Map IPv{4,6} addresses to ethernet addresses

...in accordance with RFCs 1112 and 2464.

Fixes IPv4 multicast when IP_MULTICAST_IF is specified.

Don't return ErrNoRoute when no route is needed.
Don't set Route.NextHop when no route is needed.

PiperOrigin-RevId: 236199813
Change-Id: I48ed33e1b7f760deaa37e18ad7f1b8b62819ab43

4 files changed, 75 insertions, 44 deletions

diff --git a/pkg/tcpip/network/arp/arp.go b/pkg/tcpip/network/arp/arp.go
index 2e0024925..ed39640c1 100644
--- a/pkg/tcpip/network/arp/arp.go
+++ b/pkg/tcpip/network/arp/arp.go
@@ -160,9 +160,27 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
 func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
-	if addr == "\xff\xff\xff\xff" {
+	if addr == header.IPv4Broadcast {
 		return broadcastMAC, true
 	}
+	if header.IsV4MulticastAddress(addr) {
+		// RFC 1112 Host Extensions for IP Multicasting
+		//
+		// 6.4. Extensions to an Ethernet Local Network Module:
+		//
+		// An IP host group address is mapped to an Ethernet multicast
+		// address by placing the low-order 23-bits of the IP address
+		// into the low-order 23 bits of the Ethernet multicast address
+		// 01-00-5E-00-00-00 (hex).
+		return tcpip.LinkAddress([]byte{
+			0x01,
+			0x00,
+			0x5e,
+			addr[header.IPv4AddressSize-3] & 0x7f,
+			addr[header.IPv4AddressSize-2],
+			addr[header.IPv4AddressSize-1],
+		}), true
+	}
 	return "", false
 }
 
diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 5a3c17768..e43253d3e 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -206,6 +206,25 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 
 // ResolveStaticAddress implements stack.LinkAddressResolver.
 func (*protocol) ResolveStaticAddress(addr tcpip.Address) (tcpip.LinkAddress, bool) {
+	if header.IsV6MulticastAddress(addr) {
+		// RFC 2464 Transmission of IPv6 Packets over Ethernet Networks
+		//
+		// 7. Address Mapping -- Multicast
+		//
+		// An IPv6 packet with a multicast destination address DST,
+		// consisting of the sixteen octets DST[1] through DST[16], is
+		// transmitted to the Ethernet multicast address whose first
+		// two octets are the value 3333 hexadecimal and whose last
+		// four octets are the last four octets of DST.
+		return tcpip.LinkAddress([]byte{
+			0x33,
+			0x33,
+			addr[header.IPv6AddressSize-4],
+			addr[header.IPv6AddressSize-3],
+			addr[header.IPv6AddressSize-2],
+			addr[header.IPv6AddressSize-1],
+		}), true
+	}
 	return "", false
 }
 
diff --git a/pkg/tcpip/stack/stack.go b/pkg/tcpip/stack/stack.go
index 797489ad9..cfda7ec3c 100644
--- a/pkg/tcpip/stack/stack.go
+++ b/pkg/tcpip/stack/stack.go
@@ -752,49 +752,39 @@ func (s *Stack) FindRoute(id tcpip.NICID, localAddr, remoteAddr tcpip.Address, n
 	s.mu.RLock()
 	defer s.mu.RUnlock()
 
-	// We don't require a route in the table to send a broadcast, multicast or
-	// IPv6 link-local packet out on a NIC.
 	isBroadcast := remoteAddr == header.IPv4Broadcast
 	isMulticast := header.IsV4MulticastAddress(remoteAddr) || header.IsV6MulticastAddress(remoteAddr)
-	if id != 0 && (isBroadcast || isMulticast || header.IsV6LinkLocalAddress(remoteAddr)) {
+	needRoute := !(isBroadcast || isMulticast || header.IsV6LinkLocalAddress(remoteAddr))
+	if id != 0 && !needRoute {
 		if nic, ok := s.nics[id]; ok {
 			if ref := s.getRefEP(nic, localAddr, netProto); ref != nil {
 				return makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref), nil
 			}
 		}
-		return Route{}, tcpip.ErrNoRoute
-	}
-
-	// TODO: Route multicast packets with no specified local
-	// address or NIC.
-
-	for i := range s.routeTable {
-		if (id != 0 && id != s.routeTable[i].NIC) || (len(remoteAddr) != 0 && !s.routeTable[i].Match(remoteAddr)) {
-			continue
-		}
-
-		nic := s.nics[s.routeTable[i].NIC]
-		if nic == nil {
-			continue
-		}
-
-		ref := s.getRefEP(nic, localAddr, netProto)
-		if ref == nil {
-			continue
-		}
-
-		if len(remoteAddr) == 0 {
-			// If no remote address was provided, then the route
-			// provided will refer to the link local address.
-			remoteAddr = ref.ep.ID().LocalAddress
+	} else {
+		for _, route := range s.routeTable {
+			if (id != 0 && id != route.NIC) || (len(remoteAddr) != 0 && !route.Match(remoteAddr)) {
+				continue
+			}
+			if nic, ok := s.nics[route.NIC]; ok {
+				if ref := s.getRefEP(nic, localAddr, netProto); ref != nil {
+					if len(remoteAddr) == 0 {
+						// If no remote address was provided, then the route
+						// provided will refer to the link local address.
+						remoteAddr = ref.ep.ID().LocalAddress
+					}
+
+					r := makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref)
+					if needRoute {
+						r.NextHop = route.Gateway
+					}
+					return r, nil
+				}
+			}
 		}
-
-		r := makeRoute(netProto, ref.ep.ID().LocalAddress, remoteAddr, nic.linkEP.LinkAddress(), ref)
-		r.NextHop = s.routeTable[i].Gateway
-		return r, nil
 	}
 
-	if isMulticast {
+	if !needRoute {
 		return Route{}, tcpip.ErrNetworkUnreachable
 	}
 
diff --git a/pkg/tcpip/stack/stack_test.go b/pkg/tcpip/stack/stack_test.go
index 28743f3d5..aba1e984c 100644
--- a/pkg/tcpip/stack/stack_test.go
+++ b/pkg/tcpip/stack/stack_test.go
@@ -654,8 +654,8 @@ func TestBroadcastNeedsNoRoute(t *testing.T) {
 	s.SetRouteTable([]tcpip.Route{})
 
 	// If there is no endpoint, it won't work.
-	if _, err := s.FindRoute(1, header.IPv4Any, header.IPv4Broadcast, fakeNetNumber); err != tcpip.ErrNoRoute {
-		t.Fatalf("got FindRoute(1, %v, %v, %v) = %v, want = %v", header.IPv4Any, header.IPv4Broadcast, fakeNetNumber, err, tcpip.ErrNoRoute)
+	if _, err := s.FindRoute(1, header.IPv4Any, header.IPv4Broadcast, fakeNetNumber); err != tcpip.ErrNetworkUnreachable {
+		t.Fatalf("got FindRoute(1, %v, %v, %v) = %v, want = %v", header.IPv4Any, header.IPv4Broadcast, fakeNetNumber, err, tcpip.ErrNetworkUnreachable)
 	}
 
 	if err := s.AddAddress(1, fakeNetNumber, header.IPv4Any); err != nil {
@@ -675,8 +675,8 @@ func TestBroadcastNeedsNoRoute(t *testing.T) {
 	}
 
 	// If the NIC doesn't exist, it won't work.
-	if _, err := s.FindRoute(2, header.IPv4Any, header.IPv4Broadcast, fakeNetNumber); err != tcpip.ErrNoRoute {
-		t.Fatalf("got FindRoute(2, %v, %v, %v) = %v want = %v", header.IPv4Any, header.IPv4Broadcast, fakeNetNumber, err, tcpip.ErrNoRoute)
+	if _, err := s.FindRoute(2, header.IPv4Any, header.IPv4Broadcast, fakeNetNumber); err != tcpip.ErrNetworkUnreachable {
+		t.Fatalf("got FindRoute(2, %v, %v, %v) = %v want = %v", header.IPv4Any, header.IPv4Broadcast, fakeNetNumber, err, tcpip.ErrNetworkUnreachable)
 	}
 }
 
@@ -732,17 +732,21 @@ func TestMulticastOrIPv6LinkLocalNeedsNoRoute(t *testing.T) {
 				anyAddr = header.IPv6Any
 			}
 
+			want := tcpip.ErrNetworkUnreachable
+			if tc.routeNeeded {
+				want = tcpip.ErrNoRoute
+			}
+
 			// If there is no endpoint, it won't work.
-			if _, err := s.FindRoute(1, anyAddr, tc.address, fakeNetNumber); err != tcpip.ErrNoRoute {
-				t.Fatalf("got FindRoute(1, %v, %v, %v) = %v, want = %v", anyAddr, tc.address, fakeNetNumber, err, tcpip.ErrNoRoute)
+			if _, err := s.FindRoute(1, anyAddr, tc.address, fakeNetNumber); err != want {
+				t.Fatalf("got FindRoute(1, %v, %v, %v) = %v, want = %v", anyAddr, tc.address, fakeNetNumber, err, want)
 			}
 
 			if err := s.AddAddress(1, fakeNetNumber, anyAddr); err != nil {
 				t.Fatalf("AddAddress(%v, %v) failed: %v", fakeNetNumber, anyAddr, err)
 			}
 
-			r, err := s.FindRoute(1, anyAddr, tc.address, fakeNetNumber)
-			if tc.routeNeeded {
+			if r, err := s.FindRoute(1, anyAddr, tc.address, fakeNetNumber); tc.routeNeeded {
 				// Route table is empty but we need a route, this should cause an error.
 				if err != tcpip.ErrNoRoute {
 					t.Fatalf("got FindRoute(1, %v, %v, %v) = %v, want = %v", anyAddr, tc.address, fakeNetNumber, err, tcpip.ErrNoRoute)
@@ -759,8 +763,8 @@ func TestMulticastOrIPv6LinkLocalNeedsNoRoute(t *testing.T) {
 				}
 			}
 			// If the NIC doesn't exist, it won't work.
-			if _, err := s.FindRoute(2, anyAddr, tc.address, fakeNetNumber); err != tcpip.ErrNoRoute {
-				t.Fatalf("got FindRoute(2, %v, %v, %v) = %v want = %v", anyAddr, tc.address, fakeNetNumber, err, tcpip.ErrNoRoute)
+			if _, err := s.FindRoute(2, anyAddr, tc.address, fakeNetNumber); err != want {
+				t.Fatalf("got FindRoute(2, %v, %v, %v) = %v want = %v", anyAddr, tc.address, fakeNetNumber, err, want)
 			}
 		})
 	}