Ensure TCP TIME-WAIT is not terminated prematurely.

Netstack's TIME-WAIT state for a TCP socket could be terminated prematurely if
the socket entered TIME-WAIT using shutdown(..., SHUT_RDWR) and then was closed
using close(). This fixes that bug and updates the tests to verify that Netstack
correctly honors TIME-WAIT under such conditions.

Fixes #3106

PiperOrigin-RevId: 326456443

5 files changed, 150 insertions, 18 deletions

diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index 8dd759ba2..46702906b 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -1706,7 +1706,7 @@ func (e *endpoint) doTimeWait() (twReuse func()) {
 			}
 		case notification:
 			n := e.fetchNotifications()
-			if n&notifyClose != 0 || n&notifyAbort != 0 {
+			if n&notifyAbort != 0 {
 				return nil
 			}
 			if n&notifyDrain != 0 {
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index b8b52b03d..d08cfe0ff 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -449,10 +449,11 @@ type endpoint struct {
 	// recentTS is the timestamp that should be sent in the TSEcr field of
 	// the timestamp for future segments sent by the endpoint. This field is
 	// updated if required when a new segment is received by this endpoint.
-	//
-	// recentTS must be read/written atomically.
 	recentTS uint32
 
+	// recentTSTime is the unix time when we updated recentTS last.
+	recentTSTime time.Time `state:".(unixTime)"`
+
 	// tsOffset is a randomized offset added to the value of the
 	// TSVal field in the timestamp option.
 	tsOffset uint32
@@ -795,15 +796,15 @@ func (e *endpoint) EndpointState() EndpointState {
 	return EndpointState(atomic.LoadUint32((*uint32)(&e.state)))
 }
 
-// setRecentTimestamp atomically sets the recentTS field to the
-// provided value.
+// setRecentTimestamp sets the recentTS field to the provided value.
 func (e *endpoint) setRecentTimestamp(recentTS uint32) {
-	atomic.StoreUint32(&e.recentTS, recentTS)
+	e.recentTS = recentTS
+	e.recentTSTime = time.Now()
 }
 
-// recentTimestamp atomically reads and returns the value of the recentTS field.
+// recentTimestamp returns the value of the recentTS field.
 func (e *endpoint) recentTimestamp() uint32 {
-	return atomic.LoadUint32(&e.recentTS)
+	return e.recentTS
 }
 
 // keepalive is a synchronization wrapper used to appease stateify. See the
@@ -902,7 +903,7 @@ func (e *endpoint) Readiness(mask waiter.EventMask) waiter.EventMask {
 	case StateInitial, StateBound, StateConnecting, StateSynSent, StateSynRecv:
 		// Ready for nothing.
 
-	case StateClose, StateError:
+	case StateClose, StateError, StateTimeWait:
 		// Ready for anything.
 		result = mask
 
@@ -2148,12 +2149,66 @@ func (e *endpoint) connect(addr tcpip.FullAddress, handshake bool, run bool) *tc
 		h.Write(portBuf)
 		portOffset := h.Sum32()
 
+		var twReuse tcpip.TCPTimeWaitReuseOption
+		if err := e.stack.TransportProtocolOption(ProtocolNumber, &twReuse); err != nil {
+			panic(fmt.Sprintf("e.stack.TransportProtocolOption(%d, %#v) = %s", ProtocolNumber, &twReuse, err))
+		}
+
+		reuse := twReuse == tcpip.TCPTimeWaitReuseGlobal
+		if twReuse == tcpip.TCPTimeWaitReuseLoopbackOnly {
+			switch netProto {
+			case header.IPv4ProtocolNumber:
+				reuse = header.IsV4LoopbackAddress(e.ID.LocalAddress) && header.IsV4LoopbackAddress(e.ID.RemoteAddress)
+			case header.IPv6ProtocolNumber:
+				reuse = e.ID.LocalAddress == header.IPv6Loopback && e.ID.RemoteAddress == header.IPv6Loopback
+			}
+		}
+
 		if _, err := e.stack.PickEphemeralPortStable(portOffset, func(p uint16) (bool, *tcpip.Error) {
 			if sameAddr && p == e.ID.RemotePort {
 				return false, nil
 			}
 			if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr); err != nil {
-				return false, nil
+				if err != tcpip.ErrPortInUse || !reuse {
+					return false, nil
+				}
+				transEPID := e.ID
+				transEPID.LocalPort = p
+				// Check if an endpoint is registered with demuxer in TIME-WAIT and if
+				// we can reuse it. If we can't find a transport endpoint then we just
+				// skip using this port as it's possible that either an endpoint has
+				// bound the port but not registered with demuxer yet (no listen/connect
+				// done yet) or the reservation was freed between the check above and
+				// the FindTransportEndpoint below. But rather than retry the same port
+				// we just skip it and move on.
+				transEP := e.stack.FindTransportEndpoint(netProto, ProtocolNumber, transEPID, &r)
+				if transEP == nil {
+					// ReservePort failed but there is no registered endpoint with
+					// demuxer. Which indicates there is at least some endpoint that has
+					// bound the port.
+					return false, nil
+				}
+
+				tcpEP := transEP.(*endpoint)
+				tcpEP.LockUser()
+				// If the endpoint is not in TIME-WAIT or if it is in TIME-WAIT but
+				// less than 1 second has elapsed since its recentTS was updated then
+				// we cannot reuse the port.
+				if tcpEP.EndpointState() != StateTimeWait || time.Since(tcpEP.recentTSTime) < 1*time.Second {
+					tcpEP.UnlockUser()
+					return false, nil
+				}
+				// Since the endpoint is in TIME-WAIT it should be safe to acquire its
+				// Lock while holding the lock for this endpoint as endpoints in
+				// TIME-WAIT do not acquire locks on other endpoints.
+				tcpEP.workerCleanup = false
+				tcpEP.cleanupLocked()
+				tcpEP.notifyProtocolGoroutine(notifyAbort)
+				tcpEP.UnlockUser()
+				// Now try and Reserve again if it fails then we skip.
+				if _, err := e.stack.ReservePort(netProtos, ProtocolNumber, e.ID.LocalAddress, p, e.portFlags, e.bindToDevice, addr); err != nil {
+					return false, nil
+				}
 			}
 
 			id := e.ID
diff --git a/pkg/tcpip/transport/tcp/endpoint_state.go b/pkg/tcpip/transport/tcp/endpoint_state.go
index abf1ac5c9..723e47ddc 100644
--- a/pkg/tcpip/transport/tcp/endpoint_state.go
+++ b/pkg/tcpip/transport/tcp/endpoint_state.go
@@ -309,6 +309,16 @@ func (e *endpoint) loadLastError(s string) {
 	e.lastError = tcpip.StringToError(s)
 }
 
+// saveRecentTSTime is invoked by stateify.
+func (e *endpoint) saveRecentTSTime() unixTime {
+	return unixTime{e.recentTSTime.Unix(), e.recentTSTime.UnixNano()}
+}
+
+// loadRecentTSTime is invoked by stateify.
+func (e *endpoint) loadRecentTSTime(unix unixTime) {
+	e.recentTSTime = time.Unix(unix.second, unix.nano)
+}
+
 // saveHardError is invoked by stateify.
 func (e *EndpointInfo) saveHardError() string {
 	if e.HardError == nil {
diff --git a/pkg/tcpip/transport/tcp/protocol.go b/pkg/tcpip/transport/tcp/protocol.go
index 2e5093b36..49a673b42 100644
--- a/pkg/tcpip/transport/tcp/protocol.go
+++ b/pkg/tcpip/transport/tcp/protocol.go
@@ -191,8 +191,9 @@ type protocol struct {
 	congestionControl          string
 	availableCongestionControl []string
 	moderateReceiveBuffer      bool
-	tcpLingerTimeout           time.Duration
-	tcpTimeWaitTimeout         time.Duration
+	lingerTimeout              time.Duration
+	timeWaitTimeout            time.Duration
+	timeWaitReuse              tcpip.TCPTimeWaitReuseOption
 	minRTO                     time.Duration
 	maxRTO                     time.Duration
 	maxRetries                 uint32
@@ -358,7 +359,7 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 			v = 0
 		}
 		p.mu.Lock()
-		p.tcpLingerTimeout = time.Duration(v)
+		p.lingerTimeout = time.Duration(v)
 		p.mu.Unlock()
 		return nil
 
@@ -367,7 +368,16 @@ func (p *protocol) SetOption(option interface{}) *tcpip.Error {
 			v = 0
 		}
 		p.mu.Lock()
-		p.tcpTimeWaitTimeout = time.Duration(v)
+		p.timeWaitTimeout = time.Duration(v)
+		p.mu.Unlock()
+		return nil
+
+	case tcpip.TCPTimeWaitReuseOption:
+		if v < tcpip.TCPTimeWaitReuseDisabled || v > tcpip.TCPTimeWaitReuseLoopbackOnly {
+			return tcpip.ErrInvalidOptionValue
+		}
+		p.mu.Lock()
+		p.timeWaitReuse = v
 		p.mu.Unlock()
 		return nil
 
@@ -468,13 +478,19 @@ func (p *protocol) Option(option interface{}) *tcpip.Error {
 
 	case *tcpip.TCPLingerTimeoutOption:
 		p.mu.RLock()
-		*v = tcpip.TCPLingerTimeoutOption(p.tcpLingerTimeout)
+		*v = tcpip.TCPLingerTimeoutOption(p.lingerTimeout)
 		p.mu.RUnlock()
 		return nil
 
 	case *tcpip.TCPTimeWaitTimeoutOption:
 		p.mu.RLock()
-		*v = tcpip.TCPTimeWaitTimeoutOption(p.tcpTimeWaitTimeout)
+		*v = tcpip.TCPTimeWaitTimeoutOption(p.timeWaitTimeout)
+		p.mu.RUnlock()
+		return nil
+
+	case *tcpip.TCPTimeWaitReuseOption:
+		p.mu.RLock()
+		*v = tcpip.TCPTimeWaitReuseOption(p.timeWaitReuse)
 		p.mu.RUnlock()
 		return nil
 
@@ -564,8 +580,9 @@ func NewProtocol() stack.TransportProtocol {
 		},
 		congestionControl:          ccReno,
 		availableCongestionControl: []string{ccReno, ccCubic},
-		tcpLingerTimeout:           DefaultTCPLingerTimeout,
-		tcpTimeWaitTimeout:         DefaultTCPTimeWaitTimeout,
+		lingerTimeout:              DefaultTCPLingerTimeout,
+		timeWaitTimeout:            DefaultTCPTimeWaitTimeout,
+		timeWaitReuse:              tcpip.TCPTimeWaitReuseLoopbackOnly,
 		synRcvdCount:               synRcvdCounter{threshold: SynRcvdCountThreshold},
 		synRetries:                 DefaultSynRetries,
 		minRTO:                     MinRTO,
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index 1b58eb91b..0f7e958e4 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -7297,3 +7297,53 @@ func TestResetDuringClose(t *testing.T) {
 
 	wg.Wait()
 }
+
+func TestStackTimeWaitReuse(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	s := c.Stack()
+	var twReuse tcpip.TCPTimeWaitReuseOption
+	if err := s.TransportProtocolOption(tcp.ProtocolNumber, &twReuse); err != nil {
+		t.Fatalf("s.TransportProtocolOption(%v, %v) = %v", tcp.ProtocolNumber, &twReuse, err)
+	}
+	if got, want := twReuse, tcpip.TCPTimeWaitReuseLoopbackOnly; got != want {
+		t.Fatalf("got tcpip.TCPTimeWaitReuseOption: %v, want: %v", got, want)
+	}
+}
+
+func TestSetStackTimeWaitReuse(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	s := c.Stack()
+	testCases := []struct {
+		v   int
+		err *tcpip.Error
+	}{
+		{int(tcpip.TCPTimeWaitReuseDisabled), nil},
+		{int(tcpip.TCPTimeWaitReuseGlobal), nil},
+		{int(tcpip.TCPTimeWaitReuseLoopbackOnly), nil},
+		{int(tcpip.TCPTimeWaitReuseLoopbackOnly) + 1, tcpip.ErrInvalidOptionValue},
+		{int(tcpip.TCPTimeWaitReuseDisabled) - 1, tcpip.ErrInvalidOptionValue},
+	}
+
+	for _, tc := range testCases {
+		err := s.SetTransportProtocolOption(tcp.ProtocolNumber, tcpip.TCPTimeWaitReuseOption(tc.v))
+		if got, want := err, tc.err; got != want {
+			t.Fatalf("s.TransportProtocolOption(%v, %v) = %v, want %v", tcp.ProtocolNumber, tc.v, err, tc.err)
+		}
+		if tc.err != nil {
+			continue
+		}
+
+		var twReuse tcpip.TCPTimeWaitReuseOption
+		if err := s.TransportProtocolOption(tcp.ProtocolNumber, &twReuse); err != nil {
+			t.Fatalf("s.TransportProtocolOption(%v, %v) = %v, want nil", tcp.ProtocolNumber, &twReuse, err)
+		}
+
+		if got, want := twReuse, tcpip.TCPTimeWaitReuseOption(tc.v); got != want {
+			t.Fatalf("got tcpip.TCPTimeWaitReuseOption: %v, want: %v", got, want)
+		}
+	}
+}