ipn/ipnlocal: add optional TLS termination on proxied TCP connections

Updates tailscale/corp#7515

Change-Id: Ib250fa20275971563adccfa72db48e0cec02b7a5
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

ipn/ipn_clone.go

@@ -107,7 +107,7 @@ func (src *TCPPortHandler) Clone() *TCPPortHandler {
 var _TCPPortHandlerCloneNeedsRegeneration = TCPPortHandler(struct {
 	HTTPS        bool
 	TCPForward   string
-	TerminateTLS bool
+	TerminateTLS string
 }{})
 
 // Clone makes a deep copy of HTTPHandler.

ipn/ipn_view.go

@@ -232,15 +232,15 @@ func (v *TCPPortHandlerView) UnmarshalJSON(b []byte) error {
 	return nil
 }
 
-func (v TCPPortHandlerView) HTTPS() bool        { return v.ж.HTTPS }
-func (v TCPPortHandlerView) TCPForward() string { return v.ж.TCPForward }
-func (v TCPPortHandlerView) TerminateTLS() bool { return v.ж.TerminateTLS }
+func (v TCPPortHandlerView) HTTPS() bool          { return v.ж.HTTPS }
+func (v TCPPortHandlerView) TCPForward() string   { return v.ж.TCPForward }
+func (v TCPPortHandlerView) TerminateTLS() string { return v.ж.TerminateTLS }
 
 // A compilation failure here means this code must be regenerated, with the command at the top of this file.
 var _TCPPortHandlerViewNeedsRegeneration = TCPPortHandler(struct {
 	HTTPS        bool
 	TCPForward   string
-	TerminateTLS bool
+	TerminateTLS string
 }{})
 
 // View returns a readonly view of HTTPHandler.

ipn/ipnlocal/serve.go

@@ -112,11 +112,6 @@ func (b *LocalBackend) HandleInterceptedTCPConn(dport uint16, srcAddr netip.Addr
 	}
 
 	if backDst := tcph.TCPForward(); backDst != "" {
-		if tcph.TerminateTLS() {
-			b.logf("TODO(bradfitz): finish")
-			sendRST()
-			return
-		}
 		ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
 		backConn, err := b.dialer.SystemDial(ctx, "tcp", backDst)
 		cancel()
@@ -134,6 +129,24 @@ func (b *LocalBackend) HandleInterceptedTCPConn(dport uint16, srcAddr netip.Addr
 		defer conn.Close()
 		defer backConn.Close()
 
+		if sni := tcph.TerminateTLS(); sni != "" {
+			conn = tls.Server(conn, &tls.Config{
+				GetCertificate: func(hi *tls.ClientHelloInfo) (*tls.Certificate, error) {
+					ctx, cancel := context.WithTimeout(context.Background(), time.Minute)
+					defer cancel()
+					pair, err := b.GetCertPEM(ctx, sni)
+					if err != nil {
+						return nil, err
+					}
+					cert, err := tls.X509KeyPair(pair.CertPEM, pair.KeyPEM)
+					if err != nil {
+						return nil, err
+					}
+					return &cert, nil
+				},
+			})
+		}
+
 		// TODO(bradfitz): do the RegisterIPPortIdentity and
 		// UnregisterIPPortIdentity stuff that netstack does
 

ipn/store.go

@@ -112,10 +112,11 @@ type TCPPortHandler struct {
 	// It is mutually exclusive with HTTPS.
 	TCPForward string `json:",omitempty"`
 
-	// TerminateTLS is whether tailscaled should terminate TLS
-	// connections before forwarding them to TCPForward. It is only
-	// used if TCPForward is non-empty. (the HTTPS mode )
-	TerminateTLS bool `json:",omitempty"`
+	// TerminateTLS, if non-empty, means that tailscaled should terminate the
+	// TLS connections before forwarding them to TCPForward, permitting only the
+	// SNI name with this value. It is only used if TCPForward is non-empty.
+	// (the HTTPS mode uses ServeConfig.Web)
+	TerminateTLS string `json:",omitempty"`
 }
 
 // HTTPHandler is either a path or a proxy to serve.