quic: version negotiation

Servers respond to packets containing an unrecognized version
with a Version Negotiation packet.

Clients respond to Version Negotiation packets by aborting
the connection attempt, since we support only one version.

RFC 9000, Section 6

For golang/go#58547

Change-Id: I3f3a66a4d69950cc7dc22146ad2eddb93cbe34f7
Reviewed-on: https://go-review.googlesource.com/c/net/+/529739
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Jonathan Amsterdam <jba@google.com>

internal/quic/conn_recv.go

@@ -7,6 +7,9 @@
 package quic
 
 import (
+	"bytes"
+	"encoding/binary"
+	"errors"
 	"time"
 )
 
@@ -31,6 +34,9 @@ func (c *Conn) handleDatagram(now time.Time, dgram *datagram) {
 			n = c.handleLongHeader(now, ptype, handshakeSpace, c.keysHandshake.r, buf)
 		case packetType1RTT:
 			n = c.handle1RTT(now, buf)
+		case packetTypeVersionNegotiation:
+			c.handleVersionNegotiation(now, buf)
+			return
 		default:
 			return
 		}
@@ -59,6 +65,11 @@ func (c *Conn) handleLongHeader(now time.Time, ptype packetType, space numberSpa
 		c.abort(now, localTransportError(errProtocolViolation))
 		return -1
 	}
+	if p.version != quicVersion1 {
+		// The peer has changed versions on us mid-handshake?
+		c.abort(now, localTransportError(errProtocolViolation))
+		return -1
+	}
 
 	if !c.acks[space].shouldProcess(p.num) {
 		return n
@@ -117,6 +128,42 @@ func (c *Conn) handle1RTT(now time.Time, buf []byte) int {
 	return len(buf)
 }
 
+var errVersionNegotiation = errors.New("server does not support QUIC version 1")
+
+func (c *Conn) handleVersionNegotiation(now time.Time, pkt []byte) {
+	if c.side != clientSide {
+		return // servers don't handle Version Negotiation packets
+	}
+	// "A client MUST discard any Version Negotiation packet if it has
+	// received and successfully processed any other packet [...]"
+	// https://www.rfc-editor.org/rfc/rfc9000#section-6.2-2
+	if !c.keysInitial.canRead() {
+		return // discarded Initial keys, connection is already established
+	}
+	if c.acks[initialSpace].seen.numRanges() != 0 {
+		return // processed at least one packet
+	}
+	_, srcConnID, versions := parseVersionNegotiation(pkt)
+	if len(c.connIDState.remote) < 1 || !bytes.Equal(c.connIDState.remote[0].cid, srcConnID) {
+		return // Source Connection ID doesn't match what we sent
+	}
+	for len(versions) >= 4 {
+		ver := binary.BigEndian.Uint32(versions)
+		if ver == 1 {
+			// "A client MUST discard a Version Negotiation packet that lists
+			// the QUIC version selected by the client."
+			// https://www.rfc-editor.org/rfc/rfc9000#section-6.2-2
+			return
+		}
+		versions = versions[4:]
+	}
+	// "A client that supports only this version of QUIC MUST
+	// abandon the current connection attempt if it receives
+	// a Version Negotiation packet, [with the two exceptions handled above]."
+	// https://www.rfc-editor.org/rfc/rfc9000#section-6.2-2
+	c.abortImmediately(now, errVersionNegotiation)
+}
+
 func (c *Conn) handleFrames(now time.Time, ptype packetType, space numberSpace, payload []byte) (ackEliciting bool) {
 	if len(payload) == 0 {
 		// "An endpoint MUST treat receipt of a packet containing no frames

internal/quic/conn_send.go

@@ -64,7 +64,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 			pnum := c.loss.nextNumber(initialSpace)
 			p := longPacket{
 				ptype:     packetTypeInitial,
-				version:   1,
+				version:   quicVersion1,
 				num:       pnum,
 				dstConnID: dstConnID,
 				srcConnID: c.connIDState.srcConnID(),
@@ -91,7 +91,7 @@ func (c *Conn) maybeSend(now time.Time) (next time.Time) {
 			pnum := c.loss.nextNumber(handshakeSpace)
 			p := longPacket{
 				ptype:     packetTypeHandshake,
-				version:   1,
+				version:   quicVersion1,
 				num:       pnum,
 				dstConnID: dstConnID,
 				srcConnID: c.connIDState.srcConnID(),

internal/quic/conn_test.go

@@ -409,7 +409,7 @@ func (tc *testConn) writeFrames(ptype packetType, frames ...debugFrame) {
 			keyNumber:   tc.sendKeyNumber,
 			keyPhaseBit: tc.sendKeyPhaseBit,
 			frames:      frames,
-			version:     1,
+			version:     quicVersion1,
 			dstConnID:   dstConnID,
 			srcConnID:   tc.peerConnID,
 		}},

internal/quic/listener.go

@@ -239,39 +239,83 @@ func (l *Listener) listen() {
 func (l *Listener) handleDatagram(m *datagram, conns map[string]*Conn) {
 	dstConnID, ok := dstConnIDForDatagram(m.b)
 	if !ok {
+		m.recycle()
 		return
 	}
 	c := conns[string(dstConnID)]
 	if c == nil {
-		if getPacketType(m.b) != packetTypeInitial {
-			// This packet isn't trying to create a new connection.
-			// It might be associated with some connection we've lost state for.
-			// TODO: Send a stateless reset when appropriate.
-			// https://www.rfc-editor.org/rfc/rfc9000.html#section-10.3
-			return
-		}
-		var now time.Time
-		if l.testHooks != nil {
-			now = l.testHooks.timeNow()
-		} else {
-			now = time.Now()
-		}
-		var err error
-		c, err = l.newConn(now, serverSide, dstConnID, m.addr)
-		if err != nil {
-			// The accept queue is probably full.
-			// We could send a CONNECTION_CLOSE to the peer to reject the connection.
-			// Currently, we just drop the datagram.
-			// https://www.rfc-editor.org/rfc/rfc9000.html#section-5.2.2-5
-			return
-		}
+		// TODO: Move this branch into a separate goroutine to avoid blocking
+		// the listener while processing packets.
+		l.handleUnknownDestinationDatagram(m)
+		return
 	}
 
 	// TODO: This can block the listener while waiting for the conn to accept the dgram.
 	// Think about buffering between the receive loop and the conn.
 	c.sendMsg(m)
 }
 
+func (l *Listener) handleUnknownDestinationDatagram(m *datagram) {
+	defer func() {
+		if m != nil {
+			m.recycle()
+		}
+	}()
+	if len(m.b) < minimumClientInitialDatagramSize {
+		return
+	}
+	p, ok := parseGenericLongHeaderPacket(m.b)
+	if !ok {
+		// Not a long header packet, or not parseable.
+		// Short header (1-RTT) packets don't contain enough information
+		// to do anything useful with if we don't recognize the
+		// connection ID.
+		return
+	}
+
+	switch p.version {
+	case quicVersion1:
+	case 0:
+		// Version Negotiation for an unknown connection.
+		return
+	default:
+		// Unknown version.
+		l.sendVersionNegotiation(p, m.addr)
+		return
+	}
+	if getPacketType(m.b) != packetTypeInitial {
+		// This packet isn't trying to create a new connection.
+		// It might be associated with some connection we've lost state for.
+		// TODO: Send a stateless reset when appropriate.
+		// https://www.rfc-editor.org/rfc/rfc9000.html#section-10.3
+		return
+	}
+	var now time.Time
+	if l.testHooks != nil {
+		now = l.testHooks.timeNow()
+	} else {
+		now = time.Now()
+	}
+	var err error
+	c, err := l.newConn(now, serverSide, p.dstConnID, m.addr)
+	if err != nil {
+		// The accept queue is probably full.
+		// We could send a CONNECTION_CLOSE to the peer to reject the connection.
+		// Currently, we just drop the datagram.
+		// https://www.rfc-editor.org/rfc/rfc9000.html#section-5.2.2-5
+		return
+	}
+	c.sendMsg(m)
+	m = nil // don't recycle, sendMsg takes ownership
+}
+
+func (l *Listener) sendVersionNegotiation(p genericLongPacket, addr netip.AddrPort) {
+	m := newDatagram()
+	m.b = appendVersionNegotiation(m.b[:0], p.srcConnID, p.dstConnID, quicVersion1)
+	l.sendDatagram(m.b, addr)
+	m.recycle()
+}
+
 func (l *Listener) sendDatagram(p []byte, addr netip.AddrPort) error {
 	_, err := l.udpConn.WriteToUDPAddrPort(p, addr)
 	return err

internal/quic/packet.go

@@ -6,7 +6,10 @@
 
 package quic
 
-import "fmt"
+import (
+	"encoding/binary"
+	"fmt"
+)
 
 // packetType is a QUIC packet type.
 // https://www.rfc-editor.org/rfc/rfc9000.html#section-17
@@ -157,6 +160,33 @@ func dstConnIDForDatagram(pkt []byte) (id []byte, ok bool) {
 	return b[:n], true
 }
 
+// parseVersionNegotiation parses a Version Negotiation packet.
+// The returned versions is a slice of big-endian uint32s.
+// It returns (nil, nil, nil) for an invalid packet.
+func parseVersionNegotiation(pkt []byte) (dstConnID, srcConnID, versions []byte) {
+	p, ok := parseGenericLongHeaderPacket(pkt)
+	if !ok {
+		return nil, nil, nil
+	}
+	if len(p.data)%4 != 0 {
+		return nil, nil, nil
+	}
+	return p.dstConnID, p.srcConnID, p.data
+}
+
+// appendVersionNegotiation appends a Version Negotiation packet to pkt,
+// returning the result.
+func appendVersionNegotiation(pkt, dstConnID, srcConnID []byte, versions ...uint32) []byte {
+	pkt = append(pkt, headerFormLong|fixedBit) // header byte
+	pkt = append(pkt, 0, 0, 0, 0)              // Version (0 for Version Negotiation)
+	pkt = appendUint8Bytes(pkt, dstConnID)     // Destination Connection ID
+	pkt = appendUint8Bytes(pkt, srcConnID)     // Source Connection ID
+	for _, v := range versions {
+		pkt = binary.BigEndian.AppendUint32(pkt, v) // Supported Version
+	}
+	return pkt
+}
+
 // A longPacket is a long header packet.
 type longPacket struct {
 	ptype     packetType
@@ -177,3 +207,42 @@ type shortPacket struct {
 	num     packetNumber
 	payload []byte
 }
+
+// A genericLongPacket is a long header packet of an arbitrary QUIC version.
+// https://www.rfc-editor.org/rfc/rfc8999#section-5.1
+type genericLongPacket struct {
+	version   uint32
+	dstConnID []byte
+	srcConnID []byte
+	data      []byte
+}
+
+func parseGenericLongHeaderPacket(b []byte) (p genericLongPacket, ok bool) {
+	if len(b) < 5 || !isLongHeader(b[0]) {
+		return genericLongPacket{}, false
+	}
+	b = b[1:]
+	// Version (32),
+	var n int
+	p.version, n = consumeUint32(b)
+	if n < 0 {
+		return genericLongPacket{}, false
+	}
+	b = b[n:]
+	// Destination Connection ID Length (8),
+	// Destination Connection ID (0..2048),
+	p.dstConnID, n = consumeUint8Bytes(b)
+	if n < 0 || len(p.dstConnID) > 2048/8 {
+		return genericLongPacket{}, false
+	}
+	b = b[n:]
+	// Source Connection ID Length (8),
+	// Source Connection ID (0..2048),
+	p.srcConnID, n = consumeUint8Bytes(b)
+	if n < 0 || len(p.dstConnID) > 2048/8 {
+		return genericLongPacket{}, false
+	}
+	b = b[n:]
+	p.data = b
+	return p, true
+}