FF"
+
+// LoadOrCreateManager loads the installation-specific CA, generating it on
+// first run. The private key is persisted only in the supplied local path.
+func LoadOrCreateManager(certPath, keyPath string) (*Manager, []byte, error) {
+	certPEM, certErr := os.ReadFile(certPath)
+	keyPEM, keyErr := os.ReadFile(keyPath)
+
+	if certErr == nil && isLegacySharedCA(certPEM) {
+		return generateAndPersistManager(certPath, keyPath)
+	}
+	if certErr == nil && keyErr == nil {
+		manager, err := NewManagerFromPEM(certPEM, keyPEM)
+		if err != nil {
+			return nil, nil, fmt.Errorf("load installation CA: %w", err)
+		}
+		if err := os.Chmod(keyPath, 0o600); err != nil {
+			return nil, nil, fmt.Errorf("restrict installation CA private key permissions: %w", err)
+		}
+		return manager, manager.CACertPEM(), nil
+	}
+	if errors.Is(certErr, os.ErrNotExist) && errors.Is(keyErr, os.ErrNotExist) {
+		return generateAndPersistManager(certPath, keyPath)
+	}
+	// A key without a certificate cannot have been installed as a trusted root.
+	// This is safe to recover if the first-run write was interrupted.
+	if errors.Is(certErr, os.ErrNotExist) && keyErr == nil {
+		return generateAndPersistManager(certPath, keyPath)
+	}
+	if certErr != nil && !errors.Is(certErr, os.ErrNotExist) {
+		return nil, nil, fmt.Errorf("read installation CA certificate: %w", certErr)
+	}
+	if keyErr != nil && !errors.Is(keyErr, os.ErrNotExist) {
+		return nil, nil, fmt.Errorf("read installation CA private key: %w", keyErr)
+	}
+	return nil, nil, errors.New("installation CA is incomplete; both certificate and private key are required")
+}
+
+// NewGeneratedManager creates an in-memory CA suitable for short-lived tools.
+func NewGeneratedManager() (*Manager, []byte, error) {
+	certPEM, keyPEM, err := generateCA()
+	if err != nil {
+		return nil, nil, err
+	}
+	manager, err := NewManagerFromPEM(certPEM, keyPEM)
+	if err != nil {
+		return nil, nil, err
+	}
+	return manager, manager.CACertPEM(), nil
+}
+
+func generateAndPersistManager(certPath, keyPath string) (*Manager, []byte, error) {
+	if filepath.Dir(certPath) != filepath.Dir(keyPath) {
+		return nil, nil, errors.New("installation CA certificate and key must share a directory")
+	}
+	certPEM, keyPEM, err := generateCA()
+	if err != nil {
+		return nil, nil, err
+	}
+	if err := os.MkdirAll(filepath.Dir(certPath), 0o700); err != nil {
+		return nil, nil, fmt.Errorf("create installation CA directory: %w", err)
+	}
+	// Write the private key first so a crash cannot leave a new certificate
+	// without the signing key needed by the proxy.
+	if err := writeLocalCAFile(keyPath, keyPEM, 0o600); err != nil {
+		return nil, nil, fmt.Errorf("persist installation CA private key: %w", err)
+	}
+	if err := writeLocalCAFile(certPath, certPEM, 0o644); err != nil {
+		return nil, nil, fmt.Errorf("persist installation CA certificate: %w", err)
+	}
+	manager, err := NewManagerFromPEM(certPEM, keyPEM)
+	if err != nil {
+		return nil, nil, err
+	}
+	return manager, manager.CACertPEM(), nil
+}
+
+func generateCA() ([]byte, []byte, error) {
+	privateKey, err := rsa.GenerateKey(rand.Reader, 3072)
+	if err != nil {
+		return nil, nil, fmt.Errorf("generate installation CA private key: %w", err)
+	}
+	serial, err := rand.Int(rand.Reader, new(big.Int).Lsh(big.NewInt(1), 128))
+	if err != nil {
+		return nil, nil, fmt.Errorf("generate installation CA serial: %w", err)
+	}
+	publicKeyDER, err := x509.MarshalPKIXPublicKey(&privateKey.PublicKey)
+	if err != nil {
+		return nil, nil, fmt.Errorf("marshal installation CA public key: %w", err)
+	}
+	subjectKeyID := sha256.Sum256(publicKeyDER)
+	now := time.Now()
+	template := &x509.Certificate{
+		SerialNumber: serial,
+		Subject: pkix.Name{
+			CommonName:   "Cursor BYOK Local CA",
+			Organization: []string{"Cursor BYOK"},
+		},
+		NotBefore:             now.Add(-5 * time.Minute),
+		NotAfter:              now.AddDate(10, 0, 0),
+		KeyUsage:              x509.KeyUsageDigitalSignature | x509.KeyUsageCertSign | x509.KeyUsageCRLSign,
+		BasicConstraintsValid: true,
+		IsCA:                  true,
+		MaxPathLen:            0,
+		MaxPathLenZero:        true,
+		SubjectKeyId:          append([]byte(nil), subjectKeyID[:20]...),
+	}
+	der, err := x509.CreateCertificate(rand.Reader, template, template, &privateKey.PublicKey, privateKey)
+	if err != nil {
+		return nil, nil, fmt.Errorf("create installation CA certificate: %w", err)
+	}
+	certPEM := pem.EncodeToMemory(&pem.Block{Type: "CERTIFICATE", Bytes: der})
+	keyPEM := pem.EncodeToMemory(&pem.Block{Type: "RSA PRIVATE KEY", Bytes: x509.MarshalPKCS1PrivateKey(privateKey)})
+	return certPEM, keyPEM, nil
+}
+
+func writeLocalCAFile(path string, data []byte, mode os.FileMode) error {
+	temp, err := os.CreateTemp(filepath.Dir(path), ".ca-*")
+	if err != nil {
+		return err
+	}
+	tempPath := temp.Name()
+	defer os.Remove(tempPath)
+	if err := temp.Chmod(mode); err != nil {
+		_ = temp.Close()
+		return err
+	}
+	if _, err := temp.Write(data); err != nil {
+		_ = temp.Close()
+		return err
+	}
+	if err := temp.Sync(); err != nil {
+		_ = temp.Close()
+		return err
+	}
+	if err := temp.Close(); err != nil {
+		return err
+	}
+	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
+		return err
+	}
+	if err := os.Rename(tempPath, path); err != nil {
+		return err
+	}
+	return os.Chmod(path, mode)
+}
+
+func isLegacySharedCA(certPEM []byte) bool {
+	block, _ := pem.Decode(certPEM)
+	if block == nil {
+		return false
+	}
+	cert, err := x509.ParseCertificate(block.Bytes)
+	if err != nil {
+		return false
+	}
+	sum := sha256.Sum256(cert.Raw)
+	return strings.EqualFold(hex.EncodeToString(sum[:]), legacySharedCASHA256)
+}
+
+// loadCAPEMFromFiles reads an explicitly supplied CA pair.
+func loadCAPEMFromFiles(certPath, keyPath string) ([]byte, []byte, error) {
+	certPEM, err := os.ReadFile(certPath)
+	if err != nil {
+		return nil, nil, err
+	}
+	keyPEM, err := os.ReadFile(keyPath)
+	if err != nil {
+		return nil, nil, err
+	}
+	return certPEM, keyPEM, nil
+}