Introduce IPv4 options serializer and add RouterAlert to IGMP

PiperOrigin-RevId: 345701623

12 files changed, 451 insertions, 184 deletions

diff --git a/pkg/tcpip/checker/checker.go b/pkg/tcpip/checker/checker.go
index e669397dd..d3ae56ac6 100644
--- a/pkg/tcpip/checker/checker.go
+++ b/pkg/tcpip/checker/checker.go
@@ -217,6 +217,42 @@ func IPv4Options(want header.IPv4Options) NetworkChecker {
 	}
 }
 
+// IPv4RouterAlert returns a checker that checks that the RouterAlert option is
+// set in an IPv4 packet.
+func IPv4RouterAlert() NetworkChecker {
+	return func(t *testing.T, h []header.Network) {
+		t.Helper()
+		ip, ok := h[0].(header.IPv4)
+		if !ok {
+			t.Fatalf("unexpected network header passed to checker, got = %T, want = header.IPv4", h[0])
+		}
+		iterator := ip.Options().MakeIterator()
+		for {
+			opt, done, err := iterator.Next()
+			if err != nil {
+				t.Fatalf("error acquiring next IPv4 option %s", err)
+			}
+			if done {
+				break
+			}
+			if opt.Type() != header.IPv4OptionRouterAlertType {
+				continue
+			}
+			want := [header.IPv4OptionRouterAlertLength]byte{
+				byte(header.IPv4OptionRouterAlertType),
+				header.IPv4OptionRouterAlertLength,
+				header.IPv4OptionRouterAlertValue,
+				header.IPv4OptionRouterAlertValue,
+			}
+			if diff := cmp.Diff(want[:], opt.Contents()); diff != "" {
+				t.Errorf("router alert option mismatch (-want +got):\n%s", diff)
+			}
+			return
+		}
+		t.Errorf("failed to find router alert option in %v", ip.Options())
+	}
+}
+
 // FragmentOffset creates a checker that checks the FragmentOffset field.
 func FragmentOffset(offset uint16) NetworkChecker {
 	return func(t *testing.T, h []header.Network) {
diff --git a/pkg/tcpip/header/BUILD b/pkg/tcpip/header/BUILD
index 144093c3a..0bdc12d53 100644
--- a/pkg/tcpip/header/BUILD
+++ b/pkg/tcpip/header/BUILD
@@ -42,6 +42,7 @@ go_test(
     srcs = [
         "checksum_test.go",
         "igmp_test.go",
+        "ipv4_test.go",
         "ipv6_test.go",
         "ipversion_test.go",
         "tcp_test.go",
diff --git a/pkg/tcpip/header/ipv4.go b/pkg/tcpip/header/ipv4.go
index 5fddd2af6..e6103f4bc 100644
--- a/pkg/tcpip/header/ipv4.go
+++ b/pkg/tcpip/header/ipv4.go
@@ -100,7 +100,7 @@ type IPv4Fields struct {
 	//
 	// That leaves ten 32 bit (4 byte) fields for options. An attempt to encode
 	// more will fail.
-	Options IPv4Options
+	Options IPv4OptionsSerializer
 }
 
 // IPv4 is an IPv4 header.
@@ -285,18 +285,17 @@ func (b IPv4) DestinationAddress() tcpip.Address {
 	return tcpip.Address(b[dstAddr : dstAddr+IPv4AddressSize])
 }
 
-// IPv4Options is a buffer that holds all the raw IP options.
-type IPv4Options []byte
-
-// SizeWithPadding implements stack.NetOptions.
-// It reports the size to allocate for the Options. RFC 791 page 23 (end of
-// section 3.1) says of the padding at the end of the options:
+// padIPv4OptionsLength returns the total length for IPv4 options of length l
+// after applying padding according to RFC 791:
 //    The internet header padding is used to ensure that the internet
 //    header ends on a 32 bit boundary.
-func (o IPv4Options) SizeWithPadding() int {
-	return (len(o) + IPv4IHLStride - 1) & ^(IPv4IHLStride - 1)
+func padIPv4OptionsLength(length uint8) uint8 {
+	return (length + IPv4IHLStride - 1) & ^uint8(IPv4IHLStride-1)
 }
 
+// IPv4Options is a buffer that holds all the raw IP options.
+type IPv4Options []byte
+
 // Options returns a buffer holding the options.
 func (b IPv4) Options() IPv4Options {
 	hdrLen := b.HeaderLength()
@@ -375,26 +374,16 @@ func (b IPv4) CalculateChecksum() uint16 {
 func (b IPv4) Encode(i *IPv4Fields) {
 	// The size of the options defines the size of the whole header and thus the
 	// IHL field. Options are rare and this is a heavily used function so it is
-	// worth a bit of optimisation here to keep the copy out of the fast path.
-	hdrLen := IPv4MinimumSize
+	// worth a bit of optimisation here to keep the serializer out of the fast
+	// path.
+	hdrLen := uint8(IPv4MinimumSize)
 	if len(i.Options) != 0 {
-		// SizeWithPadding is always >= len(i.Options).
-		aLen := i.Options.SizeWithPadding()
-		hdrLen += aLen
-		if hdrLen > len(b) {
-			panic(fmt.Sprintf("encode received %d bytes, wanted >= %d", len(b), hdrLen))
-		}
-		opts := b[options:]
-		// This avoids bounds checks on the next line(s) which would happen even
-		// if there's no work to do.
-		if n := copy(opts, i.Options); n != aLen {
-			padding := opts[n:][:aLen-n]
-			for i := range padding {
-				padding[i] = 0
-			}
-		}
+		hdrLen += i.Options.Serialize(b[options:])
 	}
-	b.SetHeaderLength(uint8(hdrLen))
+	if hdrLen > IPv4MaximumHeaderSize {
+		panic(fmt.Sprintf("%d is larger than maximum IPv4 header size of %d", hdrLen, IPv4MaximumHeaderSize))
+	}
+	b.SetHeaderLength(hdrLen)
 	b[tos] = i.TOS
 	b.SetTotalLength(i.TotalLength)
 	binary.BigEndian.PutUint16(b[id:], i.ID)
@@ -474,6 +463,10 @@ const (
 	// options and may appear multiple times.
 	IPv4OptionNOPType IPv4OptionType = 1
 
+	// IPv4OptionRouterAlertType is the option type for the Router Alert option,
+	// defined in RFC 2113 Section 2.1.
+	IPv4OptionRouterAlertType IPv4OptionType = 20 | 0x80
+
 	// IPv4OptionRecordRouteType is used by each router on the path of the packet
 	// to record its path. It is carried over to an Echo Reply.
 	IPv4OptionRecordRouteType IPv4OptionType = 7
@@ -874,3 +867,162 @@ func (rr *IPv4OptionRecordRoute) Size() uint8 { return uint8(len(*rr)) }
 
 // Contents implements IPv4Option.
 func (rr *IPv4OptionRecordRoute) Contents() []byte { return []byte(*rr) }
+
+// Router Alert option specific related constants.
+//
+// from RFC 2113 section 2.1:
+//
+//     +--------+--------+--------+--------+
+//     |10010100|00000100|  2 octet value  |
+//     +--------+--------+--------+--------+
+//
+//     Type:
+//     Copied flag:  1 (all fragments must carry the option)
+//     Option class: 0 (control)
+//     Option number: 20 (decimal)
+//
+//     Length: 4
+//
+//     Value:  A two octet code with the following values:
+//     0 - Router shall examine packet
+//     1-65535 - Reserved
+const (
+	// IPv4OptionRouterAlertLength is the length of a Router Alert option.
+	IPv4OptionRouterAlertLength = 4
+
+	// IPv4OptionRouterAlertValue is the only permissible value of the 16 bit
+	// payload of the router alert option.
+	IPv4OptionRouterAlertValue = 0
+
+	// iPv4OptionRouterAlertValueOffset is the offset for the value of a
+	// RouterAlert option.
+	iPv4OptionRouterAlertValueOffset = 2
+)
+
+// IPv4SerializableOption is an interface to represent serializable IPv4 option
+// types.
+type IPv4SerializableOption interface {
+	// optionType returns the type identifier of the option.
+	optionType() IPv4OptionType
+}
+
+// IPv4SerializableOptionPayload is an interface providing serialization of the
+// payload of an IPv4 option.
+type IPv4SerializableOptionPayload interface {
+	// length returns the size of the payload.
+	length() uint8
+
+	// serializeInto serializes the payload into the provided byte buffer.
+	//
+	// Note, the caller MUST provide a byte buffer with size of at least
+	// Length. Implementers of this function may assume that the byte buffer
+	// is of sufficient size. serializeInto MUST panic if the provided byte
+	// buffer is not of sufficient size.
+	//
+	// serializeInto will return the number of bytes that was used to
+	// serialize the receiver. Implementers must only use the number of
+	// bytes required to serialize the receiver. Callers MAY provide a
+	// larger buffer than required to serialize into.
+	serializeInto(buffer []byte) uint8
+}
+
+// IPv4OptionsSerializer is a serializer for IPv4 options.
+type IPv4OptionsSerializer []IPv4SerializableOption
+
+// Length returns the total number of bytes required to serialize the options.
+func (s IPv4OptionsSerializer) Length() uint8 {
+	var total uint8
+	for _, opt := range s {
+		total++
+		if withPayload, ok := opt.(IPv4SerializableOptionPayload); ok {
+			// Add 1 to reported length to account for the length byte.
+			total += 1 + withPayload.length()
+		}
+	}
+	return padIPv4OptionsLength(total)
+}
+
+// Serialize serializes the provided list of IPV4 options into b.
+//
+// Note, b must be of sufficient size to hold all the options in s. See
+// IPv4OptionsSerializer.Length for details on the getting the total size
+// of a serialized IPv4OptionsSerializer.
+//
+// Serialize panics if b is not of sufficient size to hold all the options in s.
+func (s IPv4OptionsSerializer) Serialize(b []byte) uint8 {
+	var total uint8
+	for _, opt := range s {
+		ty := opt.optionType()
+		if withPayload, ok := opt.(IPv4SerializableOptionPayload); ok {
+			// Serialize first to reduce bounds checks.
+			l := 2 + withPayload.serializeInto(b[2:])
+			b[0] = byte(ty)
+			b[1] = l
+			b = b[l:]
+			total += l
+			continue
+		}
+		// Options without payload consist only of the type field.
+		//
+		// NB: Repeating code from the branch above is intentional to minimize
+		// bounds checks.
+		b[0] = byte(ty)
+		b = b[1:]
+		total++
+	}
+
+	// According to RFC 791:
+	//
+	//  The internet header padding is used to ensure that the internet
+	//  header ends on a 32 bit boundary. The padding is zero.
+	padded := padIPv4OptionsLength(total)
+	b = b[:padded-total]
+	for i := range b {
+		b[i] = 0
+	}
+	return padded
+}
+
+var _ IPv4SerializableOptionPayload = (*IPv4SerializableRouterAlertOption)(nil)
+var _ IPv4SerializableOption = (*IPv4SerializableRouterAlertOption)(nil)
+
+// IPv4SerializableRouterAlertOption provides serialization of the Router Alert
+// IPv4 option according to RFC 2113.
+type IPv4SerializableRouterAlertOption struct{}
+
+// Type implements IPv4SerializableOption.
+func (*IPv4SerializableRouterAlertOption) optionType() IPv4OptionType {
+	return IPv4OptionRouterAlertType
+}
+
+// Length implements IPv4SerializableOption.
+func (*IPv4SerializableRouterAlertOption) length() uint8 {
+	return IPv4OptionRouterAlertLength - iPv4OptionRouterAlertValueOffset
+}
+
+// SerializeInto implements IPv4SerializableOption.
+func (o *IPv4SerializableRouterAlertOption) serializeInto(buffer []byte) uint8 {
+	binary.BigEndian.PutUint16(buffer, IPv4OptionRouterAlertValue)
+	return o.length()
+}
+
+var _ IPv4SerializableOption = (*IPv4SerializableNOPOption)(nil)
+
+// IPv4SerializableNOPOption provides serialization for the IPv4 no-op option.
+type IPv4SerializableNOPOption struct{}
+
+// Type implements IPv4SerializableOption.
+func (*IPv4SerializableNOPOption) optionType() IPv4OptionType {
+	return IPv4OptionNOPType
+}
+
+var _ IPv4SerializableOption = (*IPv4SerializableListEndOption)(nil)
+
+// IPv4SerializableListEndOption provides serialization for the IPv4 List End
+// option.
+type IPv4SerializableListEndOption struct{}
+
+// Type implements IPv4SerializableOption.
+func (*IPv4SerializableListEndOption) optionType() IPv4OptionType {
+	return IPv4OptionListEndType
+}
diff --git a/pkg/tcpip/header/ipv4_test.go b/pkg/tcpip/header/ipv4_test.go
new file mode 100644
index 000000000..6475cd694
--- /dev/null
+++ b/pkg/tcpip/header/ipv4_test.go
@@ -0,0 +1,179 @@
+// 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 header_test
+
+import (
+	"testing"
+
+	"github.com/google/go-cmp/cmp"
+	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/header"
+)
+
+func TestIPv4OptionsSerializer(t *testing.T) {
+	optCases := []struct {
+		name   string
+		option []header.IPv4SerializableOption
+		expect []byte
+	}{
+		{
+			name: "NOP",
+			option: []header.IPv4SerializableOption{
+				&header.IPv4SerializableNOPOption{},
+			},
+			expect: []byte{1, 0, 0, 0},
+		},
+		{
+			name: "ListEnd",
+			option: []header.IPv4SerializableOption{
+				&header.IPv4SerializableListEndOption{},
+			},
+			expect: []byte{0, 0, 0, 0},
+		},
+		{
+			name: "RouterAlert",
+			option: []header.IPv4SerializableOption{
+				&header.IPv4SerializableRouterAlertOption{},
+			},
+			expect: []byte{148, 4, 0, 0},
+		}, {
+			name: "NOP and RouterAlert",
+			option: []header.IPv4SerializableOption{
+				&header.IPv4SerializableNOPOption{},
+				&header.IPv4SerializableRouterAlertOption{},
+			},
+			expect: []byte{1, 148, 4, 0, 0, 0, 0, 0},
+		},
+	}
+
+	for _, opt := range optCases {
+		t.Run(opt.name, func(t *testing.T) {
+			s := header.IPv4OptionsSerializer(opt.option)
+			l := s.Length()
+			if got := len(opt.expect); got != int(l) {
+				t.Fatalf("s.Length() = %d, want = %d", got, l)
+			}
+			b := make([]byte, l)
+			for i := range b {
+				// Fill the buffer with full bytes to ensure padding is being set
+				// correctly.
+				b[i] = 0xFF
+			}
+			if serializedLength := s.Serialize(b); serializedLength != l {
+				t.Fatalf("s.Serialize(_) = %d, want %d", serializedLength, l)
+			}
+			if diff := cmp.Diff(opt.expect, b); diff != "" {
+				t.Errorf("mismatched serialized option (-want +got):\n%s", diff)
+			}
+		})
+	}
+}
+
+// TestIPv4Encode checks that ipv4.Encode correctly fills out the requested
+// fields when options are supplied.
+func TestIPv4EncodeOptions(t *testing.T) {
+	tests := []struct {
+		name           string
+		numberOfNops   int
+		encodedOptions header.IPv4Options // reply should look like this
+		wantIHL        int
+	}{
+		{
+			name:    "valid no options",
+			wantIHL: header.IPv4MinimumSize,
+		},
+		{
+			name:           "one byte options",
+			numberOfNops:   1,
+			encodedOptions: header.IPv4Options{1, 0, 0, 0},
+			wantIHL:        header.IPv4MinimumSize + 4,
+		},
+		{
+			name:           "two byte options",
+			numberOfNops:   2,
+			encodedOptions: header.IPv4Options{1, 1, 0, 0},
+			wantIHL:        header.IPv4MinimumSize + 4,
+		},
+		{
+			name:           "three byte options",
+			numberOfNops:   3,
+			encodedOptions: header.IPv4Options{1, 1, 1, 0},
+			wantIHL:        header.IPv4MinimumSize + 4,
+		},
+		{
+			name:           "four byte options",
+			numberOfNops:   4,
+			encodedOptions: header.IPv4Options{1, 1, 1, 1},
+			wantIHL:        header.IPv4MinimumSize + 4,
+		},
+		{
+			name:           "five byte options",
+			numberOfNops:   5,
+			encodedOptions: header.IPv4Options{1, 1, 1, 1, 1, 0, 0, 0},
+			wantIHL:        header.IPv4MinimumSize + 8,
+		},
+		{
+			name:         "thirty nine byte options",
+			numberOfNops: 39,
+			encodedOptions: header.IPv4Options{
+				1, 1, 1, 1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1, 1, 1, 1,
+				1, 1, 1, 1, 1, 1, 1, 0,
+			},
+			wantIHL: header.IPv4MinimumSize + 40,
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			serializeOpts := header.IPv4OptionsSerializer(make([]header.IPv4SerializableOption, test.numberOfNops))
+			for i := range serializeOpts {
+				serializeOpts[i] = &header.IPv4SerializableNOPOption{}
+			}
+			paddedOptionLength := serializeOpts.Length()
+			ipHeaderLength := int(header.IPv4MinimumSize + paddedOptionLength)
+			if ipHeaderLength > header.IPv4MaximumHeaderSize {
+				t.Fatalf("IP header length too large: got = %d, want <= %d ", ipHeaderLength, header.IPv4MaximumHeaderSize)
+			}
+			totalLen := uint16(ipHeaderLength)
+			hdr := buffer.NewPrependable(int(totalLen))
+			ip := header.IPv4(hdr.Prepend(ipHeaderLength))
+			// To check the padding works, poison the last byte of the options space.
+			if paddedOptionLength != serializeOpts.Length() {
+				ip.SetHeaderLength(uint8(ipHeaderLength))
+				ip.Options()[paddedOptionLength-1] = 0xff
+				ip.SetHeaderLength(0)
+			}
+			ip.Encode(&header.IPv4Fields{
+				Options: serializeOpts,
+			})
+			options := ip.Options()
+			wantOptions := test.encodedOptions
+			if got, want := int(ip.HeaderLength()), test.wantIHL; got != want {
+				t.Errorf("got IHL of %d, want %d", got, want)
+			}
+
+			// cmp.Diff does not consider nil slices equal to empty slices, but we do.
+			if len(wantOptions) == 0 && len(options) == 0 {
+				return
+			}
+
+			if diff := cmp.Diff(wantOptions, options); diff != "" {
+				t.Errorf("options mismatch (-want +got):\n%s", diff)
+			}
+		})
+	}
+}
diff --git a/pkg/tcpip/header/ndp_options.go b/pkg/tcpip/header/ndp_options.go
index 5d3975c56..554242f0c 100644
--- a/pkg/tcpip/header/ndp_options.go
+++ b/pkg/tcpip/header/ndp_options.go
@@ -298,7 +298,7 @@ func (b NDPOptions) Iter(check bool) (NDPOptionIterator, error) {
 	return it, nil
 }
 
-// Serialize serializes the provided list of NDP options into o.
+// Serialize serializes the provided list of NDP options into b.
 //
 // Note, b must be of sufficient size to hold all the options in s. See
 // NDPOptionsSerializer.Length for details on the getting the total size
diff --git a/pkg/tcpip/network/ip_test.go b/pkg/tcpip/network/ip_test.go
index 66d6c3f99..a314dd386 100644
--- a/pkg/tcpip/network/ip_test.go
+++ b/pkg/tcpip/network/ip_test.go
@@ -1089,7 +1089,19 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 	dataBuf := [dataLen]byte{1, 2, 3, 4}
 	data := dataBuf[:]
 
-	ipv4Options := header.IPv4Options{0, 1, 0, 1}
+	ipv4Options := header.IPv4OptionsSerializer{
+		&header.IPv4SerializableListEndOption{},
+		&header.IPv4SerializableNOPOption{},
+		&header.IPv4SerializableListEndOption{},
+		&header.IPv4SerializableNOPOption{},
+	}
+
+	expectOptions := header.IPv4Options{
+		byte(header.IPv4OptionListEndType),
+		byte(header.IPv4OptionNOPType),
+		byte(header.IPv4OptionListEndType),
+		byte(header.IPv4OptionNOPType),
+	}
 
 	ipv6FragmentExtHdrBuf := [header.IPv6FragmentExtHdrLength]byte{transportProto, 0, 62, 4, 1, 2, 3, 4}
 	ipv6FragmentExtHdr := ipv6FragmentExtHdrBuf[:]
@@ -1239,7 +1251,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 			nicAddr:      localIPv4Addr,
 			remoteAddr:   remoteIPv4Addr,
 			pktGen: func(t *testing.T, src tcpip.Address) buffer.VectorisedView {
-				ipHdrLen := header.IPv4MinimumSize + ipv4Options.SizeWithPadding()
+				ipHdrLen := int(header.IPv4MinimumSize + ipv4Options.Length())
 				totalLen := ipHdrLen + len(data)
 				hdr := buffer.NewPrependable(totalLen)
 				if n := copy(hdr.Prepend(len(data)), data); n != len(data) {
@@ -1262,7 +1274,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 
 				netHdr := pkt.NetworkHeader()
 
-				hdrLen := header.IPv4MinimumSize + len(ipv4Options)
+				hdrLen := int(header.IPv4MinimumSize + ipv4Options.Length())
 				if len(netHdr.View()) != hdrLen {
 					t.Errorf("got len(netHdr.View()) = %d, want = %d", len(netHdr.View()), hdrLen)
 				}
@@ -1272,7 +1284,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 					checker.DstAddr(remoteIPv4Addr),
 					checker.IPv4HeaderLength(hdrLen),
 					checker.IPFullLength(uint16(hdrLen+len(data))),
-					checker.IPv4Options(ipv4Options),
+					checker.IPv4Options(expectOptions),
 					checker.IPPayload(data),
 				)
 			},
@@ -1284,7 +1296,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 			nicAddr:      localIPv4Addr,
 			remoteAddr:   remoteIPv4Addr,
 			pktGen: func(t *testing.T, src tcpip.Address) buffer.VectorisedView {
-				ip := header.IPv4(make([]byte, header.IPv4MinimumSize+ipv4Options.SizeWithPadding()))
+				ip := header.IPv4(make([]byte, header.IPv4MinimumSize+ipv4Options.Length()))
 				ip.Encode(&header.IPv4Fields{
 					Protocol: transportProto,
 					TTL:      ipv4.DefaultTTL,
@@ -1303,7 +1315,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 
 				netHdr := pkt.NetworkHeader()
 
-				hdrLen := header.IPv4MinimumSize + len(ipv4Options)
+				hdrLen := int(header.IPv4MinimumSize + ipv4Options.Length())
 				if len(netHdr.View()) != hdrLen {
 					t.Errorf("got len(netHdr.View()) = %d, want = %d", len(netHdr.View()), hdrLen)
 				}
@@ -1313,7 +1325,7 @@ func TestWriteHeaderIncludedPacket(t *testing.T) {
 					checker.DstAddr(remoteIPv4Addr),
 					checker.IPv4HeaderLength(hdrLen),
 					checker.IPFullLength(uint16(hdrLen+len(data))),
-					checker.IPv4Options(ipv4Options),
+					checker.IPv4Options(expectOptions),
 					checker.IPPayload(data),
 				)
 			},
diff --git a/pkg/tcpip/network/ipv4/igmp.go b/pkg/tcpip/network/ipv4/igmp.go
index 18ccd28c3..0134fadc0 100644
--- a/pkg/tcpip/network/ipv4/igmp.go
+++ b/pkg/tcpip/network/ipv4/igmp.go
@@ -250,10 +250,10 @@ func (igmp *igmpState) writePacket(destAddress tcpip.Address, groupAddress tcpip
 		Protocol: header.IGMPProtocolNumber,
 		TTL:      header.IGMPTTL,
 		TOS:      stack.DefaultTOS,
+	}, header.IPv4OptionsSerializer{
+		&header.IPv4SerializableRouterAlertOption{},
 	})
 
-	// TODO(b/162198658): set the ROUTER_ALERT option when sending Host
-	// Membership Reports.
 	sent := igmp.ep.protocol.stack.Stats().IGMP.PacketsSent
 	if err := igmp.ep.nic.WritePacketToRemote(header.EthernetAddressFromMulticastIPv4Address(destAddress), nil /* gso */, ProtocolNumber, pkt); err != nil {
 		sent.Dropped.Increment()
diff --git a/pkg/tcpip/network/ipv4/igmp_test.go b/pkg/tcpip/network/ipv4/igmp_test.go
index d83b6c4a4..5e139377b 100644
--- a/pkg/tcpip/network/ipv4/igmp_test.go
+++ b/pkg/tcpip/network/ipv4/igmp_test.go
@@ -42,6 +42,9 @@ func validateIgmpPacket(t *testing.T, p channel.PacketInfo, remoteAddress tcpip.
 	payload := header.IPv4(stack.PayloadSince(p.Pkt.NetworkHeader()))
 	checker.IPv4(t, payload,
 		checker.DstAddr(remoteAddress),
+		// TTL for an IGMP message must be 1 as per RFC 2236 section 2.
+		checker.TTL(1),
+		checker.IPv4RouterAlert(),
 		checker.IGMP(
 			checker.IGMPType(igmpType),
 			checker.IGMPMaxRespTime(header.DecisecondToDuration(maxRespTime)),
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 354ac1e1d..4b34d0bfb 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -215,21 +215,18 @@ func (e *endpoint) NetworkProtocolNumber() tcpip.NetworkProtocolNumber {
 	return e.protocol.Number()
 }
 
-func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams) {
+func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.PacketBuffer, params stack.NetworkHeaderParams, options header.IPv4OptionsSerializer) {
 	hdrLen := header.IPv4MinimumSize
-	var opts header.IPv4Options
-	if params.Options != nil {
-		var ok bool
-		if opts, ok = params.Options.(header.IPv4Options); !ok {
-			panic(fmt.Sprintf("want IPv4Options, got %T", params.Options))
-		}
-		hdrLen += opts.SizeWithPadding()
-		if hdrLen > header.IPv4MaximumHeaderSize {
-			// Since we have no way to report an error we must either panic or create
-			// a packet which is different to what was requested. Choose panic as this
-			// would be a programming error that should be caught in testing.
-			panic(fmt.Sprintf("IPv4 Options %d bytes, Max %d", params.Options.SizeWithPadding(), header.IPv4MaximumOptionsSize))
-		}
+	var optLen int
+	if options != nil {
+		optLen = int(options.Length())
+	}
+	hdrLen += optLen
+	if hdrLen > header.IPv4MaximumHeaderSize {
+		// Since we have no way to report an error we must either panic or create
+		// a packet which is different to what was requested. Choose panic as this
+		// would be a programming error that should be caught in testing.
+		panic(fmt.Sprintf("IPv4 Options %d bytes, Max %d", optLen, header.IPv4MaximumOptionsSize))
 	}
 	ip := header.IPv4(pkt.NetworkHeader().Push(hdrLen))
 	length := uint16(pkt.Size())
@@ -245,7 +242,7 @@ func (e *endpoint) addIPHeader(srcAddr, dstAddr tcpip.Address, pkt *stack.Packet
 		Protocol:    uint8(params.Protocol),
 		SrcAddr:     srcAddr,
 		DstAddr:     dstAddr,
-		Options:     opts,
+		Options:     options,
 	})
 	ip.SetChecksum(^ip.CalculateChecksum())
 	pkt.NetworkProtocolNumber = ProtocolNumber
@@ -276,7 +273,7 @@ func (e *endpoint) handleFragments(r *stack.Route, gso *stack.GSO, networkMTU ui
 
 // WritePacket writes a packet to the given destination address and protocol.
 func (e *endpoint) WritePacket(r *stack.Route, gso *stack.GSO, params stack.NetworkHeaderParams, pkt *stack.PacketBuffer) *tcpip.Error {
-	e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params)
+	e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */)
 
 	// iptables filtering. All packets that reach here are locally
 	// generated.
@@ -364,7 +361,7 @@ func (e *endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts stack.Packe
 	}
 
 	for pkt := pkts.Front(); pkt != nil; pkt = pkt.Next() {
-		e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params)
+		e.addIPHeader(r.LocalAddress, r.RemoteAddress, pkt, params, nil /* options */)
 		networkMTU, err := calculateNetworkMTU(e.nic.MTU(), uint32(pkt.NetworkHeader().View().Size()))
 		if err != nil {
 			r.Stats().IP.OutgoingPacketErrors.IncrementBy(uint64(pkts.Len()))
diff --git a/pkg/tcpip/network/ipv4/ipv4_test.go b/pkg/tcpip/network/ipv4/ipv4_test.go
index 2d633ca23..9e2d2cfd6 100644
--- a/pkg/tcpip/network/ipv4/ipv4_test.go
+++ b/pkg/tcpip/network/ipv4/ipv4_test.go
@@ -103,105 +103,6 @@ func TestExcludeBroadcast(t *testing.T) {
 	})
 }
 
-// TestIPv4Encode checks that ipv4.Encode correctly fills out the requested
-// fields when options are supplied.
-func TestIPv4EncodeOptions(t *testing.T) {
-	tests := []struct {
-		name           string
-		options        header.IPv4Options
-		encodedOptions header.IPv4Options // reply should look like this
-		wantIHL        int
-	}{
-		{
-			name:    "valid no options",
-			wantIHL: header.IPv4MinimumSize,
-		},
-		{
-			name:           "one byte options",
-			options:        header.IPv4Options{1},
-			encodedOptions: header.IPv4Options{1, 0, 0, 0},
-			wantIHL:        header.IPv4MinimumSize + 4,
-		},
-		{
-			name:           "two byte options",
-			options:        header.IPv4Options{1, 1},
-			encodedOptions: header.IPv4Options{1, 1, 0, 0},
-			wantIHL:        header.IPv4MinimumSize + 4,
-		},
-		{
-			name:           "three byte options",
-			options:        header.IPv4Options{1, 1, 1},
-			encodedOptions: header.IPv4Options{1, 1, 1, 0},
-			wantIHL:        header.IPv4MinimumSize + 4,
-		},
-		{
-			name:           "four byte options",
-			options:        header.IPv4Options{1, 1, 1, 1},
-			encodedOptions: header.IPv4Options{1, 1, 1, 1},
-			wantIHL:        header.IPv4MinimumSize + 4,
-		},
-		{
-			name:           "five byte options",
-			options:        header.IPv4Options{1, 1, 1, 1, 1},
-			encodedOptions: header.IPv4Options{1, 1, 1, 1, 1, 0, 0, 0},
-			wantIHL:        header.IPv4MinimumSize + 8,
-		},
-		{
-			name: "thirty nine byte options",
-			options: header.IPv4Options{
-				1, 2, 3, 4, 5, 6, 7, 8,
-				9, 10, 11, 12, 13, 14, 15, 16,
-				17, 18, 19, 20, 21, 22, 23, 24,
-				25, 26, 27, 28, 29, 30, 31, 32,
-				33, 34, 35, 36, 37, 38, 39,
-			},
-			encodedOptions: header.IPv4Options{
-				1, 2, 3, 4, 5, 6, 7, 8,
-				9, 10, 11, 12, 13, 14, 15, 16,
-				17, 18, 19, 20, 21, 22, 23, 24,
-				25, 26, 27, 28, 29, 30, 31, 32,
-				33, 34, 35, 36, 37, 38, 39, 0,
-			},
-			wantIHL: header.IPv4MinimumSize + 40,
-		},
-	}
-	for _, test := range tests {
-		t.Run(test.name, func(t *testing.T) {
-			paddedOptionLength := test.options.SizeWithPadding()
-			ipHeaderLength := header.IPv4MinimumSize + paddedOptionLength
-			if ipHeaderLength > header.IPv4MaximumHeaderSize {
-				t.Fatalf("IP header length too large: got = %d, want <= %d ", ipHeaderLength, header.IPv4MaximumHeaderSize)
-			}
-			totalLen := uint16(ipHeaderLength)
-			hdr := buffer.NewPrependable(int(totalLen))
-			ip := header.IPv4(hdr.Prepend(ipHeaderLength))
-			// To check the padding works, poison the last byte of the options space.
-			if paddedOptionLength != len(test.options) {
-				ip.SetHeaderLength(uint8(ipHeaderLength))
-				ip.Options()[paddedOptionLength-1] = 0xff
-				ip.SetHeaderLength(0)
-			}
-			ip.Encode(&header.IPv4Fields{
-				Options: test.options,
-			})
-			options := ip.Options()
-			wantOptions := test.encodedOptions
-			if got, want := int(ip.HeaderLength()), test.wantIHL; got != want {
-				t.Errorf("got IHL of %d, want %d", got, want)
-			}
-
-			// cmp.Diff does not consider nil slices equal to empty slices, but we do.
-			if len(wantOptions) == 0 && len(options) == 0 {
-				return
-			}
-
-			if diff := cmp.Diff(wantOptions, options); diff != "" {
-				t.Errorf("options mismatch (-want +got):\n%s", diff)
-			}
-		})
-	}
-}
-
 func TestForwarding(t *testing.T) {
 	const (
 		nicID1         = 1
@@ -453,14 +354,6 @@ func TestIPv4Sanity(t *testing.T) {
 			replyOptions:      header.IPv4Options{1, 1, 0, 0},
 		},
 		{
-			name:              "Check option padding",
-			maxTotalLength:    ipv4.MaxTotalSize,
-			transportProtocol: uint8(header.ICMPv4ProtocolNumber),
-			TTL:               ttl,
-			options:           header.IPv4Options{1, 1, 1},
-			replyOptions:      header.IPv4Options{1, 1, 1, 0},
-		},
-		{
 			name:              "bad header length",
 			headerLength:      header.IPv4MinimumSize - 1,
 			maxTotalLength:    ipv4.MaxTotalSize,
@@ -583,7 +476,7 @@ func TestIPv4Sanity(t *testing.T) {
 				68, 7, 5, 0,
 				//  ^  ^ Linux points here which is wrong.
 				//  | Not a multiple of 4
-				1, 2, 3,
+				1, 2, 3, 0,
 			},
 			shouldFail:          true,
 			expectErrorICMP:     true,
@@ -967,8 +860,10 @@ func TestIPv4Sanity(t *testing.T) {
 				},
 			})
 
-			paddedOptionLength := test.options.SizeWithPadding()
-			ipHeaderLength := header.IPv4MinimumSize + paddedOptionLength
+			if len(test.options)%4 != 0 {
+				t.Fatalf("options must be aligned to 32 bits, invalid test options: %x (len=%d)", test.options, len(test.options))
+			}
+			ipHeaderLength := header.IPv4MinimumSize + len(test.options)
 			if ipHeaderLength > header.IPv4MaximumHeaderSize {
 				t.Fatalf("IP header length too large: got = %d, want <= %d ", ipHeaderLength, header.IPv4MaximumHeaderSize)
 			}
@@ -987,11 +882,6 @@ func TestIPv4Sanity(t *testing.T) {
 			if test.maxTotalLength < totalLen {
 				totalLen = test.maxTotalLength
 			}
-			// To check the padding works, poison the options space.
-			if paddedOptionLength != len(test.options) {
-				ip.SetHeaderLength(uint8(ipHeaderLength))
-				ip.Options()[paddedOptionLength-1] = 0x01
-			}
 
 			ip.Encode(&header.IPv4Fields{
 				TotalLength: totalLen,
@@ -999,10 +889,19 @@ func TestIPv4Sanity(t *testing.T) {
 				TTL:         test.TTL,
 				SrcAddr:     remoteIPv4Addr,
 				DstAddr:     ipv4Addr.Address,
-				Options:     test.options,
 			})
 			if test.headerLength != 0 {
 				ip.SetHeaderLength(test.headerLength)
+			} else {
+				// Set the calculated header length, since we may manually add options.
+				ip.SetHeaderLength(uint8(ipHeaderLength))
+			}
+			if len(test.options) != 0 {
+				// Copy options manually. We do not use Encode for options so we can
+				// verify malformed options with handcrafted payloads.
+				if want, got := copy(ip.Options(), test.options), len(test.options); want != got {
+					t.Fatalf("got copy(ip.Options(), test.options) = %d, want = %d", got, want)
+				}
 			}
 			ip.SetChecksum(0)
 			ipHeaderChecksum := ip.CalculateChecksum()
@@ -1107,7 +1006,7 @@ func TestIPv4Sanity(t *testing.T) {
 				}
 				// If the IP options change size then the packet will change size, so
 				// some IP header fields will need to be adjusted for the checks.
-				sizeChange := len(test.replyOptions) - paddedOptionLength
+				sizeChange := len(test.replyOptions) - len(test.options)
 
 				checker.IPv4(t, replyIPHeader,
 					checker.IPv4HeaderLength(ipHeaderLength+sizeChange),
diff --git a/pkg/tcpip/network/multicast_group_test.go b/pkg/tcpip/network/multicast_group_test.go
index 5276f1b44..95fb67986 100644
--- a/pkg/tcpip/network/multicast_group_test.go
+++ b/pkg/tcpip/network/multicast_group_test.go
@@ -90,6 +90,7 @@ func validateIGMPPacket(t *testing.T, p channel.PacketInfo, remoteAddress tcpip.
 		checker.DstAddr(remoteAddress),
 		// TTL for an IGMP message must be 1 as per RFC 2236 section 2.
 		checker.TTL(1),
+		checker.IPv4RouterAlert(),
 		checker.IGMP(
 			checker.IGMPType(header.IGMPType(igmpType)),
 			checker.IGMPMaxRespTime(header.DecisecondToDuration(maxRespTime)),
diff --git a/pkg/tcpip/stack/registration.go b/pkg/tcpip/stack/registration.go
index 236e4e4c7..b334e27c4 100644
--- a/pkg/tcpip/stack/registration.go
+++ b/pkg/tcpip/stack/registration.go
@@ -259,15 +259,6 @@ const (
 	PacketLoop
 )
 
-// NetOptions is an interface that allows us to pass network protocol specific
-// options through the Stack layer code.
-type NetOptions interface {
-	// SizeWithPadding returns the amount of memory that must be allocated to
-	// hold the options given that the value must be rounded up to the next
-	// multiple of 4 bytes.
-	SizeWithPadding() int
-}
-
 // NetworkHeaderParams are the header parameters given as input by the
 // transport endpoint to the network.
 type NetworkHeaderParams struct {
@@ -279,10 +270,6 @@ type NetworkHeaderParams struct {
 
 	// TOS refers to TypeOfService or TrafficClass field of the IP-header.
 	TOS uint8
-
-	// Options is a set of options to add to a network header (or nil).
-	// It will be protocol specific opaque information from higher layers.
-	Options NetOptions
 }
 
 // GroupAddressableEndpoint is an endpoint that supports group addressing.