Add ability to send unicast ARP requests and Neighbor Solicitations

The previous implementation of LinkAddressRequest only supported sending
broadcast ARP requests and multicast Neighbor Solicitations. The ability to
send these packets as unicast is required for Neighbor Unreachability
Detection.

Tests:
 pkg/tcpip/network/arp:arp_test
 - TestLinkAddressRequest

 pkg/tcpip/network/ipv6:ipv6_test
 - TestLinkAddressRequest

Updates #1889
Updates #1894
Updates #1895
Updates #1947
Updates #1948
Updates #1949
Updates #1950

PiperOrigin-RevId: 323451569

2 files changed, 55 insertions, 5 deletions

diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index ff1cb53dd..24600d877 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -504,7 +504,7 @@ func (*protocol) LinkAddressProtocol() tcpip.NetworkProtocolNumber {
 }
 
 // LinkAddressRequest implements stack.LinkAddressResolver.
-func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.LinkEndpoint) *tcpip.Error {
+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
@@ -513,8 +513,12 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 	r := &stack.Route{
 		LocalAddress:      localAddr,
 		RemoteAddress:     snaddr,
-		RemoteLinkAddress: header.EthernetAddressFromMulticastIPv6Address(snaddr),
+		RemoteLinkAddress: remoteLinkAddr,
 	}
+	if len(r.RemoteLinkAddress) == 0 {
+		r.RemoteLinkAddress = header.EthernetAddressFromMulticastIPv6Address(snaddr)
+	}
+
 	hdr := buffer.NewPrependable(int(linkEP.MaxHeaderLength()) + header.IPv6MinimumSize + header.ICMPv6NeighborAdvertSize)
 	pkt := header.ICMPv6(hdr.Prepend(header.ICMPv6NeighborAdvertSize))
 	pkt.SetType(header.ICMPv6NeighborSolicit)
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index 52a01b44e..f86aaed1d 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -34,6 +34,9 @@ const (
 	linkAddr0 = tcpip.LinkAddress("\x02\x02\x03\x04\x05\x06")
 	linkAddr1 = tcpip.LinkAddress("\x0a\x0b\x0c\x0d\x0e\x0e")
 	linkAddr2 = tcpip.LinkAddress("\x0a\x0b\x0c\x0d\x0e\x0f")
+
+	defaultChannelSize = 1
+	defaultMTU         = 65536
 )
 
 var (
@@ -257,8 +260,7 @@ func newTestContext(t *testing.T) *testContext {
 		}),
 	}
 
-	const defaultMTU = 65536
-	c.linkEP0 = channel.New(256, defaultMTU, linkAddr0)
+	c.linkEP0 = channel.New(defaultChannelSize, defaultMTU, linkAddr0)
 
 	wrappedEP0 := stack.LinkEndpoint(endpointWithResolutionCapability{LinkEndpoint: c.linkEP0})
 	if testing.Verbose() {
@@ -271,7 +273,7 @@ func newTestContext(t *testing.T) *testContext {
 		t.Fatalf("AddAddress lladdr0: %v", err)
 	}
 
-	c.linkEP1 = channel.New(256, defaultMTU, linkAddr1)
+	c.linkEP1 = channel.New(defaultChannelSize, defaultMTU, linkAddr1)
 	wrappedEP1 := stack.LinkEndpoint(endpointWithResolutionCapability{LinkEndpoint: c.linkEP1})
 	if err := c.s1.CreateNIC(1, wrappedEP1); err != nil {
 		t.Fatalf("CreateNIC failed: %v", err)
@@ -951,3 +953,47 @@ func TestICMPChecksumValidationWithPayloadMultipleViews(t *testing.T) {
 		})
 	}
 }
+
+func TestLinkAddressRequest(t *testing.T) {
+	snaddr := header.SolicitedNodeAddr(lladdr0)
+	mcaddr := header.EthernetAddressFromMulticastIPv6Address(snaddr)
+
+	tests := []struct {
+		name           string
+		remoteLinkAddr tcpip.LinkAddress
+		expectLinkAddr tcpip.LinkAddress
+	}{
+		{
+			name:           "Unicast",
+			remoteLinkAddr: linkAddr1,
+			expectLinkAddr: linkAddr1,
+		},
+		{
+			name:           "Multicast",
+			remoteLinkAddr: "",
+			expectLinkAddr: mcaddr,
+		},
+	}
+
+	for _, test := range tests {
+		p := NewProtocol()
+		linkRes, ok := p.(stack.LinkAddressResolver)
+		if !ok {
+			t.Fatalf("expected IPv6 protocol to implement stack.LinkAddressResolver")
+		}
+
+		linkEP := channel.New(defaultChannelSize, defaultMTU, linkAddr0)
+		if err := linkRes.LinkAddressRequest(lladdr0, lladdr1, test.remoteLinkAddr, linkEP); err != nil {
+			t.Errorf("got p.LinkAddressRequest(%s, %s, %s, _) = %s", lladdr0, lladdr1, test.remoteLinkAddr, err)
+		}
+
+		pkt, ok := linkEP.Read()
+		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)
+		}
+	}
+}