Change segment/pending queue to use receive buffer limits.

segment_queue today has its own standalone limit of MaxUnprocessedSegments but
this can be a problem in UnlockUser() we do not release the lock till there are
segments to be processed. What can happen is as handleSegments dequeues packets
more keep getting queued and we will never release the lock. This can keep
happening even if the receive buffer is full because nothing can read() till we
release the lock.

Further having a separate limit for pending segments makes it harder to track
memory usage etc. Unifying the limits makes it easier to reason about memory in
use and makes the overall buffer behaviour more consistent.

PiperOrigin-RevId: 333508122

2 files changed, 90 insertions, 0 deletions

diff --git a/test/packetimpact/tests/BUILD b/test/packetimpact/tests/BUILD
index fbfea61e1..94731c64b 100644
--- a/test/packetimpact/tests/BUILD
+++ b/test/packetimpact/tests/BUILD
@@ -340,3 +340,13 @@ packetimpact_go_test(
         "@org_golang_x_sys//unix:go_default_library",
     ],
 )
+
+packetimpact_go_test(
+    name = "tcp_rcv_buf_space",
+    srcs = ["tcp_rcv_buf_space_test.go"],
+    deps = [
+        "//pkg/tcpip/header",
+        "//test/packetimpact/testbench",
+        "@org_golang_x_sys//unix:go_default_library",
+    ],
+)
diff --git a/test/packetimpact/tests/tcp_rcv_buf_space_test.go b/test/packetimpact/tests/tcp_rcv_buf_space_test.go
new file mode 100644
index 000000000..cfbba1e8e
--- /dev/null
+++ b/test/packetimpact/tests/tcp_rcv_buf_space_test.go
@@ -0,0 +1,80 @@
+// 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_rcv_buf_space_test
+
+import (
+	"context"
+	"flag"
+	"syscall"
+	"testing"
+
+	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+	"gvisor.dev/gvisor/test/packetimpact/testbench"
+)
+
+func init() {
+	testbench.RegisterFlags(flag.CommandLine)
+}
+
+// TestReduceRecvBuf tests that a packet within window is still dropped
+// if the available buffer space drops below the size of the incoming
+// segment.
+func TestReduceRecvBuf(t *testing.T) {
+	dut := testbench.NewDUT(t)
+	defer dut.TearDown()
+	listenFd, remotePort := dut.CreateListener(t, unix.SOCK_STREAM, unix.IPPROTO_TCP, 1)
+	defer dut.Close(t, listenFd)
+	conn := testbench.NewTCPIPv4(t, testbench.TCP{DstPort: &remotePort}, testbench.TCP{SrcPort: &remotePort})
+	defer conn.Close(t)
+
+	conn.Connect(t)
+	acceptFd, _ := dut.Accept(t, listenFd)
+	defer dut.Close(t, acceptFd)
+
+	// Set a small receive buffer for the test.
+	const rcvBufSz = 4096
+	dut.SetSockOptInt(t, acceptFd, unix.SOL_SOCKET, unix.SO_RCVBUF, rcvBufSz)
+
+	// Retrieve the actual buffer.
+	bufSz := dut.GetSockOptInt(t, acceptFd, unix.SOL_SOCKET, unix.SO_RCVBUF)
+
+	// Generate a payload of 1 more than the actual buffer size used by the
+	// DUT.
+	sampleData := testbench.GenerateRandomPayload(t, int(bufSz)+1)
+	// Send and receive sample data to the dut.
+	const pktSize = 1400
+	for payload := sampleData; len(payload) != 0; {
+		payloadBytes := pktSize
+		if l := len(payload); l < payloadBytes {
+			payloadBytes = l
+		}
+
+		conn.Send(t, testbench.TCP{Flags: testbench.Uint8(header.TCPFlagAck)}, []testbench.Layer{&testbench.Payload{Bytes: payload[:payloadBytes]}}...)
+		payload = payload[payloadBytes:]
+	}
+
+	// First read should read < len(sampleData)
+	if ret, _, err := dut.RecvWithErrno(context.Background(), t, acceptFd, int32(len(sampleData)), 0); ret == -1 || int(ret) == len(sampleData) {
+		t.Fatalf("dut.RecvWithErrno(ctx, t, %d, %d, 0) = %d,_, %s", acceptFd, int32(len(sampleData)), ret, err)
+	}
+
+	// Second read should return EAGAIN as the last segment should have been
+	// dropped due to it exceeding the receive buffer space available in the
+	// socket.
+	if ret, got, err := dut.RecvWithErrno(context.Background(), t, acceptFd, int32(len(sampleData)), syscall.MSG_DONTWAIT); got != nil || ret != -1 || err != syscall.EAGAIN {
+		t.Fatalf("expected no packets but got: %s", got)
+	}
+}