ipn,cmd/tailscale/cli: set correct SNI name for TLS-terminated TCP Services

Fixes #17749.

Signed-off-by: Naman Sood <mail@nsood.in>

cmd/tailscale/cli/serve_v2.go

@@ -966,7 +966,7 @@ func (e *serveEnv) setServe(sc *ipn.ServeConfig, dnsName string, srvType serveTy
 		if e.setPath != "" {
 			return fmt.Errorf("cannot mount a path for TCP serve")
 		}
-		err := e.applyTCPServe(sc, dnsName, srvType, srvPort, target)
+		err := e.applyTCPServe(sc, dnsName, srvType, srvPort, target, mds)
 		if err != nil {
 			return fmt.Errorf("failed to apply TCP serve: %w", err)
 		}
@@ -1170,7 +1170,7 @@ func (e *serveEnv) applyWebServe(sc *ipn.ServeConfig, dnsName string, srvPort ui
 	return nil
 }
 
-func (e *serveEnv) applyTCPServe(sc *ipn.ServeConfig, dnsName string, srcType serveType, srcPort uint16, target string) error {
+func (e *serveEnv) applyTCPServe(sc *ipn.ServeConfig, dnsName string, srcType serveType, srcPort uint16, target string, mds string) error {
 	var terminateTLS bool
 	switch srcType {
 	case serveTypeTCP:
@@ -1192,9 +1192,11 @@ func (e *serveEnv) applyTCPServe(sc *ipn.ServeConfig, dnsName string, srcType se
 	}
 
 	// TODO: needs to account for multiple configs from foreground mode
-	svcName := tailcfg.AsServiceName(dnsName)
-	if sc.IsServingWeb(srcPort, svcName) {
-		return fmt.Errorf("cannot serve TCP; already serving web on %d for %s", srcPort, dnsName)
+	if svcName := tailcfg.AsServiceName(dnsName); svcName != "" {
+		if sc.IsServingWeb(srcPort, svcName) {
+			return fmt.Errorf("cannot serve TCP; already serving web on %d for %s", srcPort, dnsName)
+		}
+		sc.SetTCPForwardingForService(srcPort, dstURL.Host, terminateTLS, svcName, mds)
 	}
 
 	sc.SetTCPForwarding(srcPort, dstURL.Host, terminateTLS, dnsName)

ipn/serve.go

@@ -408,19 +408,30 @@ func (sc *ServeConfig) SetTCPForwarding(port uint16, fwdAddr string, terminateTL
 	if sc == nil {
 		sc = new(ServeConfig)
 	}
-	tcpPortHandler := &sc.TCP
-	if svcName := tailcfg.AsServiceName(host); svcName != "" {
-		svcConfig, ok := sc.Services[svcName]
-		if !ok {
-			svcConfig = new(ServiceConfig)
-			mak.Set(&sc.Services, svcName, svcConfig)
-		}
-		tcpPortHandler = &svcConfig.TCP
+	mak.Set(&sc.TCP, port, &TCPPortHandler{TCPForward: fwdAddr})
+
+	if terminateTLS {
+		sc.TCP[port].TerminateTLS = host
+	}
+}
+
+// SetTCPForwardingForService is sets the fwdAddr (IP:port form) to which to
+// forward connections from the given port on the service. If terminateTLS
+// is true, TLS connections are terminated, with only the FQDN that corresponds
+// to the given service being permitted, before passing them to the fwdAddr.
+func (sc *ServeConfig) SetTCPForwardingForService(port uint16, fwdAddr string, terminateTLS bool, svcName tailcfg.ServiceName, magicDNSSuffix string) {
+	if sc == nil {
+		sc = new(ServeConfig)
+	}
+	svcConfig, ok := sc.Services[svcName]
+	if !ok {
+		svcConfig = new(ServiceConfig)
+		mak.Set(&sc.Services, svcName, svcConfig)
 	}
-	mak.Set(tcpPortHandler, port, &TCPPortHandler{TCPForward: fwdAddr})
+	mak.Set(&svcConfig.TCP, port, &TCPPortHandler{TCPForward: fwdAddr})
 
 	if terminateTLS {
-		(*tcpPortHandler)[port].TerminateTLS = host
+		svcConfig.TCP[port].TerminateTLS = fmt.Sprintf("%s.%s", svcName.WithoutPrefix(), magicDNSSuffix)
 	}
 }