Remove local LAN address ICE candidates

Unfortunately, the "public" RTCIceTransportPolicy was removed.

https://developer.mozilla.org/en-US/docs/Web/API/RTCConfiguration#RTCIceTransportPolicy_enum

Trac: 19026

client/lib/lib_test.go

@@ -288,15 +288,15 @@ func TestSnowflakeClient(t *testing.T) {
 		fakeOffer := deserializeSessionDescription(`{"type":"offer","sdp":"test"}`)
 
 		Convey("Construct BrokerChannel with no front domain", func() {
-			b, err := NewBrokerChannel("test.broker", "", transport)
+			b, err := NewBrokerChannel("test.broker", "", transport, false)
 			So(b.url, ShouldNotBeNil)
 			So(err, ShouldBeNil)
 			So(b.url.Path, ShouldResemble, "test.broker")
 			So(b.transport, ShouldNotBeNil)
 		})
 
 		Convey("Construct BrokerChannel *with* front domain", func() {
-			b, err := NewBrokerChannel("test.broker", "front", transport)
+			b, err := NewBrokerChannel("test.broker", "front", transport, false)
 			So(b.url, ShouldNotBeNil)
 			So(err, ShouldBeNil)
 			So(b.url.Path, ShouldResemble, "test.broker")
@@ -305,7 +305,7 @@ func TestSnowflakeClient(t *testing.T) {
 		})
 
 		Convey("BrokerChannel.Negotiate responds with answer", func() {
-			b, err := NewBrokerChannel("test.broker", "", transport)
+			b, err := NewBrokerChannel("test.broker", "", transport, false)
 			So(err, ShouldBeNil)
 			answer, err := b.Negotiate(fakeOffer)
 			So(err, ShouldBeNil)
@@ -315,7 +315,8 @@ func TestSnowflakeClient(t *testing.T) {
 
 		Convey("BrokerChannel.Negotiate fails with 503", func() {
 			b, err := NewBrokerChannel("test.broker", "",
-				&MockTransport{http.StatusServiceUnavailable, []byte("\n")})
+				&MockTransport{http.StatusServiceUnavailable, []byte("\n")},
+				false)
 			So(err, ShouldBeNil)
 			answer, err := b.Negotiate(fakeOffer)
 			So(err, ShouldNotBeNil)
@@ -325,7 +326,8 @@ func TestSnowflakeClient(t *testing.T) {
 
 		Convey("BrokerChannel.Negotiate fails with 400", func() {
 			b, err := NewBrokerChannel("test.broker", "",
-				&MockTransport{http.StatusBadRequest, []byte("\n")})
+				&MockTransport{http.StatusBadRequest, []byte("\n")},
+				false)
 			So(err, ShouldBeNil)
 			answer, err := b.Negotiate(fakeOffer)
 			So(err, ShouldNotBeNil)
@@ -335,7 +337,8 @@ func TestSnowflakeClient(t *testing.T) {
 
 		Convey("BrokerChannel.Negotiate fails with large read", func() {
 			b, err := NewBrokerChannel("test.broker", "",
-				&MockTransport{http.StatusOK, make([]byte, 100001, 100001)})
+				&MockTransport{http.StatusOK, make([]byte, 100001, 100001)},
+				false)
 			So(err, ShouldBeNil)
 			answer, err := b.Negotiate(fakeOffer)
 			So(err, ShouldNotBeNil)
@@ -345,12 +348,30 @@ func TestSnowflakeClient(t *testing.T) {
 
 		Convey("BrokerChannel.Negotiate fails with unexpected error", func() {
 			b, err := NewBrokerChannel("test.broker", "",
-				&MockTransport{123, []byte("")})
+				&MockTransport{123, []byte("")}, false)
 			So(err, ShouldBeNil)
 			answer, err := b.Negotiate(fakeOffer)
 			So(err, ShouldNotBeNil)
 			So(answer, ShouldBeNil)
 			So(err.Error(), ShouldResemble, BrokerErrorUnexpected)
 		})
 	})
+
+	Convey("Strip", t, func() {
+		const offerStart = `{"type":"offer","sdp":"v=0\r\no=- 4358805017720277108 2 IN IP4 8.8.8.8\r\ns=-\r\nt=0 0\r\na=group:BUNDLE data\r\na=msid-semantic: WMS\r\nm=application 56688 DTLS/SCTP 5000\r\nc=IN IP4 8.8.8.8\r\n`
+		const goodCandidate = `a=candidate:3769337065 1 udp 2122260223 8.8.8.8 56688 typ host generation 0 network-id 1 network-cost 50\r\n`
+		const offerEnd = `a=ice-ufrag:aMAZ\r\na=ice-pwd:jcHb08Jjgrazp2dzjdrvPPvV\r\na=ice-options:trickle\r\na=fingerprint:sha-256 C8:88:EE:B9:E7:02:2E:21:37:ED:7A:D1:EB:2B:A3:15:A2:3B:5B:1C:3D:D4:D5:1F:06:CF:52:40:03:F8:DD:66\r\na=setup:actpass\r\na=mid:data\r\na=sctpmap:5000 webrtc-datachannel 1024\r\n"}`
+
+		offer := offerStart + goodCandidate +
+			`a=candidate:3769337065 1 udp 2122260223 192.168.0.100 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsLocal IPv4
+			`a=candidate:3769337065 1 udp 2122260223 fdf8:f53b:82e4::53 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsLocal IPv6
+			`a=candidate:3769337065 1 udp 2122260223 0.0.0.0 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsUnspecified IPv4
+			`a=candidate:3769337065 1 udp 2122260223 :: 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsUnspecified IPv6
+			`a=candidate:3769337065 1 udp 2122260223 127.0.0.1 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsLoopback IPv4
+			`a=candidate:3769337065 1 udp 2122260223 ::1 56688 typ host generation 0 network-id 1 network-cost 50\r\n` + // IsLoopback IPv6
+			offerEnd
+
+		So(stripLocalAddresses(offer), ShouldEqual, offerStart+goodCandidate+offerEnd)
+	})
+
 }

client/lib/rendezvous.go

@@ -14,9 +14,12 @@ import (
 	"io"
 	"io/ioutil"
 	"log"
+	"net"
 	"net/http"
 	"net/url"
+	"regexp"
 
+	"github.com/pion/sdp"
 	"github.com/pion/webrtc"
 )
 
@@ -31,9 +34,10 @@ const (
 type BrokerChannel struct {
 	// The Host header to put in the HTTP request (optional and may be
 	// different from the host name in URL).
-	Host      string
-	url       *url.URL
-	transport http.RoundTripper // Used to make all requests.
+	Host               string
+	url                *url.URL
+	transport          http.RoundTripper // Used to make all requests.
+	keepLocalAddresses bool
 }
 
 // We make a copy of DefaultTransport because we want the default Dial
@@ -48,7 +52,7 @@ func CreateBrokerTransport() http.RoundTripper {
 // Construct a new BrokerChannel, where:
 // |broker| is the full URL of the facilitating program which assigns proxies
 // to clients, and |front| is the option fronting domain.
-func NewBrokerChannel(broker string, front string, transport http.RoundTripper) (*BrokerChannel, error) {
+func NewBrokerChannel(broker string, front string, transport http.RoundTripper, keepLocalAddresses bool) (*BrokerChannel, error) {
 	targetURL, err := url.Parse(broker)
 	if err != nil {
 		return nil, err
@@ -63,6 +67,7 @@ func NewBrokerChannel(broker string, front string, transport http.RoundTripper)
 	}
 
 	bc.transport = transport
+	bc.keepLocalAddresses = keepLocalAddresses
 	return bc, nil
 }
 
@@ -76,6 +81,41 @@ func limitedRead(r io.Reader, limit int64) ([]byte, error) {
 	return p, err
 }
 
+// Stolen from https://github.com/golang/go/pull/30278
+func IsLocal(ip net.IP) bool {
+	if ip4 := ip.To4(); ip4 != nil {
+		// Local IPv4 addresses are defined in https://tools.ietf.org/html/rfc1918
+		return ip4[0] == 10 ||
+			(ip4[0] == 172 && ip4[1]&0xf0 == 16) ||
+			(ip4[0] == 192 && ip4[1] == 168)
+	}
+	// Local IPv6 addresses are defined in https://tools.ietf.org/html/rfc4193
+	return len(ip) == net.IPv6len && ip[0]&0xfe == 0xfc
+}
+
+// Removes local LAN address ICE candidates
+func stripLocalAddresses(str string) string {
+	re := regexp.MustCompile(`a=candidate:.*?\\r\\n`)
+	return re.ReplaceAllStringFunc(str, func(s string) string {
+		t := s[len("a=candidate:") : len(s)-len("\\r\\n")]
+		var ice sdp.ICECandidate
+		err := ice.Unmarshal(t)
+		if err != nil {
+			return s
+		}
+		if ice.Typ == "host" {
+			ip := net.ParseIP(ice.Address)
+			if ip == nil {
+				return s
+			}
+			if IsLocal(ip) || ip.IsUnspecified() || ip.IsLoopback() {
+				return ""
+			}
+		}
+		return s
+	})
+}
+
 // Roundtrip HTTP POST using WebRTC SessionDescriptions.
 //
 // Send an SDP offer to the broker, which assigns a proxy and responds
@@ -84,7 +124,20 @@ func (bc *BrokerChannel) Negotiate(offer *webrtc.SessionDescription) (
 	*webrtc.SessionDescription, error) {
 	log.Println("Negotiating via BrokerChannel...\nTarget URL: ",
 		bc.Host, "\nFront URL:  ", bc.url.Host)
-	data := bytes.NewReader([]byte(serializeSessionDescription(offer)))
+	str := serializeSessionDescription(offer)
+	// Ideally, we could specify an `RTCIceTransportPolicy` that would handle
+	// this for us.  However, "public" was removed from the draft spec.
+	// See https://developer.mozilla.org/en-US/docs/Web/API/RTCConfiguration#RTCIceTransportPolicy_enum
+	//
+	// FIXME: We are stripping local addresses from the JSON serialized string,
+	// which is expedient but unsatisfying.  We could advocate upstream to
+	// implement a non-standard ICE transport policy, or to somehow alter
+	// APIs to avoid adding the undesirable candidates or a method to filter
+	// them from the marshalled session description.
+	if !bc.keepLocalAddresses {
+		str = stripLocalAddresses(str)
+	}
+	data := bytes.NewReader([]byte(str))
 	// Suffix with broker's client registration handler.
 	clientURL := bc.url.ResolveReference(&url.URL{Path: "client"})
 	request, err := http.NewRequest("POST", clientURL.String(), data)

client/snowflake.go

@@ -90,6 +90,7 @@ func main() {
 	frontDomain := flag.String("front", "", "front domain")
 	logFilename := flag.String("log", "", "name of log file")
 	logToStateDir := flag.Bool("logToStateDir", false, "resolve the log file relative to tor's pt state dir")
+	keepLocalAddresses := flag.Bool("keepLocalAddresses", false, "keep local LAN address ICE candidates")
 	max := flag.Int("max", DefaultSnowflakeCapacity,
 		"capacity for number of multiplexed WebRTC peers")
 	flag.Parse()
@@ -133,7 +134,7 @@ func main() {
 	snowflakes := sf.NewPeers(*max)
 
 	// Use potentially domain-fronting broker to rendezvous.
-	broker, err := sf.NewBrokerChannel(*brokerURL, *frontDomain, sf.CreateBrokerTransport())
+	broker, err := sf.NewBrokerChannel(*brokerURL, *frontDomain, sf.CreateBrokerTransport(), *keepLocalAddresses)
 	if err != nil {
 		log.Fatalf("parsing broker URL: %v", err)
 	}

client/torrc-localhost

@@ -3,5 +3,6 @@ DataDirectory datadir
 
 ClientTransportPlugin snowflake exec ./client \
 -url http://localhost:8080/ \
+-keepLocalAddresses
 
 Bridge snowflake 0.0.3.0:1