Validate IGMP packets

This change also adds support for Router Alert option processing on
incoming packets, a new stat for Router Alert option, and exports
all the IP-option related stats.

Fixes #5491

PiperOrigin-RevId: 358238123

6 files changed, 348 insertions, 99 deletions

diff --git a/pkg/tcpip/network/internal/ip/stats.go b/pkg/tcpip/network/internal/ip/stats.go
index 898f8b356..5f7e60c5c 100644
--- a/pkg/tcpip/network/internal/ip/stats.go
+++ b/pkg/tcpip/network/internal/ip/stats.go
@@ -68,11 +68,17 @@ type MultiCounterIPStats struct {
 	// Output chain.
 	IPTablesOutputDropped tcpip.MultiCounterStat
 
-	// OptionTSReceived is the number of Timestamp options seen.
-	OptionTSReceived tcpip.MultiCounterStat
+	// TODO(https://gvisor.dev/issues/5529): Move the IPv4-only option stats out
 
-	// OptionRRReceived is the number of Record Route options seen.
-	OptionRRReceived tcpip.MultiCounterStat
+	// of IPStats.
+	// OptionTimestampReceived is the number of Timestamp options seen.
+	OptionTimestampReceived tcpip.MultiCounterStat
+
+	// OptionRecordRouteReceived is the number of Record Route options seen.
+	OptionRecordRouteReceived tcpip.MultiCounterStat
+
+	// OptionRouterAlertReceived is the number of Router Alert options seen.
+	OptionRouterAlertReceived tcpip.MultiCounterStat
 
 	// OptionUnknownReceived is the number of unknown IP options seen.
 	OptionUnknownReceived tcpip.MultiCounterStat
@@ -92,9 +98,10 @@ func (m *MultiCounterIPStats) Init(a, b *tcpip.IPStats) {
 	m.IPTablesPreroutingDropped.Init(a.IPTablesPreroutingDropped, b.IPTablesPreroutingDropped)
 	m.IPTablesInputDropped.Init(a.IPTablesInputDropped, b.IPTablesInputDropped)
 	m.IPTablesOutputDropped.Init(a.IPTablesOutputDropped, b.IPTablesOutputDropped)
-	m.OptionTSReceived.Init(a.OptionTSReceived, b.OptionTSReceived)
-	m.OptionRRReceived.Init(a.OptionRRReceived, b.OptionRRReceived)
+	m.OptionTimestampReceived.Init(a.OptionTimestampReceived, b.OptionTimestampReceived)
+	m.OptionRecordRouteReceived.Init(a.OptionRecordRouteReceived, b.OptionRecordRouteReceived)
+	m.OptionRouterAlertReceived.Init(a.OptionRouterAlertReceived, b.OptionRouterAlertReceived)
 	m.OptionUnknownReceived.Init(a.OptionUnknownReceived, b.OptionUnknownReceived)
 }
 
-// LINT.ThenChange(:MultiCounterIPStats, ../../tcpip.go:IPStats)
+// LINT.ThenChange(:MultiCounterIPStats, ../../../tcpip.go:IPStats)
diff --git a/pkg/tcpip/network/ipv4/icmp.go b/pkg/tcpip/network/ipv4/icmp.go
index b44304cee..bd0eabad1 100644
--- a/pkg/tcpip/network/ipv4/icmp.go
+++ b/pkg/tcpip/network/ipv4/icmp.go
@@ -214,7 +214,7 @@ func (e *endpoint) handleICMP(pkt *stack.PacketBuffer) {
 			op = &optionUsageReceive{}
 		}
 		var optProblem *header.IPv4OptParameterProblem
-		newOptions, optProblem = e.processIPOptions(pkt, opts, op)
+		newOptions, _, optProblem = e.processIPOptions(pkt, opts, op)
 		if optProblem != nil {
 			if optProblem.NeedICMP {
 				_ = e.protocol.returnError(&icmpReasonParamProblem{
diff --git a/pkg/tcpip/network/ipv4/igmp.go b/pkg/tcpip/network/ipv4/igmp.go
index 12632aceb..0a15ae897 100644
--- a/pkg/tcpip/network/ipv4/igmp.go
+++ b/pkg/tcpip/network/ipv4/igmp.go
@@ -145,10 +145,57 @@ func (igmp *igmpState) init(ep *endpoint) {
 	})
 }
 
+// Precondition: igmp.ep.mu must be locked.
+func (igmp *igmpState) isSourceIPValidLocked(src tcpip.Address, messageType header.IGMPType) bool {
+	if messageType == header.IGMPMembershipQuery {
+		// RFC 2236 does not require the IGMP implementation to check the source IP
+		// for Membership Query messages.
+		return true
+	}
+
+	// As per RFC 2236 section 10,
+	//
+	//   Ignore the Report if you cannot identify the source address of the
+	//   packet as belonging to a subnet assigned to the interface on which the
+	//   packet was received.
+	//
+	//   Ignore the Leave message if you cannot identify the source address of
+	//   the packet as belonging to a subnet assigned to the interface on which
+	//   the packet was received.
+	//
+	// Note: this rule applies to both V1 and V2 Membership Reports.
+	var isSourceIPValid bool
+	igmp.ep.mu.addressableEndpointState.ForEachPrimaryEndpoint(func(addressEndpoint stack.AddressEndpoint) bool {
+		if subnet := addressEndpoint.Subnet(); subnet.Contains(src) {
+			isSourceIPValid = true
+			return false
+		}
+		return true
+	})
+
+	return isSourceIPValid
+}
+
+// Precondition: igmp.ep.mu must be locked.
+func (igmp *igmpState) isPacketValidLocked(pkt *stack.PacketBuffer, messageType header.IGMPType, hasRouterAlertOption bool) bool {
+	// We can safely assume that the IP header is valid if we got this far.
+	iph := header.IPv4(pkt.NetworkHeader().View())
+
+	// As per RFC 2236 section 2,
+	//
+	//   All IGMP messages described in this document are sent with IP TTL 1, and
+	//   contain the IP Router Alert option [RFC 2113] in their IP header.
+	if !hasRouterAlertOption || iph.TTL() != header.IGMPTTL {
+		return false
+	}
+
+	return igmp.isSourceIPValidLocked(iph.SourceAddress(), messageType)
+}
+
 // handleIGMP handles an IGMP packet.
 //
 // Precondition: igmp.ep.mu must be locked.
-func (igmp *igmpState) handleIGMP(pkt *stack.PacketBuffer) {
+func (igmp *igmpState) handleIGMP(pkt *stack.PacketBuffer, hasRouterAlertOption bool) {
 	received := igmp.ep.stats.igmp.packetsReceived
 	headerView, ok := pkt.Data.PullUp(header.IGMPMinimumSize)
 	if !ok {
@@ -168,30 +215,38 @@ func (igmp *igmpState) handleIGMP(pkt *stack.PacketBuffer) {
 		return
 	}
 
+	isValid := func(minimumSize int) bool {
+		return len(headerView) >= minimumSize && igmp.isPacketValidLocked(pkt, h.Type(), hasRouterAlertOption)
+	}
+
 	switch h.Type() {
 	case header.IGMPMembershipQuery:
 		received.membershipQuery.Increment()
-		if len(headerView) < header.IGMPQueryMinimumSize {
+		if !isValid(header.IGMPQueryMinimumSize) {
 			received.invalid.Increment()
 			return
 		}
 		igmp.handleMembershipQuery(h.GroupAddress(), h.MaxRespTime())
 	case header.IGMPv1MembershipReport:
 		received.v1MembershipReport.Increment()
-		if len(headerView) < header.IGMPReportMinimumSize {
+		if !isValid(header.IGMPReportMinimumSize) {
 			received.invalid.Increment()
 			return
 		}
 		igmp.handleMembershipReport(h.GroupAddress())
 	case header.IGMPv2MembershipReport:
 		received.v2MembershipReport.Increment()
-		if len(headerView) < header.IGMPReportMinimumSize {
+		if !isValid(header.IGMPReportMinimumSize) {
 			received.invalid.Increment()
 			return
 		}
 		igmp.handleMembershipReport(h.GroupAddress())
 	case header.IGMPLeaveGroup:
 		received.leaveGroup.Increment()
+		if !isValid(header.IGMPLeaveMessageMinimumSize) {
+			received.invalid.Increment()
+			return
+		}
 		// As per RFC 2236 Section 6, Page 7: "IGMP messages other than Query or
 		// Report, are ignored in all states"
 
diff --git a/pkg/tcpip/network/ipv4/igmp_test.go b/pkg/tcpip/network/ipv4/igmp_test.go
index 95fd75ab7..c5f68e411 100644
--- a/pkg/tcpip/network/ipv4/igmp_test.go
+++ b/pkg/tcpip/network/ipv4/igmp_test.go
@@ -29,22 +29,25 @@ import (
 )
 
 const (
-	linkAddr      = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06")
-	addr          = tcpip.Address("\x0a\x00\x00\x01")
-	multicastAddr = tcpip.Address("\xe0\x00\x00\x03")
-	nicID         = 1
+	linkAddr            = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06")
+	stackAddr           = tcpip.Address("\x0a\x00\x00\x01")
+	remoteAddr          = tcpip.Address("\x0a\x00\x00\x02")
+	multicastAddr       = tcpip.Address("\xe0\x00\x00\x03")
+	nicID               = 1
+	defaultTTL          = 1
+	defaultPrefixLength = 24
 )
 
 // validateIgmpPacket checks that a passed PacketInfo is an IPv4 IGMP packet
 // sent to the provided address with the passed fields set. Raises a t.Error if
 // any field does not match.
-func validateIgmpPacket(t *testing.T, p channel.PacketInfo, remoteAddress tcpip.Address, igmpType header.IGMPType, maxRespTime byte, groupAddress tcpip.Address) {
+func validateIgmpPacket(t *testing.T, p channel.PacketInfo, igmpType header.IGMPType, maxRespTime byte, srcAddr, dstAddr, groupAddress tcpip.Address) {
 	t.Helper()
 
 	payload := header.IPv4(stack.PayloadSince(p.Pkt.NetworkHeader()))
 	checker.IPv4(t, payload,
-		checker.SrcAddr(addr),
-		checker.DstAddr(remoteAddress),
+		checker.SrcAddr(srcAddr),
+		checker.DstAddr(dstAddr),
 		// TTL for an IGMP message must be 1 as per RFC 2236 section 2.
 		checker.TTL(1),
 		checker.IPv4RouterAlert(),
@@ -77,20 +80,27 @@ func createStack(t *testing.T, igmpEnabled bool) (*channel.Endpoint, *stack.Stac
 	return e, s, clock
 }
 
-func createAndInjectIGMPPacket(e *channel.Endpoint, igmpType header.IGMPType, maxRespTime byte, groupAddress tcpip.Address) {
-	buf := buffer.NewView(header.IPv4MinimumSize + header.IGMPQueryMinimumSize)
+func createAndInjectIGMPPacket(e *channel.Endpoint, igmpType header.IGMPType, maxRespTime byte, ttl uint8, srcAddr, dstAddr, groupAddress tcpip.Address, hasRouterAlertOption bool) {
+	var options header.IPv4OptionsSerializer
+	if hasRouterAlertOption {
+		options = header.IPv4OptionsSerializer{
+			&header.IPv4SerializableRouterAlertOption{},
+		}
+	}
+	buf := buffer.NewView(header.IPv4MinimumSize + int(options.Length()) + header.IGMPQueryMinimumSize)
 
 	ip := header.IPv4(buf)
 	ip.Encode(&header.IPv4Fields{
 		TotalLength: uint16(len(buf)),
-		TTL:         1,
+		TTL:         ttl,
 		Protocol:    uint8(header.IGMPProtocolNumber),
-		SrcAddr:     header.IPv4Any,
-		DstAddr:     header.IPv4AllSystems,
+		SrcAddr:     srcAddr,
+		DstAddr:     dstAddr,
+		Options:     options,
 	})
 	ip.SetChecksum(^ip.CalculateChecksum())
 
-	igmp := header.IGMP(buf[header.IPv4MinimumSize:])
+	igmp := header.IGMP(ip.Payload())
 	igmp.SetType(igmpType)
 	igmp.SetMaxRespTime(maxRespTime)
 	igmp.SetGroupAddress(groupAddress)
@@ -106,8 +116,9 @@ func createAndInjectIGMPPacket(e *channel.Endpoint, igmpType header.IGMPType, ma
 // cycles.
 func TestIGMPV1Present(t *testing.T) {
 	e, s, clock := createStack(t, true)
-	if err := s.AddAddress(nicID, ipv4.ProtocolNumber, addr); err != nil {
-		t.Fatalf("AddAddress(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, addr, err)
+	addr := tcpip.AddressWithPrefix{Address: stackAddr, PrefixLen: defaultPrefixLength}
+	if err := s.AddAddressWithPrefix(nicID, ipv4.ProtocolNumber, addr); err != nil {
+		t.Fatalf("AddAddressWithPrefix(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, addr, err)
 	}
 
 	if err := s.JoinGroup(ipv4.ProtocolNumber, nicID, multicastAddr); err != nil {
@@ -124,7 +135,7 @@ func TestIGMPV1Present(t *testing.T) {
 		if got := s.Stats().IGMP.PacketsSent.V2MembershipReport.Value(); got != 1 {
 			t.Fatalf("got V2MembershipReport messages sent = %d, want = 1", got)
 		}
-		validateIgmpPacket(t, p, multicastAddr, header.IGMPv2MembershipReport, 0, multicastAddr)
+		validateIgmpPacket(t, p, header.IGMPv2MembershipReport, 0, stackAddr, multicastAddr, multicastAddr)
 	}
 	if t.Failed() {
 		t.FailNow()
@@ -134,7 +145,7 @@ func TestIGMPV1Present(t *testing.T) {
 	// membership query except the Max Response Time is set to 0, which will tell
 	// the stack that this is a router using IGMPv1. Send it to the all systems
 	// group which is the only group this host belongs to.
-	createAndInjectIGMPPacket(e, header.IGMPMembershipQuery, 0, header.IPv4AllSystems)
+	createAndInjectIGMPPacket(e, header.IGMPMembershipQuery, 0, defaultTTL, remoteAddr, stackAddr, header.IPv4AllSystems, true /* hasRouterAlertOption */)
 	if got := s.Stats().IGMP.PacketsReceived.MembershipQuery.Value(); got != 1 {
 		t.Fatalf("got Membership Queries received = %d, want = 1", got)
 	}
@@ -159,7 +170,7 @@ func TestIGMPV1Present(t *testing.T) {
 		if got := s.Stats().IGMP.PacketsSent.V1MembershipReport.Value(); got != 1 {
 			t.Fatalf("got V1MembershipReport messages sent = %d, want = 1", got)
 		}
-		validateIgmpPacket(t, p, multicastAddr, header.IGMPv1MembershipReport, 0, multicastAddr)
+		validateIgmpPacket(t, p, header.IGMPv1MembershipReport, 0, stackAddr, multicastAddr, multicastAddr)
 	}
 
 	// Cycling the interface should reset the V1 present flag.
@@ -177,7 +188,7 @@ func TestIGMPV1Present(t *testing.T) {
 		if got := s.Stats().IGMP.PacketsSent.V2MembershipReport.Value(); got != 2 {
 			t.Fatalf("got V2MembershipReport messages sent = %d, want = 2", got)
 		}
-		validateIgmpPacket(t, p, multicastAddr, header.IGMPv2MembershipReport, 0, multicastAddr)
+		validateIgmpPacket(t, p, header.IGMPv2MembershipReport, 0, stackAddr, multicastAddr, multicastAddr)
 	}
 }
 
@@ -200,8 +211,8 @@ func TestSendQueuedIGMPReports(t *testing.T) {
 
 	// The initial set of IGMP reports that were queued should be sent once an
 	// address is assigned.
-	if err := s.AddAddress(nicID, ipv4.ProtocolNumber, addr); err != nil {
-		t.Fatalf("AddAddress(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, addr, err)
+	if err := s.AddAddress(nicID, ipv4.ProtocolNumber, stackAddr); err != nil {
+		t.Fatalf("AddAddress(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, stackAddr, err)
 	}
 	if got := reportStat.Value(); got != 1 {
 		t.Errorf("got reportStat.Value() = %d, want = 1", got)
@@ -209,7 +220,7 @@ func TestSendQueuedIGMPReports(t *testing.T) {
 	if p, ok := e.Read(); !ok {
 		t.Error("expected to send an IGMP membership report")
 	} else {
-		validateIgmpPacket(t, p, multicastAddr, header.IGMPv2MembershipReport, 0, multicastAddr)
+		validateIgmpPacket(t, p, header.IGMPv2MembershipReport, 0, stackAddr, multicastAddr, multicastAddr)
 	}
 	if t.Failed() {
 		t.FailNow()
@@ -221,7 +232,7 @@ func TestSendQueuedIGMPReports(t *testing.T) {
 	if p, ok := e.Read(); !ok {
 		t.Error("expected to send an IGMP membership report")
 	} else {
-		validateIgmpPacket(t, p, multicastAddr, header.IGMPv2MembershipReport, 0, multicastAddr)
+		validateIgmpPacket(t, p, header.IGMPv2MembershipReport, 0, stackAddr, multicastAddr, multicastAddr)
 	}
 	if t.Failed() {
 		t.FailNow()
@@ -234,3 +245,139 @@ func TestSendQueuedIGMPReports(t *testing.T) {
 		t.Fatalf("got unexpected packet = %#v", p)
 	}
 }
+
+func TestIGMPPacketValidation(t *testing.T) {
+	tests := []struct {
+		name                     string
+		messageType              header.IGMPType
+		stackAddresses           []tcpip.AddressWithPrefix
+		srcAddr                  tcpip.Address
+		includeRouterAlertOption bool
+		ttl                      uint8
+		expectValidIGMP          bool
+		getMessageTypeStatValue  func(tcpip.Stats) uint64
+	}{
+		{
+			name:                     "valid",
+			messageType:              header.IGMPLeaveGroup,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  remoteAddr,
+			ttl:                      1,
+			expectValidIGMP:          true,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.LeaveGroup.Value() },
+		},
+		{
+			name:                     "bad ttl",
+			messageType:              header.IGMPv1MembershipReport,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  remoteAddr,
+			ttl:                      2,
+			expectValidIGMP:          false,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.V1MembershipReport.Value() },
+		},
+		{
+			name:                     "missing router alert ip option",
+			messageType:              header.IGMPv2MembershipReport,
+			includeRouterAlertOption: false,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  remoteAddr,
+			ttl:                      1,
+			expectValidIGMP:          false,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.V2MembershipReport.Value() },
+		},
+		{
+			name:                     "igmp leave group and src ip does not belong to nic subnet",
+			messageType:              header.IGMPLeaveGroup,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  tcpip.Address("\x0a\x00\x01\x02"),
+			ttl:                      1,
+			expectValidIGMP:          false,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.LeaveGroup.Value() },
+		},
+		{
+			name:                     "igmp query and src ip does not belong to nic subnet",
+			messageType:              header.IGMPMembershipQuery,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  tcpip.Address("\x0a\x00\x01\x02"),
+			ttl:                      1,
+			expectValidIGMP:          true,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.MembershipQuery.Value() },
+		},
+		{
+			name:                     "igmp report v1 and src ip does not belong to nic subnet",
+			messageType:              header.IGMPv1MembershipReport,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  tcpip.Address("\x0a\x00\x01\x02"),
+			ttl:                      1,
+			expectValidIGMP:          false,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.V1MembershipReport.Value() },
+		},
+		{
+			name:                     "igmp report v2 and src ip does not belong to nic subnet",
+			messageType:              header.IGMPv2MembershipReport,
+			includeRouterAlertOption: true,
+			stackAddresses:           []tcpip.AddressWithPrefix{{Address: stackAddr, PrefixLen: 24}},
+			srcAddr:                  tcpip.Address("\x0a\x00\x01\x02"),
+			ttl:                      1,
+			expectValidIGMP:          false,
+			getMessageTypeStatValue:  func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.V2MembershipReport.Value() },
+		},
+		{
+			name:                     "src ip belongs to the subnet of the nic's second address",
+			messageType:              header.IGMPv2MembershipReport,
+			includeRouterAlertOption: true,
+			stackAddresses: []tcpip.AddressWithPrefix{
+				{Address: tcpip.Address("\x0a\x00\x0f\x01"), PrefixLen: 24},
+				{Address: stackAddr, PrefixLen: 24},
+			},
+			srcAddr:                 remoteAddr,
+			ttl:                     1,
+			expectValidIGMP:         true,
+			getMessageTypeStatValue: func(stats tcpip.Stats) uint64 { return stats.IGMP.PacketsReceived.V2MembershipReport.Value() },
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			e, s, _ := createStack(t, true)
+			for _, address := range test.stackAddresses {
+				if err := s.AddAddressWithPrefix(nicID, ipv4.ProtocolNumber, address); err != nil {
+					t.Fatalf("AddAddressWithPrefix(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, address, err)
+				}
+			}
+			stats := s.Stats()
+			// Verify that every relevant stats is zero'd before we send a packet.
+			if got := test.getMessageTypeStatValue(s.Stats()); got != 0 {
+				t.Errorf("got test.getMessageTypeStatValue(s.Stats()) = %d, want = 0", got)
+			}
+			if got := stats.IGMP.PacketsReceived.Invalid.Value(); got != 0 {
+				t.Errorf("got stats.IGMP.PacketsReceived.Invalid.Value() = %d, want = 0", got)
+			}
+			if got := stats.IP.PacketsDelivered.Value(); got != 0 {
+				t.Fatalf("got stats.IP.PacketsDelivered.Value() = %d, want = 0", got)
+			}
+			createAndInjectIGMPPacket(e, test.messageType, 0, test.ttl, test.srcAddr, header.IPv4AllSystems, header.IPv4AllSystems, test.includeRouterAlertOption)
+			// We always expect the packet to pass IP validation.
+			if got := stats.IP.PacketsDelivered.Value(); got != 1 {
+				t.Fatalf("got stats.IP.PacketsDelivered.Value() = %d, want = 1", got)
+			}
+			// Even when the IGMP-specific validation checks fail, we expect the
+			// corresponding IGMP counter to be incremented.
+			if got := test.getMessageTypeStatValue(s.Stats()); got != 1 {
+				t.Errorf("got test.getMessageTypeStatValue(s.Stats()) = %d, want = 1", got)
+			}
+			var expectedInvalidCount uint64
+			if !test.expectValidIGMP {
+				expectedInvalidCount = 1
+			}
+			if got := stats.IGMP.PacketsReceived.Invalid.Value(); got != expectedInvalidCount {
+				t.Errorf("got stats.IGMP.PacketsReceived.Invalid.Value() = %d, want = %d", got, expectedInvalidCount)
+			}
+		})
+	}
+}
diff --git a/pkg/tcpip/network/ipv4/ipv4.go b/pkg/tcpip/network/ipv4/ipv4.go
index 250e4846a..4a429ea6c 100644
--- a/pkg/tcpip/network/ipv4/ipv4.go
+++ b/pkg/tcpip/network/ipv4/ipv4.go
@@ -562,7 +562,7 @@ func (e *endpoint) forwardPacket(pkt *stack.PacketBuffer) tcpip.Error {
 	}
 
 	if opts := h.Options(); len(opts) != 0 {
-		newOpts, optProblem := e.processIPOptions(pkt, opts, &optionUsageForward{})
+		newOpts, _, optProblem := e.processIPOptions(pkt, opts, &optionUsageForward{})
 		if optProblem != nil {
 			if optProblem.NeedICMP {
 				_ = e.protocol.returnError(&icmpReasonParamProblem{
@@ -776,7 +776,7 @@ func (e *endpoint) handlePacket(pkt *stack.PacketBuffer) {
 			// If there are options we need to check them before we do assembly
 			// or we could be assembling errant packets. However we do not change the
 			// options as that could lead to double processing later.
-			if _, optProblem := e.processIPOptions(pkt, opts, &optionUsageVerify{}); optProblem != nil {
+			if _, _, optProblem := e.processIPOptions(pkt, opts, &optionUsageVerify{}); optProblem != nil {
 				if optProblem.NeedICMP {
 					_ = e.protocol.returnError(&icmpReasonParamProblem{
 						pointer: optProblem.Pointer,
@@ -846,8 +846,9 @@ func (e *endpoint) handlePacket(pkt *stack.PacketBuffer) {
 		return
 	}
 	// ICMP handles options itself but do it here for all remaining destinations.
+	var hasRouterAlertOption bool
 	if opts := h.Options(); len(opts) != 0 {
-		newOpts, optProblem := e.processIPOptions(pkt, opts, &optionUsageReceive{})
+		newOpts, processedOpts, optProblem := e.processIPOptions(pkt, opts, &optionUsageReceive{})
 		if optProblem != nil {
 			if optProblem.NeedICMP {
 				_ = e.protocol.returnError(&icmpReasonParamProblem{
@@ -858,6 +859,7 @@ func (e *endpoint) handlePacket(pkt *stack.PacketBuffer) {
 			}
 			return
 		}
+		hasRouterAlertOption = processedOpts.routerAlert
 		copied := copy(opts, newOpts)
 		if copied != len(newOpts) {
 			panic(fmt.Sprintf("copied %d bytes of new options, expected %d bytes", copied, len(newOpts)))
@@ -869,7 +871,7 @@ func (e *endpoint) handlePacket(pkt *stack.PacketBuffer) {
 	}
 	if p == header.IGMPProtocolNumber {
 		e.mu.Lock()
-		e.mu.igmp.handleIGMP(pkt)
+		e.mu.igmp.handleIGMP(pkt, hasRouterAlertOption)
 		e.mu.Unlock()
 		return
 	}
@@ -1291,9 +1293,12 @@ type optionActions struct {
 	// timestamp controls what to do with a Timestamp option.
 	timestamp optionAction
 
-	// recordroute controls what to do with a Record Route option.
+	// recordRoute controls what to do with a Record Route option.
 	recordRoute optionAction
 
+	// routerAlert controls what to do with a Router Alert option.
+	routerAlert optionAction
+
 	// unknown controls what to do with an unknown option.
 	unknown optionAction
 }
@@ -1314,6 +1319,7 @@ func (*optionUsageVerify) actions() optionActions {
 	return optionActions{
 		timestamp:   optionVerify,
 		recordRoute: optionVerify,
+		routerAlert: optionVerify,
 		unknown:     optionRemove,
 	}
 }
@@ -1327,6 +1333,7 @@ func (*optionUsageReceive) actions() optionActions {
 	return optionActions{
 		timestamp:   optionProcess,
 		recordRoute: optionProcess,
+		routerAlert: optionVerify,
 		unknown:     optionPass,
 	}
 }
@@ -1341,6 +1348,7 @@ func (*optionUsageForward) actions() optionActions {
 	return optionActions{
 		timestamp:   optionProcess,
 		recordRoute: optionProcess,
+		routerAlert: optionVerify,
 		unknown:     optionPass,
 	}
 }
@@ -1354,6 +1362,7 @@ func (*optionUsageEcho) actions() optionActions {
 	return optionActions{
 		timestamp:   optionProcess,
 		recordRoute: optionProcess,
+		routerAlert: optionVerify,
 		unknown:     optionRemove,
 	}
 }
@@ -1551,45 +1560,64 @@ func handleRecordRoute(rrOpt header.IPv4OptionRecordRoute, localAddress tcpip.Ad
 	return nil
 }
 
+// handleRouterAlert performs sanity checks on a Router Alert option.
+func handleRouterAlert(raOpt header.IPv4OptionRouterAlert) *header.IPv4OptParameterProblem {
+	// Only the zero value is acceptable, as per RFC 2113, section 2.1:
+	//   Value:  A two octet code with the following values:
+	//     0 - Router shall examine packet
+	//     1-65535 - Reserved
+	if raOpt.Value() != header.IPv4OptionRouterAlertValue {
+		return &header.IPv4OptParameterProblem{
+			Pointer:  header.IPv4OptionRouterAlertValueOffset,
+			NeedICMP: true,
+		}
+	}
+	return nil
+}
+
+type optionTracker struct {
+	timestamp   bool
+	recordRoute bool
+	routerAlert bool
+}
+
 // processIPOptions parses the IPv4 options and produces a new set of options
 // suitable for use in the next step of packet processing as informed by usage.
 // The original will not be touched.
 //
-// Returns
-// - The location of an error if there was one (or 0 if no error)
-// - If there is an error, information as to what it was was.
-// - The replacement option set.
-func (e *endpoint) processIPOptions(pkt *stack.PacketBuffer, orig header.IPv4Options, usage optionsUsage) (header.IPv4Options, *header.IPv4OptParameterProblem) {
+// If there were no errors during parsing, the new set of options is returned as
+// a new buffer.
+func (e *endpoint) processIPOptions(pkt *stack.PacketBuffer, orig header.IPv4Options, usage optionsUsage) (header.IPv4Options, optionTracker, *header.IPv4OptParameterProblem) {
 	stats := e.stats.ip
 	opts := header.IPv4Options(orig)
 	optIter := opts.MakeIterator()
 
-	// Each option other than NOP must only appear (RFC 791 section 3.1, at the
-	// definition of every type). Keep track of each of the possible types in
-	// the 8 bit 'type' field.
+	// Except NOP, each option must only appear at most once (RFC 791 section 3.1,
+	// at the definition of every type).
+	// Keep track of each option we find to enable duplicate option detection.
 	var seenOptions [math.MaxUint8 + 1]bool
 
-	// TODO(gvisor.dev/issue/4586):
-	// This will need tweaking  when we start really forwarding packets
-	// as we may need to get two addresses, for rx and tx interfaces.
-	// We will also have to take usage into account.
+	// TODO(https://gvisor.dev/issue/4586): This will need tweaking when we start
+	// really forwarding packets as we may need to get two addresses, for rx and
+	// tx interfaces. We will also have to take usage into account.
 	prefixedAddress, ok := e.protocol.stack.GetMainNICAddress(e.nic.ID(), ProtocolNumber)
 	localAddress := prefixedAddress.Address
 	if !ok {
 		h := header.IPv4(pkt.NetworkHeader().View())
 		dstAddr := h.DestinationAddress()
 		if pkt.NetworkPacketInfo.LocalAddressBroadcast || header.IsV4MulticastAddress(dstAddr) {
-			return nil, &header.IPv4OptParameterProblem{
+			return nil, optionTracker{}, &header.IPv4OptParameterProblem{
 				NeedICMP: false,
 			}
 		}
 		localAddress = dstAddr
 	}
 
+	var optionsProcessed optionTracker
 	for {
 		option, done, optProblem := optIter.Next()
 		if done || optProblem != nil {
-			return optIter.Finalize(), optProblem
+			return optIter.Finalize(), optionsProcessed, optProblem
 		}
 		optType := option.Type()
 		if optType == header.IPv4OptionNOPType {
@@ -1598,53 +1626,61 @@ func (e *endpoint) processIPOptions(pkt *stack.PacketBuffer, orig header.IPv4Opt
 		}
 		if optType == header.IPv4OptionListEndType {
 			optIter.PushNOPOrEnd(optType)
-			return optIter.Finalize(), nil
+			return optIter.Finalize(), optionsProcessed, nil
 		}
 
 		// check for repeating options (multiple NOPs are OK)
 		if seenOptions[optType] {
-			return nil, &header.IPv4OptParameterProblem{
+			return nil, optionTracker{}, &header.IPv4OptParameterProblem{
 				Pointer:  optIter.ErrCursor,
 				NeedICMP: true,
 			}
 		}
 		seenOptions[optType] = true
 
-		optLen := int(option.Size())
-		switch option := option.(type) {
-		case *header.IPv4OptionTimestamp:
-			stats.OptionTSReceived.Increment()
-			if usage.actions().timestamp != optionRemove {
-				clock := e.protocol.stack.Clock()
-				newBuffer := optIter.RemainingBuffer()[:len(*option)]
-				_ = copy(newBuffer, option.Contents())
-				if optProblem := handleTimestamp(header.IPv4OptionTimestamp(newBuffer), localAddress, clock, usage); optProblem != nil {
-					optProblem.Pointer += optIter.ErrCursor
-					return nil, optProblem
+		optLen, optProblem := func() (int, *header.IPv4OptParameterProblem) {
+			switch option := option.(type) {
+			case *header.IPv4OptionTimestamp:
+				stats.OptionTimestampReceived.Increment()
+				optionsProcessed.timestamp = true
+				if usage.actions().timestamp != optionRemove {
+					clock := e.protocol.stack.Clock()
+					newBuffer := optIter.InitReplacement(option)
+					optProblem := handleTimestamp(header.IPv4OptionTimestamp(newBuffer), localAddress, clock, usage)
+					return len(newBuffer), optProblem
 				}
-				optIter.ConsumeBuffer(optLen)
-			}
 
-		case *header.IPv4OptionRecordRoute:
-			stats.OptionRRReceived.Increment()
-			if usage.actions().recordRoute != optionRemove {
-				newBuffer := optIter.RemainingBuffer()[:len(*option)]
-				_ = copy(newBuffer, option.Contents())
-				if optProblem := handleRecordRoute(header.IPv4OptionRecordRoute(newBuffer), localAddress, usage); optProblem != nil {
-					optProblem.Pointer += optIter.ErrCursor
-					return nil, optProblem
+			case *header.IPv4OptionRecordRoute:
+				stats.OptionRecordRouteReceived.Increment()
+				optionsProcessed.recordRoute = true
+				if usage.actions().recordRoute != optionRemove {
+					newBuffer := optIter.InitReplacement(option)
+					optProblem := handleRecordRoute(header.IPv4OptionRecordRoute(newBuffer), localAddress, usage)
+					return len(newBuffer), optProblem
 				}
-				optIter.ConsumeBuffer(optLen)
-			}
 
-		default:
-			stats.OptionUnknownReceived.Increment()
-			if usage.actions().unknown == optionPass {
-				newBuffer := optIter.RemainingBuffer()[:optLen]
-				// Arguments already heavily checked.. ignore result.
-				_ = copy(newBuffer, option.Contents())
-				optIter.ConsumeBuffer(optLen)
+			case *header.IPv4OptionRouterAlert:
+				stats.OptionRouterAlertReceived.Increment()
+				optionsProcessed.routerAlert = true
+				if usage.actions().routerAlert != optionRemove {
+					newBuffer := optIter.InitReplacement(option)
+					optProblem := handleRouterAlert(header.IPv4OptionRouterAlert(newBuffer))
+					return len(newBuffer), optProblem
+				}
+
+			default:
+				stats.OptionUnknownReceived.Increment()
+				if usage.actions().unknown == optionPass {
+					return len(optIter.InitReplacement(option)), nil
+				}
 			}
+			return 0, nil
+		}()
+
+		if optProblem != nil {
+			optProblem.Pointer += optIter.ErrCursor
+			return nil, optionTracker{}, optProblem
 		}
+		optIter.ConsumeBuffer(optLen)
 	}
 }
diff --git a/pkg/tcpip/network/multicast_group_test.go b/pkg/tcpip/network/multicast_group_test.go
index 0f4f0e1e1..03b7ecffb 100644
--- a/pkg/tcpip/network/multicast_group_test.go
+++ b/pkg/tcpip/network/multicast_group_test.go
@@ -35,8 +35,9 @@ import (
 const (
 	linkAddr = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06")
 
-	ipv4Addr = tcpip.Address("\x0a\x00\x00\x01")
-	ipv6Addr = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
+	stackIPv4Addr           = tcpip.Address("\x0a\x00\x00\x01")
+	defaultIPv4PrefixLength = 24
+	ipv6Addr                = tcpip.Address("\xfe\x80\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01")
 
 	ipv4MulticastAddr1 = tcpip.Address("\xe0\x00\x00\x03")
 	ipv4MulticastAddr2 = tcpip.Address("\xe0\x00\x00\x04")
@@ -99,7 +100,7 @@ func validateIGMPPacket(t *testing.T, p channel.PacketInfo, remoteAddress tcpip.
 
 	payload := header.IPv4(stack.PayloadSince(p.Pkt.NetworkHeader()))
 	checker.IPv4(t, payload,
-		checker.SrcAddr(ipv4Addr),
+		checker.SrcAddr(stackIPv4Addr),
 		checker.DstAddr(remoteAddress),
 		// TTL for an IGMP message must be 1 as per RFC 2236 section 2.
 		checker.TTL(1),
@@ -145,8 +146,12 @@ func createStackWithLinkEndpoint(t *testing.T, v4, mgpEnabled bool, e stack.Link
 	if err := s.CreateNIC(nicID, e); err != nil {
 		t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
 	}
-	if err := s.AddAddress(nicID, ipv4.ProtocolNumber, ipv4Addr); err != nil {
-		t.Fatalf("AddAddress(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, ipv4Addr, err)
+	addr := tcpip.AddressWithPrefix{
+		Address:   stackIPv4Addr,
+		PrefixLen: defaultIPv4PrefixLength,
+	}
+	if err := s.AddAddressWithPrefix(nicID, ipv4.ProtocolNumber, addr); err != nil {
+		t.Fatalf("AddAddressWithPrefix(%d, %d, %s): %s", nicID, ipv4.ProtocolNumber, addr, err)
 	}
 	if err := s.AddAddress(nicID, ipv6.ProtocolNumber, ipv6Addr); err != nil {
 		t.Fatalf("AddAddress(%d, %d, %s): %s", nicID, ipv6.ProtocolNumber, ipv6Addr, err)
@@ -202,24 +207,23 @@ func checkInitialIPv6Groups(t *testing.T, e *channel.Endpoint, s *stack.Stack, c
 
 // createAndInjectIGMPPacket creates and injects an IGMP packet with the
 // specified fields.
-//
-// Note, the router alert option is not included in this packet.
-//
-// TODO(b/162198658): set the router alert option.
 func createAndInjectIGMPPacket(e *channel.Endpoint, igmpType byte, maxRespTime byte, groupAddress tcpip.Address) {
-	buf := buffer.NewView(header.IPv4MinimumSize + header.IGMPQueryMinimumSize)
-
+	options := header.IPv4OptionsSerializer{
+		&header.IPv4SerializableRouterAlertOption{},
+	}
+	buf := buffer.NewView(header.IPv4MinimumSize + int(options.Length()) + header.IGMPQueryMinimumSize)
 	ip := header.IPv4(buf)
 	ip.Encode(&header.IPv4Fields{
 		TotalLength: uint16(len(buf)),
 		TTL:         header.IGMPTTL,
 		Protocol:    uint8(header.IGMPProtocolNumber),
-		SrcAddr:     header.IPv4Any,
+		SrcAddr:     remoteIPv4Addr,
 		DstAddr:     header.IPv4AllSystems,
+		Options:     options,
 	})
 	ip.SetChecksum(^ip.CalculateChecksum())
 
-	igmp := header.IGMP(buf[header.IPv4MinimumSize:])
+	igmp := header.IGMP(ip.Payload())
 	igmp.SetType(header.IGMPType(igmpType))
 	igmp.SetMaxRespTime(maxRespTime)
 	igmp.SetGroupAddress(groupAddress)