Use multicast Ethernet address for multicast NDP

As per RFC 2464 section 7, an IPv6 packet with a multicast destination
address is transmitted to the mapped Ethernet multicast address.

Test:
- ipv6.TestLinkResolution
- stack_test.TestDADResolve
- stack_test.TestRouterSolicitation
PiperOrigin-RevId: 292610529

pkg/tcpip/header/ipv6_test.go

@@ -17,6 +17,7 @@ package header_test
 import (
 	"bytes"
 	"crypto/sha256"
+	"fmt"
 	"testing"
 
 	"github.com/google/go-cmp/cmp"
@@ -300,3 +301,31 @@ func TestScopeForIPv6Address(t *testing.T) {
 		})
 	}
 }
+
+func TestSolicitedNodeAddr(t *testing.T) {
+	tests := []struct {
+		addr tcpip.Address
+		want tcpip.Address
+	}{
+		{
+			addr: "\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\x0d\x0e\x0f\xa0",
+			want: "\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xff\x0e\x0f\xa0",
+		},
+		{
+			addr: "\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\xdd\x0e\x0f\xa0",
+			want: "\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xff\x0e\x0f\xa0",
+		},
+		{
+			addr: "\x01\x02\x03\x04\x05\x06\x07\x08\x09\x0a\x0b\x0c\xdd\x01\x02\x03",
+			want: "\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xff\x01\x02\x03",
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(fmt.Sprintf("%s", test.addr), func(t *testing.T) {
+			if got := header.SolicitedNodeAddr(test.addr); got != test.want {
+				t.Fatalf("got header.SolicitedNodeAddr(%s) = %s, want = %s", test.addr, got, test.want)
+			}
+		})
+	}
+}

pkg/tcpip/link/channel/channel.go

@@ -30,15 +30,16 @@ type PacketInfo struct {
 	Pkt   tcpip.PacketBuffer
 	Proto tcpip.NetworkProtocolNumber
 	GSO   *stack.GSO
+	Route stack.Route
 }
 
 // Endpoint is link layer endpoint that stores outbound packets in a channel
 // and allows injection of inbound packets.
 type Endpoint struct {
-	dispatcher stack.NetworkDispatcher
-	mtu        uint32
-	linkAddr   tcpip.LinkAddress
-	GSO        bool
+	dispatcher         stack.NetworkDispatcher
+	mtu                uint32
+	linkAddr           tcpip.LinkAddress
+	LinkEPCapabilities stack.LinkEndpointCapabilities
 
 	// c is where outbound packets are queued.
 	c chan PacketInfo
@@ -122,11 +123,7 @@ func (e *Endpoint) MTU() uint32 {
 
 // Capabilities implements stack.LinkEndpoint.Capabilities.
 func (e *Endpoint) Capabilities() stack.LinkEndpointCapabilities {
-	caps := stack.LinkEndpointCapabilities(0)
-	if e.GSO {
-		caps |= stack.CapabilityHardwareGSO
-	}
-	return caps
+	return e.LinkEPCapabilities
 }
 
 // GSOMaxSize returns the maximum GSO packet size.
@@ -146,11 +143,16 @@ func (e *Endpoint) LinkAddress() tcpip.LinkAddress {
 }
 
 // WritePacket stores outbound packets into the channel.
-func (e *Endpoint) WritePacket(_ *stack.Route, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer) *tcpip.Error {
+func (e *Endpoint) WritePacket(r *stack.Route, gso *stack.GSO, protocol tcpip.NetworkProtocolNumber, pkt tcpip.PacketBuffer) *tcpip.Error {
+	// Clone r then release its resource so we only get the relevant fields from
+	// stack.Route without holding a reference to a NIC's endpoint.
+	route := r.Clone()
+	route.Release()
 	p := PacketInfo{
 		Pkt:   pkt,
 		Proto: protocol,
 		GSO:   gso,
+		Route: route,
 	}
 
 	select {
@@ -162,7 +164,11 @@ func (e *Endpoint) WritePacket(_ *stack.Route, gso *stack.GSO, protocol tcpip.Ne
 }
 
 // WritePackets stores outbound packets into the channel.
-func (e *Endpoint) WritePackets(_ *stack.Route, gso *stack.GSO, pkts []tcpip.PacketBuffer, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
+func (e *Endpoint) WritePackets(r *stack.Route, gso *stack.GSO, pkts []tcpip.PacketBuffer, protocol tcpip.NetworkProtocolNumber) (int, *tcpip.Error) {
+	// Clone r then release its resource so we only get the relevant fields from
+	// stack.Route without holding a reference to a NIC's endpoint.
+	route := r.Clone()
+	route.Release()
 	payloadView := pkts[0].Data.ToView()
 	n := 0
 packetLoop:
@@ -176,6 +182,7 @@ packetLoop:
 			},
 			Proto: protocol,
 			GSO:   gso,
+			Route: route,
 		}
 
 		select {

pkg/tcpip/network/ipv6/icmp.go

@@ -408,10 +408,14 @@ func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 // LinkAddressRequest implements stack.LinkAddressResolver.
 func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.LinkEndpoint) *tcpip.Error {
 	snaddr := header.SolicitedNodeAddr(addr)
+
+	// TODO(b/148672031): Use stack.FindRoute instead of manually creating the
+	// route here. Note, we would need the nicID to do this properly so the right
+	// NIC (associated to linkEP) is used to send the NDP NS message.
 	r := &stack.Route{
 		LocalAddress:      localAddr,
 		RemoteAddress:     snaddr,
-		RemoteLinkAddress: broadcastMAC,
+		RemoteLinkAddress: header.EthernetAddressFromMulticastIPv6Address(snaddr),
 	}
 	hdr := buffer.NewPrependable(int(linkEP.MaxHeaderLength()) + header.IPv6MinimumSize + header.ICMPv6NeighborAdvertSize)
 	pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6NeighborAdvertSize))

pkg/tcpip/network/ipv6/icmp_test.go

@@ -270,8 +270,9 @@ func (c *testContext) cleanup() {
 }
 
 type routeArgs struct {
-	src, dst *channel.Endpoint
-	typ      header.ICMPv6Type
+	src, dst       *channel.Endpoint
+	typ            header.ICMPv6Type
+	remoteLinkAddr tcpip.LinkAddress
 }
 
 func routeICMPv6Packet(t *testing.T, args routeArgs, fn func(*testing.T, header.ICMPv6)) {
@@ -292,6 +293,11 @@ func routeICMPv6Packet(t *testing.T, args routeArgs, fn func(*testing.T, header.
 		t.Errorf("unexpected protocol number %d", pi.Proto)
 		return
 	}
+
+	if len(args.remoteLinkAddr) != 0 && args.remoteLinkAddr != pi.Route.RemoteLinkAddress {
+		t.Errorf("got remote link address = %s, want = %s", pi.Route.RemoteLinkAddress, args.remoteLinkAddr)
+	}
+
 	ipv6 := header.IPv6(pi.Pkt.Header.View())
 	transProto := tcpip.TransportProtocolNumber(ipv6.NextHeader())
 	if transProto != header.ICMPv6ProtocolNumber {
@@ -339,7 +345,7 @@ func TestLinkResolution(t *testing.T) {
 				t.Fatalf("ep.Write(_) = _, <non-nil>, %s, want = _, <non-nil>, tcpip.ErrNoLinkAddress", err)
 			}
 			for _, args := range []routeArgs{
-				{src: c.linkEP0, dst: c.linkEP1, typ: header.ICMPv6NeighborSolicit},
+				{src: c.linkEP0, dst: c.linkEP1, typ: header.ICMPv6NeighborSolicit, remoteLinkAddr: header.EthernetAddressFromMulticastIPv6Address(header.SolicitedNodeAddr(lladdr1))},
 				{src: c.linkEP1, dst: c.linkEP0, typ: header.ICMPv6NeighborAdvert},
 			} {
 				routeICMPv6Packet(t, args, func(t *testing.T, icmpv6 header.ICMPv6) {

pkg/tcpip/stack/ndp.go

@@ -538,6 +538,14 @@ func (ndp *ndpState) sendDADPacket(addr tcpip.Address) *tcpip.Error {
 	r := makeRoute(header.IPv6ProtocolNumber, header.IPv6Any, snmc, ndp.nic.linkEP.LinkAddress(), ref, false, false)
 	defer r.Release()
 
+	// Route should resolve immediately since snmc is a multicast address so a
+	// remote link address can be calculated without a resolution process.
+	if c, err := r.Resolve(nil); err != nil {
+		log.Fatalf("ndp: error when resolving route to send NDP NS for DAD (%s -> %s on NIC(%d)): %s", header.IPv6Any, snmc, ndp.nic.ID(), err)
+	} else if c != nil {
+		log.Fatalf("ndp: route resolution not immediate for route to send NDP NS for DAD (%s -> %s on NIC(%d))", header.IPv6Any, snmc, ndp.nic.ID())
+	}
+
 	hdr := buffer.NewPrependable(int(r.MaxHeaderLength()) + header.ICMPv6NeighborSolicitMinimumSize)
 	pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6NeighborSolicitMinimumSize))
 	pkt.SetType(header.ICMPv6NeighborSolicit)
@@ -1197,6 +1205,15 @@ func (ndp *ndpState) startSolicitingRouters() {
 		r := makeRoute(header.IPv6ProtocolNumber, header.IPv6Any, header.IPv6AllRoutersMulticastAddress, ndp.nic.linkEP.LinkAddress(), ref, false, false)
 		defer r.Release()
 
+		// Route should resolve immediately since
+		// header.IPv6AllRoutersMulticastAddress is a multicast address so a
+		// remote link address can be calculated without a resolution process.
+		if c, err := r.Resolve(nil); err != nil {
+			log.Fatalf("ndp: error when resolving route to send NDP RS (%s -> %s on NIC(%d)): %s", header.IPv6Any, header.IPv6AllRoutersMulticastAddress, ndp.nic.ID(), err)
+		} else if c != nil {
+			log.Fatalf("ndp: route resolution not immediate for route to send NDP RS (%s -> %s on NIC(%d))", header.IPv6Any, header.IPv6AllRoutersMulticastAddress, ndp.nic.ID())
+		}
+
 		payloadSize := header.ICMPv6HeaderSize + header.NDPRSMinimumSize
 		hdr := buffer.NewPrependable(header.IPv6MinimumSize + payloadSize)
 		pkt := header.ICMPv6(hdr.Prepend(payloadSize))

pkg/tcpip/stack/ndp_test.go

@@ -336,6 +336,7 @@ func TestDADResolve(t *testing.T) {
 			opts.NDPConfigs.DupAddrDetectTransmits = test.dupAddrDetectTransmits
 
 			e := channel.New(int(test.dupAddrDetectTransmits), 1280, linkAddr1)
+			e.LinkEPCapabilities |= stack.CapabilityResolutionRequired
 			s := stack.New(opts)
 			if err := s.CreateNIC(nicID, e); err != nil {
 				t.Fatalf("CreateNIC(%d, _) = %s", nicID, err)
@@ -413,6 +414,12 @@ func TestDADResolve(t *testing.T) {
 					t.Fatalf("got Proto = %d, want = %d", p.Proto, header.IPv6ProtocolNumber)
 				}
 
+				// Make sure the right remote link address is used.
+				snmc := header.SolicitedNodeAddr(addr1)
+				if want := header.EthernetAddressFromMulticastIPv6Address(snmc); p.Route.RemoteLinkAddress != want {
+					t.Errorf("got remote link address = %s, want = %s", p.Route.RemoteLinkAddress, want)
+				}
+
 				// Check NDP NS packet.
 				//
 				// As per RFC 4861 section 4.3, a possible option is the Source Link
@@ -420,7 +427,7 @@ func TestDADResolve(t *testing.T) {
 				// address of the packet is the unspecified address.
 				checker.IPv6(t, p.Pkt.Header.View().ToVectorisedView().First(),
 					checker.SrcAddr(header.IPv6Any),
-					checker.DstAddr(header.SolicitedNodeAddr(addr1)),
+					checker.DstAddr(snmc),
 					checker.TTL(header.NDPHopLimit),
 					checker.NDPNS(
 						checker.NDPNSTargetAddress(addr1),
@@ -3292,6 +3299,7 @@ func TestRouterSolicitation(t *testing.T) {
 			t.Run(test.name, func(t *testing.T) {
 				t.Parallel()
 				e := channel.New(int(test.maxRtrSolicit), 1280, linkAddr1)
+				e.LinkEPCapabilities |= stack.CapabilityResolutionRequired
 				waitForPkt := func(timeout time.Duration) {
 					t.Helper()
 					ctx, _ := context.WithTimeout(context.Background(), timeout)
@@ -3304,6 +3312,12 @@ func TestRouterSolicitation(t *testing.T) {
 					if p.Proto != header.IPv6ProtocolNumber {
 						t.Fatalf("got Proto = %d, want = %d", p.Proto, header.IPv6ProtocolNumber)
 					}
+
+					// Make sure the right remote link address is used.
+					if want := header.EthernetAddressFromMulticastIPv6Address(header.IPv6AllRoutersMulticastAddress); p.Route.RemoteLinkAddress != want {
+						t.Errorf("got remote link address = %s, want = %s", p.Route.RemoteLinkAddress, want)
+					}
+
 					checker.IPv6(t,
 						p.Pkt.Header.View(),
 						checker.SrcAddr(header.IPv6Any),

pkg/tcpip/stack/route.go

@@ -225,7 +225,9 @@ func (r *Route) Release() {
 // Clone Clone a route such that the original one can be released and the new
 // one will remain valid.
 func (r *Route) Clone() Route {
-	r.ref.incRef()
+	if r.ref != nil {
+		r.ref.incRef()
+	}
 	return *r
 }
 

pkg/tcpip/transport/tcp/testing/context/context.go

@@ -1082,7 +1082,11 @@ func (c *Context) SACKEnabled() bool {
 
 // SetGSOEnabled enables or disables generic segmentation offload.
 func (c *Context) SetGSOEnabled(enable bool) {
-	c.linkEP.GSO = enable
+	if enable {
+		c.linkEP.LinkEPCapabilities |= stack.CapabilityHardwareGSO
+	} else {
+		c.linkEP.LinkEPCapabilities &^= stack.CapabilityHardwareGSO
+	}
 }
 
 // MSSWithoutOptions returns the value for the MSS used by the stack when no