Fix TCP segment retransmit timeout handling.

As per RFC 1122 and Linux retransmit timeout handling:
- The segment retransmit timeout needs to exponentially increase and
  cap at a predefined value.
- TCP connection needs to timeout after a predefined number of
  segment retransmissions.
- TCP connection should not timeout when the retranmission timeout
  exceeds MaxRTO, predefined upper bound.

Fixes #2673

PiperOrigin-RevId: 311463961

2 files changed, 94 insertions, 0 deletions

diff --git a/test/packetimpact/tests/BUILD b/test/packetimpact/tests/BUILD
index c25b3b8c1..fff7787c8 100644
--- a/test/packetimpact/tests/BUILD
+++ b/test/packetimpact/tests/BUILD
@@ -82,6 +82,16 @@ packetimpact_go_test(
 )
 
 packetimpact_go_test(
+    name = "tcp_retransmits",
+    srcs = ["tcp_retransmits_test.go"],
+    deps = [
+        "//pkg/tcpip/header",
+        "//test/packetimpact/testbench",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
+
+packetimpact_go_test(
     name = "tcp_outside_the_window",
     srcs = ["tcp_outside_the_window_test.go"],
     deps = [
diff --git a/test/packetimpact/tests/tcp_retransmits_test.go b/test/packetimpact/tests/tcp_retransmits_test.go
new file mode 100644
index 000000000..c043ad881
--- /dev/null
+++ b/test/packetimpact/tests/tcp_retransmits_test.go
@@ -0,0 +1,84 @@
+// Copyright 2020 The gVisor Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package tcp_retransmits_test
+
+import (
+	"flag"
+	"testing"
+	"time"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	tb "gvisor.dev/gvisor/test/packetimpact/testbench"
+)
+
+func init() {
+	tb.RegisterFlags(flag.CommandLine)
+}
+
+// TestRetransmits tests retransmits occur at exponentially increasing
+// time intervals.
+func TestRetransmits(t *testing.T) {
+	dut := tb.NewDUT(t)
+	defer dut.TearDown()
+	listenFd, remotePort := dut.CreateListener(unix.SOCK_STREAM, unix.IPPROTO_TCP, 1)
+	defer dut.Close(listenFd)
+	conn := tb.NewTCPIPv4(t, tb.TCP{DstPort: &remotePort}, tb.TCP{SrcPort: &remotePort})
+	defer conn.Close()
+
+	conn.Handshake()
+	acceptFd, _ := dut.Accept(listenFd)
+	defer dut.Close(acceptFd)
+
+	dut.SetSockOptInt(acceptFd, unix.IPPROTO_TCP, unix.TCP_NODELAY, 1)
+
+	sampleData := []byte("Sample Data")
+	samplePayload := &tb.Payload{Bytes: sampleData}
+
+	dut.Send(acceptFd, sampleData, 0)
+	if _, err := conn.ExpectData(&tb.TCP{}, samplePayload, time.Second); err != nil {
+		t.Fatalf("expected a packet with payload %v: %s", samplePayload, err)
+	}
+	// Give a chance for the dut to estimate RTO with RTT from the DATA-ACK.
+	// TODO(gvisor.dev/issue/2685) Estimate RTO during handshake, after which
+	// we can skip sending this ACK.
+	conn.Send(tb.TCP{Flags: tb.Uint8(header.TCPFlagAck)})
+
+	startRTO := time.Second
+	current := startRTO
+	first := time.Now()
+	dut.Send(acceptFd, sampleData, 0)
+	seq := tb.Uint32(uint32(*conn.RemoteSeqNum()))
+	if _, err := conn.ExpectData(&tb.TCP{SeqNum: seq}, samplePayload, startRTO); err != nil {
+		t.Fatalf("expected a packet with payload %v: %s", samplePayload, err)
+	}
+	// Expect retransmits of the same segment.
+	for i := 0; i < 5; i++ {
+		start := time.Now()
+		if _, err := conn.ExpectData(&tb.TCP{SeqNum: seq}, samplePayload, 2*current); err != nil {
+			t.Fatalf("expected a packet with payload %v: %s loop %d", samplePayload, err, i)
+		}
+		if i == 0 {
+			startRTO = time.Now().Sub(first)
+			current = 2 * startRTO
+			continue
+		}
+		// Check if the probes came at exponentially increasing intervals.
+		if p := time.Since(start); p < current-startRTO {
+			t.Fatalf("retransmit came sooner interval %d probe %d\n", p, i)
+		}
+		current *= 2
+	}
+}