Merge branch 'master' into pr_lazy_fpsimd_2

20 files changed, 700 insertions, 156 deletions

diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index 42afb3f5b..2a396e9bc 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -96,6 +96,11 @@ func (e *endpoint) UniqueID() uint64 {
 	return e.uniqueID
 }
 
+// Abort implements stack.TransportEndpoint.Abort.
+func (e *endpoint) Abort() {
+	e.Close()
+}
+
 // Close puts the endpoint in a closed state and frees all resources
 // associated with it.
 func (e *endpoint) Close() {
@@ -286,15 +291,13 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 			nicID = e.BindNICID
 		}
 
-		toCopy := *to
-		to = &toCopy
-		netProto, err := e.checkV4Mapped(to)
+		dst, netProto, err := e.checkV4MappedLocked(*to)
 		if err != nil {
 			return 0, nil, err
 		}
 
-		// Find the enpoint.
-		r, err := e.stack.FindRoute(nicID, e.BindAddr, to.Addr, netProto, false /* multicastLoop */)
+		// Find the endpoint.
+		r, err := e.stack.FindRoute(nicID, e.BindAddr, dst.Addr, netProto, false /* multicastLoop */)
 		if err != nil {
 			return 0, nil, err
 		}
@@ -475,13 +478,14 @@ func send6(r *stack.Route, ident uint16, data buffer.View, ttl uint8) *tcpip.Err
 	})
 }
 
-func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
-	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProto(*addr, false /* v6only */)
+// checkV4MappedLocked determines the effective network protocol and converts
+// addr to its canonical form.
+func (e *endpoint) checkV4MappedLocked(addr tcpip.FullAddress) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
+	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProtoLocked(addr, false /* v6only */)
 	if err != nil {
-		return 0, err
+		return tcpip.FullAddress{}, 0, err
 	}
-	*addr = unwrapped
-	return netProto, nil
+	return unwrapped, netProto, nil
 }
 
 // Disconnect implements tcpip.Endpoint.Disconnect.
@@ -512,7 +516,7 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
@@ -625,7 +629,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
diff --git a/pkg/tcpip/transport/icmp/protocol.go b/pkg/tcpip/transport/icmp/protocol.go
index 9ce500e80..113d92901 100644
--- a/pkg/tcpip/transport/icmp/protocol.go
+++ b/pkg/tcpip/transport/icmp/protocol.go
@@ -104,20 +104,26 @@ func (p *protocol) ParsePorts(v buffer.View) (src, dst uint16, err *tcpip.Error)
 
 // HandleUnknownDestinationPacket handles packets targeted at this protocol but
 // that don't match any existing endpoint.
-func (p *protocol) HandleUnknownDestinationPacket(*stack.Route, stack.TransportEndpointID, tcpip.PacketBuffer) bool {
+func (*protocol) HandleUnknownDestinationPacket(*stack.Route, stack.TransportEndpointID, tcpip.PacketBuffer) bool {
 	return true
 }
 
-// SetOption implements TransportProtocol.SetOption.
-func (p *protocol) SetOption(option interface{}) *tcpip.Error {
+// SetOption implements stack.TransportProtocol.SetOption.
+func (*protocol) SetOption(option interface{}) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
-// Option implements TransportProtocol.Option.
-func (p *protocol) Option(option interface{}) *tcpip.Error {
+// Option implements stack.TransportProtocol.Option.
+func (*protocol) Option(option interface{}) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
+// Close implements stack.TransportProtocol.Close.
+func (*protocol) Close() {}
+
+// Wait implements stack.TransportProtocol.Wait.
+func (*protocol) Wait() {}
+
 // NewProtocol4 returns an ICMPv4 transport protocol.
 func NewProtocol4() stack.TransportProtocol {
 	return &protocol{ProtocolNumber4}
diff --git a/pkg/tcpip/transport/packet/endpoint.go b/pkg/tcpip/transport/packet/endpoint.go
index fc5bc69fa..09a1cd436 100644
--- a/pkg/tcpip/transport/packet/endpoint.go
+++ b/pkg/tcpip/transport/packet/endpoint.go
@@ -76,6 +76,7 @@ type endpoint struct {
 	sndBufSize int
 	closed     bool
 	stats      tcpip.TransportEndpointStats `state:"nosave"`
+	bound      bool
 }
 
 // NewEndpoint returns a new packet endpoint.
@@ -98,6 +99,11 @@ func NewEndpoint(s *stack.Stack, cooked bool, netProto tcpip.NetworkProtocolNumb
 	return ep, nil
 }
 
+// Abort implements stack.TransportEndpoint.Abort.
+func (e *endpoint) Abort() {
+	e.Close()
+}
+
 // Close implements tcpip.Endpoint.Close.
 func (ep *endpoint) Close() {
 	ep.mu.Lock()
@@ -120,6 +126,7 @@ func (ep *endpoint) Close() {
 	}
 
 	ep.closed = true
+	ep.bound = false
 	ep.waiterQueue.Notify(waiter.EventHUp | waiter.EventErr | waiter.EventIn | waiter.EventOut)
 }
 
@@ -211,7 +218,24 @@ func (ep *endpoint) Bind(addr tcpip.FullAddress) *tcpip.Error {
 	// sll_family (should be AF_PACKET), sll_protocol, and sll_ifindex."
 	// - packet(7).
 
-	return tcpip.ErrNotSupported
+	ep.mu.Lock()
+	defer ep.mu.Unlock()
+
+	if ep.bound {
+		return tcpip.ErrAlreadyBound
+	}
+
+	// Unregister endpoint with all the nics.
+	ep.stack.UnregisterPacketEndpoint(0, ep.netProto, ep)
+
+	// Bind endpoint to receive packets from specific interface.
+	if err := ep.stack.RegisterPacketEndpoint(addr.NIC, ep.netProto, ep); err != nil {
+		return err
+	}
+
+	ep.bound = true
+
+	return nil
 }
 
 // GetLocalAddress implements tcpip.Endpoint.GetLocalAddress.
diff --git a/pkg/tcpip/transport/raw/endpoint.go b/pkg/tcpip/transport/raw/endpoint.go
index ee9c4c58b..2ef5fac76 100644
--- a/pkg/tcpip/transport/raw/endpoint.go
+++ b/pkg/tcpip/transport/raw/endpoint.go
@@ -121,6 +121,11 @@ func newEndpoint(s *stack.Stack, netProto tcpip.NetworkProtocolNumber, transProt
 	return e, nil
 }
 
+// Abort implements stack.TransportEndpoint.Abort.
+func (e *endpoint) Abort() {
+	e.Close()
+}
+
 // Close implements tcpip.Endpoint.Close.
 func (e *endpoint) Close() {
 	e.mu.Lock()
diff --git a/pkg/tcpip/transport/tcp/BUILD b/pkg/tcpip/transport/tcp/BUILD
index 4acd9fb9a..a32f9eacf 100644
--- a/pkg/tcpip/transport/tcp/BUILD
+++ b/pkg/tcpip/transport/tcp/BUILD
@@ -32,6 +32,7 @@ go_library(
     srcs = [
         "accept.go",
         "connect.go",
+        "connect_unsafe.go",
         "cubic.go",
         "cubic_state.go",
         "dispatcher.go",
@@ -57,6 +58,7 @@ go_library(
     imports = ["gvisor.dev/gvisor/pkg/tcpip/buffer"],
     visibility = ["//visibility:public"],
     deps = [
+        "//pkg/log",
         "//pkg/rand",
         "//pkg/sleep",
         "//pkg/sync",
@@ -90,6 +92,7 @@ go_test(
     tags = ["flaky"],
     deps = [
         ":tcp",
+        "//pkg/sync",
         "//pkg/tcpip",
         "//pkg/tcpip/buffer",
         "//pkg/tcpip/checker",
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index d469758eb..85049e54e 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -222,13 +222,13 @@ func (l *listenContext) isCookieValid(id stack.TransportEndpointID, cookie seqnu
 
 // createConnectingEndpoint creates a new endpoint in a connecting state, with
 // the connection parameters given by the arguments.
-func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, irs seqnum.Value, rcvdSynOpts *header.TCPSynOptions) (*endpoint, *tcpip.Error) {
+func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, irs seqnum.Value, rcvdSynOpts *header.TCPSynOptions, queue *waiter.Queue) (*endpoint, *tcpip.Error) {
 	// Create a new endpoint.
 	netProto := l.netProto
 	if netProto == 0 {
 		netProto = s.route.NetProto
 	}
-	n := newEndpoint(l.stack, netProto, nil)
+	n := newEndpoint(l.stack, netProto, queue)
 	n.v6only = l.v6only
 	n.ID = s.id
 	n.boundNICID = s.route.NICID()
@@ -236,6 +236,7 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	n.effectiveNetProtos = []tcpip.NetworkProtocolNumber{s.route.NetProto}
 	n.rcvBufSize = int(l.rcvWnd)
 	n.amss = mssForRoute(&n.route)
+	n.setEndpointState(StateConnecting)
 
 	n.maybeEnableTimestamp(rcvdSynOpts)
 	n.maybeEnableSACKPermitted(rcvdSynOpts)
@@ -271,18 +272,19 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	return n, nil
 }
 
-// createEndpoint creates a new endpoint in connected state and then performs
-// the TCP 3-way handshake.
-func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *header.TCPSynOptions) (*endpoint, *tcpip.Error) {
+// createEndpointAndPerformHandshake creates a new endpoint in connected state
+// and then performs the TCP 3-way handshake.
+func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *header.TCPSynOptions, queue *waiter.Queue) (*endpoint, *tcpip.Error) {
 	// Create new endpoint.
 	irs := s.sequenceNumber
 	isn := generateSecureISN(s.id, l.stack.Seed())
-	ep, err := l.createConnectingEndpoint(s, isn, irs, opts)
+	ep, err := l.createConnectingEndpoint(s, isn, irs, opts, queue)
 	if err != nil {
 		return nil, err
 	}
 
 	// listenEP is nil when listenContext is used by tcp.Forwarder.
+	deferAccept := time.Duration(0)
 	if l.listenEP != nil {
 		l.listenEP.mu.Lock()
 		if l.listenEP.EndpointState() != StateListen {
@@ -290,15 +292,21 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 			return nil, tcpip.ErrConnectionAborted
 		}
 		l.addPendingEndpoint(ep)
+		deferAccept = l.listenEP.deferAccept
 		l.listenEP.mu.Unlock()
 	}
 
 	// Perform the 3-way handshake.
-	h := newHandshake(ep, seqnum.Size(ep.initialReceiveWindow()))
-
-	h.resetToSynRcvd(isn, irs, opts)
+	h := newPassiveHandshake(ep, seqnum.Size(ep.initialReceiveWindow()), isn, irs, opts, deferAccept)
 	if err := h.execute(); err != nil {
 		ep.Close()
+		// Wake up any waiters. This is strictly not required normally
+		// as a socket that was never accepted can't really have any
+		// registered waiters except when stack.Wait() is called which
+		// waits for all registered endpoints to stop and expects an
+		// EventHUp.
+		ep.waiterQueue.Notify(waiter.EventHUp | waiter.EventErr | waiter.EventIn | waiter.EventOut)
+
 		if l.listenEP != nil {
 			l.removePendingEndpoint(ep)
 		}
@@ -377,16 +385,14 @@ func (e *endpoint) handleSynSegment(ctx *listenContext, s *segment, opts *header
 	defer e.decSynRcvdCount()
 	defer s.decRef()
 
-	n, err := ctx.createEndpointAndPerformHandshake(s, opts)
+	n, err := ctx.createEndpointAndPerformHandshake(s, opts, &waiter.Queue{})
 	if err != nil {
 		e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
 		e.stats.FailedConnectionAttempts.Increment()
 		return
 	}
 	ctx.removePendingEndpoint(n)
-	// Start the protocol goroutine.
-	wq := &waiter.Queue{}
-	n.startAcceptedLoop(wq)
+	n.startAcceptedLoop()
 	e.stack.Stats().TCP.PassiveConnectionOpenings.Increment()
 
 	e.deliverAccepted(n)
@@ -546,7 +552,7 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 			rcvdSynOptions.TSEcr = s.parsedOptions.TSEcr
 		}
 
-		n, err := ctx.createConnectingEndpoint(s, s.ackNumber-1, s.sequenceNumber-1, rcvdSynOptions)
+		n, err := ctx.createConnectingEndpoint(s, s.ackNumber-1, s.sequenceNumber-1, rcvdSynOptions, &waiter.Queue{})
 		if err != nil {
 			e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
 			e.stats.FailedConnectionAttempts.Increment()
@@ -576,8 +582,7 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 		// space available in the backlog.
 
 		// Start the protocol goroutine.
-		wq := &waiter.Queue{}
-		n.startAcceptedLoop(wq)
+		n.startAcceptedLoop()
 		e.stack.Stats().TCP.PassiveConnectionOpenings.Increment()
 		go e.deliverAccepted(n)
 	}
@@ -610,7 +615,7 @@ func (e *endpoint) protocolListenLoop(rcvWnd seqnum.Size) *tcpip.Error {
 		e.mu.Unlock()
 
 		// Notify waiters that the endpoint is shutdown.
-		e.waiterQueue.Notify(waiter.EventIn | waiter.EventOut)
+		e.waiterQueue.Notify(waiter.EventIn | waiter.EventOut | waiter.EventHUp | waiter.EventErr)
 	}()
 
 	s := sleep.Sleeper{}
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 4e3c5419c..c0f73ef16 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -86,6 +86,19 @@ type handshake struct {
 
 	// rcvWndScale is the receive window scale, as defined in RFC 1323.
 	rcvWndScale int
+
+	// startTime is the time at which the first SYN/SYN-ACK was sent.
+	startTime time.Time
+
+	// deferAccept if non-zero will drop the final ACK for a passive
+	// handshake till an ACK segment with data is received or the timeout is
+	// hit.
+	deferAccept time.Duration
+
+	// acked is true if the the final ACK for a 3-way handshake has
+	// been received. This is required to stop retransmitting the
+	// original SYN-ACK when deferAccept is enabled.
+	acked bool
 }
 
 func newHandshake(ep *endpoint, rcvWnd seqnum.Size) handshake {
@@ -112,6 +125,12 @@ func newHandshake(ep *endpoint, rcvWnd seqnum.Size) handshake {
 	return h
 }
 
+func newPassiveHandshake(ep *endpoint, rcvWnd seqnum.Size, isn, irs seqnum.Value, opts *header.TCPSynOptions, deferAccept time.Duration) handshake {
+	h := newHandshake(ep, rcvWnd)
+	h.resetToSynRcvd(isn, irs, opts, deferAccept)
+	return h
+}
+
 // FindWndScale determines the window scale to use for the given maximum window
 // size.
 func FindWndScale(wnd seqnum.Size) int {
@@ -181,7 +200,7 @@ func (h *handshake) effectiveRcvWndScale() uint8 {
 
 // resetToSynRcvd resets the state of the handshake object to the SYN-RCVD
 // state.
-func (h *handshake) resetToSynRcvd(iss seqnum.Value, irs seqnum.Value, opts *header.TCPSynOptions) {
+func (h *handshake) resetToSynRcvd(iss seqnum.Value, irs seqnum.Value, opts *header.TCPSynOptions, deferAccept time.Duration) {
 	h.active = false
 	h.state = handshakeSynRcvd
 	h.flags = header.TCPFlagSyn | header.TCPFlagAck
@@ -189,6 +208,7 @@ func (h *handshake) resetToSynRcvd(iss seqnum.Value, irs seqnum.Value, opts *hea
 	h.ackNum = irs + 1
 	h.mss = opts.MSS
 	h.sndWndScale = opts.WS
+	h.deferAccept = deferAccept
 	h.ep.mu.Lock()
 	h.ep.setEndpointState(StateSynRecv)
 	h.ep.mu.Unlock()
@@ -275,6 +295,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 	h.state = handshakeSynRcvd
 	h.ep.mu.Lock()
 	ttl := h.ep.ttl
+	amss := h.ep.amss
 	h.ep.setEndpointState(StateSynRecv)
 	h.ep.mu.Unlock()
 	synOpts := header.TCPSynOptions{
@@ -287,7 +308,7 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 		// permits SACK. This is not explicitly defined in the RFC but
 		// this is the behaviour implemented by Linux.
 		SACKPermitted: rcvSynOpts.SACKPermitted,
-		MSS:           h.ep.amss,
+		MSS:           amss,
 	}
 	if ttl == 0 {
 		ttl = s.route.DefaultTTL()
@@ -336,6 +357,10 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			return tcpip.ErrInvalidEndpointState
 		}
 
+		h.ep.mu.RLock()
+		amss := h.ep.amss
+		h.ep.mu.RUnlock()
+
 		h.resetState()
 		synOpts := header.TCPSynOptions{
 			WS:            h.rcvWndScale,
@@ -343,7 +368,7 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			TSVal:         h.ep.timestamp(),
 			TSEcr:         h.ep.recentTimestamp(),
 			SACKPermitted: h.ep.sackPermitted,
-			MSS:           h.ep.amss,
+			MSS:           amss,
 		}
 		h.ep.sendSynTCP(&s.route, h.ep.ID, h.ep.ttl, h.ep.sendTOS, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
 		return nil
@@ -352,6 +377,14 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 	// We have previously received (and acknowledged) the peer's SYN. If the
 	// peer acknowledges our SYN, the handshake is completed.
 	if s.flagIsSet(header.TCPFlagAck) {
+		// If deferAccept is not zero and this is a bare ACK and the
+		// timeout is not hit then drop the ACK.
+		if h.deferAccept != 0 && s.data.Size() == 0 && time.Since(h.startTime) < h.deferAccept {
+			h.acked = true
+			h.ep.stack.Stats().DroppedPackets.Increment()
+			return nil
+		}
+
 		// If the timestamp option is negotiated and the segment does
 		// not carry a timestamp option then the segment must be dropped
 		// as per https://tools.ietf.org/html/rfc7323#section-3.2.
@@ -365,10 +398,16 @@ func (h *handshake) synRcvdState(s *segment) *tcpip.Error {
 			h.ep.updateRecentTimestamp(s.parsedOptions.TSVal, h.ackNum, s.sequenceNumber)
 		}
 		h.state = handshakeCompleted
+
 		h.ep.mu.Lock()
 		h.ep.transitionToStateEstablishedLocked(h)
+		// If the segment has data then requeue it for the receiver
+		// to process it again once main loop is started.
+		if s.data.Size() > 0 {
+			s.incRef()
+			h.ep.enqueueSegment(s)
+		}
 		h.ep.mu.Unlock()
-
 		return nil
 	}
 
@@ -471,6 +510,7 @@ func (h *handshake) execute() *tcpip.Error {
 		}
 	}
 
+	h.startTime = time.Now()
 	// Initialize the resend timer.
 	resendWaker := sleep.Waker{}
 	timeOut := time.Duration(time.Second)
@@ -495,6 +535,7 @@ func (h *handshake) execute() *tcpip.Error {
 
 	// Send the initial SYN segment and loop until the handshake is
 	// completed.
+	h.ep.mu.Lock()
 	h.ep.amss = calculateAdvertisedMSS(h.ep.userMSS, h.ep.route)
 
 	synOpts := header.TCPSynOptions{
@@ -505,6 +546,7 @@ func (h *handshake) execute() *tcpip.Error {
 		SACKPermitted: bool(sackEnabled),
 		MSS:           h.ep.amss,
 	}
+	h.ep.mu.Unlock()
 
 	// Execute is also called in a listen context so we want to make sure we
 	// only send the TS/SACK option when we received the TS/SACK in the
@@ -524,15 +566,25 @@ func (h *handshake) execute() *tcpip.Error {
 		switch index, _ := s.Fetch(true); index {
 		case wakerForResend:
 			timeOut *= 2
-			if timeOut > 60*time.Second {
+			if timeOut > MaxRTO {
 				return tcpip.ErrTimeout
 			}
 			rt.Reset(timeOut)
-			h.ep.sendSynTCP(&h.ep.route, h.ep.ID, h.ep.ttl, h.ep.sendTOS, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
+			// Resend the SYN/SYN-ACK only if the following conditions hold.
+			//  - It's an active handshake (deferAccept does not apply)
+			//  - It's a passive handshake and we have not yet got the final-ACK.
+			//  - It's a passive handshake and we got an ACK but deferAccept is
+			//    enabled and we are now past the deferAccept duration.
+			// The last is required to provide a way for the peer to complete
+			// the connection with another ACK or data (as ACKs are never
+			// retransmitted on their own).
+			if h.active || !h.acked || h.deferAccept != 0 && time.Since(h.startTime) > h.deferAccept {
+				h.ep.sendSynTCP(&h.ep.route, h.ep.ID, h.ep.ttl, h.ep.sendTOS, h.flags, h.iss, h.ackNum, h.rcvWnd, synOpts)
+			}
 
 		case wakerForNotification:
 			n := h.ep.fetchNotifications()
-			if n&notifyClose != 0 {
+			if (n&notifyClose)|(n&notifyAbort) != 0 {
 				return tcpip.ErrAborted
 			}
 			if n&notifyDrain != 0 {
@@ -572,17 +624,17 @@ func parseSynSegmentOptions(s *segment) header.TCPSynOptions {
 
 var optionPool = sync.Pool{
 	New: func() interface{} {
-		return make([]byte, maxOptionSize)
+		return &[maxOptionSize]byte{}
 	},
 }
 
 func getOptions() []byte {
-	return optionPool.Get().([]byte)
+	return (*optionPool.Get().(*[maxOptionSize]byte))[:]
 }
 
 func putOptions(options []byte) {
 	// Reslice to full capacity.
-	optionPool.Put(options[0:cap(options)])
+	optionPool.Put(optionsToArray(options))
 }
 
 func makeSynOptions(opts header.TCPSynOptions) []byte {
@@ -944,6 +996,10 @@ func (e *endpoint) transitionToStateCloseLocked() {
 // to any other listening endpoint. We reply with RST if we cannot find one.
 func (e *endpoint) tryDeliverSegmentFromClosedEndpoint(s *segment) {
 	ep := e.stack.FindTransportEndpoint(e.NetProto, e.TransProto, e.ID, &s.route)
+	if ep == nil && e.NetProto == header.IPv6ProtocolNumber && e.EndpointInfo.TransportEndpointInfo.ID.LocalAddress.To4() != "" {
+		// Dual-stack socket, try IPv4.
+		ep = e.stack.FindTransportEndpoint(header.IPv4ProtocolNumber, e.TransProto, e.ID, &s.route)
+	}
 	if ep == nil {
 		replyWithReset(s)
 		s.decRef()
@@ -1323,7 +1379,7 @@ func (e *endpoint) protocolMainLoop(handshake bool, wakerInitDone chan<- struct{
 					e.snd.updateMaxPayloadSize(mtu, count)
 				}
 
-				if n&notifyReset != 0 {
+				if n&notifyReset != 0 || n&notifyAbort != 0 {
 					return tcpip.ErrConnectionAborted
 				}
 
@@ -1606,7 +1662,7 @@ func (e *endpoint) doTimeWait() (twReuse func()) {
 			}
 		case notification:
 			n := e.fetchNotifications()
-			if n&notifyClose != 0 {
+			if n&notifyClose != 0 || n&notifyAbort != 0 {
 				return nil
 			}
 			if n&notifyDrain != 0 {
diff --git a/pkg/tcpip/transport/tcp/connect_unsafe.go b/pkg/tcpip/transport/tcp/connect_unsafe.go
new file mode 100644
index 000000000..cfc304616
--- /dev/null
+++ b/pkg/tcpip/transport/tcp/connect_unsafe.go
@@ -0,0 +1,30 @@
+// Copyright 2018 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+// optionsToArray converts a slice of capacity >-= maxOptionSize to an array.
+//
+// optionsToArray panics if the capacity of options is smaller than
+// maxOptionSize.
+func optionsToArray(options []byte) *[maxOptionSize]byte {
+	// Reslice to full capacity.
+	options = options[0:maxOptionSize]
+	return (*[maxOptionSize]byte)(unsafe.Pointer((*reflect.SliceHeader)(unsafe.Pointer(&options)).Data))
+}
diff --git a/pkg/tcpip/transport/tcp/dispatcher.go b/pkg/tcpip/transport/tcp/dispatcher.go
index e18012ac0..d792b07d6 100644
--- a/pkg/tcpip/transport/tcp/dispatcher.go
+++ b/pkg/tcpip/transport/tcp/dispatcher.go
@@ -68,17 +68,28 @@ func (q *epQueue) empty() bool {
 type processor struct {
 	epQ              epQueue
 	newEndpointWaker sleep.Waker
+	closeWaker       sleep.Waker
 	id               int
+	wg               sync.WaitGroup
 }
 
 func newProcessor(id int) *processor {
 	p := &processor{
 		id: id,
 	}
+	p.wg.Add(1)
 	go p.handleSegments()
 	return p
 }
 
+func (p *processor) close() {
+	p.closeWaker.Assert()
+}
+
+func (p *processor) wait() {
+	p.wg.Wait()
+}
+
 func (p *processor) queueEndpoint(ep *endpoint) {
 	// Queue an endpoint for processing by the processor goroutine.
 	p.epQ.enqueue(ep)
@@ -87,11 +98,17 @@ func (p *processor) queueEndpoint(ep *endpoint) {
 
 func (p *processor) handleSegments() {
 	const newEndpointWaker = 1
+	const closeWaker = 2
 	s := sleep.Sleeper{}
 	s.AddWaker(&p.newEndpointWaker, newEndpointWaker)
+	s.AddWaker(&p.closeWaker, closeWaker)
 	defer s.Done()
 	for {
-		s.Fetch(true)
+		id, ok := s.Fetch(true)
+		if ok && id == closeWaker {
+			p.wg.Done()
+			return
+		}
 		for ep := p.epQ.dequeue(); ep != nil; ep = p.epQ.dequeue() {
 			if ep.segmentQueue.empty() {
 				continue
@@ -160,6 +177,18 @@ func newDispatcher(nProcessors int) *dispatcher {
 	}
 }
 
+func (d *dispatcher) close() {
+	for _, p := range d.processors {
+		p.close()
+	}
+}
+
+func (d *dispatcher) wait() {
+	for _, p := range d.processors {
+		p.wait()
+	}
+}
+
 func (d *dispatcher) queuePacket(r *stack.Route, stackEP stack.TransportEndpoint, id stack.TransportEndpointID, pkt tcpip.PacketBuffer) {
 	ep := stackEP.(*endpoint)
 	s := newSegment(r, id, pkt)
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 13718ff55..dc9c18b6f 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -121,6 +121,8 @@ const (
 	notifyDrain
 	notifyReset
 	notifyResetByPeer
+	// notifyAbort is a request for an expedited teardown.
+	notifyAbort
 	notifyKeepaliveChanged
 	notifyMSSChanged
 	// notifyTickleWorker is used to tickle the protocol main loop during a
@@ -498,6 +500,13 @@ type endpoint struct {
 	// without any data being acked.
 	userTimeout time.Duration
 
+	// deferAccept if non-zero specifies a user specified time during
+	// which the final ACK of a handshake will be dropped provided the
+	// ACK is a bare ACK and carries no data. If the timeout is crossed then
+	// the bare ACK is accepted and the connection is delivered to the
+	// listener.
+	deferAccept time.Duration
+
 	// pendingAccepted is a synchronization primitive used to track number
 	// of connections that are queued up to be delivered to the accepted
 	// channel. We use this to ensure that all goroutines blocked on writing
@@ -778,6 +787,38 @@ func (e *endpoint) notifyProtocolGoroutine(n uint32) {
 	}
 }
 
+// Abort implements stack.TransportEndpoint.Abort.
+func (e *endpoint) Abort() {
+	// The abort notification is not processed synchronously, so no
+	// synchronization is needed.
+	//
+	// If the endpoint becomes connected after this check, we still close
+	// the endpoint. This worst case results in a slower abort.
+	//
+	// If the endpoint disconnected after the check, nothing needs to be
+	// done, so sending a notification which will potentially be ignored is
+	// fine.
+	//
+	// If the endpoint connecting finishes after the check, the endpoint
+	// is either in a connected state (where we would notifyAbort anyway),
+	// SYN-RECV (where we would also notifyAbort anyway), or in an error
+	// state where nothing is required and the notification can be safely
+	// ignored.
+	//
+	// Endpoints where a Close during connecting or SYN-RECV state would be
+	// problematic are set to state connecting before being registered (and
+	// thus possible to be Aborted). They are never available in initial
+	// state.
+	//
+	// Endpoints transitioning from initial to connecting state may be
+	// safely either closed or sent notifyAbort.
+	if s := e.EndpointState(); s == StateConnecting || s == StateSynRecv || s.connected() {
+		e.notifyProtocolGoroutine(notifyAbort)
+		return
+	}
+	e.Close()
+}
+
 // Close puts the endpoint in a closed state and frees all resources associated
 // with it. It must be called only once and with no other concurrent calls to
 // the endpoint.
@@ -822,9 +863,18 @@ func (e *endpoint) closeNoShutdown() {
 	// Either perform the local cleanup or kick the worker to make sure it
 	// knows it needs to cleanup.
 	tcpip.AddDanglingEndpoint(e)
-	if !e.workerRunning {
+	switch e.EndpointState() {
+	// Sockets in StateSynRecv state(passive connections) are closed when
+	// the handshake fails or if the listening socket is closed while
+	// handshake was in progress. In such cases the handshake goroutine
+	// is already gone by the time Close is called and we need to cleanup
+	// here.
+	case StateInitial, StateBound, StateSynRecv:
 		e.cleanupLocked()
-	} else {
+		e.setEndpointState(StateClose)
+	case StateError, StateClose:
+		// do nothing.
+	default:
 		e.workerCleanup = true
 		e.notifyProtocolGoroutine(notifyClose)
 	}
@@ -909,15 +959,18 @@ func (e *endpoint) initialReceiveWindow() int {
 // ModerateRecvBuf adjusts the receive buffer and the advertised window
 // based on the number of bytes copied to user space.
 func (e *endpoint) ModerateRecvBuf(copied int) {
+	e.mu.RLock()
 	e.rcvListMu.Lock()
 	if e.rcvAutoParams.disabled {
 		e.rcvListMu.Unlock()
+		e.mu.RUnlock()
 		return
 	}
 	now := time.Now()
 	if rtt := e.rcvAutoParams.rtt; rtt == 0 || now.Sub(e.rcvAutoParams.measureTime) < rtt {
 		e.rcvAutoParams.copied += copied
 		e.rcvListMu.Unlock()
+		e.mu.RUnlock()
 		return
 	}
 	prevRTTCopied := e.rcvAutoParams.copied + copied
@@ -958,7 +1011,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {
 			e.rcvBufSize = rcvWnd
 			availAfter := e.receiveBufferAvailableLocked()
 			mask := uint32(notifyReceiveWindowChanged)
-			if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
+			if crossed, above := e.windowCrossedACKThresholdLocked(availAfter - availBefore); crossed && above {
 				mask |= notifyNonZeroReceiveWindow
 			}
 			e.notifyProtocolGoroutine(mask)
@@ -973,6 +1026,7 @@ func (e *endpoint) ModerateRecvBuf(copied int) {
 	e.rcvAutoParams.measureTime = now
 	e.rcvAutoParams.copied = 0
 	e.rcvListMu.Unlock()
+	e.mu.RUnlock()
 }
 
 // IPTables implements tcpip.Endpoint.IPTables.
@@ -996,13 +1050,12 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 		if s == StateError {
 			return buffer.View{}, tcpip.ControlMessages{}, he
 		}
-		e.stats.ReadErrors.InvalidEndpointState.Increment()
-		return buffer.View{}, tcpip.ControlMessages{}, tcpip.ErrInvalidEndpointState
+		e.stats.ReadErrors.NotConnected.Increment()
+		return buffer.View{}, tcpip.ControlMessages{}, tcpip.ErrNotConnected
 	}
 
 	v, err := e.readLocked()
 	e.rcvListMu.Unlock()
-
 	e.mu.RUnlock()
 
 	if err == tcpip.ErrClosedForReceive {
@@ -1035,7 +1088,7 @@ func (e *endpoint) readLocked() (buffer.View, *tcpip.Error) {
 	// enough buffer space, to either fit an aMSS or half a receive buffer
 	// (whichever smaller), then notify the protocol goroutine to send a
 	// window update.
-	if crossed, above := e.windowCrossedACKThreshold(len(v)); crossed && above {
+	if crossed, above := e.windowCrossedACKThresholdLocked(len(v)); crossed && above {
 		e.notifyProtocolGoroutine(notifyNonZeroReceiveWindow)
 	}
 
@@ -1253,9 +1306,9 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
 	return num, tcpip.ControlMessages{}, nil
 }
 
-// windowCrossedACKThreshold checks if the receive window to be announced now
-// would be under aMSS or under half receive buffer, whichever smaller. This is
-// useful as a receive side silly window syndrome prevention mechanism. If
+// windowCrossedACKThresholdLocked checks if the receive window to be announced
+// now would be under aMSS or under half receive buffer, whichever smaller. This
+// is useful as a receive side silly window syndrome prevention mechanism. If
 // window grows to reasonable value, we should send ACK to the sender to inform
 // the rx space is now large. We also want ensure a series of small read()'s
 // won't trigger a flood of spurious tiny ACK's.
@@ -1266,7 +1319,9 @@ func (e *endpoint) Peek(vec [][]byte) (int64, tcpip.ControlMessages, *tcpip.Erro
 // crossed will be true if the window size crossed the ACK threshold.
 // above will be true if the new window is >= ACK threshold and false
 // otherwise.
-func (e *endpoint) windowCrossedACKThreshold(deltaBefore int) (crossed bool, above bool) {
+//
+// Precondition: e.mu and e.rcvListMu must be held.
+func (e *endpoint) windowCrossedACKThresholdLocked(deltaBefore int) (crossed bool, above bool) {
 	newAvail := e.receiveBufferAvailableLocked()
 	oldAvail := newAvail - deltaBefore
 	if oldAvail < 0 {
@@ -1329,6 +1384,7 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 
 		mask := uint32(notifyReceiveWindowChanged)
 
+		e.mu.RLock()
 		e.rcvListMu.Lock()
 
 		// Make sure the receive buffer size allows us to send a
@@ -1355,11 +1411,11 @@ func (e *endpoint) SetSockOptInt(opt tcpip.SockOptInt, v int) *tcpip.Error {
 		// Immediately send an ACK to uncork the sender silly window
 		// syndrome prevetion, when our available space grows above aMSS
 		// or half receive buffer, whichever smaller.
-		if crossed, above := e.windowCrossedACKThreshold(availAfter - availBefore); crossed && above {
+		if crossed, above := e.windowCrossedACKThresholdLocked(availAfter - availBefore); crossed && above {
 			mask |= notifyNonZeroReceiveWindow
 		}
 		e.rcvListMu.Unlock()
-
+		e.mu.RUnlock()
 		e.notifyProtocolGoroutine(mask)
 		return nil
 
@@ -1574,6 +1630,15 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		e.mu.Unlock()
 		return nil
 
+	case tcpip.TCPDeferAcceptOption:
+		e.mu.Lock()
+		if time.Duration(v) > MaxRTO {
+			v = tcpip.TCPDeferAcceptOption(MaxRTO)
+		}
+		e.deferAccept = time.Duration(v)
+		e.mu.Unlock()
+		return nil
+
 	default:
 		return nil
 	}
@@ -1798,18 +1863,25 @@ func (e *endpoint) GetSockOpt(opt interface{}) *tcpip.Error {
 		e.mu.Unlock()
 		return nil
 
+	case *tcpip.TCPDeferAcceptOption:
+		e.mu.Lock()
+		*o = tcpip.TCPDeferAcceptOption(e.deferAccept)
+		e.mu.Unlock()
+		return nil
+
 	default:
 		return tcpip.ErrUnknownProtocolOption
 	}
 }
 
-func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
-	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProto(*addr, e.v6only)
+// checkV4MappedLocked determines the effective network protocol and converts
+// addr to its canonical form.
+func (e *endpoint) checkV4MappedLocked(addr tcpip.FullAddress) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
+	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProtoLocked(addr, e.v6only)
 	if err != nil {
-		return 0, err
+		return tcpip.FullAddress{}, 0, err
 	}
-	*addr = unwrapped
-	return netProto, nil
+	return unwrapped, netProto, nil
 }
 
 // Disconnect implements tcpip.Endpoint.Disconnect.
@@ -1839,7 +1911,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 
 	connectingAddr := addr.Addr
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
@@ -2025,8 +2097,14 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 				// work mutex is available.
 				if e.workMu.TryLock() {
 					e.mu.Lock()
-					e.resetConnectionLocked(tcpip.ErrConnectionAborted)
-					e.notifyProtocolGoroutine(notifyTickleWorker)
+					// We need to double check here to make
+					// sure worker has not transitioned the
+					// endpoint out of a connected state
+					// before trying to send a reset.
+					if e.EndpointState().connected() {
+						e.resetConnectionLocked(tcpip.ErrConnectionAborted)
+						e.notifyProtocolGoroutine(notifyTickleWorker)
+					}
 					e.mu.Unlock()
 					e.workMu.Unlock()
 				} else {
@@ -2039,10 +2117,13 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 		// Close for write.
 		if (e.shutdownFlags & tcpip.ShutdownWrite) != 0 {
 			e.sndBufMu.Lock()
-
 			if e.sndClosed {
 				// Already closed.
 				e.sndBufMu.Unlock()
+				if e.EndpointState() == StateTimeWait {
+					e.mu.Unlock()
+					return tcpip.ErrNotConnected
+				}
 				break
 			}
 
@@ -2138,6 +2219,9 @@ func (e *endpoint) listen(backlog int) *tcpip.Error {
 	e.isRegistered = true
 	e.setEndpointState(StateListen)
 
+	// The channel may be non-nil when we're restoring the endpoint, and it
+	// may be pre-populated with some previously accepted (but not Accepted)
+	// endpoints.
 	if e.acceptedChan == nil {
 		e.acceptedChan = make(chan *endpoint, backlog)
 	}
@@ -2149,9 +2233,8 @@ func (e *endpoint) listen(backlog int) *tcpip.Error {
 
 // startAcceptedLoop sets up required state and starts a goroutine with the
 // main loop for accepted connections.
-func (e *endpoint) startAcceptedLoop(waiterQueue *waiter.Queue) {
+func (e *endpoint) startAcceptedLoop() {
 	e.mu.Lock()
-	e.waiterQueue = waiterQueue
 	e.workerRunning = true
 	e.mu.Unlock()
 	wakerInitDone := make(chan struct{})
@@ -2177,7 +2260,6 @@ func (e *endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
 	default:
 		return nil, nil, tcpip.ErrWouldBlock
 	}
-
 	return n, n.waiterQueue, nil
 }
 
@@ -2198,7 +2280,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 	}
 
 	e.BindAddr = addr.Addr
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
@@ -2342,13 +2424,14 @@ func (e *endpoint) updateSndBufferUsage(v int) {
 // to be read, or when the connection is closed for receiving (in which case
 // s will be nil).
 func (e *endpoint) readyToRead(s *segment) {
+	e.mu.RLock()
 	e.rcvListMu.Lock()
 	if s != nil {
 		s.incRef()
 		e.rcvBufUsed += s.data.Size()
 		// Increase counter if the receive window falls down below MSS
 		// or half receive buffer size, whichever smaller.
-		if crossed, above := e.windowCrossedACKThreshold(-s.data.Size()); crossed && !above {
+		if crossed, above := e.windowCrossedACKThresholdLocked(-s.data.Size()); crossed && !above {
 			e.stats.ReceiveErrors.ZeroRcvWindowState.Increment()
 		}
 		e.rcvList.PushBack(s)
@@ -2356,7 +2439,7 @@ func (e *endpoint) readyToRead(s *segment) {
 		e.rcvClosed = true
 	}
 	e.rcvListMu.Unlock()
-
+	e.mu.RUnlock()
 	e.waiterQueue.Notify(waiter.EventIn)
 }
 
diff --git a/pkg/tcpip/transport/tcp/forwarder.go b/pkg/tcpip/transport/tcp/forwarder.go
index 7eb613be5..c9ee5bf06 100644
--- a/pkg/tcpip/transport/tcp/forwarder.go
+++ b/pkg/tcpip/transport/tcp/forwarder.go
@@ -157,13 +157,13 @@ func (r *ForwarderRequest) CreateEndpoint(queue *waiter.Queue) (tcpip.Endpoint,
 		TSVal:         r.synOptions.TSVal,
 		TSEcr:         r.synOptions.TSEcr,
 		SACKPermitted: r.synOptions.SACKPermitted,
-	})
+	}, queue)
 	if err != nil {
 		return nil, err
 	}
 
 	// Start the protocol goroutine.
-	ep.startAcceptedLoop(queue)
+	ep.startAcceptedLoop()
 
 	return ep, nil
 }
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 958c06fa7..73098d904 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -194,7 +194,7 @@ func replyWithReset(s *segment) {
 	sendTCP(&s.route, s.id, buffer.VectorisedView{}, s.route.DefaultTTL(), stack.DefaultTOS, flags, seq, ack, 0 /* rcvWnd */, nil /* options */, nil /* gso */)
 }
 
-// SetOption implements TransportProtocol.SetOption.
+// SetOption implements stack.TransportProtocol.SetOption.
 func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 	switch v := option.(type) {
 	case SACKEnabled:
@@ -269,7 +269,7 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 	}
 }
 
-// Option implements TransportProtocol.Option.
+// Option implements stack.TransportProtocol.Option.
 func (p *protocol) Option(option interface{}) *tcpip.Error {
 	switch v := option.(type) {
 	case *SACKEnabled:
@@ -331,6 +331,16 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 	}
 }
 
+// Close implements stack.TransportProtocol.Close.
+func (p *protocol) Close() {
+	p.dispatcher.close()
+}
+
+// Wait implements stack.TransportProtocol.Wait.
+func (p *protocol) Wait() {
+	p.dispatcher.wait()
+}
+
 // NewProtocol returns a TCP transport protocol.
 func NewProtocol() stack.TransportProtocol {
 	return &protocol{
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index 958f03ac1..d80aff1b6 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -195,6 +195,10 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 
 		for i := first; i < len(r.pendingRcvdSegments); i++ {
 			r.pendingRcvdSegments[i].decRef()
+			// Note that slice truncation does not allow garbage collection of
+			// truncated items, thus truncated items must be set to nil to avoid
+			// memory leaks.
+			r.pendingRcvdSegments[i] = nil
 		}
 		r.pendingRcvdSegments = r.pendingRcvdSegments[:first]
 
diff --git a/pkg/tcpip/transport/tcp/segment_heap.go b/pkg/tcpip/transport/tcp/segment_heap.go
index 9fd061d7d..e28f213ba 100644
--- a/pkg/tcpip/transport/tcp/segment_heap.go
+++ b/pkg/tcpip/transport/tcp/segment_heap.go
@@ -41,6 +41,7 @@ func (h *segmentHeap) Pop() interface{} {
 	old := *h
 	n := len(old)
 	x := old[n-1]
+	old[n-1] = nil
 	*h = old[:n-1]
 	return x
 }
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index df2fb1071..5b2b16afa 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -21,6 +21,7 @@ import (
 	"testing"
 	"time"
 
+	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
 	"gvisor.dev/gvisor/pkg/tcpip/checker"
@@ -542,8 +543,9 @@ func TestCurrentConnectedIncrement(t *testing.T) {
 		),
 	)
 
-	// Wait for the TIME-WAIT state to transition to CLOSED.
-	time.Sleep(1 * time.Second)
+	// Wait for a little more than the TIME-WAIT duration for the socket to
+	// transition to CLOSED state.
+	time.Sleep(1200 * time.Millisecond)
 
 	if got := c.Stack().Stats().TCP.CurrentEstablished.Value(); got != 0 {
 		t.Errorf("got stats.TCP.CurrentEstablished.Value() = %v, want = 0", got)
@@ -5404,12 +5406,11 @@ func TestEndpointBindListenAcceptState(t *testing.T) {
 		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
 	}
 
-	// Expect InvalidEndpointState errors on a read at this point.
-	if _, _, err := ep.Read(nil); err != tcpip.ErrInvalidEndpointState {
-		t.Fatalf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrInvalidEndpointState)
+	if _, _, err := ep.Read(nil); err != tcpip.ErrNotConnected {
+		t.Errorf("got c.EP.Read(nil) = %v, want = %v", err, tcpip.ErrNotConnected)
 	}
-	if got := ep.Stats().(*tcp.Stats).ReadErrors.InvalidEndpointState.Value(); got != 1 {
-		t.Fatalf("got EP stats Stats.ReadErrors.InvalidEndpointState got %v want %v", got, 1)
+	if got := ep.Stats().(*tcp.Stats).ReadErrors.NotConnected.Value(); got != 1 {
+		t.Errorf("got EP stats Stats.ReadErrors.NotConnected got %v want %v", got, 1)
 	}
 
 	if err := ep.Listen(10); err != nil {
@@ -6787,3 +6788,183 @@ func TestIncreaseWindowOnBufferResize(t *testing.T) {
 		),
 	)
 }
+
+func TestTCPDeferAccept(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	c.Create(-1)
+
+	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
+		t.Fatal("Bind failed:", err)
+	}
+
+	if err := c.EP.Listen(10); err != nil {
+		t.Fatal("Listen failed:", err)
+	}
+
+	const tcpDeferAccept = 1 * time.Second
+	if err := c.EP.SetSockOpt(tcpip.TCPDeferAcceptOption(tcpDeferAccept)); err != nil {
+		t.Fatalf("c.EP.SetSockOpt(TCPDeferAcceptOption(%s) failed: %v", tcpDeferAccept, err)
+	}
+
+	irs, iss := executeHandshake(t, c, context.TestPort, false /* synCookiesInUse */)
+
+	if _, _, err := c.EP.Accept(); err != tcpip.ErrWouldBlock {
+		t.Fatalf("c.EP.Accept() returned unexpected error got: %v, want: %s", err, tcpip.ErrWouldBlock)
+	}
+
+	// Send data. This should result in an acceptable endpoint.
+	c.SendPacket([]byte{1, 2, 3, 4}, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: context.StackPort,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  irs + 1,
+		AckNum:  iss + 1,
+	})
+
+	// Receive ACK for the data we sent.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagAck),
+		checker.SeqNum(uint32(iss+1)),
+		checker.AckNum(uint32(irs+5))))
+
+	// Give a bit of time for the socket to be delivered to the accept queue.
+	time.Sleep(50 * time.Millisecond)
+	aep, _, err := c.EP.Accept()
+	if err != nil {
+		t.Fatalf("c.EP.Accept() returned unexpected error got: %v, want: nil", err)
+	}
+
+	aep.Close()
+	// Closing aep without reading the data should trigger a RST.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck),
+		checker.SeqNum(uint32(iss+1)),
+		checker.AckNum(uint32(irs+5))))
+}
+
+func TestTCPDeferAcceptTimeout(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	c.Create(-1)
+
+	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
+		t.Fatal("Bind failed:", err)
+	}
+
+	if err := c.EP.Listen(10); err != nil {
+		t.Fatal("Listen failed:", err)
+	}
+
+	const tcpDeferAccept = 1 * time.Second
+	if err := c.EP.SetSockOpt(tcpip.TCPDeferAcceptOption(tcpDeferAccept)); err != nil {
+		t.Fatalf("c.EP.SetSockOpt(TCPDeferAcceptOption(%s) failed: %v", tcpDeferAccept, err)
+	}
+
+	irs, iss := executeHandshake(t, c, context.TestPort, false /* synCookiesInUse */)
+
+	if _, _, err := c.EP.Accept(); err != tcpip.ErrWouldBlock {
+		t.Fatalf("c.EP.Accept() returned unexpected error got: %v, want: %s", err, tcpip.ErrWouldBlock)
+	}
+
+	// Sleep for a little of the tcpDeferAccept timeout.
+	time.Sleep(tcpDeferAccept + 100*time.Millisecond)
+
+	// On timeout expiry we should get a SYN-ACK retransmission.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.SrcPort(context.StackPort),
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagAck|header.TCPFlagSyn),
+		checker.AckNum(uint32(irs)+1)))
+
+	// Send data. This should result in an acceptable endpoint.
+	c.SendPacket([]byte{1, 2, 3, 4}, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: context.StackPort,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  irs + 1,
+		AckNum:  iss + 1,
+	})
+
+	// Receive ACK for the data we sent.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.SrcPort(context.StackPort),
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagAck),
+		checker.SeqNum(uint32(iss+1)),
+		checker.AckNum(uint32(irs+5))))
+
+	// Give sometime for the endpoint to be delivered to the accept queue.
+	time.Sleep(50 * time.Millisecond)
+	aep, _, err := c.EP.Accept()
+	if err != nil {
+		t.Fatalf("c.EP.Accept() returned unexpected error got: %v, want: nil", err)
+	}
+
+	aep.Close()
+	// Closing aep without reading the data should trigger a RST.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.SrcPort(context.StackPort),
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagRst|header.TCPFlagAck),
+		checker.SeqNum(uint32(iss+1)),
+		checker.AckNum(uint32(irs+5))))
+}
+
+func TestResetDuringClose(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	iss := seqnum.Value(789)
+	c.CreateConnected(iss, 30000, -1 /* epRecvBuf */)
+	// Send some data to make sure there is some unread
+	// data to trigger a reset on c.Close.
+	irs := c.IRS
+	c.SendPacket([]byte{1, 2, 3, 4}, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  iss.Add(1),
+		AckNum:  irs.Add(1),
+		RcvWnd:  30000,
+	})
+
+	// Receive ACK for the data we sent.
+	checker.IPv4(t, c.GetPacket(), checker.TCP(
+		checker.DstPort(context.TestPort),
+		checker.TCPFlags(header.TCPFlagAck),
+		checker.SeqNum(uint32(irs.Add(1))),
+		checker.AckNum(uint32(iss.Add(5)))))
+
+	// Close in a separate goroutine so that we can trigger
+	// a race with the RST we send below. This should not
+	// panic due to the route being released depeding on
+	// whether Close() sends an active RST or the RST sent
+	// below is processed by the worker first.
+	var wg sync.WaitGroup
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		c.SendPacket(nil, &context.Headers{
+			SrcPort: context.TestPort,
+			DstPort: c.Port,
+			SeqNum:  iss.Add(5),
+			AckNum:  c.IRS.Add(5),
+			RcvWnd:  30000,
+			Flags:   header.TCPFlagRst,
+		})
+	}()
+
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+		c.EP.Close()
+	}()
+
+	wg.Wait()
+}
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 730ac4292..8cea20fb5 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -204,6 +204,7 @@ func (c *Context) Cleanup() {
 	if c.EP != nil {
 		c.EP.Close()
 	}
+	c.Stack().Close()
 }
 
 // Stack returns a reference to the stack in the Context.
@@ -1082,7 +1083,11 @@ func (c *Context) SACKEnabled() bool {
 
 // SetGSOEnabled enables or disables generic segmentation offload.
 func (c *Context) SetGSOEnabled(enable bool) {
-	c.linkEP.GSO = enable
+	if enable {
+		c.linkEP.LinkEPCapabilities |= stack.CapabilityHardwareGSO
+	} else {
+		c.linkEP.LinkEPCapabilities &^= stack.CapabilityHardwareGSO
+	}
 }
 
 // MSSWithoutOptions returns the value for the MSS used by the stack when no
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index c9cbed8f4..0af4514e1 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -29,9 +29,11 @@ import (
 type udpPacket struct {
 	udpPacketEntry
 	senderAddress tcpip.FullAddress
+	packetInfo    tcpip.IPPacketInfo
 	data          buffer.VectorisedView `state:".(buffer.VectorisedView)"`
 	timestamp     int64
-	tos           uint8
+	// tos stores either the receiveTOS or receiveTClass value.
+	tos uint8
 }
 
 // EndpointState represents the state of a UDP endpoint.
@@ -118,6 +120,13 @@ type endpoint struct {
 	// as ancillary data to ControlMessages on Read.
 	receiveTOS bool
 
+	// receiveTClass determines if the incoming IPv6 TClass header field is
+	// passed as ancillary data to ControlMessages on Read.
+	receiveTClass bool
+
+	// receiveIPPacketInfo determines if the packet info is returned by Read.
+	receiveIPPacketInfo bool
+
 	// shutdownFlags represent the current shutdown state of the endpoint.
 	shutdownFlags tcpip.ShutdownFlags
 
@@ -177,6 +186,11 @@ func (e *endpoint) UniqueID() uint64 {
 	return e.uniqueID
 }
 
+// Abort implements stack.TransportEndpoint.Abort.
+func (e *endpoint) Abort() {
+	e.Close()
+}
+
 // Close puts the endpoint in a closed state and frees all resources
 // associated with it.
 func (e *endpoint) Close() {
@@ -254,11 +268,22 @@ func (e *endpoint) Read(addr *tcpip.FullAddress) (buffer.View, tcpip.ControlMess
 	}
 	e.mu.RLock()
 	receiveTOS := e.receiveTOS
+	receiveTClass := e.receiveTClass
+	receiveIPPacketInfo := e.receiveIPPacketInfo
 	e.mu.RUnlock()
 	if receiveTOS {
 		cm.HasTOS = true
 		cm.TOS = p.tos
 	}
+	if receiveTClass {
+		cm.HasTClass = true
+		// Although TClass is an 8-bit value it's read in the CMsg as a uint32.
+		cm.TClass = uint32(p.tos)
+	}
+	if receiveIPPacketInfo {
+		cm.HasIPPacketInfo = true
+		cm.PacketInfo = p.packetInfo
+	}
 	return p.data.ToView(), cm, nil
 }
 
@@ -418,19 +443,19 @@ func (e *endpoint) write(p tcpip.Payloader, opts tcpip.WriteOptions) (int64, <-c
 			return 0, nil, tcpip.ErrBroadcastDisabled
 		}
 
-		netProto, err := e.checkV4Mapped(to)
+		dst, netProto, err := e.checkV4MappedLocked(*to)
 		if err != nil {
 			return 0, nil, err
 		}
 
-		r, _, err := e.connectRoute(nicID, *to, netProto)
+		r, _, err := e.connectRoute(nicID, dst, netProto)
 		if err != nil {
 			return 0, nil, err
 		}
 		defer r.Release()
 
 		route = &r
-		dstPort = to.Port
+		dstPort = dst.Port
 	}
 
 	if route.IsResolutionRequired() {
@@ -480,6 +505,17 @@ func (e *endpoint) SetSockOptBool(opt tcpip.SockOptBool, v bool) *tcpip.Error {
 		e.mu.Unlock()
 		return nil
 
+	case tcpip.ReceiveTClassOption:
+		// We only support this option on v6 endpoints.
+		if e.NetProto != header.IPv6ProtocolNumber {
+			return tcpip.ErrNotSupported
+		}
+
+		e.mu.Lock()
+		e.receiveTClass = v
+		e.mu.Unlock()
+		return nil
+
 	case tcpip.V6OnlyOption:
 		// We only recognize this option on v6 endpoints.
 		if e.NetProto != header.IPv6ProtocolNumber {
@@ -495,6 +531,13 @@ func (e *endpoint) SetSockOptBool(opt tcpip.SockOptBool, v bool) *tcpip.Error {
 		}
 
 		e.v6only = v
+		return nil
+
+	case tcpip.ReceiveIPPacketInfoOption:
+		e.mu.Lock()
+		e.receiveIPPacketInfo = v
+		e.mu.Unlock()
+		return nil
 	}
 
 	return nil
@@ -523,7 +566,7 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		defer e.mu.Unlock()
 
 		fa := tcpip.FullAddress{Addr: v.InterfaceAddr}
-		netProto, err := e.checkV4Mapped(&fa)
+		fa, netProto, err := e.checkV4MappedLocked(fa)
 		if err != nil {
 			return err
 		}
@@ -692,6 +735,17 @@ func (e *endpoint) GetSockOptBool(opt tcpip.SockOptBool) (bool, *tcpip.Error) {
 		e.mu.RUnlock()
 		return v, nil
 
+	case tcpip.ReceiveTClassOption:
+		// We only support this option on v6 endpoints.
+		if e.NetProto != header.IPv6ProtocolNumber {
+			return false, tcpip.ErrNotSupported
+		}
+
+		e.mu.RLock()
+		v := e.receiveTClass
+		e.mu.RUnlock()
+		return v, nil
+
 	case tcpip.V6OnlyOption:
 		// We only recognize this option on v6 endpoints.
 		if e.NetProto != header.IPv6ProtocolNumber {
@@ -703,6 +757,12 @@ func (e *endpoint) GetSockOptBool(opt tcpip.SockOptBool) (bool, *tcpip.Error) {
 		e.mu.RUnlock()
 
 		return v, nil
+
+	case tcpip.ReceiveIPPacketInfoOption:
+		e.mu.RLock()
+		v := e.receiveIPPacketInfo
+		e.mu.RUnlock()
+		return v, nil
 	}
 
 	return false, tcpip.ErrUnknownProtocolOption
@@ -867,13 +927,14 @@ func sendUDP(r *stack.Route, data buffer.VectorisedView, localPort, remotePort u
 	return nil
 }
 
-func (e *endpoint) checkV4Mapped(addr *tcpip.FullAddress) (tcpip.NetworkProtocolNumber, *tcpip.Error) {
-	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProto(*addr, e.v6only)
+// checkV4MappedLocked determines the effective network protocol and converts
+// addr to its canonical form.
+func (e *endpoint) checkV4MappedLocked(addr tcpip.FullAddress) (tcpip.FullAddress, tcpip.NetworkProtocolNumber, *tcpip.Error) {
+	unwrapped, netProto, err := e.TransportEndpointInfo.AddrNetProtoLocked(addr, e.v6only)
 	if err != nil {
-		return 0, err
+		return tcpip.FullAddress{}, 0, err
 	}
-	*addr = unwrapped
-	return netProto, nil
+	return unwrapped, netProto, nil
 }
 
 // Disconnect implements tcpip.Endpoint.Disconnect.
@@ -921,10 +982,6 @@ func (e *endpoint) Disconnect() *tcpip.Error {
 
 // Connect connects the endpoint to its peer. Specifying a NIC is optional.
 func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
-	netProto, err := e.checkV4Mapped(&addr)
-	if err != nil {
-		return err
-	}
 	if addr.Port == 0 {
 		// We don't support connecting to port zero.
 		return tcpip.ErrInvalidEndpointState
@@ -952,6 +1009,11 @@ func (e *endpoint) Connect(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
+	addr, netProto, err := e.checkV4MappedLocked(addr)
+	if err != nil {
+		return err
+	}
+
 	r, nicID, err := e.connectRoute(nicID, addr, netProto)
 	if err != nil {
 		return err
@@ -1079,7 +1141,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) *tcpip.Error {
 		return tcpip.ErrInvalidEndpointState
 	}
 
-	netProto, err := e.checkV4Mapped(&addr)
+	addr, netProto, err := e.checkV4MappedLocked(addr)
 	if err != nil {
 		return err
 	}
@@ -1247,6 +1309,11 @@ func (e *endpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, pk
 	switch r.NetProto {
 	case header.IPv4ProtocolNumber:
 		packet.tos, _ = header.IPv4(pkt.NetworkHeader).TOS()
+		packet.packetInfo.LocalAddr = r.LocalAddress
+		packet.packetInfo.DestinationAddr = r.RemoteAddress
+		packet.packetInfo.NIC = r.NICID()
+	case header.IPv6ProtocolNumber:
+		packet.tos, _ = header.IPv6(pkt.NetworkHeader).TOS()
 	}
 
 	packet.timestamp = e.stack.NowNanoseconds()
diff --git a/pkg/tcpip/transport/udp/endpoint_state.go b/pkg/tcpip/transport/udp/endpoint_state.go
index 43fb047ed..466bd9381 100644
--- a/pkg/tcpip/transport/udp/endpoint_state.go
+++ b/pkg/tcpip/transport/udp/endpoint_state.go
@@ -69,6 +69,9 @@ func (e *endpoint) afterLoad() {
 
 // Resume implements tcpip.ResumableEndpoint.Resume.
 func (e *endpoint) Resume(s *stack.Stack) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+
 	e.stack = s
 
 	for _, m := range e.multicastMemberships {
diff --git a/pkg/tcpip/transport/udp/protocol.go b/pkg/tcpip/transport/udp/protocol.go
index 259c3072a..8df089d22 100644
--- a/pkg/tcpip/transport/udp/protocol.go
+++ b/pkg/tcpip/transport/udp/protocol.go
@@ -180,16 +180,22 @@ func (p *protocol) HandleUnknownDestinationPacket(r *stack.Route, id stack.Trans
 	return true
 }
 
-// SetOption implements TransportProtocol.SetOption.
-func (p *protocol) SetOption(option interface{}) *tcpip.Error {
+// SetOption implements stack.TransportProtocol.SetOption.
+func (*protocol) SetOption(option interface{}) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
-// Option implements TransportProtocol.Option.
-func (p *protocol) Option(option interface{}) *tcpip.Error {
+// Option implements stack.TransportProtocol.Option.
+func (*protocol) Option(option interface{}) *tcpip.Error {
 	return tcpip.ErrUnknownProtocolOption
 }
 
+// Close implements stack.TransportProtocol.Close.
+func (*protocol) Close() {}
+
+// Wait implements stack.TransportProtocol.Wait.
+func (*protocol) Wait() {}
+
 // NewProtocol returns a UDP transport protocol.
 func NewProtocol() stack.TransportProtocol {
 	return &protocol{}
diff --git a/pkg/tcpip/transport/udp/udp_test.go b/pkg/tcpip/transport/udp/udp_test.go
index f0ff3fe71..34b7c2360 100644
--- a/pkg/tcpip/transport/udp/udp_test.go
+++ b/pkg/tcpip/transport/udp/udp_test.go
@@ -409,6 +409,7 @@ func (c *testContext) injectV6Packet(payload []byte, h *header4Tuple, valid bool
 	// Initialize the IP header.
 	ip := header.IPv6(buf)
 	ip.Encode(&header.IPv6Fields{
+		TrafficClass:  testTOS,
 		PayloadLength: uint16(header.UDPMinimumSize + len(payload)),
 		NextHeader:    uint8(udp.ProtocolNumber),
 		HopLimit:      65,
@@ -1336,7 +1337,7 @@ func TestSetTTL(t *testing.T) {
 	}
 }
 
-func TestTOSV4(t *testing.T) {
+func TestSetTOS(t *testing.T) {
 	for _, flow := range []testFlow{unicastV4, multicastV4, broadcast} {
 		t.Run(fmt.Sprintf("flow:%s", flow), func(t *testing.T) {
 			c := newDualTestContext(t, defaultMTU)
@@ -1347,23 +1348,23 @@ func TestTOSV4(t *testing.T) {
 			const tos = testTOS
 			var v tcpip.IPv4TOSOption
 			if err := c.ep.GetSockOpt(&v); err != nil {
-				c.t.Errorf("GetSockopt failed: %s", err)
+				c.t.Errorf("GetSockopt(%T) failed: %s", v, err)
 			}
 			// Test for expected default value.
 			if v != 0 {
-				c.t.Errorf("got GetSockOpt(...) = %#v, want = %#v", v, 0)
+				c.t.Errorf("got GetSockOpt(%T) = 0x%x, want = 0x%x", v, v, 0)
 			}
 
 			if err := c.ep.SetSockOpt(tcpip.IPv4TOSOption(tos)); err != nil {
-				c.t.Errorf("SetSockOpt(%#v) failed: %s", tcpip.IPv4TOSOption(tos), err)
+				c.t.Errorf("SetSockOpt(%T, 0x%x) failed: %s", v, tcpip.IPv4TOSOption(tos), err)
 			}
 
 			if err := c.ep.GetSockOpt(&v); err != nil {
-				c.t.Errorf("GetSockopt failed: %s", err)
+				c.t.Errorf("GetSockopt(%T) failed: %s", v, err)
 			}
 
 			if want := tcpip.IPv4TOSOption(tos); v != want {
-				c.t.Errorf("got GetSockOpt(...) = %#v, want = %#v", v, want)
+				c.t.Errorf("got GetSockOpt(%T) = 0x%x, want = 0x%x", v, v, want)
 			}
 
 			testWrite(c, flow, checker.TOS(tos, 0))
@@ -1371,7 +1372,7 @@ func TestTOSV4(t *testing.T) {
 	}
 }
 
-func TestTOSV6(t *testing.T) {
+func TestSetTClass(t *testing.T) {
 	for _, flow := range []testFlow{unicastV4in6, unicastV6, unicastV6Only, multicastV4in6, multicastV6, broadcastIn6} {
 		t.Run(fmt.Sprintf("flow:%s", flow), func(t *testing.T) {
 			c := newDualTestContext(t, defaultMTU)
@@ -1379,71 +1380,92 @@ func TestTOSV6(t *testing.T) {
 
 			c.createEndpointForFlow(flow)
 
-			const tos = testTOS
+			const tClass = testTOS
 			var v tcpip.IPv6TrafficClassOption
 			if err := c.ep.GetSockOpt(&v); err != nil {
-				c.t.Errorf("GetSockopt failed: %s", err)
+				c.t.Errorf("GetSockopt(%T) failed: %s", v, err)
 			}
 			// Test for expected default value.
 			if v != 0 {
-				c.t.Errorf("got GetSockOpt(...) = %#v, want = %#v", v, 0)
+				c.t.Errorf("got GetSockOpt(%T) = 0x%x, want = 0x%x", v, v, 0)
 			}
 
-			if err := c.ep.SetSockOpt(tcpip.IPv6TrafficClassOption(tos)); err != nil {
-				c.t.Errorf("SetSockOpt failed: %s", err)
+			if err := c.ep.SetSockOpt(tcpip.IPv6TrafficClassOption(tClass)); err != nil {
+				c.t.Errorf("SetSockOpt(%T, 0x%x) failed: %s", v, tcpip.IPv6TrafficClassOption(tClass), err)
 			}
 
 			if err := c.ep.GetSockOpt(&v); err != nil {
-				c.t.Errorf("GetSockopt failed: %s", err)
+				c.t.Errorf("GetSockopt(%T) failed: %s", v, err)
 			}
 
-			if want := tcpip.IPv6TrafficClassOption(tos); v != want {
-				c.t.Errorf("got GetSockOpt(...) = %#v, want = %#v", v, want)
+			if want := tcpip.IPv6TrafficClassOption(tClass); v != want {
+				c.t.Errorf("got GetSockOpt(%T) = 0x%x, want = 0x%x", v, v, want)
 			}
 
-			testWrite(c, flow, checker.TOS(tos, 0))
+			// The header getter for TClass is called TOS, so use that checker.
+			testWrite(c, flow, checker.TOS(tClass, 0))
 		})
 	}
 }
 
-func TestReceiveTOSV4(t *testing.T) {
-	for _, flow := range []testFlow{unicastV4, broadcast} {
-		t.Run(fmt.Sprintf("flow:%s", flow), func(t *testing.T) {
-			c := newDualTestContext(t, defaultMTU)
-			defer c.cleanup()
+func TestReceiveTosTClass(t *testing.T) {
+	testCases := []struct {
+		name             string
+		getReceiveOption tcpip.SockOptBool
+		tests            []testFlow
+	}{
+		{"ReceiveTosOption", tcpip.ReceiveTOSOption, []testFlow{unicastV4, broadcast}},
+		{"ReceiveTClassOption", tcpip.ReceiveTClassOption, []testFlow{unicastV4in6, unicastV6, unicastV6Only, broadcastIn6}},
+	}
+	for _, testCase := range testCases {
+		for _, flow := range testCase.tests {
+			t.Run(fmt.Sprintf("%s:flow:%s", testCase.name, flow), func(t *testing.T) {
+				c := newDualTestContext(t, defaultMTU)
+				defer c.cleanup()
 
-			c.createEndpointForFlow(flow)
+				c.createEndpointForFlow(flow)
+				option := testCase.getReceiveOption
+				name := testCase.name
 
-			// Verify that setting and reading the option works.
-			v, err := c.ep.GetSockOptBool(tcpip.ReceiveTOSOption)
-			if err != nil {
-				c.t.Fatal("GetSockOptBool(tcpip.ReceiveTOSOption) failed:", err)
-			}
-			// Test for expected default value.
-			if v != false {
-				c.t.Errorf("got GetSockOptBool(tcpip.ReceiveTOSOption) = %t, want = %t", v, false)
-			}
+				// Verify that setting and reading the option works.
+				v, err := c.ep.GetSockOptBool(option)
+				if err != nil {
+					c.t.Errorf("GetSockoptBool(%s) failed: %s", name, err)
+				}
+				// Test for expected default value.
+				if v != false {
+					c.t.Errorf("got GetSockOptBool(%s) = %t, want = %t", name, v, false)
+				}
 
-			want := true
-			if err := c.ep.SetSockOptBool(tcpip.ReceiveTOSOption, want); err != nil {
-				c.t.Fatalf("SetSockOptBool(tcpip.ReceiveTOSOption, %t) failed: %s", want, err)
-			}
+				want := true
+				if err := c.ep.SetSockOptBool(option, want); err != nil {
+					c.t.Fatalf("SetSockOptBool(%s, %t) failed: %s", name, want, err)
+				}
 
-			got, err := c.ep.GetSockOptBool(tcpip.ReceiveTOSOption)
-			if err != nil {
-				c.t.Fatal("GetSockOptBool(tcpip.ReceiveTOSOption) failed:", err)
-			}
-			if got != want {
-				c.t.Fatalf("got GetSockOptBool(tcpip.ReceiveTOSOption) = %t, want = %t", got, want)
-			}
+				got, err := c.ep.GetSockOptBool(option)
+				if err != nil {
+					c.t.Errorf("GetSockoptBool(%s) failed: %s", name, err)
+				}
 
-			// Verify that the correct received TOS is handed through as
-			// ancillary data to the ControlMessages struct.
-			if err := c.ep.Bind(tcpip.FullAddress{Port: stackPort}); err != nil {
-				c.t.Fatal("Bind failed:", err)
-			}
-			testRead(c, flow, checker.ReceiveTOS(testTOS))
-		})
+				if got != want {
+					c.t.Errorf("got GetSockOptBool(%s) = %t, want = %t", name, got, want)
+				}
+
+				// Verify that the correct received TOS or TClass is handed through as
+				// ancillary data to the ControlMessages struct.
+				if err := c.ep.Bind(tcpip.FullAddress{Port: stackPort}); err != nil {
+					c.t.Fatalf("Bind failed: %s", err)
+				}
+				switch option {
+				case tcpip.ReceiveTClassOption:
+					testRead(c, flow, checker.ReceiveTClass(testTOS))
+				case tcpip.ReceiveTOSOption:
+					testRead(c, flow, checker.ReceiveTOS(testTOS))
+				default:
+					t.Fatalf("unknown test variant: %s", name)
+				}
+			})
+		}
 	}
 }