Track and export socket state.

This is necessary for implementing network diagnostic interfaces like
/proc/net/{tcp,udp,unix} and sock_diag(7).

For pass-through endpoints such as hostinet, we obtain the socket
state from the backend. For netstack, we add explicit tracking of TCP
states.

PiperOrigin-RevId: 251934850

26 files changed, 518 insertions, 127 deletions

diff --git a/pkg/abi/linux/socket.go b/pkg/abi/linux/socket.go
index 417840731..44bd69df6 100644
--- a/pkg/abi/linux/socket.go
+++ b/pkg/abi/linux/socket.go
@@ -200,6 +200,22 @@ const (
 	SS_DISCONNECTING = 4 // In process of disconnecting.
 )
 
+// TCP protocol states, from include/net/tcp_states.h.
+const (
+	TCP_ESTABLISHED uint32 = iota + 1
+	TCP_SYN_SENT
+	TCP_SYN_RECV
+	TCP_FIN_WAIT1
+	TCP_FIN_WAIT2
+	TCP_TIME_WAIT
+	TCP_CLOSE
+	TCP_CLOSE_WAIT
+	TCP_LAST_ACK
+	TCP_LISTEN
+	TCP_CLOSING
+	TCP_NEW_SYN_RECV
+)
+
 // SockAddrMax is the maximum size of a struct sockaddr, from
 // uapi/linux/socket.h.
 const SockAddrMax = 128
diff --git a/pkg/sentry/fs/proc/net.go b/pkg/sentry/fs/proc/net.go
index 4a107c739..3daaa962c 100644
--- a/pkg/sentry/fs/proc/net.go
+++ b/pkg/sentry/fs/proc/net.go
@@ -240,24 +240,6 @@ func (n *netUnix) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]s
 			}
 		}
 
-		var sockState int
-		switch sops.Endpoint().Type() {
-		case linux.SOCK_DGRAM:
-			sockState = linux.SS_CONNECTING
-			// Unlike Linux, we don't have unbound connection-less sockets,
-			// so no SS_DISCONNECTING.
-
-		case linux.SOCK_SEQPACKET:
-			fallthrough
-		case linux.SOCK_STREAM:
-			// Connectioned.
-			if sops.Endpoint().(transport.ConnectingEndpoint).Connected() {
-				sockState = linux.SS_CONNECTED
-			} else {
-				sockState = linux.SS_UNCONNECTED
-			}
-		}
-
 		// In the socket entry below, the value for the 'Num' field requires
 		// some consideration. Linux prints the address to the struct
 		// unix_sock representing a socket in the kernel, but may redact the
@@ -282,7 +264,7 @@ func (n *netUnix) ReadSeqFileData(ctx context.Context, h seqfile.SeqHandle) ([]s
 			0,                             // Protocol, always 0 for UDS.
 			sockFlags,                     // Flags.
 			sops.Endpoint().Type(),        // Type.
-			sockState,                     // State.
+			sops.State(),                  // State.
 			sfile.InodeID(),               // Inode.
 		)
 
diff --git a/pkg/sentry/socket/epsocket/epsocket.go b/pkg/sentry/socket/epsocket/epsocket.go
index de4b963da..f91c5127a 100644
--- a/pkg/sentry/socket/epsocket/epsocket.go
+++ b/pkg/sentry/socket/epsocket/epsocket.go
@@ -52,6 +52,7 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/buffer"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip/stack"
+	"gvisor.googlesource.com/gvisor/pkg/tcpip/transport/tcp"
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
 
@@ -2281,3 +2282,46 @@ func nicStateFlagsToLinux(f stack.NICStateFlags) uint32 {
 	}
 	return rv
 }
+
+// State implements socket.Socket.State. State translates the internal state
+// returned by netstack to values defined by Linux.
+func (s *SocketOperations) State() uint32 {
+	if s.family != linux.AF_INET && s.family != linux.AF_INET6 {
+		// States not implemented for this socket's family.
+		return 0
+	}
+
+	if !s.isPacketBased() {
+		// TCP socket.
+		switch tcp.EndpointState(s.Endpoint.State()) {
+		case tcp.StateEstablished:
+			return linux.TCP_ESTABLISHED
+		case tcp.StateSynSent:
+			return linux.TCP_SYN_SENT
+		case tcp.StateSynRecv:
+			return linux.TCP_SYN_RECV
+		case tcp.StateFinWait1:
+			return linux.TCP_FIN_WAIT1
+		case tcp.StateFinWait2:
+			return linux.TCP_FIN_WAIT2
+		case tcp.StateTimeWait:
+			return linux.TCP_TIME_WAIT
+		case tcp.StateClose, tcp.StateInitial, tcp.StateBound, tcp.StateConnecting, tcp.StateError:
+			return linux.TCP_CLOSE
+		case tcp.StateCloseWait:
+			return linux.TCP_CLOSE_WAIT
+		case tcp.StateLastAck:
+			return linux.TCP_LAST_ACK
+		case tcp.StateListen:
+			return linux.TCP_LISTEN
+		case tcp.StateClosing:
+			return linux.TCP_CLOSING
+		default:
+			// Internal or unknown state.
+			return 0
+		}
+	}
+
+	// TODO(b/112063468): Export states for UDP, ICMP, and raw sockets.
+	return 0
+}
diff --git a/pkg/sentry/socket/hostinet/socket.go b/pkg/sentry/socket/hostinet/socket.go
index 41f9693bb..0d75580a3 100644
--- a/pkg/sentry/socket/hostinet/socket.go
+++ b/pkg/sentry/socket/hostinet/socket.go
@@ -19,7 +19,9 @@ import (
 	"syscall"
 
 	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
+	"gvisor.googlesource.com/gvisor/pkg/binary"
 	"gvisor.googlesource.com/gvisor/pkg/fdnotifier"
+	"gvisor.googlesource.com/gvisor/pkg/log"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/context"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs"
 	"gvisor.googlesource.com/gvisor/pkg/sentry/fs/fsutil"
@@ -519,6 +521,28 @@ func translateIOSyscallError(err error) error {
 	return err
 }
 
+// State implements socket.Socket.State.
+func (s *socketOperations) State() uint32 {
+	info := linux.TCPInfo{}
+	buf, err := getsockopt(s.fd, syscall.SOL_TCP, syscall.TCP_INFO, linux.SizeOfTCPInfo)
+	if err != nil {
+		if err != syscall.ENOPROTOOPT {
+			log.Warningf("Failed to get TCP socket info from %+v: %v", s, err)
+		}
+		// For non-TCP sockets, silently ignore the failure.
+		return 0
+	}
+	if len(buf) != linux.SizeOfTCPInfo {
+		// Unmarshal below will panic if getsockopt returns a buffer of
+		// unexpected size.
+		log.Warningf("Failed to get TCP socket info from %+v: getsockopt(2) returned %d bytes, expecting %d bytes.", s, len(buf), linux.SizeOfTCPInfo)
+		return 0
+	}
+
+	binary.Unmarshal(buf, usermem.ByteOrder, &info)
+	return uint32(info.State)
+}
+
 type socketProvider struct {
 	family int
 }
diff --git a/pkg/sentry/socket/netlink/socket.go b/pkg/sentry/socket/netlink/socket.go
index afd06ca33..16c79aa33 100644
--- a/pkg/sentry/socket/netlink/socket.go
+++ b/pkg/sentry/socket/netlink/socket.go
@@ -616,3 +616,8 @@ func (s *Socket) Write(ctx context.Context, _ *fs.File, src usermem.IOSequence,
 	n, err := s.sendMsg(ctx, src, nil, 0, socket.ControlMessages{})
 	return int64(n), err.ToError()
 }
+
+// State implements socket.Socket.State.
+func (s *Socket) State() uint32 {
+	return s.ep.State()
+}
diff --git a/pkg/sentry/socket/rpcinet/socket.go b/pkg/sentry/socket/rpcinet/socket.go
index 55e0b6665..bf42bdf69 100644
--- a/pkg/sentry/socket/rpcinet/socket.go
+++ b/pkg/sentry/socket/rpcinet/socket.go
@@ -830,6 +830,12 @@ func (s *socketOperations) SendMsg(t *kernel.Task, src usermem.IOSequence, to []
 	}
 }
 
+// State implements socket.Socket.State.
+func (s *socketOperations) State() uint32 {
+	// TODO(b/127845868): Define a new rpc to query the socket state.
+	return 0
+}
+
 type socketProvider struct {
 	family int
 }
diff --git a/pkg/sentry/socket/socket.go b/pkg/sentry/socket/socket.go
index 9393acd28..a99423365 100644
--- a/pkg/sentry/socket/socket.go
+++ b/pkg/sentry/socket/socket.go
@@ -116,6 +116,10 @@ type Socket interface {
 	// SendTimeout gets the current timeout (in ns) for send operations. Zero
 	// means no timeout, and negative means DONTWAIT.
 	SendTimeout() int64
+
+	// State returns the current state of the socket, as represented by Linux in
+	// procfs. The returned state value is protocol-specific.
+	State() uint32
 }
 
 // Provider is the interface implemented by providers of sockets for specific
diff --git a/pkg/sentry/socket/unix/transport/BUILD b/pkg/sentry/socket/unix/transport/BUILD
index 5a2de0c4c..52f324eed 100644
--- a/pkg/sentry/socket/unix/transport/BUILD
+++ b/pkg/sentry/socket/unix/transport/BUILD
@@ -28,6 +28,7 @@ go_library(
     importpath = "gvisor.googlesource.com/gvisor/pkg/sentry/socket/unix/transport",
     visibility = ["//:sandbox"],
     deps = [
+        "//pkg/abi/linux",
         "//pkg/ilist",
         "//pkg/refs",
         "//pkg/syserr",
diff --git a/pkg/sentry/socket/unix/transport/connectioned.go b/pkg/sentry/socket/unix/transport/connectioned.go
index 18e492862..9c8ec0365 100644
--- a/pkg/sentry/socket/unix/transport/connectioned.go
+++ b/pkg/sentry/socket/unix/transport/connectioned.go
@@ -17,6 +17,7 @@ package transport
 import (
 	"sync"
 
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/syserr"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
@@ -458,3 +459,11 @@ func (e *connectionedEndpoint) Readiness(mask waiter.EventMask) waiter.EventMask
 
 	return ready
 }
+
+// State implements socket.Socket.State.
+func (e *connectionedEndpoint) State() uint32 {
+	if e.Connected() {
+		return linux.SS_CONNECTED
+	}
+	return linux.SS_UNCONNECTED
+}
diff --git a/pkg/sentry/socket/unix/transport/connectionless.go b/pkg/sentry/socket/unix/transport/connectionless.go
index 43ff875e4..c034cf984 100644
--- a/pkg/sentry/socket/unix/transport/connectionless.go
+++ b/pkg/sentry/socket/unix/transport/connectionless.go
@@ -15,6 +15,7 @@
 package transport
 
 import (
+	"gvisor.googlesource.com/gvisor/pkg/abi/linux"
 	"gvisor.googlesource.com/gvisor/pkg/syserr"
 	"gvisor.googlesource.com/gvisor/pkg/tcpip"
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
@@ -194,3 +195,18 @@ func (e *connectionlessEndpoint) Readiness(mask waiter.EventMask) waiter.EventMa
 
 	return ready
 }
+
+// State implements socket.Socket.State.
+func (e *connectionlessEndpoint) State() uint32 {
+	e.Lock()
+	defer e.Unlock()
+
+	switch {
+	case e.isBound():
+		return linux.SS_UNCONNECTED
+	case e.Connected():
+		return linux.SS_CONNECTING
+	default:
+		return linux.SS_DISCONNECTING
+	}
+}
diff --git a/pkg/sentry/socket/unix/transport/unix.go b/pkg/sentry/socket/unix/transport/unix.go
index 37d82bb6b..5fc09af55 100644
--- a/pkg/sentry/socket/unix/transport/unix.go
+++ b/pkg/sentry/socket/unix/transport/unix.go
@@ -191,6 +191,10 @@ type Endpoint interface {
 	// GetSockOpt gets a socket option. opt should be a pointer to one of the
 	// tcpip.*Option types.
 	GetSockOpt(opt interface{}) *tcpip.Error
+
+	// State returns the current state of the socket, as represented by Linux in
+	// procfs.
+	State() uint32
 }
 
 // A Credentialer is a socket or endpoint that supports the SO_PASSCRED socket
diff --git a/pkg/sentry/socket/unix/unix.go b/pkg/sentry/socket/unix/unix.go
index 388cc0d8b..375542350 100644
--- a/pkg/sentry/socket/unix/unix.go
+++ b/pkg/sentry/socket/unix/unix.go
@@ -596,6 +596,11 @@ func (s *SocketOperations) RecvMsg(t *kernel.Task, dst usermem.IOSequence, flags
 	}
 }
 
+// State implements socket.Socket.State.
+func (s *SocketOperations) State() uint32 {
+	return s.ep.State()
+}
+
 // provider is a unix domain socket provider.
 type provider struct{}
 
diff --git a/pkg/tcpip/stack/transport_test.go b/pkg/tcpip/stack/transport_test.go
index 8d74f1543..e8a9392b5 100644
--- a/pkg/tcpip/stack/transport_test.go
+++ b/pkg/tcpip/stack/transport_test.go
@@ -188,6 +188,10 @@ func (f *fakeTransportEndpoint) HandleControlPacket(stack.TransportEndpointID, s
 	f.proto.controlCount++
 }
 
+func (f *fakeTransportEndpoint) State() uint32 {
+	return 0
+}
+
 type fakeTransportGoodOption bool
 
 type fakeTransportBadOption bool
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index f9886c6e4..85ef014d0 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -377,6 +377,10 @@ type Endpoint interface {
 	// GetSockOpt gets a socket option. opt should be a pointer to one of the
 	// *Option types.
 	GetSockOpt(opt interface{}) *Error
+
+	// State returns a socket's lifecycle state. The returned value is
+	// protocol-specific and is primarily used for diagnostics.
+	State() uint32
 }
 
 // WriteOptions contains options for Endpoint.Write.
diff --git a/pkg/tcpip/transport/icmp/BUILD b/pkg/tcpip/transport/icmp/BUILD
index 9aa6f3978..84a2b53b7 100644
--- a/pkg/tcpip/transport/icmp/BUILD
+++ b/pkg/tcpip/transport/icmp/BUILD
@@ -33,6 +33,7 @@ go_library(
         "//pkg/tcpip/header",
         "//pkg/tcpip/stack",
         "//pkg/tcpip/transport/raw",
+        "//pkg/tcpip/transport/tcp",
         "//pkg/waiter",
     ],
 )
diff --git a/pkg/tcpip/transport/icmp/endpoint.go b/pkg/tcpip/transport/icmp/endpoint.go
index e2b90ef10..b8005093a 100644
--- a/pkg/tcpip/transport/icmp/endpoint.go
+++ b/pkg/tcpip/transport/icmp/endpoint.go
@@ -708,3 +708,9 @@ func (e *endpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, vv
 // HandleControlPacket implements stack.TransportEndpoint.HandleControlPacket.
 func (e *endpoint) HandleControlPacket(id stack.TransportEndpointID, typ stack.ControlType, extra uint32, vv buffer.VectorisedView) {
 }
+
+// State implements tcpip.Endpoint.State. The ICMP endpoint currently doesn't
+// expose internal socket state.
+func (e *endpoint) State() uint32 {
+	return 0
+}
diff --git a/pkg/tcpip/transport/raw/endpoint.go b/pkg/tcpip/transport/raw/endpoint.go
index 1daf5823f..e4ff50c91 100644
--- a/pkg/tcpip/transport/raw/endpoint.go
+++ b/pkg/tcpip/transport/raw/endpoint.go
@@ -519,3 +519,8 @@ func (ep *endpoint) HandlePacket(route *stack.Route, netHeader buffer.View, vv b
 		ep.waiterQueue.Notify(waiter.EventIn)
 	}
 }
+
+// State implements socket.Socket.State.
+func (ep *endpoint) State() uint32 {
+	return 0
+}
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index 31e365ae5..a32e20b06 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -226,7 +226,6 @@ func (l *listenContext) createConnectingEndpoint(s *segment, iss seqnum.Value, i
 	}
 
 	n.isRegistered = true
-	n.state = stateConnecting
 
 	// Create sender and receiver.
 	//
@@ -258,8 +257,9 @@ func (l *listenContext) createEndpointAndPerformHandshake(s *segment, opts *head
 		ep.Close()
 		return nil, err
 	}
-
-	ep.state = stateConnected
+	ep.mu.Lock()
+	ep.state = StateEstablished
+	ep.mu.Unlock()
 
 	// Update the receive window scaling. We can't do it before the
 	// handshake because it's possible that the peer doesn't support window
@@ -276,7 +276,7 @@ func (e *endpoint) deliverAccepted(n *endpoint) {
 	e.mu.RLock()
 	state := e.state
 	e.mu.RUnlock()
-	if state == stateListen {
+	if state == StateListen {
 		e.acceptedChan <- n
 		e.waiterQueue.Notify(waiter.EventIn)
 	} else {
@@ -406,7 +406,7 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 		n.tsOffset = 0
 
 		// Switch state to connected.
-		n.state = stateConnected
+		n.state = StateEstablished
 
 		// Do the delivery in a separate goroutine so
 		// that we don't block the listen loop in case
@@ -429,7 +429,7 @@ func (e *endpoint) protocolListenLoop(rcvWnd seqnum.Size) *tcpip.Error {
 		// handleSynSegment() from attempting to queue new connections
 		// to the endpoint.
 		e.mu.Lock()
-		e.state = stateClosed
+		e.state = StateClose
 
 		// Do cleanup if needed.
 		e.completeWorkerLocked()
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 371d2ed29..0ad7bfb38 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -151,6 +151,9 @@ func (h *handshake) resetToSynRcvd(iss seqnum.Value, irs seqnum.Value, opts *hea
 	h.mss = opts.MSS
 	h.sndWndScale = opts.WS
 	h.listenEP = listenEP
+	h.ep.mu.Lock()
+	h.ep.state = StateSynRecv
+	h.ep.mu.Unlock()
 }
 
 // checkAck checks if the ACK number, if present, of a segment received during
@@ -219,6 +222,9 @@ func (h *handshake) synSentState(s *segment) *tcpip.Error {
 	// but resend our own SYN and wait for it to be acknowledged in the
 	// SYN-RCVD state.
 	h.state = handshakeSynRcvd
+	h.ep.mu.Lock()
+	h.ep.state = StateSynRecv
+	h.ep.mu.Unlock()
 	synOpts := header.TCPSynOptions{
 		WS:    h.rcvWndScale,
 		TS:    rcvSynOpts.TS,
@@ -668,7 +674,7 @@ func (e *endpoint) makeOptions(sackBlocks []header.SACKBlock) []byte {
 // sendRaw sends a TCP segment to the endpoint's peer.
 func (e *endpoint) sendRaw(data buffer.VectorisedView, flags byte, seq, ack seqnum.Value, rcvWnd seqnum.Size) *tcpip.Error {
 	var sackBlocks []header.SACKBlock
-	if e.state == stateConnected && e.rcv.pendingBufSize > 0 && (flags&header.TCPFlagAck != 0) {
+	if e.state == StateEstablished && e.rcv.pendingBufSize > 0 && (flags&header.TCPFlagAck != 0) {
 		sackBlocks = e.sack.Blocks[:e.sack.NumBlocks]
 	}
 	options := e.makeOptions(sackBlocks)
@@ -719,8 +725,7 @@ func (e *endpoint) handleClose() *tcpip.Error {
 // protocol goroutine.
 func (e *endpoint) resetConnectionLocked(err *tcpip.Error) {
 	e.sendRaw(buffer.VectorisedView{}, header.TCPFlagAck|header.TCPFlagRst, e.snd.sndUna, e.rcv.rcvNxt, 0)
-
-	e.state = stateError
+	e.state = StateError
 	e.hardError = err
 }
 
@@ -876,14 +881,19 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 		// handshake, and then inform potential waiters about its
 		// completion.
 		h := newHandshake(e, seqnum.Size(e.receiveBufferAvailable()))
+		e.mu.Lock()
+		h.ep.state = StateSynSent
+		e.mu.Unlock()
+
 		if err := h.execute(); err != nil {
 			e.lastErrorMu.Lock()
 			e.lastError = err
 			e.lastErrorMu.Unlock()
 
 			e.mu.Lock()
-			e.state = stateError
+			e.state = StateError
 			e.hardError = err
+
 			// Lock released below.
 			epilogue()
 
@@ -905,7 +915,7 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 
 	// Tell waiters that the endpoint is connected and writable.
 	e.mu.Lock()
-	e.state = stateConnected
+	e.state = StateEstablished
 	drained := e.drainDone != nil
 	e.mu.Unlock()
 	if drained {
@@ -1005,7 +1015,7 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 							return err
 						}
 					}
-					if e.state != stateError {
+					if e.state != StateError {
 						close(e.drainDone)
 						<-e.undrain
 					}
@@ -1061,8 +1071,8 @@ func (e *endpoint) protocolMainLoop(handshake bool) *tcpip.Error {
 
 	// Mark endpoint as closed.
 	e.mu.Lock()
-	if e.state != stateError {
-		e.state = stateClosed
+	if e.state != StateError {
+		e.state = StateClose
 	}
 	// Lock released below.
 	epilogue()
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index fd697402e..23422ca5e 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -32,18 +32,81 @@ import (
 	"gvisor.googlesource.com/gvisor/pkg/waiter"
 )
 
-type endpointState int
+// EndpointState represents the state of a TCP endpoint.
+type EndpointState uint32
 
+// Endpoint states. Note that are represented in a netstack-specific manner and
+// may not be meaningful externally. Specifically, they need to be translated to
+// Linux's representation for these states if presented to userspace.
 const (
-	stateInitial endpointState = iota
-	stateBound
-	stateListen
-	stateConnecting
-	stateConnected
-	stateClosed
-	stateError
+	// Endpoint states internal to netstack. These map to the TCP state CLOSED.
+	StateInitial EndpointState = iota
+	StateBound
+	StateConnecting // Connect() called, but the initial SYN hasn't been sent.
+	StateError
+
+	// TCP protocol states.
+	StateEstablished
+	StateSynSent
+	StateSynRecv
+	StateFinWait1
+	StateFinWait2
+	StateTimeWait
+	StateClose
+	StateCloseWait
+	StateLastAck
+	StateListen
+	StateClosing
 )
 
+// connected is the set of states where an endpoint is connected to a peer.
+func (s EndpointState) connected() bool {
+	switch s {
+	case StateEstablished, StateFinWait1, StateFinWait2, StateTimeWait, StateCloseWait, StateLastAck, StateClosing:
+		return true
+	default:
+		return false
+	}
+}
+
+// String implements fmt.Stringer.String.
+func (s EndpointState) String() string {
+	switch s {
+	case StateInitial:
+		return "INITIAL"
+	case StateBound:
+		return "BOUND"
+	case StateConnecting:
+		return "CONNECTING"
+	case StateError:
+		return "ERROR"
+	case StateEstablished:
+		return "ESTABLISHED"
+	case StateSynSent:
+		return "SYN-SENT"
+	case StateSynRecv:
+		return "SYN-RCVD"
+	case StateFinWait1:
+		return "FIN-WAIT1"
+	case StateFinWait2:
+		return "FIN-WAIT2"
+	case StateTimeWait:
+		return "TIME-WAIT"
+	case StateClose:
+		return "CLOSED"
+	case StateCloseWait:
+		return "CLOSE-WAIT"
+	case StateLastAck:
+		return "LAST-ACK"
+	case StateListen:
+		return "LISTEN"
+	case StateClosing:
+		return "CLOSING"
+	default:
+		panic("unreachable")
+	}
+}
+
 // Reasons for notifying the protocol goroutine.
 const (
 	notifyNonZeroReceiveWindow = 1 << iota
@@ -108,10 +171,14 @@ type endpoint struct {
 	rcvBufUsed int
 
 	// The following fields are protected by the mutex.
-	mu                sync.RWMutex `state:"nosave"`
-	id                stack.TransportEndpointID
-	state             endpointState `state:".(endpointState)"`
-	isPortReserved    bool          `state:"manual"`
+	mu sync.RWMutex `state:"nosave"`
+	id stack.TransportEndpointID
+
+	// state             endpointState `state:".(endpointState)"`
+	// pState            ProtocolState
+	state EndpointState `state:".(EndpointState)"`
+
+	isPortReserved    bool `state:"manual"`
 	isRegistered      bool
 	boundNICID        tcpip.NICID `state:"manual"`
 	route             stack.Route `state:"manual"`
@@ -304,6 +371,7 @@ func newEndpoint(stack *stack.Stack, netProto tcpip.NetworkProtocolNumber, waite
 		stack:       stack,
 		netProto:    netProto,
 		waiterQueue: waiterQueue,
+		state:       StateInitial,
 		rcvBufSize:  DefaultBufferSize,
 		sndBufSize:  DefaultBufferSize,
 		sndMTU:      int(math.MaxInt32),
@@ -351,14 +419,14 @@ func (e *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
 	defer e.mu.RUnlock()
 
 	switch e.state {
-	case stateInitial, stateBound, stateConnecting:
+	case StateInitial, StateBound, StateConnecting, StateSynSent, StateSynRecv:
 		// Ready for nothing.
 
-	case stateClosed, stateError:
+	case StateClose, StateError:
 		// Ready for anything.
 		result = mask
 
-	case stateListen:
+	case StateListen:
 		// Check if there's anything in the accepted channel.
 		if (mask & waiter.EventIn) != 0 {
 			if len(e.acceptedChan) > 0 {
@@ -366,7 +434,7 @@ func (e *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
 			}
 		}
 
-	case stateConnected:
+	case StateEstablished, StateFinWait1, StateFinWait2, StateTimeWait, StateCloseWait, StateLastAck, StateClosing:
 		// Determine if the endpoint is writable if requested.
 		if (mask & waiter.EventOut) != 0 {
 			e.sndBufMu.Lock()
@@ -427,7 +495,7 @@ func (e *endpoint) Close() {
 	// are immediately available for reuse after Close() is called. If also
 	// registered, we unregister as well otherwise the next user would fail
 	// in Listen() when trying to register.
-	if e.state == stateListen && e.isPortReserved {
+	if e.state == StateListen && e.isPortReserved {
 		if e.isRegistered {
 			e.stack.UnregisterTransportEndpoint(e.boundNICID, e.effectiveNetProtos, ProtocolNumber, e.id, e)
 			e.isRegistered = false
@@ -487,15 +555,15 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 	e.mu.RLock()
 	// The endpoint can be read if it's connected, or if it's already closed
 	// but has some pending unread data. Also note that a RST being received
-	// would cause the state to become stateError so we should allow the
+	// would cause the state to become StateError so we should allow the
 	// reads to proceed before returning a ECONNRESET.
 	e.rcvListMu.Lock()
 	bufUsed := e.rcvBufUsed
-	if s := e.state; s != stateConnected && s != stateClosed && bufUsed == 0 {
+	if s := e.state; !s.connected() && s != StateClose && bufUsed == 0 {
 		e.rcvListMu.Unlock()
 		he := e.hardError
 		e.mu.RUnlock()
-		if s == stateError {
+		if s == StateError {
 			return buffer.View{}, tcpip.ControlMessages{}, he
 		}
 		return buffer.View{}, tcpip.ControlMessages{}, tcpip.ErrInvalidEndpointState
@@ -511,7 +579,7 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 
 func (e *endpoint) readLocked() (buffer.View, *tcpip.Error) {
 	if e.rcvBufUsed == 0 {
-		if e.rcvClosed || e.state != stateConnected {
+		if e.rcvClosed || !e.state.connected() {
 			return buffer.View{}, tcpip.ErrClosedForReceive
 		}
 		return buffer.View{}, tcpip.ErrWouldBlock
@@ -547,9 +615,9 @@ func (e *endpoint) Write(p tcpip.Payload, opts tcpip.WriteOptions) (uintptr, <-c
 	defer e.mu.RUnlock()
 
 	// The endpoint cannot be written to if it's not connected.
-	if e.state != stateConnected {
+	if !e.state.connected() {
 		switch e.state {
-		case stateError:
+		case StateError:
 			return 0, nil, e.hardError
 		default:
 			return 0, nil, tcpip.ErrClosedForSend
@@ -612,8 +680,8 @@ func (e *endpoint) Peek(vec [][]byte) (uintptr, tcpip.ControlMessages, *tcpip.Er
 
 	// The endpoint can be read if it's connected, or if it's already closed
 	// but has some pending unread data.
-	if s := e.state; s != stateConnected && s != stateClosed {
-		if s == stateError {
+	if s := e.state; !s.connected() && s != StateClose {
+		if s == StateError {
 			return 0, tcpip.ControlMessages{}, e.hardError
 		}
 		return 0, tcpip.ControlMessages{}, tcpip.ErrInvalidEndpointState
@@ -623,7 +691,7 @@ func (e *endpoint) Peek(vec [][]byte) (uintptr, tcpip.ControlMessages, *tcpip.Er
 	defer e.rcvListMu.Unlock()
 
 	if e.rcvBufUsed == 0 {
-		if e.rcvClosed || e.state != stateConnected {
+		if e.rcvClosed || !e.state.connected() {
 			return 0, tcpip.ControlMessages{}, tcpip.ErrClosedForReceive
 		}
 		return 0, tcpip.ControlMessages{}, tcpip.ErrWouldBlock
@@ -789,7 +857,7 @@ func (e *endpoint) SetSockOpt(opt interface{}) *tcpip.Error {
 		defer e.mu.Unlock()
 
 		// We only allow this to be set when we're in the initial state.
-		if e.state != stateInitial {
+		if e.state != StateInitial {
 			return tcpip.ErrInvalidEndpointState
 		}
 
@@ -841,7 +909,7 @@ func (e *endpoint) readyReceiveSize() (int, *tcpip.Error) {
 	defer e.mu.RUnlock()
 
 	// The endpoint cannot be in listen state.
-	if e.state == stateListen {
+	if e.state == StateListen {
 		return 0, tcpip.ErrInvalidEndpointState
 	}
 
@@ -1057,7 +1125,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 
 	nicid := addr.NIC
 	switch e.state {
-	case stateBound:
+	case StateBound:
 		// If we're already bound to a NIC but the caller is requesting
 		// that we use a different one now, we cannot proceed.
 		if e.boundNICID == 0 {
@@ -1070,16 +1138,16 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 
 		nicid = e.boundNICID
 
-	case stateInitial:
-		// Nothing to do. We'll eventually fill-in the gaps in the ID
-		// (if any) when we find a route.
+	case StateInitial:
+		// Nothing to do. We'll eventually fill-in the gaps in the ID (if any)
+		// when we find a route.
 
-	case stateConnecting:
-		// A connection request has already been issued but hasn't
-		// completed yet.
+	case StateConnecting, StateSynSent, StateSynRecv:
+		// A connection request has already been issued but hasn't completed
+		// yet.
 		return tcpip.ErrAlreadyConnecting
 
-	case stateConnected:
+	case StateEstablished:
 		// The endpoint is already connected. If caller hasn't been notified yet, return success.
 		if !e.isConnectNotified {
 			e.isConnectNotified = true
@@ -1088,7 +1156,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 		// Otherwise return that it's already connected.
 		return tcpip.ErrAlreadyConnected
 
-	case stateError:
+	case StateError:
 		return e.hardError
 
 	default:
@@ -1154,7 +1222,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 	}
 
 	e.isRegistered = true
-	e.state = stateConnecting
+	e.state = StateConnecting
 	e.route = r.Clone()
 	e.boundNICID = nicid
 	e.effectiveNetProtos = netProtos
@@ -1175,7 +1243,7 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) (er
 		}
 		e.segmentQueue.mu.Unlock()
 		e.snd.updateMaxPayloadSize(int(e.route.MTU()), 0)
-		e.state = stateConnected
+		e.state = StateEstablished
 	}
 
 	if run {
@@ -1199,8 +1267,8 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 	defer e.mu.Unlock()
 	e.shutdownFlags |= flags
 
-	switch e.state {
-	case stateConnected:
+	switch {
+	case e.state.connected():
 		// Close for read.
 		if (e.shutdownFlags & tcpip.ShutdownRead) != 0 {
 			// Mark read side as closed.
@@ -1241,7 +1309,7 @@ func (e *endpoint) Shutdown(flags tcpip.ShutdownFlags) *tcpip.Error {
 			e.sndCloseWaker.Assert()
 		}
 
-	case stateListen:
+	case e.state == StateListen:
 		// Tell protocolListenLoop to stop.
 		if flags&tcpip.ShutdownRead != 0 {
 			e.notifyProtocolGoroutine(notifyClose)
@@ -1269,7 +1337,7 @@ func (e *endpoint) Listen(backlog int) (err *tcpip.Error) {
 	// When the endpoint shuts down, it sets workerCleanup to true, and from
 	// that point onward, acceptedChan is the responsibility of the cleanup()
 	// method (and should not be touched anywhere else, including here).
-	if e.state == stateListen && !e.workerCleanup {
+	if e.state == StateListen && !e.workerCleanup {
 		// Adjust the size of the channel iff we can fix existing
 		// pending connections into the new one.
 		if len(e.acceptedChan) > backlog {
@@ -1288,7 +1356,7 @@ func (e *endpoint) Listen(backlog int) (err *tcpip.Error) {
 	}
 
 	// Endpoint must be bound before it can transition to listen mode.
-	if e.state != stateBound {
+	if e.state != StateBound {
 		return tcpip.ErrInvalidEndpointState
 	}
 
@@ -1298,7 +1366,7 @@ func (e *endpoint) Listen(backlog int) (err *tcpip.Error) {
 	}
 
 	e.isRegistered = true
-	e.state = stateListen
+	e.state = StateListen
 	if e.acceptedChan == nil {
 		e.acceptedChan = make(chan *endpoint, backlog)
 	}
@@ -1325,7 +1393,7 @@ func (e *endpoint) Accept() (tcpip.Endpoint, *waiter.Queue, *tcpip.Error) {
 	defer e.mu.RUnlock()
 
 	// Endpoint must be in listen state before it can accept connections.
-	if e.state != stateListen {
+	if e.state != StateListen {
 		return nil, nil, tcpip.ErrInvalidEndpointState
 	}
 
@@ -1353,7 +1421,7 @@ func (e *endpoint) Bind(addr tcpip.FullAddress) (err *tcpip.Error) {
 	// Don't allow binding once endpoint is not in the initial state
 	// anymore. This is because once the endpoint goes into a connected or
 	// listen state, it is already bound.
-	if e.state != stateInitial {
+	if e.state != StateInitial {
 		return tcpip.ErrAlreadyBound
 	}
 
@@ -1408,7 +1476,7 @@ func (e *endpoint) Bind(addr tcpip.FullAddress) (err *tcpip.Error) {
 	}
 
 	// Mark endpoint as bound.
-	e.state = stateBound
+	e.state = StateBound
 
 	return nil
 }
@@ -1430,7 +1498,7 @@ func (e *endpoint) GetRemoteAddress() (tcpip.FullAddress, *tcpip.Error) {
 	e.mu.RLock()
 	defer e.mu.RUnlock()
 
-	if e.state != stateConnected {
+	if !e.state.connected() {
 		return tcpip.FullAddress{}, tcpip.ErrNotConnected
 	}
 
@@ -1739,3 +1807,11 @@ func (e *endpoint) initGSO() {
 	gso.MaxSize = e.route.GSOMaxSize()
 	e.gso = gso
 }
+
+// State implements tcpip.Endpoint.State. It exports the endpoint's protocol
+// state for diagnostics.
+func (e *endpoint) State() uint32 {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	return uint32(e.state)
+}
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index e8aed2875..5f30c2374 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -49,8 +49,8 @@ func (e *endpoint) beforeSave() {
 	defer e.mu.Unlock()
 
 	switch e.state {
-	case stateInitial, stateBound:
-	case stateConnected:
+	case StateInitial, StateBound:
+	case StateEstablished, StateSynSent, StateSynRecv, StateFinWait1, StateFinWait2, StateTimeWait, StateCloseWait, StateLastAck, StateClosing:
 		if e.route.Capabilities()&stack.CapabilitySaveRestore == 0 {
 			if e.route.Capabilities()&stack.CapabilityDisconnectOk == 0 {
 				panic(tcpip.ErrSaveRejection{fmt.Errorf("endpoint cannot be saved in connected state: local %v:%d, remote %v:%d", e.id.LocalAddress, e.id.LocalPort, e.id.RemoteAddress, e.id.RemotePort)})
@@ -66,17 +66,17 @@ func (e *endpoint) beforeSave() {
 			break
 		}
 		fallthrough
-	case stateListen, stateConnecting:
+	case StateListen, StateConnecting:
 		e.drainSegmentLocked()
-		if e.state != stateClosed && e.state != stateError {
+		if e.state != StateClose && e.state != StateError {
 			if !e.workerRunning {
 				panic("endpoint has no worker running in listen, connecting, or connected state")
 			}
 			break
 		}
 		fallthrough
-	case stateError, stateClosed:
-		for e.state == stateError && e.workerRunning {
+	case StateError, StateClose:
+		for e.state == StateError && e.workerRunning {
 			e.mu.Unlock()
 			time.Sleep(100 * time.Millisecond)
 			e.mu.Lock()
@@ -92,7 +92,7 @@ func (e *endpoint) beforeSave() {
 		panic("endpoint still has waiters upon save")
 	}
 
-	if e.state != stateClosed && !((e.state == stateBound || e.state == stateListen) == e.isPortReserved) {
+	if e.state != StateClose && !((e.state == StateBound || e.state == 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")
 	}
 }
@@ -132,7 +132,7 @@ func (e *endpoint) loadAcceptedChan(acceptedEndpoints []*endpoint) {
 }
 
 // saveState is invoked by stateify.
-func (e *endpoint) saveState() endpointState {
+func (e *endpoint) saveState() EndpointState {
 	return e.state
 }
 
@@ -146,15 +146,15 @@ var connectingLoading sync.WaitGroup
 // Bound endpoint loading happens last.
 
 // loadState is invoked by stateify.
-func (e *endpoint) loadState(state endpointState) {
+func (e *endpoint) loadState(state EndpointState) {
 	// This is to ensure that the loading wait groups include all applicable
 	// endpoints before any asynchronous calls to the Wait() methods.
 	switch state {
-	case stateConnected:
+	case StateEstablished, StateFinWait1, StateFinWait2, StateTimeWait, StateCloseWait, StateLastAck, StateClosing:
 		connectedLoading.Add(1)
-	case stateListen:
+	case StateListen:
 		listenLoading.Add(1)
-	case stateConnecting:
+	case StateConnecting, StateSynSent, StateSynRecv:
 		connectingLoading.Add(1)
 	}
 	e.state = state
@@ -168,7 +168,7 @@ func (e *endpoint) afterLoad() {
 
 	state := e.state
 	switch state {
-	case stateInitial, stateBound, stateListen, stateConnecting, stateConnected:
+	case StateInitial, StateBound, StateListen, StateConnecting, StateEstablished:
 		var ss SendBufferSizeOption
 		if err := e.stack.TransportProtocolOption(ProtocolNumber, &ss); err == nil {
 			if e.sndBufSize < ss.Min || e.sndBufSize > ss.Max {
@@ -181,7 +181,7 @@ func (e *endpoint) afterLoad() {
 	}
 
 	bind := func() {
-		e.state = stateInitial
+		e.state = StateInitial
 		if len(e.bindAddress) == 0 {
 			e.bindAddress = e.id.LocalAddress
 		}
@@ -191,7 +191,7 @@ func (e *endpoint) afterLoad() {
 	}
 
 	switch state {
-	case stateConnected:
+	case StateEstablished, StateFinWait1, StateFinWait2, StateTimeWait, StateCloseWait, StateLastAck, StateClosing:
 		bind()
 		if len(e.connectingAddress) == 0 {
 			// This endpoint is accepted by netstack but not yet by
@@ -211,7 +211,7 @@ func (e *endpoint) afterLoad() {
 			panic("endpoint connecting failed: " + err.String())
 		}
 		connectedLoading.Done()
-	case stateListen:
+	case StateListen:
 		tcpip.AsyncLoading.Add(1)
 		go func() {
 			connectedLoading.Wait()
@@ -223,7 +223,7 @@ func (e *endpoint) afterLoad() {
 			listenLoading.Done()
 			tcpip.AsyncLoading.Done()
 		}()
-	case stateConnecting:
+	case StateConnecting, StateSynSent, StateSynRecv:
 		tcpip.AsyncLoading.Add(1)
 		go func() {
 			connectedLoading.Wait()
@@ -235,7 +235,7 @@ func (e *endpoint) afterLoad() {
 			connectingLoading.Done()
 			tcpip.AsyncLoading.Done()
 		}()
-	case stateBound:
+	case StateBound:
 		tcpip.AsyncLoading.Add(1)
 		go func() {
 			connectedLoading.Wait()
@@ -244,7 +244,7 @@ func (e *endpoint) afterLoad() {
 			bind()
 			tcpip.AsyncLoading.Done()
 		}()
-	case stateClosed:
+	case StateClose:
 		if e.isPortReserved {
 			tcpip.AsyncLoading.Add(1)
 			go func() {
@@ -252,12 +252,12 @@ func (e *endpoint) afterLoad() {
 				listenLoading.Wait()
 				connectingLoading.Wait()
 				bind()
-				e.state = stateClosed
+				e.state = StateClose
 				tcpip.AsyncLoading.Done()
 			}()
 		}
 		fallthrough
-	case stateError:
+	case StateError:
 		tcpip.DeleteDanglingEndpoint(e)
 	}
 }
diff --git a/pkg/tcpip/transport/tcp/rcv.go b/pkg/tcpip/transport/tcp/rcv.go
index b08a0e356..f02fa6105 100644
--- a/pkg/tcpip/transport/tcp/rcv.go
+++ b/pkg/tcpip/transport/tcp/rcv.go
@@ -134,6 +134,7 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 	// sequence numbers that have been consumed.
 	TrimSACKBlockList(&r.ep.sack, r.rcvNxt)
 
+	// Handle FIN or FIN-ACK.
 	if s.flagIsSet(header.TCPFlagFin) {
 		r.rcvNxt++
 
@@ -144,6 +145,25 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 		r.closed = true
 		r.ep.readyToRead(nil)
 
+		// We just received a FIN, our next state depends on whether we sent a
+		// FIN already or not.
+		r.ep.mu.Lock()
+		switch r.ep.state {
+		case StateEstablished:
+			r.ep.state = StateCloseWait
+		case StateFinWait1:
+			if s.flagIsSet(header.TCPFlagAck) {
+				// FIN-ACK, transition to TIME-WAIT.
+				r.ep.state = StateTimeWait
+			} else {
+				// Simultaneous close, expecting a final ACK.
+				r.ep.state = StateClosing
+			}
+		case StateFinWait2:
+			r.ep.state = StateTimeWait
+		}
+		r.ep.mu.Unlock()
+
 		// Flush out any pending segments, except the very first one if
 		// it happens to be the one we're handling now because the
 		// caller is using it.
@@ -156,6 +176,23 @@ func (r *receiver) consumeSegment(s *segment, segSeq seqnum.Value, segLen seqnum
 			r.pendingRcvdSegments[i].decRef()
 		}
 		r.pendingRcvdSegments = r.pendingRcvdSegments[:first]
+
+		return true
+	}
+
+	// Handle ACK (not FIN-ACK, which we handled above) during one of the
+	// shutdown states.
+	if s.flagIsSet(header.TCPFlagAck) {
+		r.ep.mu.Lock()
+		switch r.ep.state {
+		case StateFinWait1:
+			r.ep.state = StateFinWait2
+		case StateClosing:
+			r.ep.state = StateTimeWait
+		case StateLastAck:
+			r.ep.state = StateClose
+		}
+		r.ep.mu.Unlock()
 	}
 
 	return true
diff --git a/pkg/tcpip/transport/tcp/snd.go b/pkg/tcpip/transport/tcp/snd.go
index 3464e4be7..b236d7af2 100644
--- a/pkg/tcpip/transport/tcp/snd.go
+++ b/pkg/tcpip/transport/tcp/snd.go
@@ -632,6 +632,10 @@ func (s *sender) maybeSendSegment(seg *segment, limit int, end seqnum.Value) (se
 		}
 		seg.flags = header.TCPFlagAck | header.TCPFlagFin
 		segEnd = seg.sequenceNumber.Add(1)
+		// Transition to FIN-WAIT1 state since we're initiating an active close.
+		s.ep.mu.Lock()
+		s.ep.state = StateFinWait1
+		s.ep.mu.Unlock()
 	} else {
 		// We're sending a non-FIN segment.
 		if seg.flags&header.TCPFlagFin != 0 {
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index b8f0ccaf1..56b490aaa 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -168,8 +168,8 @@ func TestTCPResetsSentIncrement(t *testing.T) {
 
 	// Receive the SYN-ACK reply.
 	b := c.GetPacket()
-	tcp := header.TCP(header.IPv4(b).Payload())
-	c.IRS = seqnum.Value(tcp.SequenceNumber())
+	tcpHdr := header.TCP(header.IPv4(b).Payload())
+	c.IRS = seqnum.Value(tcpHdr.SequenceNumber())
 
 	ackHeaders := &context.Headers{
 		SrcPort: context.TestPort,
@@ -269,8 +269,8 @@ func TestConnectResetAfterClose(t *testing.T) {
 	time.Sleep(3 * time.Second)
 	for {
 		b := c.GetPacket()
-		tcp := header.TCP(header.IPv4(b).Payload())
-		if tcp.Flags() == header.TCPFlagAck|header.TCPFlagFin {
+		tcpHdr := header.TCP(header.IPv4(b).Payload())
+		if tcpHdr.Flags() == header.TCPFlagAck|header.TCPFlagFin {
 			// This is a retransmit of the FIN, ignore it.
 			continue
 		}
@@ -553,9 +553,13 @@ func TestRstOnCloseWithUnreadData(t *testing.T) {
 			// We shouldn't consume a sequence number on RST.
 			checker.SeqNum(uint32(c.IRS)+1),
 		))
+	// The RST puts the endpoint into an error state.
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateError; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
-	// This final should be ignored because an ACK on a reset doesn't
-	// mean anything.
+	// This final ACK should be ignored because an ACK on a reset doesn't mean
+	// anything.
 	c.SendPacket(nil, &context.Headers{
 		SrcPort: context.TestPort,
 		DstPort: c.Port,
@@ -618,6 +622,10 @@ func TestRstOnCloseWithUnreadDataFinConvertRst(t *testing.T) {
 			checker.SeqNum(uint32(c.IRS)+1),
 		))
 
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateFinWait1; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
 	// Cause a RST to be generated by closing the read end now since we have
 	// unread data.
 	c.EP.Shutdown(tcpip.ShutdownRead)
@@ -630,6 +638,10 @@ func TestRstOnCloseWithUnreadDataFinConvertRst(t *testing.T) {
 			// We shouldn't consume a sequence number on RST.
 			checker.SeqNum(uint32(c.IRS)+1),
 		))
+	// The RST puts the endpoint into an error state.
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateError; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	// The ACK to the FIN should now be rejected since the connection has been
 	// closed by a RST.
@@ -1510,8 +1522,8 @@ func testBrokenUpWrite(t *testing.T, c *context.Context, maxPayload int) {
 	for bytesReceived != dataLen {
 		b := c.GetPacket()
 		numPackets++
-		tcp := header.TCP(header.IPv4(b).Payload())
-		payloadLen := len(tcp.Payload())
+		tcpHdr := header.TCP(header.IPv4(b).Payload())
+		payloadLen := len(tcpHdr.Payload())
 		checker.IPv4(t, b,
 			checker.TCP(
 				checker.DstPort(context.TestPort),
@@ -1522,7 +1534,7 @@ func testBrokenUpWrite(t *testing.T, c *context.Context, maxPayload int) {
 		)
 
 		pdata := data[bytesReceived : bytesReceived+payloadLen]
-		if p := tcp.Payload(); !bytes.Equal(pdata, p) {
+		if p := tcpHdr.Payload(); !bytes.Equal(pdata, p) {
 			t.Fatalf("got data = %v, want = %v", p, pdata)
 		}
 		bytesReceived += payloadLen
@@ -1530,7 +1542,7 @@ func testBrokenUpWrite(t *testing.T, c *context.Context, maxPayload int) {
 		if c.TimeStampEnabled {
 			// If timestamp option is enabled, echo back the timestamp and increment
 			// the TSEcr value included in the packet and send that back as the TSVal.
-			parsedOpts := tcp.ParsedOptions()
+			parsedOpts := tcpHdr.ParsedOptions()
 			tsOpt := [12]byte{header.TCPOptionNOP, header.TCPOptionNOP}
 			header.EncodeTSOption(parsedOpts.TSEcr+1, parsedOpts.TSVal, tsOpt[2:])
 			options = tsOpt[:]
@@ -1757,8 +1769,8 @@ func TestSynOptionsOnActiveConnect(t *testing.T) {
 		),
 	)
 
-	tcp := header.TCP(header.IPv4(b).Payload())
-	c.IRS = seqnum.Value(tcp.SequenceNumber())
+	tcpHdr := header.TCP(header.IPv4(b).Payload())
+	c.IRS = seqnum.Value(tcpHdr.SequenceNumber())
 
 	// Wait for retransmit.
 	time.Sleep(1 * time.Second)
@@ -1766,8 +1778,8 @@ func TestSynOptionsOnActiveConnect(t *testing.T) {
 		checker.TCP(
 			checker.DstPort(context.TestPort),
 			checker.TCPFlags(header.TCPFlagSyn),
-			checker.SrcPort(tcp.SourcePort()),
-			checker.SeqNum(tcp.SequenceNumber()),
+			checker.SrcPort(tcpHdr.SourcePort()),
+			checker.SeqNum(tcpHdr.SequenceNumber()),
 			checker.TCPSynOptions(header.TCPSynOptions{MSS: mss, WS: wndScale}),
 		),
 	)
@@ -1775,8 +1787,8 @@ func TestSynOptionsOnActiveConnect(t *testing.T) {
 	// Send SYN-ACK.
 	iss := seqnum.Value(789)
 	c.SendPacket(nil, &context.Headers{
-		SrcPort: tcp.DestinationPort(),
-		DstPort: tcp.SourcePort(),
+		SrcPort: tcpHdr.DestinationPort(),
+		DstPort: tcpHdr.SourcePort(),
 		Flags:   header.TCPFlagSyn | header.TCPFlagAck,
 		SeqNum:  iss,
 		AckNum:  c.IRS.Add(1),
@@ -2523,8 +2535,8 @@ func TestReceivedSegmentQueuing(t *testing.T) {
 				checker.TCPFlags(header.TCPFlagAck),
 			),
 		)
-		tcp := header.TCP(header.IPv4(b).Payload())
-		ack := seqnum.Value(tcp.AckNumber())
+		tcpHdr := header.TCP(header.IPv4(b).Payload())
+		ack := seqnum.Value(tcpHdr.AckNumber())
 		if ack == last {
 			break
 		}
@@ -2568,6 +2580,10 @@ func TestReadAfterClosedState(t *testing.T) {
 		),
 	)
 
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateFinWait1; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
 	// Send some data and acknowledge the FIN.
 	data := []byte{1, 2, 3}
 	c.SendPacket(data, &context.Headers{
@@ -2589,9 +2605,15 @@ func TestReadAfterClosedState(t *testing.T) {
 		),
 	)
 
-	// Give the stack the chance to transition to closed state.
+	// Give the stack the chance to transition to closed state. Note that since
+	// both the sender and receiver are now closed, we effectively skip the
+	// TIME-WAIT state.
 	time.Sleep(1 * time.Second)
 
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateClose; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
 	// Wait for receive to be notified.
 	select {
 	case <-ch:
@@ -3680,9 +3702,15 @@ func TestPassiveConnectionAttemptIncrement(t *testing.T) {
 	if err := ep.Bind(tcpip.FullAddress{Addr: context.StackAddr, Port: context.StackPort}); err != nil {
 		t.Fatalf("Bind failed: %v", err)
 	}
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateBound; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 	if err := c.EP.Listen(1); err != nil {
 		t.Fatalf("Listen failed: %v", err)
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateListen; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	stats := c.Stack().Stats()
 	want := stats.TCP.PassiveConnectionOpenings.Value() + 1
@@ -3826,3 +3854,68 @@ func TestPassiveFailedConnectionAttemptIncrement(t *testing.T) {
 		}
 	}
 }
+
+func TestEndpointBindListenAcceptState(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+	wq := &waiter.Queue{}
+	ep, err := c.Stack().NewEndpoint(tcp.ProtocolNumber, ipv4.ProtocolNumber, wq)
+	if err != nil {
+		t.Fatalf("NewEndpoint failed: %v", err)
+	}
+
+	if err := ep.Bind(tcpip.FullAddress{Port: context.StackPort}); err != nil {
+		t.Fatalf("Bind failed: %v", err)
+	}
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateBound; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
+	if err := ep.Listen(10); err != nil {
+		t.Fatalf("Listen failed: %v", err)
+	}
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateListen; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
+	c.PassiveConnectWithOptions(100, 5, header.TCPSynOptions{MSS: defaultIPv4MSS})
+
+	// Try to accept the connection.
+	we, ch := waiter.NewChannelEntry(nil)
+	wq.EventRegister(&we, waiter.EventIn)
+	defer wq.EventUnregister(&we)
+
+	aep, _, err := ep.Accept()
+	if err == tcpip.ErrWouldBlock {
+		// Wait for connection to be established.
+		select {
+		case <-ch:
+			aep, _, err = ep.Accept()
+			if err != nil {
+				t.Fatalf("Accept failed: %v", err)
+			}
+
+		case <-time.After(1 * time.Second):
+			t.Fatalf("Timed out waiting for accept")
+		}
+	}
+	if got, want := tcp.EndpointState(aep.State()), tcp.StateEstablished; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+	// Listening endpoint remains in listen state.
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateListen; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
+	ep.Close()
+	// Give worker goroutines time to receive the close notification.
+	time.Sleep(1 * time.Second)
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateClose; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+	// Accepted endpoint remains open when the listen endpoint is closed.
+	if got, want := tcp.EndpointState(aep.State()), tcp.StateEstablished; got != want {
+		t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
+}
diff --git a/pkg/tcpip/transport/tcp/testing/context/context.go b/pkg/tcpip/transport/tcp/testing/context/context.go
index 6e12413c6..69a43b6f4 100644
--- a/pkg/tcpip/transport/tcp/testing/context/context.go
+++ b/pkg/tcpip/transport/tcp/testing/context/context.go
@@ -532,6 +532,9 @@ func (c *Context) CreateConnectedWithRawOptions(iss seqnum.Value, rcvWnd seqnum.
 	if err != nil {
 		c.t.Fatalf("NewEndpoint failed: %v", err)
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateInitial; got != want {
+		c.t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	if epRcvBuf != nil {
 		if err := c.EP.SetSockOpt(*epRcvBuf); err != nil {
@@ -557,13 +560,16 @@ func (c *Context) CreateConnectedWithRawOptions(iss seqnum.Value, rcvWnd seqnum.
 			checker.TCPFlags(header.TCPFlagSyn),
 		),
 	)
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateSynSent; got != want {
+		c.t.Fatalf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
-	tcp := header.TCP(header.IPv4(b).Payload())
-	c.IRS = seqnum.Value(tcp.SequenceNumber())
+	tcpHdr := header.TCP(header.IPv4(b).Payload())
+	c.IRS = seqnum.Value(tcpHdr.SequenceNumber())
 
 	c.SendPacket(nil, &Headers{
-		SrcPort: tcp.DestinationPort(),
-		DstPort: tcp.SourcePort(),
+		SrcPort: tcpHdr.DestinationPort(),
+		DstPort: tcpHdr.SourcePort(),
 		Flags:   header.TCPFlagSyn | header.TCPFlagAck,
 		SeqNum:  iss,
 		AckNum:  c.IRS.Add(1),
@@ -591,8 +597,11 @@ func (c *Context) CreateConnectedWithRawOptions(iss seqnum.Value, rcvWnd seqnum.
 	case <-time.After(1 * time.Second):
 		c.t.Fatalf("Timed out waiting for connection")
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateEstablished; got != want {
+		c.t.Fatalf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
-	c.Port = tcp.SourcePort()
+	c.Port = tcpHdr.SourcePort()
 }
 
 // RawEndpoint is just a small wrapper around a TCP endpoint's state to make
@@ -690,6 +699,9 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 	if err != nil {
 		c.t.Fatalf("c.s.NewEndpoint(tcp, ipv4...) = %v", err)
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateInitial; got != want {
+		c.t.Fatalf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	// Start connection attempt.
 	waitEntry, notifyCh := waiter.NewChannelEntry(nil)
@@ -719,6 +731,10 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 			}),
 		),
 	)
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateSynSent; got != want {
+		c.t.Fatalf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
 	tcpSeg := header.TCP(header.IPv4(b).Payload())
 	synOptions := header.ParseSynOptions(tcpSeg.Options(), false)
 
@@ -782,6 +798,9 @@ func (c *Context) CreateConnectedWithOptions(wantOptions header.TCPSynOptions) *
 	case <-time.After(1 * time.Second):
 		c.t.Fatalf("Timed out waiting for connection")
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateEstablished; got != want {
+		c.t.Fatalf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	// Store the source port in use by the endpoint.
 	c.Port = tcpSeg.SourcePort()
@@ -821,10 +840,16 @@ func (c *Context) AcceptWithOptions(wndScale int, synOptions header.TCPSynOption
 	if err := ep.Bind(tcpip.FullAddress{Port: StackPort}); err != nil {
 		c.t.Fatalf("Bind failed: %v", err)
 	}
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateBound; got != want {
+		c.t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	if err := ep.Listen(10); err != nil {
 		c.t.Fatalf("Listen failed: %v", err)
 	}
+	if got, want := tcp.EndpointState(ep.State()), tcp.StateListen; got != want {
+		c.t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
 
 	rep := c.PassiveConnectWithOptions(100, wndScale, synOptions)
 
@@ -847,6 +872,10 @@ func (c *Context) AcceptWithOptions(wndScale int, synOptions header.TCPSynOption
 			c.t.Fatalf("Timed out waiting for accept")
 		}
 	}
+	if got, want := tcp.EndpointState(c.EP.State()), tcp.StateEstablished; got != want {
+		c.t.Errorf("Unexpected endpoint state: want %v, got %v", want, got)
+	}
+
 	return rep
 }
 
diff --git a/pkg/tcpip/transport/udp/endpoint.go b/pkg/tcpip/transport/udp/endpoint.go
index 3d52a4f31..fa7278286 100644
--- a/pkg/tcpip/transport/udp/endpoint.go
+++ b/pkg/tcpip/transport/udp/endpoint.go
@@ -1000,3 +1000,9 @@ func (e *endpoint) HandlePacket(r *stack.Route, id stack.TransportEndpointID, vv
 // HandleControlPacket implements stack.TransportEndpoint.HandleControlPacket.
 func (e *endpoint) HandleControlPacket(id stack.TransportEndpointID, typ stack.ControlType, extra uint32, vv buffer.VectorisedView) {
 }
+
+// State implements socket.Socket.State.
+func (e *endpoint) State() uint32 {
+	// TODO(b/112063468): Translate internal state to values returned by Linux.
+	return 0
+}