Send unicast probes when link address is known

When the neighbor table already has link address for a neighbor but is
trying to confirm reachability, it may send unicast probes to the
neighbor.

PiperOrigin-RevId: 336166711

pkg/tcpip/network/ipv6/icmp.go

@@ -646,18 +646,21 @@ func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 
 // LinkAddressRequest implements stack.LinkAddressResolver.
 func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAddr tcpip.LinkAddress, 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{
+	r := stack.Route{
 		LocalAddress:      localAddr,
-		RemoteAddress:     snaddr,
+		RemoteAddress:     addr,
 		RemoteLinkAddress: remoteLinkAddr,
 	}
+
+	// If a remote address is not already known, then send a multicast
+	// solicitation since multicast addresses have a static mapping to link
+	// addresses.
 	if len(r.RemoteLinkAddress) == 0 {
-		r.RemoteLinkAddress = header.EthernetAddressFromMulticastIPv6Address(snaddr)
+		r.RemoteAddress = header.SolicitedNodeAddr(addr)
+		r.RemoteLinkAddress = header.EthernetAddressFromMulticastIPv6Address(r.RemoteAddress)
 	}
 
 	pkt := stack.NewPacketBuffer(stack.PacketBufferOptions{
@@ -683,7 +686,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, remoteLinkAdd
 	})
 
 	// TODO(stijlist): count this in ICMP stats.
-	return linkEP.WritePacket(r, nil /* gso */, ProtocolNumber, pkt)
+	return linkEP.WritePacket(&r, nil /* gso */, ProtocolNumber, pkt)
 }
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.

pkg/tcpip/network/ipv6/icmp_test.go

@@ -22,6 +22,7 @@ import (
 
 	"gvisor.dev/gvisor/pkg/tcpip"
 	"gvisor.dev/gvisor/pkg/tcpip/buffer"
+	"gvisor.dev/gvisor/pkg/tcpip/checker"
 	"gvisor.dev/gvisor/pkg/tcpip/header"
 	"gvisor.dev/gvisor/pkg/tcpip/link/channel"
 	"gvisor.dev/gvisor/pkg/tcpip/link/sniffer"
@@ -1223,19 +1224,22 @@ func TestLinkAddressRequest(t *testing.T) {
 	mcaddr := header.EthernetAddressFromMulticastIPv6Address(snaddr)
 
 	tests := []struct {
-		name           string
-		remoteLinkAddr tcpip.LinkAddress
-		expectLinkAddr tcpip.LinkAddress
+		name             string
+		remoteLinkAddr   tcpip.LinkAddress
+		expectedLinkAddr tcpip.LinkAddress
+		expectedAddr     tcpip.Address
 	}{
 		{
-			name:           "Unicast",
-			remoteLinkAddr: linkAddr1,
-			expectLinkAddr: linkAddr1,
+			name:             "Unicast",
+			remoteLinkAddr:   linkAddr1,
+			expectedLinkAddr: linkAddr1,
+			expectedAddr:     lladdr0,
 		},
 		{
-			name:           "Multicast",
-			remoteLinkAddr: "",
-			expectLinkAddr: mcaddr,
+			name:             "Multicast",
+			remoteLinkAddr:   "",
+			expectedLinkAddr: mcaddr,
+			expectedAddr:     snaddr,
 		},
 	}
 
@@ -1258,9 +1262,22 @@ func TestLinkAddressRequest(t *testing.T) {
 		if !ok {
 			t.Fatal("expected to send a link address request")
 		}
-
-		if got, want := pkt.Route.RemoteLinkAddress, test.expectLinkAddr; got != want {
-			t.Errorf("got pkt.Route.RemoteLinkAddress = %s, want = %s", got, want)
+		if pkt.Route.RemoteLinkAddress != test.expectedLinkAddr {
+			t.Errorf("got pkt.Route.RemoteLinkAddress = %s, want = %s", pkt.Route.RemoteLinkAddress, test.expectedLinkAddr)
 		}
+		if pkt.Route.RemoteAddress != test.expectedAddr {
+			t.Errorf("got pkt.Route.RemoteAddress = %s, want = %s", pkt.Route.RemoteAddress, test.expectedAddr)
+		}
+		if pkt.Route.LocalAddress != lladdr1 {
+			t.Errorf("got pkt.Route.LocalAddress = %s, want = %s", pkt.Route.LocalAddress, lladdr1)
+		}
+		checker.IPv6(t, stack.PayloadSince(pkt.Pkt.NetworkHeader()),
+			checker.SrcAddr(lladdr1),
+			checker.DstAddr(test.expectedAddr),
+			checker.TTL(header.NDPHopLimit),
+			checker.NDPNS(
+				checker.NDPNSTargetAddress(lladdr0),
+				checker.NDPNSOptions([]header.NDPOption{header.NDPSourceLinkLayerAddressOption(linkAddr0)}),
+			))
 	}
 }