lnd: prepare TLS code for extraction

lnd.go

@@ -57,8 +57,10 @@ import (
 )
 
 const (
-	// Make certificate valid for 14 months.
-	autogenCertValidity = 14 /*months*/ * 30 /*days*/ * 24 * time.Hour
+	// defaultAutogenCertValidity is the default validity of a self-signed
+	// certificate. The value corresponds to 14 months
+	// (14 months * 30 days * 24 hours).
+	defaultAutogenCertValidity = 14 * 30 * 24 * time.Hour
 )
 
 var (
@@ -77,7 +79,8 @@ var (
 	serialNumberLimit = new(big.Int).Lsh(big.NewInt(1), 128)
 
 	/*
-	 * These cipher suites fit the following criteria:
+	 * tlsCipherSuites is the list of cipher suites we accept for TLS
+	 * connections. These cipher suites fit the following criteria:
 	 * - Don't use outdated algorithms like SHA-1 and 3DES
 	 * - Don't use ECB mode or other insecure symmetric methods
 	 * - Included in the TLS v1.2 suite
@@ -661,28 +664,28 @@ func getTLSConfig(tlsCertPath string, tlsKeyPath string, tlsExtraIPs,
 	tlsExtraDomains []string, rpcListeners []net.Addr) (*tls.Config,
 	*credentials.TransportCredentials, string, error) {
 
-	// Ensure we create TLS key and certificate if they don't exist
+	// Ensure we create TLS key and certificate if they don't exist.
 	if !fileExists(tlsCertPath) && !fileExists(tlsKeyPath) {
+		rpcsLog.Infof("Generating TLS certificates...")
 		err := genCertPair(
-			tlsCertPath, tlsKeyPath, tlsExtraIPs, tlsExtraDomains,
+			"lnd autogenerated cert", tlsCertPath, tlsKeyPath,
+			tlsExtraIPs, tlsExtraDomains,
+			defaultAutogenCertValidity,
 		)
 		if err != nil {
 			return nil, nil, "", err
 		}
+		rpcsLog.Infof("Done generating TLS certificates")
 	}
 
-	certData, err := tls.LoadX509KeyPair(tlsCertPath, tlsKeyPath)
+	certData, parsedCert, err := loadCert(tlsCertPath, tlsKeyPath)
 	if err != nil {
 		return nil, nil, "", err
 	}
 
-	cert, err := x509.ParseCertificate(certData.Certificate[0])
-	if err != nil {
-		return nil, nil, "", err
-	}
-
-	// If the certificate expired, delete it and the TLS key and generate a new pair
-	if time.Now().After(cert.NotAfter) {
+	// If the certificate expired, delete it and the TLS key and generate a
+	// new pair.
+	if time.Now().After(parsedCert.NotAfter) {
 		ltndLog.Info("TLS certificate is expired, generating a new one")
 
 		err := os.Remove(tlsCertPath)
@@ -695,21 +698,19 @@ func getTLSConfig(tlsCertPath string, tlsKeyPath string, tlsExtraIPs,
 			return nil, nil, "", err
 		}
 
+		rpcsLog.Infof("Generating TLS certificates...")
 		err = genCertPair(
-			tlsCertPath, tlsKeyPath, tlsExtraIPs, tlsExtraDomains,
+			"lnd autogenerated cert", tlsCertPath, tlsKeyPath,
+			tlsExtraIPs, tlsExtraDomains,
+			defaultAutogenCertValidity,
 		)
 		if err != nil {
 			return nil, nil, "", err
 		}
-
-	}
-
-	tlsCfg := &tls.Config{
-		Certificates: []tls.Certificate{certData},
-		CipherSuites: tlsCipherSuites,
-		MinVersion:   tls.VersionTLS12,
+		rpcsLog.Infof("Done generating TLS certificates")
 	}
 
+	tlsCfg := tlsConfFromCert(certData)
 	restCreds, err := credentials.NewClientTLSFromFile(tlsCertPath, "")
 	if err != nil {
 		return nil, nil, "", err
@@ -742,6 +743,41 @@ func fileExists(name string) bool {
 	return true
 }
 
+// loadCert loads a certificate and its corresponding private key from the PEM
+// files indicated and returns the certificate in the two formats it is most
+// commonly used.
+func loadCert(certPath, keyPath string) (tls.Certificate, *x509.Certificate,
+	error) {
+
+	// The certData returned here is just a wrapper around the PEM blocks
+	// loaded from the file. The PEM is not yet fully parsed but a basic
+	// check is performed that the certificate and private key actually
+	// belong together.
+	certData, err := tls.LoadX509KeyPair(certPath, keyPath)
+	if err != nil {
+		return tls.Certificate{}, nil, err
+	}
+
+	// Now parse the the PEM block of the certificate into its x509 data
+	// structure so it can be examined in more detail.
+	x509Cert, err := x509.ParseCertificate(certData.Certificate[0])
+	if err != nil {
+		return tls.Certificate{}, nil, err
+	}
+
+	return certData, x509Cert, nil
+}
+
+// tLSConfFromCert returns the default TLS configuration used for a server,
+// using the given certificate as identity.
+func tlsConfFromCert(certData tls.Certificate) *tls.Config {
+	return &tls.Config{
+		Certificates: []tls.Certificate{certData},
+		CipherSuites: tlsCipherSuites,
+		MinVersion:   tls.VersionTLS12,
+	}
+}
+
 // genCertPair generates a key/cert pair to the paths provided. The
 // auto-generated certificates should *not* be used in production for public
 // access as they're self-signed and don't necessarily contain all of the
@@ -750,14 +786,11 @@ func fileExists(name string) bool {
 //
 // This function is adapted from https://github.com/btcsuite/btcd and
 // https://github.com/btcsuite/btcutil
-func genCertPair(certFile, keyFile string, tlsExtraIPs,
-	tlsExtraDomains []string) error {
+func genCertPair(org, certFile, keyFile string, tlsExtraIPs,
+	tlsExtraDomains []string, certValidity time.Duration) error {
 
-	rpcsLog.Infof("Generating TLS certificates...")
-
-	org := "lnd autogenerated cert"
 	now := time.Now()
-	validUntil := now.Add(autogenCertValidity)
+	validUntil := now.Add(certValidity)
 
 	// Check that the certificate validity isn't past the ASN.1 end of time.
 	if validUntil.After(endOfTime) {
@@ -776,7 +809,7 @@ func genCertPair(certFile, keyFile string, tlsExtraIPs,
 	// addIP appends an IP address only if it isn't already in the slice.
 	addIP := func(ipAddr net.IP) {
 		for _, ip := range ipAddresses {
-			if bytes.Equal(ip, ipAddr) {
+			if ip.Equal(ipAddr) {
 				return
 			}
 		}
@@ -806,8 +839,10 @@ func genCertPair(certFile, keyFile string, tlsExtraIPs,
 	// Collect the host's names into a slice.
 	host, err := os.Hostname()
 	if err != nil {
-		rpcsLog.Errorf("Failed getting hostname, falling back to "+
-			"localhost: %v", err)
+		// Nothing much we can do here, other than falling back to
+		// localhost as fallback. A hostname can still be provided with
+		// the tlsExtraDomain parameter if the problem persists on a
+		// system.
 		host = "localhost"
 	}
 
@@ -879,7 +914,6 @@ func genCertPair(certFile, keyFile string, tlsExtraIPs,
 		return err
 	}
 
-	rpcsLog.Infof("Done generating TLS certificates")
 	return nil
 }