Respect SO_BINDTODEVICE in unconnected UDP writes

Previously, sending on an unconnected UDP socket would ignore the
SO_BINDTODEVICE option. Send on the configured interface when an UDP socket
is bound to an interface through setsockop SO_BINDTODEVICE.

Add packetimpact tests exercising UDP reads and writes with every combination
of bound/unbound, broadcast/multicast/unicast destination, and bound/not-bound
to device.

PiperOrigin-RevId: 354299670

6 files changed, 325 insertions, 187 deletions

diff --git a/test/packetimpact/runner/defs.bzl b/test/packetimpact/runner/defs.bzl
index 2b9bfac76..a7c46781f 100644
--- a/test/packetimpact/runner/defs.bzl
+++ b/test/packetimpact/runner/defs.bzl
@@ -175,9 +175,6 @@ ALL_TESTS = [
         name = "udp_discard_mcast_source_addr",
     ),
     PacketimpactTestInfo(
-        name = "udp_recv_mcast_bcast",
-    ),
-    PacketimpactTestInfo(
         name = "udp_any_addr_recv_unicast",
     ),
     PacketimpactTestInfo(
diff --git a/test/packetimpact/testbench/connections.go b/test/packetimpact/testbench/connections.go
index 576577310..1453ac232 100644
--- a/test/packetimpact/testbench/connections.go
+++ b/test/packetimpact/testbench/connections.go
@@ -1008,6 +1008,13 @@ func (conn *UDPIPv4) LocalAddr(t *testing.T) *unix.SockaddrInet4 {
 	return sa
 }
 
+// SrcPort returns the source port of this connection.
+func (conn *UDPIPv4) SrcPort(t *testing.T) uint16 {
+	t.Helper()
+
+	return *conn.udpState(t).out.SrcPort
+}
+
 // Send sends a packet with reasonable defaults, potentially overriding the UDP
 // layer and adding additionLayers.
 func (conn *UDPIPv4) Send(t *testing.T, udp UDP, additionalLayers ...Layer) {
@@ -1024,6 +1031,11 @@ func (conn *UDPIPv4) SendIP(t *testing.T, ip IPv4, udp UDP, additionalLayers ...
 	(*Connection)(conn).send(t, Layers{&ip, &udp}, additionalLayers...)
 }
 
+// SendFrame sends a frame on the wire and updates the state of all layers.
+func (conn *UDPIPv4) SendFrame(t *testing.T, overrideLayers Layers, additionalLayers ...Layer) {
+	(*Connection)(conn).send(t, overrideLayers, additionalLayers...)
+}
+
 // Expect expects a frame with the UDP layer matching the provided UDP within
 // the timeout specified. If it doesn't arrive in time, an error is returned.
 func (conn *UDPIPv4) Expect(t *testing.T, udp UDP, timeout time.Duration) (*UDP, error) {
@@ -1053,6 +1065,14 @@ func (conn *UDPIPv4) ExpectData(t *testing.T, udp UDP, payload Payload, timeout
 	return (*Connection)(conn).ExpectFrame(t, expected, timeout)
 }
 
+// ExpectFrame expects a frame that matches the provided Layers within the
+// timeout specified. If it doesn't arrive in time, an error is returned.
+func (conn *UDPIPv4) ExpectFrame(t *testing.T, frame Layers, timeout time.Duration) (Layers, error) {
+	t.Helper()
+
+	return (*Connection)(conn).ExpectFrame(t, frame, timeout)
+}
+
 // Close frees associated resources held by the UDPIPv4 connection.
 func (conn *UDPIPv4) Close(t *testing.T) {
 	t.Helper()
@@ -1136,6 +1156,13 @@ func (conn *UDPIPv6) LocalAddr(t *testing.T, zoneID uint32) *unix.SockaddrInet6
 	return sa
 }
 
+// SrcPort returns the source port of this connection.
+func (conn *UDPIPv6) SrcPort(t *testing.T) uint16 {
+	t.Helper()
+
+	return *conn.udpState(t).out.SrcPort
+}
+
 // Send sends a packet with reasonable defaults, potentially overriding the UDP
 // layer and adding additionLayers.
 func (conn *UDPIPv6) Send(t *testing.T, udp UDP, additionalLayers ...Layer) {
@@ -1152,6 +1179,11 @@ func (conn *UDPIPv6) SendIPv6(t *testing.T, ip IPv6, udp UDP, additionalLayers .
 	(*Connection)(conn).send(t, Layers{&ip, &udp}, additionalLayers...)
 }
 
+// SendFrame sends a frame on the wire and updates the state of all layers.
+func (conn *UDPIPv6) SendFrame(t *testing.T, overrideLayers Layers, additionalLayers ...Layer) {
+	(*Connection)(conn).send(t, overrideLayers, additionalLayers...)
+}
+
 // Expect expects a frame with the UDP layer matching the provided UDP within
 // the timeout specified. If it doesn't arrive in time, an error is returned.
 func (conn *UDPIPv6) Expect(t *testing.T, udp UDP, timeout time.Duration) (*UDP, error) {
@@ -1181,6 +1213,14 @@ func (conn *UDPIPv6) ExpectData(t *testing.T, udp UDP, payload Payload, timeout
 	return (*Connection)(conn).ExpectFrame(t, expected, timeout)
 }
 
+// ExpectFrame expects a frame that matches the provided Layers within the
+// timeout specified. If it doesn't arrive in time, an error is returned.
+func (conn *UDPIPv6) ExpectFrame(t *testing.T, frame Layers, timeout time.Duration) (Layers, error) {
+	t.Helper()
+
+	return (*Connection)(conn).ExpectFrame(t, frame, timeout)
+}
+
 // Close frees associated resources held by the UDPIPv6 connection.
 func (conn *UDPIPv6) Close(t *testing.T) {
 	t.Helper()
diff --git a/test/packetimpact/testbench/dut.go b/test/packetimpact/testbench/dut.go
index 66a0255b8..d40890e12 100644
--- a/test/packetimpact/testbench/dut.go
+++ b/test/packetimpact/testbench/dut.go
@@ -544,7 +544,7 @@ func (dut *DUT) SendToWithErrno(ctx context.Context, t *testing.T, sockfd int32,
 	}
 	resp, err := dut.posixServer.SendTo(ctx, &req)
 	if err != nil {
-		t.Fatalf("faled to call SendTo: %s", err)
+		t.Fatalf("failed to call SendTo: %s", err)
 	}
 	return resp.GetRet(), syscall.Errno(resp.GetErrno_())
 }
diff --git a/test/packetimpact/tests/BUILD b/test/packetimpact/tests/BUILD
index 42aad541f..baa3ae5e9 100644
--- a/test/packetimpact/tests/BUILD
+++ b/test/packetimpact/tests/BUILD
@@ -38,18 +38,6 @@ packetimpact_testbench(
 )
 
 packetimpact_testbench(
-    name = "udp_recv_mcast_bcast",
-    srcs = ["udp_recv_mcast_bcast_test.go"],
-    deps = [
-        "//pkg/tcpip",
-        "//pkg/tcpip/header",
-        "//test/packetimpact/testbench",
-        "@com_github_google_go_cmp//cmp:go_default_library",
-        "@org_golang_x_sys//unix:go_default_library",
-    ],
-)
-
-packetimpact_testbench(
     name = "udp_any_addr_recv_unicast",
     srcs = ["udp_any_addr_recv_unicast_test.go"],
     deps = [
@@ -340,6 +328,8 @@ packetimpact_testbench(
     name = "udp_send_recv_dgram",
     srcs = ["udp_send_recv_dgram_test.go"],
     deps = [
+        "//pkg/tcpip",
+        "//pkg/tcpip/header",
         "//test/packetimpact/testbench",
         "@com_github_google_go_cmp//cmp:go_default_library",
         "@org_golang_x_sys//unix:go_default_library",
diff --git a/test/packetimpact/tests/udp_recv_mcast_bcast_test.go b/test/packetimpact/tests/udp_recv_mcast_bcast_test.go
deleted file mode 100644
index b29c07825..000000000
--- a/test/packetimpact/tests/udp_recv_mcast_bcast_test.go
+++ /dev/null
@@ -1,115 +0,0 @@
-// 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 udp_recv_mcast_bcast_test
-
-import (
-	"context"
-	"flag"
-	"fmt"
-	"net"
-	"syscall"
-	"testing"
-
-	"github.com/google/go-cmp/cmp"
-	"golang.org/x/sys/unix"
-	"gvisor.dev/gvisor/pkg/tcpip"
-	"gvisor.dev/gvisor/test/packetimpact/testbench"
-)
-
-func init() {
-	testbench.Initialize(flag.CommandLine)
-}
-
-func TestUDPRecvMcastBcast(t *testing.T) {
-	dut := testbench.NewDUT(t)
-	subnetBcastAddr := broadcastAddr(dut.Net.RemoteIPv4, net.CIDRMask(dut.Net.IPv4PrefixLength, 32))
-	for _, v := range []struct {
-		bound, to net.IP
-	}{
-		{bound: net.IPv4zero, to: subnetBcastAddr},
-		{bound: net.IPv4zero, to: net.IPv4bcast},
-		{bound: net.IPv4zero, to: net.IPv4allsys},
-
-		{bound: subnetBcastAddr, to: subnetBcastAddr},
-
-		// FIXME(gvisor.dev/issue/4896):  Previously by the time subnetBcastAddr is
-		// created, IPv4PrefixLength is still 0 because genPseudoFlags is not called
-		// yet, it was only called in NewDUT, so the test didn't do what the author
-		// original intended to and becomes failing because we process all flags at
-		// the very beginning.
-		//
-		// {bound: subnetBcastAddr, to: net.IPv4bcast},
-
-		{bound: net.IPv4bcast, to: net.IPv4bcast},
-		{bound: net.IPv4allsys, to: net.IPv4allsys},
-	} {
-		t.Run(fmt.Sprintf("bound=%s,to=%s", v.bound, v.to), func(t *testing.T) {
-			boundFD, remotePort := dut.CreateBoundSocket(t, unix.SOCK_DGRAM, unix.IPPROTO_UDP, v.bound)
-			defer dut.Close(t, boundFD)
-			conn := dut.Net.NewUDPIPv4(t, testbench.UDP{DstPort: &remotePort}, testbench.UDP{SrcPort: &remotePort})
-			defer conn.Close(t)
-
-			payload := testbench.GenerateRandomPayload(t, 1<<10 /* 1 KiB */)
-			conn.SendIP(
-				t,
-				testbench.IPv4{DstAddr: testbench.Address(tcpip.Address(v.to.To4()))},
-				testbench.UDP{},
-				&testbench.Payload{Bytes: payload},
-			)
-			got, want := dut.Recv(t, boundFD, int32(len(payload)+1), 0), payload
-			if diff := cmp.Diff(want, got); diff != "" {
-				t.Errorf("received payload does not match sent payload, diff (-want, +got):\n%s", diff)
-			}
-		})
-	}
-}
-
-func TestUDPDoesntRecvMcastBcastOnUnicastAddr(t *testing.T) {
-	dut := testbench.NewDUT(t)
-	boundFD, remotePort := dut.CreateBoundSocket(t, unix.SOCK_DGRAM, unix.IPPROTO_UDP, dut.Net.RemoteIPv4)
-	dut.SetSockOptTimeval(t, boundFD, unix.SOL_SOCKET, unix.SO_RCVTIMEO, &unix.Timeval{Sec: 1, Usec: 0})
-	defer dut.Close(t, boundFD)
-	conn := dut.Net.NewUDPIPv4(t, testbench.UDP{DstPort: &remotePort}, testbench.UDP{SrcPort: &remotePort})
-	defer conn.Close(t)
-
-	for _, to := range []net.IP{
-		broadcastAddr(dut.Net.RemoteIPv4, net.CIDRMask(dut.Net.IPv4PrefixLength, 32)),
-		net.IPv4(255, 255, 255, 255),
-		net.IPv4(224, 0, 0, 1),
-	} {
-		t.Run(fmt.Sprint("to=%s", to), func(t *testing.T) {
-			payload := testbench.GenerateRandomPayload(t, 1<<10 /* 1 KiB */)
-			conn.SendIP(
-				t,
-				testbench.IPv4{DstAddr: testbench.Address(tcpip.Address(to.To4()))},
-				testbench.UDP{},
-				&testbench.Payload{Bytes: payload},
-			)
-			ret, payload, errno := dut.RecvWithErrno(context.Background(), t, boundFD, 100, 0)
-			if errno != syscall.EAGAIN || errno != syscall.EWOULDBLOCK {
-				t.Errorf("Recv got unexpected result, ret=%d, payload=%q, errno=%s", ret, payload, errno)
-			}
-		})
-	}
-}
-
-func broadcastAddr(ip net.IP, mask net.IPMask) net.IP {
-	result := make(net.IP, net.IPv4len)
-	ip4 := ip.To4()
-	for i := range ip4 {
-		result[i] = ip4[i] | ^mask[i]
-	}
-	return result
-}
diff --git a/test/packetimpact/tests/udp_send_recv_dgram_test.go b/test/packetimpact/tests/udp_send_recv_dgram_test.go
index 7ee2c8014..6e45cb143 100644
--- a/test/packetimpact/tests/udp_send_recv_dgram_test.go
+++ b/test/packetimpact/tests/udp_send_recv_dgram_test.go
@@ -15,13 +15,18 @@
 package udp_send_recv_dgram_test
 
 import (
+	"context"
 	"flag"
+	"fmt"
 	"net"
+	"syscall"
 	"testing"
 	"time"
 
 	"github.com/google/go-cmp/cmp"
 	"golang.org/x/sys/unix"
+	"gvisor.dev/gvisor/pkg/tcpip"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/test/packetimpact/testbench"
 )
 
@@ -30,74 +35,295 @@ func init() {
 }
 
 type udpConn interface {
-	Send(*testing.T, testbench.UDP, ...testbench.Layer)
-	ExpectData(*testing.T, testbench.UDP, testbench.Payload, time.Duration) (testbench.Layers, error)
-	Drain(*testing.T)
+	SrcPort(*testing.T) uint16
+	SendFrame(*testing.T, testbench.Layers, ...testbench.Layer)
+	ExpectFrame(*testing.T, testbench.Layers, time.Duration) (testbench.Layers, error)
 	Close(*testing.T)
 }
 
+type testCase struct {
+	bindTo, sendTo                            net.IP
+	sendToBroadcast, bindToDevice, expectData bool
+}
+
 func TestUDP(t *testing.T) {
 	dut := testbench.NewDUT(t)
+	subnetBcast := func() net.IP {
+		subnet := (&tcpip.AddressWithPrefix{
+			Address:   tcpip.Address(dut.Net.RemoteIPv4.To4()),
+			PrefixLen: dut.Net.IPv4PrefixLength,
+		}).Subnet()
+		return net.IP(subnet.Broadcast())
+	}()
 
-	for _, isIPv4 := range []bool{true, false} {
-		ipVersionName := "IPv6"
-		if isIPv4 {
-			ipVersionName = "IPv4"
-		}
-		t.Run(ipVersionName, func(t *testing.T) {
-			var addr net.IP
-			if isIPv4 {
-				addr = dut.Net.RemoteIPv4
-			} else {
-				addr = dut.Net.RemoteIPv6
+	t.Run("Send", func(t *testing.T) {
+		var testCases []testCase
+		// Test every valid combination of bound/unbound, broadcast/multicast/unicast
+		// bound/destination address, and bound/not-bound to device.
+		for _, bindTo := range []net.IP{
+			nil, // Do not bind.
+			net.IPv4zero,
+			net.IPv4bcast,
+			net.IPv4allsys,
+			subnetBcast,
+			dut.Net.RemoteIPv4,
+			dut.Net.RemoteIPv6,
+		} {
+			for _, sendTo := range []net.IP{
+				net.IPv4bcast,
+				net.IPv4allsys,
+				subnetBcast,
+				dut.Net.LocalIPv4,
+				dut.Net.LocalIPv6,
+			} {
+				// Cannot send to an IPv4 address from a socket bound to IPv6 (except for IPv4-mapped IPv6),
+				// and viceversa.
+				if bindTo != nil && ((bindTo.To4() == nil) != (sendTo.To4() == nil)) {
+					continue
+				}
+				for _, bindToDevice := range []bool{true, false} {
+					expectData := true
+					switch {
+					case bindTo.Equal(dut.Net.RemoteIPv4):
+						// If we're explicitly bound to an interface's unicast address,
+						// packets are always sent on that interface.
+					case bindToDevice:
+						// If we're explicitly bound to an interface, packets are always
+						// sent on that interface.
+					case !sendTo.Equal(net.IPv4bcast) && !sendTo.IsMulticast():
+						// If we're not sending to limited broadcast or multicast, the route table
+						// will be consulted and packets will be sent on the correct interface.
+					default:
+						expectData = false
+					}
+					testCases = append(
+						testCases,
+						testCase{
+							bindTo:          bindTo,
+							sendTo:          sendTo,
+							sendToBroadcast: sendTo.Equal(subnetBcast) || sendTo.Equal(net.IPv4bcast),
+							bindToDevice:    bindToDevice,
+							expectData:      expectData,
+						},
+					)
+				}
 			}
-			boundFD, remotePort := dut.CreateBoundSocket(t, unix.SOCK_DGRAM, unix.IPPROTO_UDP, addr)
-			defer dut.Close(t, boundFD)
-
-			var conn udpConn
-			var localAddr unix.Sockaddr
-			if isIPv4 {
-				v4Conn := dut.Net.NewUDPIPv4(t, testbench.UDP{DstPort: &remotePort}, testbench.UDP{SrcPort: &remotePort})
-				localAddr = v4Conn.LocalAddr(t)
-				conn = &v4Conn
-			} else {
-				v6Conn := dut.Net.NewUDPIPv6(t, testbench.UDP{DstPort: &remotePort}, testbench.UDP{SrcPort: &remotePort})
-				localAddr = v6Conn.LocalAddr(t, dut.Net.RemoteDevID)
-				conn = &v6Conn
-			}
-			defer conn.Close(t)
-
-			testCases := []struct {
-				name    string
-				payload []byte
-			}{
-				{"emptypayload", nil},
-				{"small payload", []byte("hello world")},
-				{"1kPayload", testbench.GenerateRandomPayload(t, 1<<10)},
-				// Even though UDP allows larger dgrams we don't test it here as
-				// they need to be fragmented and written out as individual
-				// frames.
+		}
+		for _, tc := range testCases {
+			boundTestCaseName := "unbound"
+			if tc.bindTo != nil {
+				boundTestCaseName = fmt.Sprintf("bindTo=%s", tc.bindTo)
 			}
-			for _, tc := range testCases {
-				t.Run(tc.name, func(t *testing.T) {
-					t.Run("Send", func(t *testing.T) {
-						conn.Send(t, testbench.UDP{}, &testbench.Payload{Bytes: tc.payload})
-						got, want := dut.Recv(t, boundFD, int32(len(tc.payload)+1), 0), tc.payload
-						if diff := cmp.Diff(want, got); diff != "" {
-							t.Fatalf("received payload does not match sent payload, diff (-want, +got):\n%s", diff)
+			t.Run(fmt.Sprintf("%s/sendTo=%s/bindToDevice=%t/expectData=%t", boundTestCaseName, tc.sendTo, tc.bindToDevice, tc.expectData), func(t *testing.T) {
+				runTestCase(
+					t,
+					dut,
+					tc,
+					func(t *testing.T, dut testbench.DUT, conn udpConn, socketFD int32, tc testCase, payload []byte, layers testbench.Layers) {
+						var destSockaddr unix.Sockaddr
+						if sendTo4 := tc.sendTo.To4(); sendTo4 != nil {
+							addr := unix.SockaddrInet4{
+								Port: int(conn.SrcPort(t)),
+							}
+							copy(addr.Addr[:], sendTo4)
+							destSockaddr = &addr
+						} else {
+							addr := unix.SockaddrInet6{
+								Port:   int(conn.SrcPort(t)),
+								ZoneId: dut.Net.RemoteDevID,
+							}
+							copy(addr.Addr[:], tc.sendTo.To16())
+							destSockaddr = &addr
 						}
-					})
-					t.Run("Recv", func(t *testing.T) {
-						conn.Drain(t)
-						if got, want := int(dut.SendTo(t, boundFD, tc.payload, 0, localAddr)), len(tc.payload); got != want {
-							t.Fatalf("short write got: %d, want: %d", got, want)
+						if got, want := dut.SendTo(t, socketFD, payload, 0, destSockaddr), len(payload); int(got) != want {
+							t.Fatalf("got dut.SendTo = %d, want %d", got, want)
 						}
-						if _, err := conn.ExpectData(t, testbench.UDP{SrcPort: &remotePort}, testbench.Payload{Bytes: tc.payload}, time.Second); err != nil {
+						layers = append(layers, &testbench.Payload{
+							Bytes: payload,
+						})
+						_, err := conn.ExpectFrame(t, layers, time.Second)
+
+						if !tc.expectData && err == nil {
+							t.Fatal("received unexpected packet, socket is not bound to device")
+						}
+						if err != nil && tc.expectData {
 							t.Fatal(err)
 						}
-					})
-				})
+					},
+				)
+			})
+		}
+	})
+	t.Run("Recv", func(t *testing.T) {
+		// Test every valid combination of broadcast/multicast/unicast
+		// bound/destination address, and bound/not-bound to device.
+		var testCases []testCase
+		for _, addr := range []net.IP{
+			net.IPv4bcast,
+			net.IPv4allsys,
+			dut.Net.RemoteIPv4,
+			dut.Net.RemoteIPv6,
+		} {
+			for _, bindToDevice := range []bool{true, false} {
+				testCases = append(
+					testCases,
+					testCase{
+						bindTo:          addr,
+						sendTo:          addr,
+						sendToBroadcast: addr.Equal(subnetBcast) || addr.Equal(net.IPv4bcast),
+						bindToDevice:    bindToDevice,
+						expectData:      true,
+					},
+				)
 			}
-		})
+		}
+		for _, bindTo := range []net.IP{
+			net.IPv4zero,
+			subnetBcast,
+			dut.Net.RemoteIPv4,
+		} {
+			for _, sendTo := range []net.IP{
+				subnetBcast,
+				net.IPv4bcast,
+				net.IPv4allsys,
+			} {
+				// TODO(gvisor.dev/issue/4896): Add bindTo=subnetBcast/sendTo=IPv4bcast
+				// and bindTo=subnetBcast/sendTo=IPv4allsys test cases.
+				if bindTo.Equal(subnetBcast) && (sendTo.Equal(net.IPv4bcast) || sendTo.IsMulticast()) {
+					continue
+				}
+				// Expect that a socket bound to a unicast address does not receive
+				// packets sent to an address other than the bound unicast address.
+				//
+				// Note: we cannot use net.IP.IsGlobalUnicast to test this condition
+				// because IsGlobalUnicast does not check whether the address is the
+				// subnet broadcast, and returns true in that case.
+				expectData := !bindTo.Equal(dut.Net.RemoteIPv4) || sendTo.Equal(dut.Net.RemoteIPv4)
+				for _, bindToDevice := range []bool{true, false} {
+					testCases = append(
+						testCases,
+						testCase{
+							bindTo:          bindTo,
+							sendTo:          sendTo,
+							sendToBroadcast: sendTo.Equal(subnetBcast) || sendTo.Equal(net.IPv4bcast),
+							bindToDevice:    bindToDevice,
+							expectData:      expectData,
+						},
+					)
+				}
+			}
+		}
+		for _, tc := range testCases {
+			t.Run(fmt.Sprintf("bindTo=%s/sendTo=%s/bindToDevice=%t/expectData=%t", tc.bindTo, tc.sendTo, tc.bindToDevice, tc.expectData), func(t *testing.T) {
+				runTestCase(
+					t,
+					dut,
+					tc,
+					func(t *testing.T, dut testbench.DUT, conn udpConn, socketFD int32, tc testCase, payload []byte, layers testbench.Layers) {
+						conn.SendFrame(t, layers, &testbench.Payload{Bytes: payload})
+
+						if tc.expectData {
+							got, want := dut.Recv(t, socketFD, int32(len(payload)+1), 0), payload
+							if diff := cmp.Diff(want, got); diff != "" {
+								t.Errorf("received payload does not match sent payload, diff (-want, +got):\n%s", diff)
+							}
+						} else {
+							// Expected receive error, set a short receive timeout.
+							dut.SetSockOptTimeval(
+								t,
+								socketFD,
+								unix.SOL_SOCKET,
+								unix.SO_RCVTIMEO,
+								&unix.Timeval{
+									Sec:  1,
+									Usec: 0,
+								},
+							)
+							ret, recvPayload, errno := dut.RecvWithErrno(context.Background(), t, socketFD, 100, 0)
+							if errno != syscall.EAGAIN || errno != syscall.EWOULDBLOCK {
+								t.Errorf("Recv got unexpected result, ret=%d, payload=%q, errno=%s", ret, recvPayload, errno)
+							}
+						}
+					},
+				)
+			})
+		}
+	})
+}
+
+func runTestCase(
+	t *testing.T,
+	dut testbench.DUT,
+	tc testCase,
+	runTc func(t *testing.T, dut testbench.DUT, conn udpConn, socketFD int32, tc testCase, payload []byte, layers testbench.Layers),
+) {
+	var (
+		socketFD                 int32
+		outgoingUDP, incomingUDP testbench.UDP
+	)
+	if tc.bindTo != nil {
+		var remotePort uint16
+		socketFD, remotePort = dut.CreateBoundSocket(t, unix.SOCK_DGRAM, unix.IPPROTO_UDP, tc.bindTo)
+		outgoingUDP.DstPort = &remotePort
+		incomingUDP.SrcPort = &remotePort
+	} else {
+		// An unbound socket will auto-bind to INNADDR_ANY and a random
+		// port on sendto.
+		socketFD = dut.Socket(t, unix.AF_INET6, unix.SOCK_DGRAM, unix.IPPROTO_UDP)
+	}
+	defer dut.Close(t, socketFD)
+	if tc.bindToDevice {
+		dut.SetSockOpt(t, socketFD, unix.SOL_SOCKET, unix.SO_BINDTODEVICE, []byte(dut.Net.RemoteDevName))
+	}
+
+	var ethernetLayer testbench.Ether
+	if tc.sendToBroadcast {
+		dut.SetSockOptInt(t, socketFD, unix.SOL_SOCKET, unix.SO_BROADCAST, 1)
+
+		// When sending to broadcast (subnet or limited), the expected ethernet
+		// address is also broadcast.
+		ethernetBroadcastAddress := header.EthernetBroadcastAddress
+		ethernetLayer.DstAddr = &ethernetBroadcastAddress
+	} else if tc.sendTo.IsMulticast() {
+		ethernetMulticastAddress := header.EthernetAddressFromMulticastIPv4Address(tcpip.Address(tc.sendTo.To4()))
+		ethernetLayer.DstAddr = &ethernetMulticastAddress
+	}
+	expectedLayers := testbench.Layers{&ethernetLayer}
+
+	var conn udpConn
+	if sendTo4 := tc.sendTo.To4(); sendTo4 != nil {
+		v4Conn := dut.Net.NewUDPIPv4(t, outgoingUDP, incomingUDP)
+		conn = &v4Conn
+		expectedLayers = append(
+			expectedLayers,
+			&testbench.IPv4{
+				DstAddr: testbench.Address(tcpip.Address(sendTo4)),
+			},
+		)
+	} else {
+		v6Conn := dut.Net.NewUDPIPv6(t, outgoingUDP, incomingUDP)
+		conn = &v6Conn
+		expectedLayers = append(
+			expectedLayers,
+			&testbench.IPv6{
+				DstAddr: testbench.Address(tcpip.Address(tc.sendTo)),
+			},
+		)
+	}
+	defer conn.Close(t)
+
+	expectedLayers = append(expectedLayers, &incomingUDP)
+	for _, v := range []struct {
+		name    string
+		payload []byte
+	}{
+		{"emptypayload", nil},
+		{"small payload", []byte("hello world")},
+		{"1kPayload", testbench.GenerateRandomPayload(t, 1<<10)},
+		// Even though UDP allows larger dgrams we don't test it here as
+		// they need to be fragmented and written out as individual
+		// frames.
+	} {
+		runTc(t, dut, conn, socketFD, tc, v.payload, expectedLayers)
 	}
 }