serve TLS: validate client CNs against whitelist in config file

daemon/serve/serve_tls.go

@@ -3,6 +3,7 @@ package serve
 import (
 	"crypto/tls"
 	"crypto/x509"
+	"fmt"
 	"github.com/pkg/errors"
 	"github.com/zrepl/zrepl/config"
 	"github.com/zrepl/zrepl/tlsconf"
@@ -16,6 +17,7 @@ type TLSListenerFactory struct {
 	clientCA         *x509.CertPool
 	serverCert       tls.Certificate
 	handshakeTimeout time.Duration
+	clientCNs map[string]struct{}
 }
 
 func TLSListenerFactoryFromConfig(c *config.Global, in *config.TLSServe) (lf *TLSListenerFactory, err error) {
@@ -38,6 +40,15 @@ func TLSListenerFactoryFromConfig(c *config.Global, in *config.TLSServe) (lf *TL
 		return nil, errors.Wrap(err, "cannot parse cer/key pair")
 	}
 
+	lf.clientCNs = make(map[string]struct{}, len(in.ClientCNs))
+	for i, cn := range in.ClientCNs {
+		if err := ValidateClientIdentity(cn); err != nil {
+			return nil, errors.Wrapf(err, "unsuitable client_cn #%d %q", i, cn)
+		}
+		// dupes are ok fr now
+		lf.clientCNs[cn] = struct{}{}
+	}
+
 	return lf, nil
 }
 
@@ -47,11 +58,12 @@ func (f *TLSListenerFactory) Listen() (AuthenticatedListener, error) {
 		return nil, err
 	}
 	tl := tlsconf.NewClientAuthListener(l, f.clientCA, f.serverCert, f.handshakeTimeout)
-	return tlsAuthListener{tl}, nil
+	return tlsAuthListener{tl, f.clientCNs}, nil
 }
 
 type tlsAuthListener struct {
 	*tlsconf.ClientAuthListener
+	clientCNs map[string]struct{}
 }
 
 func (l tlsAuthListener) Accept(ctx context.Context) (AuthenticatedConn, error) {
@@ -59,6 +71,12 @@ func (l tlsAuthListener) Accept(ctx context.Context) (AuthenticatedConn, error)
 	if err != nil {
 		return nil, err
 	}
+	if _, ok := l.clientCNs[cn]; !ok {
+		if err := c.Close(); err != nil {
+			getLogger(ctx).WithError(err).Error("error closing connection with unauthorized common name")
+		}
+		return nil, fmt.Errorf("unauthorized client common name %q from %s", cn, c.RemoteAddr())
+	}
 	return authConn{c, cn}, nil
 }