ceremonyclient/go-libp2p/p2p/transport/webrtc/transport.go

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2024-06-08 11:32:45 +00:00
// Package libp2pwebrtc implements the WebRTC transport for go-libp2p,
// as described in https://github.com/libp2p/specs/tree/master/webrtc.
//
// At this point, this package is EXPERIMENTAL, and the WebRTC transport is not enabled by default.
// While we're fairly confident that the implementation correctly implements the specification,
// we're not making any guarantees regarding its security (especially regarding resource exhaustion attacks).
// Fixes, even for security-related issues, will be conducted in the open.
//
// Experimentation is encouraged. Please open an issue if you encounter any problems with this transport.
//
// The udpmux subpackage contains the logic for multiplexing multiple WebRTC (ICE)
// connections over a single UDP socket.
package libp2pwebrtc
import (
"context"
"crypto"
"crypto/ecdsa"
"crypto/elliptic"
"crypto/rand"
"crypto/x509"
"encoding/binary"
"errors"
"fmt"
"net"
"time"
mrand "golang.org/x/exp/rand"
"google.golang.org/protobuf/proto"
"github.com/libp2p/go-libp2p/core/connmgr"
ic "github.com/libp2p/go-libp2p/core/crypto"
"github.com/libp2p/go-libp2p/core/network"
"github.com/libp2p/go-libp2p/core/peer"
"github.com/libp2p/go-libp2p/core/pnet"
"github.com/libp2p/go-libp2p/core/sec"
tpt "github.com/libp2p/go-libp2p/core/transport"
"github.com/libp2p/go-libp2p/p2p/security/noise"
"github.com/libp2p/go-libp2p/p2p/transport/webrtc/pb"
"github.com/libp2p/go-msgio"
ma "github.com/multiformats/go-multiaddr"
manet "github.com/multiformats/go-multiaddr/net"
"github.com/multiformats/go-multihash"
"github.com/pion/datachannel"
"github.com/pion/webrtc/v3"
)
var webrtcComponent *ma.Component
func init() {
var err error
webrtcComponent, err = ma.NewComponent(ma.ProtocolWithCode(ma.P_WEBRTC_DIRECT).Name, "")
if err != nil {
log.Fatal(err)
}
}
const (
// handshakeChannelNegotiated is used to specify that the
// handshake data channel does not need negotiation via DCEP.
// A constant is used since the `DataChannelInit` struct takes
// references instead of values.
handshakeChannelNegotiated = true
// handshakeChannelID is the agreed ID for the handshake data
// channel. A constant is used since the `DataChannelInit` struct takes
// references instead of values. We specify the type here as this
// value is only ever copied and passed by reference
handshakeChannelID = uint16(0)
)
// timeout values for the peerconnection
// https://github.com/pion/webrtc/blob/v3.1.50/settingengine.go#L102-L109
const (
DefaultDisconnectedTimeout = 20 * time.Second
DefaultFailedTimeout = 30 * time.Second
DefaultKeepaliveTimeout = 15 * time.Second
sctpReceiveBufferSize = 100_000
)
type WebRTCTransport struct {
webrtcConfig webrtc.Configuration
rcmgr network.ResourceManager
gater connmgr.ConnectionGater
privKey ic.PrivKey
noiseTpt *noise.Transport
localPeerId peer.ID
// timeouts
peerConnectionTimeouts iceTimeouts
// in-flight connections
maxInFlightConnections uint32
}
var _ tpt.Transport = &WebRTCTransport{}
type Option func(*WebRTCTransport) error
type iceTimeouts struct {
Disconnect time.Duration
Failed time.Duration
Keepalive time.Duration
}
func New(privKey ic.PrivKey, psk pnet.PSK, gater connmgr.ConnectionGater, rcmgr network.ResourceManager, opts ...Option) (*WebRTCTransport, error) {
if psk != nil {
log.Error("WebRTC doesn't support private networks yet.")
return nil, fmt.Errorf("WebRTC doesn't support private networks yet")
}
if rcmgr == nil {
rcmgr = &network.NullResourceManager{}
}
localPeerID, err := peer.IDFromPrivateKey(privKey)
if err != nil {
return nil, fmt.Errorf("get local peer ID: %w", err)
}
// We use elliptic P-256 since it is widely supported by browsers.
//
// Implementation note: Testing with the browser,
// it seems like Chromium only supports ECDSA P-256 or RSA key signatures in the webrtc TLS certificate.
// We tried using P-228 and P-384 which caused the DTLS handshake to fail with Illegal Parameter
//
// Please refer to this is a list of suggested algorithms for the WebCrypto API.
// The algorithm for generating a certificate for an RTCPeerConnection
// must adhere to the WebCrpyto API. From my observation,
// RSA and ECDSA P-256 is supported on almost all browsers.
// Ed25519 is not present on the list.
pk, err := ecdsa.GenerateKey(elliptic.P256(), rand.Reader)
if err != nil {
return nil, fmt.Errorf("generate key for cert: %w", err)
}
cert, err := webrtc.GenerateCertificate(pk)
if err != nil {
return nil, fmt.Errorf("generate certificate: %w", err)
}
config := webrtc.Configuration{
Certificates: []webrtc.Certificate{*cert},
}
noiseTpt, err := noise.New(noise.ID, privKey, nil)
if err != nil {
return nil, fmt.Errorf("unable to create noise transport: %w", err)
}
transport := &WebRTCTransport{
rcmgr: rcmgr,
gater: gater,
webrtcConfig: config,
privKey: privKey,
noiseTpt: noiseTpt,
localPeerId: localPeerID,
peerConnectionTimeouts: iceTimeouts{
Disconnect: DefaultDisconnectedTimeout,
Failed: DefaultFailedTimeout,
Keepalive: DefaultKeepaliveTimeout,
},
maxInFlightConnections: DefaultMaxInFlightConnections,
}
for _, opt := range opts {
if err := opt(transport); err != nil {
return nil, err
}
}
return transport, nil
}
func (t *WebRTCTransport) Protocols() []int {
return []int{ma.P_WEBRTC_DIRECT}
}
func (t *WebRTCTransport) Proxy() bool {
return false
}
func (t *WebRTCTransport) CanDial(addr ma.Multiaddr) bool {
isValid, n := IsWebRTCDirectMultiaddr(addr)
return isValid && n > 0
}
// Listen returns a listener for addr.
//
// The IP, Port combination for addr must be exclusive to this listener as a WebRTC listener cannot
// be multiplexed on the same port as other UDP based transports like QUIC and WebTransport.
// See https://github.com/libp2p/go-libp2p/issues/2446 for details.
func (t *WebRTCTransport) Listen(addr ma.Multiaddr) (tpt.Listener, error) {
addr, wrtcComponent := ma.SplitLast(addr)
isWebrtc := wrtcComponent.Equal(webrtcComponent)
if !isWebrtc {
return nil, fmt.Errorf("must listen on webrtc multiaddr")
}
nw, host, err := manet.DialArgs(addr)
if err != nil {
return nil, fmt.Errorf("listener could not fetch dialargs: %w", err)
}
udpAddr, err := net.ResolveUDPAddr(nw, host)
if err != nil {
return nil, fmt.Errorf("listener could not resolve udp address: %w", err)
}
socket, err := net.ListenUDP(nw, udpAddr)
if err != nil {
return nil, fmt.Errorf("listen on udp: %w", err)
}
listener, err := t.listenSocket(socket)
if err != nil {
socket.Close()
return nil, err
}
return listener, nil
}
func (t *WebRTCTransport) listenSocket(socket *net.UDPConn) (tpt.Listener, error) {
listenerMultiaddr, err := manet.FromNetAddr(socket.LocalAddr())
if err != nil {
return nil, err
}
listenerFingerprint, err := t.getCertificateFingerprint()
if err != nil {
return nil, err
}
encodedLocalFingerprint, err := encodeDTLSFingerprint(listenerFingerprint)
if err != nil {
return nil, err
}
certComp, err := ma.NewComponent(ma.ProtocolWithCode(ma.P_CERTHASH).Name, encodedLocalFingerprint)
if err != nil {
return nil, err
}
listenerMultiaddr = listenerMultiaddr.Encapsulate(webrtcComponent).Encapsulate(certComp)
return newListener(
t,
listenerMultiaddr,
socket,
t.webrtcConfig,
)
}
func (t *WebRTCTransport) Dial(ctx context.Context, remoteMultiaddr ma.Multiaddr, p peer.ID) (tpt.CapableConn, error) {
scope, err := t.rcmgr.OpenConnection(network.DirOutbound, false, remoteMultiaddr)
if err != nil {
return nil, err
}
if err := scope.SetPeer(p); err != nil {
scope.Done()
return nil, err
}
conn, err := t.dial(ctx, scope, remoteMultiaddr, p)
if err != nil {
scope.Done()
return nil, err
}
return conn, nil
}
func (t *WebRTCTransport) dial(ctx context.Context, scope network.ConnManagementScope, remoteMultiaddr ma.Multiaddr, p peer.ID) (tConn tpt.CapableConn, err error) {
var w webRTCConnection
defer func() {
if err != nil {
if w.PeerConnection != nil {
_ = w.PeerConnection.Close()
}
if tConn != nil {
_ = tConn.Close()
}
}
}()
remoteMultihash, err := decodeRemoteFingerprint(remoteMultiaddr)
if err != nil {
return nil, fmt.Errorf("decode fingerprint: %w", err)
}
remoteHashFunction, ok := getSupportedSDPHash(remoteMultihash.Code)
if !ok {
return nil, fmt.Errorf("unsupported hash function: %w", nil)
}
rnw, rhost, err := manet.DialArgs(remoteMultiaddr)
if err != nil {
return nil, fmt.Errorf("generate dial args: %w", err)
}
raddr, err := net.ResolveUDPAddr(rnw, rhost)
if err != nil {
return nil, fmt.Errorf("resolve udp address: %w", err)
}
// Instead of encoding the local fingerprint we
// generate a random UUID as the connection ufrag.
// The only requirement here is that the ufrag and password
// must be equal, which will allow the server to determine
// the password using the STUN message.
ufrag := genUfrag()
settingEngine := webrtc.SettingEngine{
LoggerFactory: pionLoggerFactory,
}
settingEngine.SetICECredentials(ufrag, ufrag)
settingEngine.DetachDataChannels()
// use the first best address candidate
settingEngine.SetPrflxAcceptanceMinWait(0)
settingEngine.SetICETimeouts(
t.peerConnectionTimeouts.Disconnect,
t.peerConnectionTimeouts.Failed,
t.peerConnectionTimeouts.Keepalive,
)
// By default, webrtc will not collect candidates on the loopback address.
// This is disallowed in the ICE specification. However, implementations
// do not strictly follow this, for eg. Chrome gathers TCP loopback candidates.
// If you run pion on a system with only the loopback interface UP,
// it will not connect to anything.
settingEngine.SetIncludeLoopbackCandidate(true)
settingEngine.SetSCTPMaxReceiveBufferSize(sctpReceiveBufferSize)
if err := scope.ReserveMemory(sctpReceiveBufferSize, network.ReservationPriorityMedium); err != nil {
return nil, err
}
w, err = newWebRTCConnection(settingEngine, t.webrtcConfig)
if err != nil {
return nil, fmt.Errorf("instantiating peer connection failed: %w", err)
}
errC := addOnConnectionStateChangeCallback(w.PeerConnection)
// do offer-answer exchange
offer, err := w.PeerConnection.CreateOffer(nil)
if err != nil {
return nil, fmt.Errorf("create offer: %w", err)
}
err = w.PeerConnection.SetLocalDescription(offer)
if err != nil {
return nil, fmt.Errorf("set local description: %w", err)
}
answerSDPString, err := createServerSDP(raddr, ufrag, *remoteMultihash)
if err != nil {
return nil, fmt.Errorf("render server SDP: %w", err)
}
answer := webrtc.SessionDescription{SDP: answerSDPString, Type: webrtc.SDPTypeAnswer}
err = w.PeerConnection.SetRemoteDescription(answer)
if err != nil {
return nil, fmt.Errorf("set remote description: %w", err)
}
// await peerconnection opening
select {
case err := <-errC:
if err != nil {
return nil, err
}
case <-ctx.Done():
return nil, errors.New("peerconnection opening timed out")
}
// We are connected, run the noise handshake
detached, err := detachHandshakeDataChannel(ctx, w.HandshakeDataChannel)
if err != nil {
return nil, err
}
channel := newStream(w.HandshakeDataChannel, detached, func() {})
remotePubKey, err := t.noiseHandshake(ctx, w.PeerConnection, channel, p, remoteHashFunction, false)
if err != nil {
return nil, err
}
// Setup local and remote address for the connection
cp, err := w.HandshakeDataChannel.Transport().Transport().ICETransport().GetSelectedCandidatePair()
if cp == nil {
return nil, errors.New("ice connection did not have selected candidate pair: nil result")
}
if err != nil {
return nil, fmt.Errorf("ice connection did not have selected candidate pair: error: %w", err)
}
// the local address of the selected candidate pair should be the local address for the connection
localAddr, err := manet.FromNetAddr(&net.UDPAddr{IP: net.ParseIP(cp.Local.Address), Port: int(cp.Local.Port)})
if err != nil {
return nil, err
}
remoteMultiaddrWithoutCerthash, _ := ma.SplitFunc(remoteMultiaddr, func(c ma.Component) bool { return c.Protocol().Code == ma.P_CERTHASH })
conn, err := newConnection(
network.DirOutbound,
w.PeerConnection,
t,
scope,
t.localPeerId,
localAddr,
p,
remotePubKey,
remoteMultiaddrWithoutCerthash,
w.IncomingDataChannels,
)
if err != nil {
return nil, err
}
if t.gater != nil && !t.gater.InterceptSecured(network.DirOutbound, p, conn) {
return nil, fmt.Errorf("secured connection gated")
}
return conn, nil
}
func genUfrag() string {
const (
uFragAlphabet = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"
uFragPrefix = "libp2p+webrtc+v1/"
uFragIdLength = 32
uFragIdOffset = len(uFragPrefix)
uFragLength = uFragIdOffset + uFragIdLength
)
seed := [8]byte{}
rand.Read(seed[:])
r := mrand.New(mrand.NewSource(binary.BigEndian.Uint64(seed[:])))
b := make([]byte, uFragLength)
for i := uFragIdOffset; i < uFragLength; i++ {
b[i] = uFragAlphabet[r.Intn(len(uFragAlphabet))]
}
return string(b)
}
func (t *WebRTCTransport) getCertificateFingerprint() (webrtc.DTLSFingerprint, error) {
fps, err := t.webrtcConfig.Certificates[0].GetFingerprints()
if err != nil {
return webrtc.DTLSFingerprint{}, err
}
return fps[0], nil
}
func (t *WebRTCTransport) generateNoisePrologue(pc *webrtc.PeerConnection, hash crypto.Hash, inbound bool) ([]byte, error) {
raw := pc.SCTP().Transport().GetRemoteCertificate()
cert, err := x509.ParseCertificate(raw)
if err != nil {
return nil, err
}
// NOTE: should we want we can fork the cert code as well to avoid
// all the extra allocations due to unneeded string interspersing (hex)
localFp, err := t.getCertificateFingerprint()
if err != nil {
return nil, err
}
remoteFpBytes, err := parseFingerprint(cert, hash)
if err != nil {
return nil, err
}
localFpBytes, err := decodeInterspersedHexFromASCIIString(localFp.Value)
if err != nil {
return nil, err
}
localEncoded, err := multihash.Encode(localFpBytes, multihash.SHA2_256)
if err != nil {
log.Debugf("could not encode multihash for local fingerprint")
return nil, err
}
remoteEncoded, err := multihash.Encode(remoteFpBytes, multihash.SHA2_256)
if err != nil {
log.Debugf("could not encode multihash for remote fingerprint")
return nil, err
}
result := []byte("libp2p-webrtc-noise:")
if inbound {
result = append(result, remoteEncoded...)
result = append(result, localEncoded...)
} else {
result = append(result, localEncoded...)
result = append(result, remoteEncoded...)
}
return result, nil
}
func (t *WebRTCTransport) noiseHandshake(ctx context.Context, pc *webrtc.PeerConnection, s *stream, peer peer.ID, hash crypto.Hash, inbound bool) (ic.PubKey, error) {
prologue, err := t.generateNoisePrologue(pc, hash, inbound)
if err != nil {
return nil, fmt.Errorf("generate prologue: %w", err)
}
opts := make([]noise.SessionOption, 0, 2)
opts = append(opts, noise.Prologue(prologue))
if peer == "" {
opts = append(opts, noise.DisablePeerIDCheck())
}
sessionTransport, err := t.noiseTpt.WithSessionOptions(opts...)
if err != nil {
return nil, fmt.Errorf("failed to instantiate Noise transport: %w", err)
}
var secureConn sec.SecureConn
if inbound {
secureConn, err = sessionTransport.SecureOutbound(ctx, netConnWrapper{s}, peer)
if err != nil {
return nil, fmt.Errorf("failed to secure inbound connection: %w", err)
}
} else {
secureConn, err = sessionTransport.SecureInbound(ctx, netConnWrapper{s}, peer)
if err != nil {
return nil, fmt.Errorf("failed to secure outbound connection: %w", err)
}
}
return secureConn.RemotePublicKey(), nil
}
func (t *WebRTCTransport) AddCertHashes(addr ma.Multiaddr) (ma.Multiaddr, bool) {
listenerFingerprint, err := t.getCertificateFingerprint()
if err != nil {
return nil, false
}
encodedLocalFingerprint, err := encodeDTLSFingerprint(listenerFingerprint)
if err != nil {
return nil, false
}
certComp, err := ma.NewComponent(ma.ProtocolWithCode(ma.P_CERTHASH).Name, encodedLocalFingerprint)
if err != nil {
return nil, false
}
return addr.Encapsulate(certComp), true
}
type netConnWrapper struct {
*stream
}
func (netConnWrapper) LocalAddr() net.Addr { return nil }
func (netConnWrapper) RemoteAddr() net.Addr { return nil }
func (w netConnWrapper) Close() error {
// Close called while running the security handshake is an error and we should Reset the
// stream in that case rather than gracefully closing
w.stream.Reset()
return nil
}
// detachHandshakeDataChannel detaches the handshake data channel
func detachHandshakeDataChannel(ctx context.Context, dc *webrtc.DataChannel) (datachannel.ReadWriteCloser, error) {
done := make(chan struct{})
var rwc datachannel.ReadWriteCloser
var err error
dc.OnOpen(func() {
defer close(done)
rwc, err = dc.Detach()
})
// this is safe since for detached datachannels, the peerconnection runs the onOpen
// callback immediately if the SCTP transport is also connected.
select {
case <-done:
return rwc, err
case <-ctx.Done():
return nil, ctx.Err()
}
}
// webRTCConnection holds the webrtc.PeerConnection with the handshake channel and the queue for
// incoming data channels created by the peer.
//
// When creating a webrtc.PeerConnection, It is important to set the OnDataChannel handler upfront
// before connecting with the peer. If the handler's set up after connecting with the peer, there's
// a small window of time where datachannels created by the peer may not surface to us and cause a
// memory leak.
type webRTCConnection struct {
PeerConnection *webrtc.PeerConnection
HandshakeDataChannel *webrtc.DataChannel
IncomingDataChannels chan dataChannel
}
func newWebRTCConnection(settings webrtc.SettingEngine, config webrtc.Configuration) (webRTCConnection, error) {
api := webrtc.NewAPI(webrtc.WithSettingEngine(settings))
pc, err := api.NewPeerConnection(config)
if err != nil {
return webRTCConnection{}, fmt.Errorf("failed to create peer connection: %w", err)
}
negotiated, id := handshakeChannelNegotiated, handshakeChannelID
handshakeDataChannel, err := pc.CreateDataChannel("", &webrtc.DataChannelInit{
Negotiated: &negotiated,
ID: &id,
})
if err != nil {
pc.Close()
return webRTCConnection{}, fmt.Errorf("failed to create handshake channel: %w", err)
}
incomingDataChannels := make(chan dataChannel, maxAcceptQueueLen)
pc.OnDataChannel(func(dc *webrtc.DataChannel) {
dc.OnOpen(func() {
rwc, err := dc.Detach()
if err != nil {
log.Warnf("could not detach datachannel: id: %d", *dc.ID())
return
}
select {
case incomingDataChannels <- dataChannel{rwc, dc}:
default:
log.Warnf("connection busy, rejecting stream")
b, _ := proto.Marshal(&pb.Message{Flag: pb.Message_RESET.Enum()})
w := msgio.NewWriter(rwc)
w.WriteMsg(b)
rwc.Close()
}
})
})
return webRTCConnection{
PeerConnection: pc,
HandshakeDataChannel: handshakeDataChannel,
IncomingDataChannels: incomingDataChannels,
}, nil
}
// IsWebRTCDirectMultiaddr returns whether addr is a /webrtc-direct multiaddr with the count of certhashes
// in addr
func IsWebRTCDirectMultiaddr(addr ma.Multiaddr) (bool, int) {
var foundUDP, foundWebRTC bool
certHashCount := 0
ma.ForEach(addr, func(c ma.Component) bool {
if !foundUDP {
if c.Protocol().Code == ma.P_UDP {
foundUDP = true
}
return true
}
if !foundWebRTC && foundUDP {
// protocol after udp must be webrtc-direct
if c.Protocol().Code != ma.P_WEBRTC_DIRECT {
return false
}
foundWebRTC = true
return true
}
if foundWebRTC {
if c.Protocol().Code == ma.P_CERTHASH {
certHashCount++
} else {
return false
}
}
return true
})
return foundUDP && foundWebRTC, certHashCount
}