Add a new TCP stat for current open connections.

Such a stat accounts for all connections that are currently
established and not yet transitioned to close state.
Also fix bug in double increment of CurrentEstablished stat.

Fixes #1579

PiperOrigin-RevId: 290827365

6 files changed, 92 insertions, 3 deletions

diff --git a/pkg/sentry/socket/netstack/netstack.go b/pkg/sentry/socket/netstack/netstack.go
index 2662fbc0f..318acbeff 100644
--- a/pkg/sentry/socket/netstack/netstack.go
+++ b/pkg/sentry/socket/netstack/netstack.go
@@ -150,7 +150,8 @@ var Metrics = tcpip.Stats{
 	TCP: tcpip.TCPStats{
 		ActiveConnectionOpenings:           mustCreateMetric("/netstack/tcp/active_connection_openings", "Number of connections opened successfully via Connect."),
 		PassiveConnectionOpenings:          mustCreateMetric("/netstack/tcp/passive_connection_openings", "Number of connections opened successfully via Listen."),
-		CurrentEstablished:                 mustCreateMetric("/netstack/tcp/current_established", "Number of connections in either ESTABLISHED or CLOSE-WAIT state now."),
+		CurrentEstablished:                 mustCreateMetric("/netstack/tcp/current_established", "Number of connections in ESTABLISHED state now."),
+		CurrentConnected:                   mustCreateMetric("/netstack/tcp/current_open", "Number of connections that are in connected state."),
 		EstablishedResets:                  mustCreateMetric("/netstack/tcp/established_resets", "Number of times TCP connections have made a direct transition to the CLOSED state from either the ESTABLISHED state or the CLOSE-WAIT state"),
 		EstablishedClosed:                  mustCreateMetric("/netstack/tcp/established_closed", "number of times established TCP connections made a transition to CLOSED state."),
 		EstablishedTimedout:                mustCreateMetric("/netstack/tcp/established_timedout", "Number of times  an established connection was reset because of keep-alive time out."),
diff --git a/pkg/tcpip/tcpip.go b/pkg/tcpip/tcpip.go
index 3fc823a36..59c9b3fb0 100644
--- a/pkg/tcpip/tcpip.go
+++ b/pkg/tcpip/tcpip.go
@@ -938,9 +938,13 @@ type TCPStats struct {
 	PassiveConnectionOpenings *StatCounter
 
 	// CurrentEstablished is the number of TCP connections for which the
-	// current state is either ESTABLISHED or CLOSE-WAIT.
+	// current state is ESTABLISHED.
 	CurrentEstablished *StatCounter
 
+	// CurrentConnected is the number of TCP connections that
+	// are in connected state.
+	CurrentConnected *StatCounter
+
 	// EstablishedResets is the number of times TCP connections have made
 	// a direct transition to the CLOSED state from either the
 	// ESTABLISHED state or the CLOSE-WAIT state.
diff --git a/pkg/tcpip/transport/tcp/accept.go b/pkg/tcpip/transport/tcp/accept.go
index 1a2e3efa9..d469758eb 100644
--- a/pkg/tcpip/transport/tcp/accept.go
+++ b/pkg/tcpip/transport/tcp/accept.go
@@ -562,7 +562,6 @@ func (e *endpoint) handleListenSegment(ctx *listenContext, s *segment) {
 		// Switch state to connected.
 		// We do not use transitionToStateEstablishedLocked here as there is
 		// no handshake state available when doing a SYN cookie based accept.
-		n.stack.Stats().TCP.CurrentEstablished.Increment()
 		n.isConnectNotified = true
 		n.setEndpointState(StateEstablished)
 
diff --git a/pkg/tcpip/transport/tcp/connect.go b/pkg/tcpip/transport/tcp/connect.go
index a2f384384..4e3c5419c 100644
--- a/pkg/tcpip/transport/tcp/connect.go
+++ b/pkg/tcpip/transport/tcp/connect.go
@@ -934,6 +934,7 @@ func (e *endpoint) transitionToStateCloseLocked() {
 	// Mark the endpoint as fully closed for reads/writes.
 	e.cleanupLocked()
 	e.setEndpointState(StateClose)
+	e.stack.Stats().TCP.CurrentConnected.Decrement()
 	e.stack.Stats().TCP.EstablishedClosed.Increment()
 }
 
diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 4797f11d1..13718ff55 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -594,6 +594,7 @@ func (e *endpoint) setEndpointState(state EndpointState) {
 	switch state {
 	case StateEstablished:
 		e.stack.Stats().TCP.CurrentEstablished.Increment()
+		e.stack.Stats().TCP.CurrentConnected.Increment()
 	case StateError:
 		fallthrough
 	case StateClose:
diff --git a/pkg/tcpip/transport/tcp/tcp_test.go b/pkg/tcpip/transport/tcp/tcp_test.go
index a9dfbe857..df2fb1071 100644
--- a/pkg/tcpip/transport/tcp/tcp_test.go
+++ b/pkg/tcpip/transport/tcp/tcp_test.go
@@ -470,6 +470,89 @@ func TestConnectResetAfterClose(t *testing.T) {
 	}
 }
 
+// TestCurrentConnectedIncrement tests increment of the current
+// established and connected counters.
+func TestCurrentConnectedIncrement(t *testing.T) {
+	c := context.New(t, defaultMTU)
+	defer c.Cleanup()
+
+	// Set TCPTimeWaitTimeout to 1 seconds so that sockets are marked closed
+	// after 1 second in TIME_WAIT state.
+	tcpTimeWaitTimeout := 1 * time.Second
+	if err := c.Stack().SetTransportProtocolOption(tcp.ProtocolNumber, tcpip.TCPTimeWaitTimeoutOption(tcpTimeWaitTimeout)); err != nil {
+		t.Fatalf("c.stack.SetTransportProtocolOption(tcp, tcpip.TCPTimeWaitTimeout(%d) failed: %s", tcpTimeWaitTimeout, err)
+	}
+
+	c.CreateConnected(789, 30000, -1 /* epRcvBuf */)
+	ep := c.EP
+	c.EP = nil
+
+	if got := c.Stack().Stats().TCP.CurrentEstablished.Value(); got != 1 {
+		t.Errorf("got stats.TCP.CurrentEstablished.Value() = %v, want = 1", got)
+	}
+	gotConnected := c.Stack().Stats().TCP.CurrentConnected.Value()
+	if gotConnected != 1 {
+		t.Errorf("got stats.TCP.CurrentConnected.Value() = %v, want = 1", gotConnected)
+	}
+
+	ep.Close()
+
+	checker.IPv4(t, c.GetPacket(),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.SeqNum(uint32(c.IRS)+1),
+			checker.AckNum(790),
+			checker.TCPFlags(header.TCPFlagAck|header.TCPFlagFin),
+		),
+	)
+	c.SendPacket(nil, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck,
+		SeqNum:  790,
+		AckNum:  c.IRS.Add(2),
+		RcvWnd:  30000,
+	})
+
+	if got := c.Stack().Stats().TCP.CurrentEstablished.Value(); got != 0 {
+		t.Errorf("got stats.TCP.CurrentEstablished.Value() = %v, want = 0", got)
+	}
+	if got := c.Stack().Stats().TCP.CurrentConnected.Value(); got != gotConnected {
+		t.Errorf("got stats.TCP.CurrentConnected.Value() = %v, want = %v", got, gotConnected)
+	}
+
+	// Ack and send FIN as well.
+	c.SendPacket(nil, &context.Headers{
+		SrcPort: context.TestPort,
+		DstPort: c.Port,
+		Flags:   header.TCPFlagAck | header.TCPFlagFin,
+		SeqNum:  790,
+		AckNum:  c.IRS.Add(2),
+		RcvWnd:  30000,
+	})
+
+	// Check that the stack acks the FIN.
+	checker.IPv4(t, c.GetPacket(),
+		checker.PayloadLen(header.TCPMinimumSize),
+		checker.TCP(
+			checker.DstPort(context.TestPort),
+			checker.SeqNum(uint32(c.IRS)+2),
+			checker.AckNum(791),
+			checker.TCPFlags(header.TCPFlagAck),
+		),
+	)
+
+	// Wait for the TIME-WAIT state to transition to CLOSED.
+	time.Sleep(1 * time.Second)
+
+	if got := c.Stack().Stats().TCP.CurrentEstablished.Value(); got != 0 {
+		t.Errorf("got stats.TCP.CurrentEstablished.Value() = %v, want = 0", got)
+	}
+	if got := c.Stack().Stats().TCP.CurrentConnected.Value(); got != 0 {
+		t.Errorf("got stats.TCP.CurrentConnected.Value() = %v, want = 0", got)
+	}
+}
+
 // TestClosingWithEnqueuedSegments tests handling of still enqueued segments
 // when the endpoint transitions to StateClose. The in-flight segments would be
 // re-enqueued to a any listening endpoint.