Commit 61310600 authored by David Fifield's avatar David Fifield
Browse files

Automatically fetch certificates from Let's Encrypt.

This removes the --tls-cert and --tls-keys options and replaces them
with --acme-hostname and (optional) --acme-email. It uses
https://godoc.org/golang.org/x/crypto/acme/autocert, which is kind of a
successor to https://godoc.org/rsc.io/letsencrypt.

The autocert package only works when the listener runs on port 443. For
that reason, if TOR_PT_SERVER_BINDADDR asks for a port other than 443,
the program will open an *additional* listening port on 443. If there is
an error opening the listener, it is reported through an SMETHOD-ERROR
for the requested address.

The inspiration for this code came from George Tankersley's patch for
meek-server:
https://bugs.torproject.org/18655#comment:8
https://github.com/gtank/meek/tree/letsencrypt
parent af70d49e
......@@ -19,12 +19,14 @@ import (
"net/http"
"os"
"os/signal"
"strings"
"sync"
"syscall"
"time"
"git.torproject.org/pluggable-transports/goptlib.git"
"git.torproject.org/pluggable-transports/websocket.git/websocket"
"golang.org/x/crypto/acme/autocert"
)
const ptMethodName = "snowflake"
......@@ -150,7 +152,7 @@ func webSocketHandler(ws *websocket.WebSocket) {
proxy(or, &conn)
}
func listenTLS(network string, addr *net.TCPAddr, certFilename, keyFilename string) (net.Listener, error) {
func listenTLS(network string, addr *net.TCPAddr, m *autocert.Manager) (net.Listener, error) {
// This is cribbed from the source of net/http.Server.ListenAndServeTLS.
// We have to separate the Listen and Serve parts because we need to
// report the listening address before entering Serve (which is an
......@@ -158,13 +160,7 @@ func listenTLS(network string, addr *net.TCPAddr, certFilename, keyFilename stri
// https://groups.google.com/d/msg/Golang-nuts/3F1VRCCENp8/3hcayZiwYM8J
config := &tls.Config{}
config.NextProtos = []string{"http/1.1"}
var err error
config.Certificates = make([]tls.Certificate, 1)
config.Certificates[0], err = tls.LoadX509KeyPair(certFilename, keyFilename)
if err != nil {
return nil, err
}
config.GetCertificate = m.GetCertificate
conn, err := net.ListenTCP(network, addr)
if err != nil {
......@@ -190,8 +186,8 @@ func startListener(network string, addr *net.TCPAddr) (net.Listener, error) {
return startServer(ln)
}
func startListenerTLS(network string, addr *net.TCPAddr, certFilename, keyFilename string) (net.Listener, error) {
ln, err := listenTLS(network, addr, certFilename, keyFilename)
func startListenerTLS(network string, addr *net.TCPAddr, m *autocert.Manager) (net.Listener, error) {
ln, err := listenTLS(network, addr, m)
if err != nil {
return nil, err
}
......@@ -217,14 +213,13 @@ func startServer(ln net.Listener) (net.Listener, error) {
}
func main() {
var acmeHostnamesCommas string
var disableTLS bool
var certFilename, keyFilename string
var logFilename string
flag.Usage = usage
flag.StringVar(&acmeHostnamesCommas, "acme-hostnames", "", "comma-separated hostnames for TLS certificate")
flag.BoolVar(&disableTLS, "disable-tls", false, "don't use HTTPS")
flag.StringVar(&certFilename, "cert", "", "TLS certificate file (required without --disable-tls)")
flag.StringVar(&keyFilename, "key", "", "TLS private key file (required without --disable-tls)")
flag.StringVar(&logFilename, "log", "", "log file to write to")
flag.Parse()
......@@ -237,15 +232,10 @@ func main() {
log.SetOutput(f)
}
if disableTLS {
if certFilename != "" || keyFilename != "" {
log.Fatalf("the --cert and --key options are not allowed with --disable-tls")
}
} else {
if certFilename == "" || keyFilename == "" {
log.Fatalf("the --cert and --key options are required")
}
if !disableTLS && acmeHostnamesCommas == "" {
log.Fatal("the --acme-hostnames option is required")
}
acmeHostnames := strings.Split(acmeHostnamesCommas, ",")
log.Printf("starting")
var err error
......@@ -254,6 +244,28 @@ func main() {
log.Fatalf("error in setup: %s", err)
}
if !disableTLS {
log.Printf("ACME hostnames: %q", acmeHostnames)
}
certManager := autocert.Manager{
Prompt: autocert.AcceptTOS,
HostPolicy: autocert.HostWhitelist(acmeHostnames...),
}
// The ACME responder only works when it is running on port 443. In case
// there is not already going to be a TLS listener on port 443, we need
// to open an additional one. The port is actually opened in the loop
// below, so that any errors can be reported in the SMETHOD-ERROR of
// another bindaddr.
// https://letsencrypt.github.io/acme-spec/#domain-validation-with-server-name-indication-dvsni
need443Listener := !disableTLS
for _, bindaddr := range ptInfo.Bindaddrs {
if !disableTLS && bindaddr.Addr.Port == 443 {
need443Listener = false
break
}
}
listeners := make([]net.Listener, 0)
for _, bindaddr := range ptInfo.Bindaddrs {
if bindaddr.MethodName != ptMethodName {
......@@ -261,6 +273,20 @@ func main() {
continue
}
if need443Listener {
addr := *bindaddr.Addr
addr.Port = 443
log.Printf("opening additional ACME listener on %s", addr.String())
ln443, err := startListenerTLS("tcp", &addr, &certManager)
if err != nil {
log.Printf("error opening ACME listener: %s", err)
pt.SmethodError(bindaddr.MethodName, "ACME listener: "+err.Error())
continue
}
listeners = append(listeners, ln443)
need443Listener = false
}
var ln net.Listener
args := pt.Args{}
if disableTLS {
......@@ -268,7 +294,7 @@ func main() {
ln, err = startListener("tcp", bindaddr.Addr)
} else {
args.Add("tls", "yes")
ln, err = startListenerTLS("tcp", bindaddr.Addr, certFilename, keyFilename)
ln, err = startListenerTLS("tcp", bindaddr.Addr, &certManager)
}
if err != nil {
log.Printf("error opening listener: %s", err)
......
......@@ -5,5 +5,5 @@ SocksPort 0
ExitPolicy reject *:*
DataDirectory datadir
ServerTransportListenAddr snowflake 0.0.0.0:9902
ServerTransportPlugin snowflake exec ./server --disable-tls --log snowflake.log
ServerTransportListenAddr snowflake 0.0.0.0:443
ServerTransportPlugin snowflake exec ./server --acme-hostnames snowflake.example --acme-email admin@snowflake.example --log snowflake.log
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