Add support for SO_REUSEADDR to TCP sockets/endpoints.

For TCP sockets, SO_REUSEADDR relaxes the rules for binding addresses.

gVisor/netstack already supported a behavior similar to SO_REUSEADDR, but did
not allow disabling it. This change brings the SO_REUSEADDR behavior closer to
the behavior implemented by Linux and adds a new SO_REUSEADDR disabled
behavior. Like Linux, SO_REUSEADDR is now disabled by default.

PiperOrigin-RevId: 317984380

5 files changed, 174 insertions, 123 deletions

diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index 7679fe169..6e00e5526 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -27,7 +27,6 @@ import (
 	"gvisor.dev/gvisor/pkg/sync"
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
-	"gvisor.dev/gvisor/pkg/tcpip/ports"
 	"gvisor.dev/gvisor/pkg/tcpip/seqnum"
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 	"gvisor.dev/gvisor/pkg/waiter"
@@ -199,9 +198,8 @@ 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. The endpoint is returned
-// with n.mu held.
-func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, irs seqnum.Value, rcvdSynOpts *header.TCPSynOptions, queue *waiter.Queue) (*endpoint, *tcpip.Error) {
+// the connection parameters given by the arguments.
+func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, irs seqnum.Value, rcvdSynOpts *header.TCPSynOptions, queue *waiter.Queue) *endpoint {
 	// Create a new endpoint.
 	netProto := l.netProto
 	if netProto == 0 {
@@ -227,22 +225,7 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	// window to grow to a really large value.
 	n.rcvAutoParams.prevCopied = n.initialReceiveWindow()
 
-	// Lock the endpoint before registering to ensure that no out of
-	// band changes are possible due to incoming packets etc till
-	// the endpoint is done initializing.
-	n.mu.Lock()
-
-	// Register new endpoint so that packets are routed to it.
-	if err := n.stack.RegisterTransportEndpoint(n.boundNICID, n.effectiveNetProtos, ProtocolNumber, n.ID, n, ports.Flags{LoadBalanced: n.reusePort}, n.boundBindToDevice); err != nil {
-		n.mu.Unlock()
-		n.Close()
-		return nil, err
-	}
-
-	n.isRegistered = true
-	n.registeredReusePort = n.reusePort
-
-	return n, nil
+	return n
 }
 
 // createEndpointAndPerformHandshake creates a new endpoint in connected state
@@ -253,10 +236,12 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 	// Create new endpoint.
 	irs := s.sequenceNumber
 	isn := generateSecureISN(s.id, l.stack.Seed())
-	ep, err := l.createConnectingEndpoint(s, isn, irs, opts, queue)
-	if err != nil {
-		return nil, err
-	}
+	ep := l.createConnectingEndpoint(s, isn, irs, opts, queue)
+
+	// Lock the endpoint before registering to ensure that no out of
+	// band changes are possible due to incoming packets etc till
+	// the endpoint is done initializing.
+	ep.mu.Lock()
 	ep.owner = owner
 
 	// listenEP is nil when listenContext is used by tcp.Forwarder.
@@ -264,18 +249,13 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 	if l.listenEP != nil {
 		l.listenEP.mu.Lock()
 		if l.listenEP.EndpointState() != StateListen {
+
 			l.listenEP.mu.Unlock()
 			// Ensure we release any registrations done by the newly
 			// created endpoint.
 			ep.mu.Unlock()
 			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)
 			return nil, tcpip.ErrConnectionAborted
 		}
 		l.addPendingEndpoint(ep)
@@ -284,21 +264,44 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 		// to the newly created endpoint.
 		l.listenEP.propagateInheritableOptionsLocked(ep)
 
+		if !ep.reserveTupleLocked() {
+			ep.mu.Unlock()
+			ep.Close()
+
+			if l.listenEP != nil {
+				l.removePendingEndpoint(ep)
+				l.listenEP.mu.Unlock()
+			}
+
+			return nil, tcpip.ErrConnectionAborted
+		}
+
 		deferAccept = l.listenEP.deferAccept
 		l.listenEP.mu.Unlock()
 	}
 
+	// Register new endpoint so that packets are routed to it.
+	if err := ep.stack.RegisterTransportEndpoint(ep.boundNICID, ep.effectiveNetProtos, ProtocolNumber, ep.ID, ep, ep.boundPortFlags, ep.boundBindToDevice); err != nil {
+		ep.mu.Unlock()
+		ep.Close()
+
+		if l.listenEP != nil {
+			l.removePendingEndpoint(ep)
+		}
+
+		ep.drainClosingSegmentQueue()
+
+		return nil, err
+	}
+
+	ep.isRegistered = true
+
 	// Perform the 3-way handshake.
 	h := newPassiveHandshake(ep, seqnum.Size(ep.initialReceiveWindow()), isn, irs, opts, deferAccept)
 	if err := h.execute(); err != nil {
 		ep.mu.Unlock()
 		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)
+		ep.notifyAborted()
 
 		if l.listenEP != nil {
 			l.removePendingEndpoint(ep)
@@ -374,6 +377,43 @@ func (e *endpoint) deliverAccepted(n *endpoint) {
 // Precondition: e.mu and n.mu must be held.
 func (e *endpoint) propagateInheritableOptionsLocked(n *endpoint) {
 	n.userTimeout = e.userTimeout
+	n.portFlags = e.portFlags
+	n.boundBindToDevice = e.boundBindToDevice
+	n.boundPortFlags = e.boundPortFlags
+}
+
+// reserveTupleLocked reserves an accepted endpoint's tuple.
+//
+// Preconditions:
+// * propagateInheritableOptionsLocked has been called.
+// * e.mu is held.
+func (e *endpoint) reserveTupleLocked() bool {
+	dest := tcpip.FullAddress{Addr: e.ID.RemoteAddress, Port: e.ID.RemotePort}
+	if !e.stack.ReserveTuple(
+		e.effectiveNetProtos,
+		ProtocolNumber,
+		e.ID.LocalAddress,
+		e.ID.LocalPort,
+		e.boundPortFlags,
+		e.boundBindToDevice,
+		dest,
+	) {
+		return false
+	}
+
+	e.isPortReserved = true
+	e.boundDest = dest
+	return true
+}
+
+// notifyAborted wakes up any waiters on registered, but not accepted
+// endpoints.
+//
+// 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.
+func (e *endpoint) notifyAborted() {
+	e.waiterQueue.Notify(waiter.EventHUp | waiter.EventErr | waiter.EventIn | waiter.EventOut)
 }
 
 // handleSynSegment is called in its own goroutine once the listening endpoint
@@ -568,16 +608,34 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 			rcvdSynOptions.TSEcr = s.parsedOptions.TSEcr
 		}
 
-		n, err := ctx.createConnectingEndpoint(s, iss, irs, rcvdSynOptions, &waiter.Queue{})
-		if err != nil {
+		n := ctx.createConnectingEndpoint(s, iss, irs, rcvdSynOptions, &waiter.Queue{})
+
+		n.mu.Lock()
+
+		// Propagate any inheritable options from the listening endpoint
+		// to the newly created endpoint.
+		e.propagateInheritableOptionsLocked(n)
+
+		if !n.reserveTupleLocked() {
+			n.mu.Unlock()
+			n.Close()
+
 			e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
 			e.stats.FailedConnectionAttempts.Increment()
 			return
 		}
 
-		// Propagate any inheritable options from the listening endpoint
-		// to the newly created endpoint.
-		e.propagateInheritableOptionsLocked(n)
+		// Register new endpoint so that packets are routed to it.
+		if err := n.stack.RegisterTransportEndpoint(n.boundNICID, n.effectiveNetProtos, ProtocolNumber, n.ID, n, n.boundPortFlags, n.boundBindToDevice); err != nil {
+			n.mu.Unlock()
+			n.Close()
+
+			e.stack.Stats().TCP.FailedConnectionAttempts.Increment()
+			e.stats.FailedConnectionAttempts.Increment()
+			return
+		}
+
+		n.isRegistered = true
 
 		// clear the tsOffset for the newly created
 		// endpoint as the Timestamp was already
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 10df2bcd5..1e4c2f507 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -396,7 +396,8 @@ type endpoint struct {
 	mu          sync.Mutex `state:"nosave"`
 	ownedByUser uint32
 
-	// state must be read/set using the EndpointState()/setEndpointState() methods.
+	// state must be read/set using the EndpointState()/setEndpointState()
+	// methods.
 	state EndpointState `state:".(EndpointState)"`
 
 	// origEndpointState is only used during a restore phase to save the
@@ -405,8 +406,8 @@ type endpoint struct {
 	origEndpointState EndpointState `state:"nosave"`
 
 	isPortReserved    bool `state:"manual"`
-	isRegistered      bool
-	boundNICID        tcpip.NICID `state:"manual"`
+	isRegistered      bool `state:"manual"`
+	boundNICID        tcpip.NICID
 	route             stack.Route `state:"manual"`
 	ttl               uint8
 	v6only            bool
@@ -415,10 +416,14 @@ type endpoint struct {
 	// disabling SO_BROADCAST, albeit as a NOOP.
 	broadcast bool
 
+	// portFlags stores the current values of port related flags.
+	portFlags ports.Flags
+
 	// Values used to reserve a port or register a transport endpoint
 	// (which ever happens first).
 	boundBindToDevice tcpip.NICID
 	boundPortFlags    ports.Flags
+	boundDest         tcpip.FullAddress
 
 	// effectiveNetProtos contains the network protocols actually in use. In
 	// most cases it will only contain "netProto", but in cases like IPv6
@@ -426,7 +431,7 @@ type endpoint struct {
 	// protocols (e.g., IPv6 and IPv4) or a single different protocol (e.g.,
 	// IPv4 when IPv6 endpoint is bound or connected to an IPv4 mapped
 	// address).
-	effectiveNetProtos []tcpip.NetworkProtocolNumber `state:"manual"`
+	effectiveNetProtos []tcpip.NetworkProtocolNumber
 
 	// workerRunning specifies if a worker goroutine is running.
 	workerRunning bool
@@ -462,13 +467,6 @@ type endpoint struct {
 	// sack holds TCP SACK related information for this endpoint.
 	sack SACKInfo
 
-	// reusePort is set to true if SO_REUSEPORT is enabled.
-	reusePort bool
-
-	// registeredReusePort is set if the current endpoint registration was
-	// done with SO_REUSEPORT enabled.
-	registeredReusePort bool
-
 	// bindToDevice is set to the NIC on which to bind or disabled if 0.
 	bindToDevice tcpip.NICID
 
@@ -488,7 +486,6 @@ type endpoint struct {
 	// The options below aren't implemented, but we remember the user
 	// settings because applications expect to be able to set/query these
 	// options.
-	reuseAddr bool
 
 	// slowAck holds the negated state of quick ack. It is stubbed out and
 	// does nothing.
@@ -838,7 +835,6 @@ func newEndpoint(s *stack.Stack, netProto tcpip.NetworkProtocolNumber, waiterQue
 		rcvBufSize:  DefaultReceiveBufferSize,
 		sndBufSize:  DefaultSendBufferSize,
 		sndMTU:      int(math.MaxInt32),
-		reuseAddr:   true,
 		keepalive: keepalive{
 			// Linux defaults.
 			idle:     2 * time.Hour,
@@ -1025,15 +1021,15 @@ func (e *endpoint) closeNoShutdownLocked() {
 	// in Listen() when trying to register.
 	if e.EndpointState() == StateListen && e.isPortReserved {
 		if e.isRegistered {
-			e.stack.StartTransportEndpointCleanup(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, ports.Flags{LoadBalanced: e.registeredReusePort}, e.boundBindToDevice)
+			e.stack.StartTransportEndpointCleanup(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, e.boundPortFlags, e.boundBindToDevice)
 			e.isRegistered = false
-			e.registeredReusePort = false
 		}
 
-		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice)
+		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice, e.boundDest)
 		e.isPortReserved = false
 		e.boundBindToDevice = 0
 		e.boundPortFlags = ports.Flags{}
+		e.boundDest = tcpip.FullAddress{}
 	}
 
 	// Mark endpoint as closed.
@@ -1091,17 +1087,17 @@ func (e *endpoint) cleanupLocked() {
 	e.workerCleanup = false
 
 	if e.isRegistered {
-		e.stack.StartTransportEndpointCleanup(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, ports.Flags{LoadBalanced: e.registeredReusePort}, e.boundBindToDevice)
+		e.stack.StartTransportEndpointCleanup(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, e.boundPortFlags, e.boundBindToDevice)
 		e.isRegistered = false
-		e.registeredReusePort = false
 	}
 
 	if e.isPortReserved {
-		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice)
+		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice, e.boundDest)
 		e.isPortReserved = false
 	}
 	e.boundBindToDevice = 0
 	e.boundPortFlags = ports.Flags{}
+	e.boundDest = tcpip.FullAddress{}
 
 	e.route.Release()
 	e.stack.CompleteTransportEndpointCleanup(e)
@@ -1522,12 +1518,12 @@ func (e *endpoint) SetSockOptBool(opt tcpip.SockOptBool, v bool) *tcpip.Error {
 
 	case tcpip.ReuseAddressOption:
 		e.LockUser()
-		e.reuseAddr = v
+		e.portFlags.TupleOnly = v
 		e.UnlockUser()
 
 	case tcpip.ReusePortOption:
 		e.LockUser()
-		e.reusePort = v
+		e.portFlags.LoadBalanced = v
 		e.UnlockUser()
 
 	case tcpip.V6OnlyOption:
@@ -1831,14 +1827,14 @@ func (e *endpoint) GetSockOptBool(opt tcpip.SockOptBool) (bool, *tcpip.Error) {
 
 	case tcpip.ReuseAddressOption:
 		e.LockUser()
-		v := e.reuseAddr
+		v := e.portFlags.TupleOnly
 		e.UnlockUser()
 
 		return v, nil
 
 	case tcpip.ReusePortOption:
 		e.LockUser()
-		v := e.reusePort
+		v := e.portFlags.LoadBalanced
 		e.UnlockUser()
 
 		return v, nil
@@ -2091,8 +2087,6 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 	}
 	defer r.Release()
 
-	origID := e.ID
-
 	netProtos := []tcpip.NetworkProtocolNumber{netProto}
 	e.ID.LocalAddress = r.LocalAddress
 	e.ID.RemoteAddress = r.RemoteAddress
@@ -2100,11 +2094,10 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 
 	if e.ID.LocalPort != 0 {
 		// The endpoint is bound to a port, attempt to register it.
-		err := e.stack.RegisterTransportEndpoint(nicID, netProtos, ProtocolNumber, e.ID, e, ports.Flags{LoadBalanced: e.reusePort}, e.boundBindToDevice)
+		err := e.stack.RegisterTransportEndpoint(nicID, netProtos, ProtocolNumber, e.ID, e, e.boundPortFlags, e.boundBindToDevice)
 		if err != nil {
 			return err
 		}
-		e.registeredReusePort = e.reusePort
 	} else {
 		// The endpoint doesn't have a local port yet, so try to get
 		// one. Make sure that it isn't one that will result in the same
@@ -2128,40 +2121,33 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 			if sameAddr && p == e.ID.RemotePort {
 				return false, nil
 			}
-			// reusePort is false below because connect cannot reuse a port even if
-			// reusePort was set.
-			if !e.stack.IsPortAvailable(netProtos, ProtocolNumber, e.ID.LocalAddress, p, ports.Flags{LoadBalanced: false}, e.bindToDevice) {
+			if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr); err != nil {
 				return false, nil
 			}
 
 			id := e.ID
 			id.LocalPort = p
-			switch e.stack.RegisterTransportEndpoint(nicID, netProtos, ProtocolNumber, id, e, ports.Flags{LoadBalanced: e.reusePort}, e.bindToDevice) {
-			case nil:
-				// Port picking successful. Save the details of
-				// the selected port.
-				e.ID = id
-				e.boundBindToDevice = e.bindToDevice
-				e.registeredReusePort = e.reusePort
-				return true, nil
-			case tcpip.ErrPortInUse:
-				return false, nil
-			default:
+			if err := e.stack.RegisterTransportEndpoint(nicID, netProtos, ProtocolNumber, id, e, e.portFlags, e.bindToDevice); err != nil {
+				e.stack.ReleasePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr)
+				if err == tcpip.ErrPortInUse {
+					return false, nil
+				}
 				return false, err
 			}
+
+			// Port picking successful. Save the details of
+			// the selected port.
+			e.ID = id
+			e.isPortReserved = true
+			e.boundBindToDevice = e.bindToDevice
+			e.boundPortFlags = e.portFlags
+			e.boundDest = addr
+			return true, nil
 		}); err != nil {
 			return err
 		}
 	}
 
-	// Remove the port reservation. This can happen when Bind is called
-	// before Connect: in such a case we don't want to hold on to
-	// reservations anymore.
-	if e.isPortReserved {
-		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, origID.LocalAddress, origID.LocalPort, e.boundPortFlags, e.boundBindToDevice)
-		e.isPortReserved = false
-	}
-
 	e.isRegistered = true
 	e.setEndpointState(StateConnecting)
 	e.route = r.Clone()
@@ -2340,13 +2326,12 @@ func (e *endpoint) listen(backlog int) *tcpip.Error {
 	}
 
 	// Register the endpoint.
-	if err := e.stack.RegisterTransportEndpoint(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, ports.Flags{LoadBalanced: e.reusePort}, e.boundBindToDevice); err != nil {
+	if err := e.stack.RegisterTransportEndpoint(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, e.boundPortFlags, e.boundBindToDevice); err != nil {
 		return err
 	}
 
 	e.isRegistered = true
 	e.setEndpointState(StateListen)
-	e.registeredReusePort = e.reusePort
 
 	// 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)
@@ -2433,16 +2418,13 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 		}
 	}
 
-	flags := ports.Flags{
-		LoadBalanced: e.reusePort,
-	}
-	port, err := e.stack.ReservePort(netProtos, ProtocolNumber, addr.Addr, addr.Port, flags, e.bindToDevice)
+	port, err := e.stack.ReservePort(netProtos, ProtocolNumber, addr.Addr, addr.Port, e.portFlags, e.bindToDevice, tcpip.FullAddress{})
 	if err != nil {
 		return err
 	}
 
 	e.boundBindToDevice = e.bindToDevice
-	e.boundPortFlags = flags
+	e.boundPortFlags = e.portFlags
 	e.isPortReserved = true
 	e.effectiveNetProtos = netProtos
 	e.ID.LocalPort = port
@@ -2450,7 +2432,7 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 	// Any failures beyond this point must remove the port registration.
 	defer func(portFlags ports.Flags, bindToDevice tcpip.NICID) {
 		if err != nil {
-			e.stack.ReleasePort(netProtos, ProtocolNumber, addr.Addr, port, portFlags, bindToDevice)
+			e.stack.ReleasePort(netProtos, ProtocolNumber, addr.Addr, port, portFlags, bindToDevice, tcpip.FullAddress{})
 			e.isPortReserved = false
 			e.effectiveNetProtos = nil
 			e.ID.LocalPort = 0
@@ -2473,6 +2455,10 @@ func (e *endpoint) bindLocked(addr tcpip.FullAddress) (err *tcpip.Error) {
 		e.ID.LocalAddress = addr.Addr
 	}
 
+	if err := e.stack.CheckRegisterTransportEndpoint(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e.boundPortFlags, e.boundBindToDevice); err != nil {
+		return err
+	}
+
 	// Mark endpoint as bound.
 	e.setEndpointState(StateBound)
 
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index 0bebec2d1..8258c0ecc 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -93,10 +93,6 @@ func (e *endpoint) beforeSave() {
 	if e.waiterQueue != nil && !e.waiterQueue.IsEmpty() {
 		panic("endpoint still has waiters upon save")
 	}
-
-	if e.EndpointState() != StateClose && !((e.EndpointState() == StateBound || e.EndpointState() == StateListen) == e.isPortReserved) {
-		panic("endpoints which are not in the closed state must have a reserved port IFF they are in bound or listen state")
-	}
 }
 
 // saveAcceptedChan is invoked by stateify.
@@ -198,14 +194,17 @@ func (e *endpoint) Resume(s *stack.Stack) {
 	}
 
 	bind := func() {
-		if len(e.BindAddr) == 0 {
-			e.BindAddr = e.ID.LocalAddress
+		addr, _, err := e.checkV4MappedLocked(tcpip.FullAddress{Addr: e.BindAddr, Port: e.ID.LocalPort})
+		if err != nil {
+			panic("unable to parse BindAddr: " + err.String())
 		}
-		addr := e.BindAddr
-		port := e.ID.LocalPort
-		if err := e.Bind(tcpip.FullAddress{Addr: addr, Port: port}); err != nil {
-			panic(fmt.Sprintf("endpoint binding [%v]:%d failed: %v", addr, port, err))
+		if ok := e.stack.ReserveTuple(e.effectiveNetProtos, ProtocolNumber, addr.Addr, addr.Port, e.boundPortFlags, e.boundBindToDevice, e.boundDest); !ok {
+			panic(fmt.Sprintf("unable to re-reserve tuple (%v, %q, %d, %+v, %d, %v)", e.effectiveNetProtos, addr.Addr, addr.Port, e.boundPortFlags, e.boundBindToDevice, e.boundDest))
 		}
+		e.isPortReserved = true
+
+		// Mark endpoint as bound.
+		e.setEndpointState(StateBound)
 	}
 
 	switch {
@@ -277,17 +276,7 @@ func (e *endpoint) Resume(s *stack.Stack) {
 			tcpip.AsyncLoading.Done()
 		}()
 	case epState == StateClose:
-		if e.isPortReserved {
-			tcpip.AsyncLoading.Add(1)
-			go func() {
-				connectedLoading.Wait()
-				listenLoading.Wait()
-				connectingLoading.Wait()
-				bind()
-				e.setEndpointState(StateClose)
-				tcpip.AsyncLoading.Done()
-			}()
-		}
+		e.isPortReserved = false
 		e.state = StateClose
 		e.stack.CompleteTransportEndpointCleanup(e)
 		tcpip.DeleteDanglingEndpoint(e)
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index aca6a7951..2632a3c67 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -3879,6 +3879,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
@@ -3888,6 +3891,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
@@ -3898,6 +3904,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
@@ -3910,6 +3919,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
@@ -3920,6 +3932,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
@@ -3932,6 +3947,9 @@ func TestReusePort(t *testing.T) {
 	if err != nil {
 		t.Fatalf("NewEndpoint failed; %s", err)
 	}
+	if err := c.EP.SetSockOptBool(tcpip.ReuseAddressOption, true); err != nil {
+		t.Fatalf("SetSockOptBool ReuseAddressOption failed: %s", err)
+	}
 	if err := c.EP.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %s", err)
 	}
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 40d66ef09..6ea212093 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -231,7 +231,7 @@ func (e *endpoint) Close() {
 	switch e.state {
 	case StateBound, StateConnected:
 		e.stack.UnregisterTransportEndpoint(e.RegisterNICID, e.effectiveNetProtos, ProtocolNumber, e.ID, e, e.boundPortFlags, e.boundBindToDevice)
-		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice)
+		e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, e.boundPortFlags, e.boundBindToDevice, tcpip.FullAddress{})
 		e.boundBindToDevice = 0
 		e.boundPortFlags = ports.Flags{}
 	}
@@ -1047,7 +1047,7 @@ func (e *endpoint) Disconnect() *tcpip.Error {
 	} else {
 		if e.ID.LocalPort != 0 {
 			// Release the ephemeral port.
-			e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, boundPortFlags, e.boundBindToDevice)
+			e.stack.ReleasePort(e.effectiveNetProtos, ProtocolNumber, e.ID.LocalAddress, e.ID.LocalPort, boundPortFlags, e.boundBindToDevice, tcpip.FullAddress{})
 			e.boundPortFlags = ports.Flags{}
 		}
 		e.state = StateInitial
@@ -1198,7 +1198,7 @@ func (*endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
 
 func (e *endpoint) registerWithStack(nicID tcpip.NICID, netProtos []tcpip.NetworkProtocolNumber, id stack.TransportEndpointID) (stack.TransportEndpointID, tcpip.NICID, *tcpip.Error) {
 	if e.ID.LocalPort == 0 {
-		port, err := e.stack.ReservePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.portFlags, e.bindToDevice)
+		port, err := e.stack.ReservePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.portFlags, e.bindToDevice, tcpip.FullAddress{})
 		if err != nil {
 			return id, e.bindToDevice, err
 		}
@@ -1208,7 +1208,7 @@ func (e *endpoint) registerWithStack(nicID tcpip.NICID, netProtos []tcpip.Networ
 
 	err := e.stack.RegisterTransportEndpoint(nicID, netProtos, ProtocolNumber, id, e, e.boundPortFlags, e.bindToDevice)
 	if err != nil {
-		e.stack.ReleasePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.boundPortFlags, e.bindToDevice)
+		e.stack.ReleasePort(netProtos, ProtocolNumber, id.LocalAddress, id.LocalPort, e.boundPortFlags, e.bindToDevice, tcpip.FullAddress{})
 		e.boundPortFlags = ports.Flags{}
 	}
 	return id, e.bindToDevice, err