TCP receive should block when in SYN-SENT state.

The application can choose to initiate a non-blocking connect and
later block on a read, when the endpoint is still in SYN-SENT state.

PiperOrigin-RevId: 319311016

3 files changed, 98 insertions, 47 deletions

diff --git a/pkg/tcpip/transport/tcp/endpoint.go b/pkg/tcpip/transport/tcp/endpoint.go
index 99a691815..bd3ec5a8d 100644
--- a/pkg/tcpip/transport/tcp/endpoint.go
+++ b/pkg/tcpip/transport/tcp/endpoint.go
@@ -1212,6 +1212,16 @@ func (e *endpoint) SetOwner(owner tcpip.PacketOwner) {
 // Read reads data from the endpoint.
 func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages, *tcpip.Error) {
 	e.LockUser()
+	defer e.UnlockUser()
+
+	// When in SYN-SENT state, let the caller block on the receive.
+	// An application can initiate a non-blocking connect and then block
+	// on a receive. It can expect to read any data after the handshake
+	// is complete. RFC793, section 3.9, p58.
+	if e.EndpointState() == StateSynSent {
+		return buffer.View{}, tcpip.ControlMessages{}, tcpip.ErrWouldBlock
+	}
+
 	// 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
@@ -1221,7 +1231,6 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 	if s := e.EndpointState(); !s.connected() && s != StateClose && bufUsed == 0 {
 		e.rcvListMu.Unlock()
 		he := e.HardError
-		e.UnlockUser()
 		if s == StateError {
 			return buffer.View{}, tcpip.ControlMessages{}, he
 		}
@@ -1231,7 +1240,6 @@ func (e *endpoint) Read(*tcpip.FullAddress) (buffer.View, tcpip.ControlMessages,
 
 	v, err := e.readLocked()
 	e.rcvListMu.Unlock()
-	e.UnlockUser()
 
 	if err == tcpip.ErrClosedForReceive {
 		e.stats.ReadErrors.ReadClosed.Increment()
diff --git a/test/packetimpact/tests/BUILD b/test/packetimpact/tests/BUILD
index 4711c1ae6..85749c559 100644
--- a/test/packetimpact/tests/BUILD
+++ b/test/packetimpact/tests/BUILD
@@ -183,8 +183,6 @@ packetimpact_go_test(
 packetimpact_go_test(
     name = "tcp_queue_receive_in_syn_sent",
     srcs = ["tcp_queue_receive_in_syn_sent_test.go"],
-    # TODO(b/157658105): Fix netstack then remove the line below.
-    expect_netstack_failure = True,
     deps = [
         "//pkg/tcpip/header",
         "//test/packetimpact/testbench",
diff --git a/test/packetimpact/tests/tcp_queue_receive_in_syn_sent_test.go b/test/packetimpact/tests/tcp_queue_receive_in_syn_sent_test.go
index b640d8673..8fbec893b 100644
--- a/test/packetimpact/tests/tcp_queue_receive_in_syn_sent_test.go
+++ b/test/packetimpact/tests/tcp_queue_receive_in_syn_sent_test.go
@@ -35,53 +35,98 @@ func init() {
 	testbench.RegisterFlags(flag.CommandLine)
 }
 
+// TestQueueReceiveInSynSent tests receive behavior when the TCP state
+// is SYN-SENT.
+// It tests for 2 variants where the receive is blocked and:
+// (1) we complete handshake and send sample data.
+// (2) we send a TCP RST.
 func TestQueueReceiveInSynSent(t *testing.T) {
-	dut := testbench.NewDUT(t)
-	defer dut.TearDown()
+	for _, tt := range []struct {
+		description string
+		reset       bool
+	}{
+		{description: "Send DATA", reset: false},
+		{description: "Send RST", reset: true},
+	} {
+		t.Run(tt.description, func(t *testing.T) {
+			dut := testbench.NewDUT(t)
+			defer dut.TearDown()
 
-	socket, remotePort := dut.CreateBoundSocket(unix.SOCK_STREAM, unix.IPPROTO_TCP, net.ParseIP(testbench.RemoteIPv4))
-	conn := testbench.NewTCPIPv4(t, testbench.TCP{DstPort: &remotePort}, testbench.TCP{SrcPort: &remotePort})
-	defer conn.Close()
+			socket, remotePort := dut.CreateBoundSocket(unix.SOCK_STREAM, unix.IPPROTO_TCP, net.ParseIP(testbench.RemoteIPv4))
+			conn := testbench.NewTCPIPv4(t, testbench.TCP{DstPort: &remotePort}, testbench.TCP{SrcPort: &remotePort})
+			defer conn.Close()
 
-	sampleData := []byte("Sample Data")
+			sampleData := []byte("Sample Data")
 
-	dut.SetNonBlocking(socket, true)
-	if _, err := dut.ConnectWithErrno(context.Background(), socket, conn.LocalAddr()); !errors.Is(err, syscall.EINPROGRESS) {
-		t.Fatalf("failed to bring DUT to SYN-SENT, got: %s, want EINPROGRESS", err)
-	}
-	if _, err := conn.Expect(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagSyn)}, time.Second); err != nil {
-		t.Fatalf("expected a SYN from DUT, but got none: %s", err)
-	}
+			dut.SetNonBlocking(socket, true)
+			if _, err := dut.ConnectWithErrno(context.Background(), socket, conn.LocalAddr()); !errors.Is(err, syscall.EINPROGRESS) {
+				t.Fatalf("failed to bring DUT to SYN-SENT, got: %s, want EINPROGRESS", err)
+			}
+			if _, err := conn.Expect(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagSyn)}, time.Second); err != nil {
+				t.Fatalf("expected a SYN from DUT, but got none: %s", err)
+			}
 
-	// Issue RECEIVE call in SYN-SENT, this should be queued for process until the connection
-	// is established.
-	dut.SetNonBlocking(socket, false)
-	var wg sync.WaitGroup
-	defer wg.Wait()
-	wg.Add(1)
-	go func() {
-		defer wg.Done()
-		ctx, cancel := context.WithTimeout(context.Background(), time.Second*3)
-		defer cancel()
-		n, buff, err := dut.RecvWithErrno(ctx, socket, int32(len(sampleData)), 0)
-		if n == -1 {
-			t.Fatalf("failed to recv on DUT: %s", err)
-		}
-		if got := buff[:n]; !bytes.Equal(got, sampleData) {
-			t.Fatalf("received data don't match, got:\n%s, want:\n%s", hex.Dump(got), hex.Dump(sampleData))
-		}
-	}()
-
-	// The following sleep is used to prevent the connection from being established while the
-	// RPC is in flight.
-	time.Sleep(time.Second)
-
-	// Bring the connection to Established.
-	conn.Send(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagSyn | header.TCPFlagAck)})
-	if _, err := conn.Expect(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, time.Second); err != nil {
-		t.Fatalf("expected an ACK from DUT, but got none: %s", err)
-	}
+			if _, _, err := dut.RecvWithErrno(context.Background(), socket, int32(len(sampleData)), 0); err != syscall.Errno(unix.EWOULDBLOCK) {
+				t.Fatalf("expected error %s, got %s", syscall.Errno(unix.EWOULDBLOCK), err)
+			}
+
+			// Test blocking read.
+			dut.SetNonBlocking(socket, false)
+
+			var wg sync.WaitGroup
+			defer wg.Wait()
+			wg.Add(1)
+			var block sync.WaitGroup
+			block.Add(1)
+			go func() {
+				defer wg.Done()
+				ctx, cancel := context.WithTimeout(context.Background(), time.Second*3)
+				defer cancel()
 
-	// Send sample data to DUT.
-	conn.Send(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, &testbench.Payload{Bytes: sampleData})
+				block.Done()
+				// Issue RECEIVE call in SYN-SENT, this should be queued for
+				// process until the connection is established.
+				n, buff, err := dut.RecvWithErrno(ctx, socket, int32(len(sampleData)), 0)
+				if tt.reset {
+					if err != syscall.Errno(unix.ECONNREFUSED) {
+						t.Errorf("expected error %s, got %s", syscall.Errno(unix.ECONNREFUSED), err)
+					}
+					if n != -1 {
+						t.Errorf("expected return value %d, got %d", -1, n)
+					}
+					return
+				}
+				if n == -1 {
+					t.Errorf("failed to recv on DUT: %s", err)
+				}
+				if got := buff[:n]; !bytes.Equal(got, sampleData) {
+					t.Errorf("received data doesn't match, got:\n%s, want:\n%s", hex.Dump(got), hex.Dump(sampleData))
+				}
+			}()
+
+			// Wait for the goroutine to be scheduled and before it
+			// blocks on endpoint receive.
+			block.Wait()
+			// The following sleep is used to prevent the connection
+			// from being established before we are blocked on Recv.
+			time.Sleep(100 * time.Millisecond)
+
+			if tt.reset {
+				conn.Send(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagRst | header.TCPFlagAck)})
+				return
+			}
+
+			// Bring the connection to Established.
+			conn.Send(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagSyn | header.TCPFlagAck)})
+			if _, err := conn.Expect(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, time.Second); err != nil {
+				t.Fatalf("expected an ACK from DUT, but got none: %s", err)
+			}
+
+			// Send sample payload and expect an ACK.
+			conn.Send(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, &testbench.Payload{Bytes: sampleData})
+			if _, err := conn.Expect(testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, time.Second); err != nil {
+				t.Fatalf("expected an ACK from DUT, but got none: %s", err)
+			}
+		})
+	}
 }