Discard invalid Neighbor Solicitations

...per RFC 4861 s7.1.1.

PiperOrigin-RevId: 335742851

pkg/tcpip/header/ipv6.go

@@ -309,14 +309,21 @@ func IsV6UnicastAddress(addr tcpip.Address) bool {
 	return addr[0] != 0xff
 }
 
+const solicitedNodeMulticastPrefix = "\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xff"
+
 // SolicitedNodeAddr computes the solicited-node multicast address. This is
 // used for NDP. Described in RFC 4291. The argument must be a full-length IPv6
 // address.
 func SolicitedNodeAddr(addr tcpip.Address) tcpip.Address {
-	const solicitedNodeMulticastPrefix = "\xff\x02\x00\x00\x00\x00\x00\x00\x00\x00\x00\x01\xff"
 	return solicitedNodeMulticastPrefix + addr[len(addr)-3:]
 }
 
+// IsSolicitedNodeAddr determines whether the address is a solicited-node
+// multicast address.
+func IsSolicitedNodeAddr(addr tcpip.Address) bool {
+	return solicitedNodeMulticastPrefix == addr[:len(addr)-3]
+}
+
 // EthernetAdddressToModifiedEUI64IntoBuf populates buf with a modified EUI-64
 // from a 48-bit Ethernet/MAC address, as per RFC 4291 section 2.5.1.
 //

pkg/tcpip/network/ipv6/icmp.go

@@ -286,6 +286,17 @@ func (e *endpoint) handleICMP(r *stack.Route, pkt *stack.PacketBuffer, hasFragme
 			e.linkAddrCache.AddLinkAddress(e.nic.ID(), r.RemoteAddress, sourceLinkAddr)
 		}
 
+		// As per RFC 4861 section 7.1.1:
+		//   A node MUST silently discard any received Neighbor Solicitation
+		//   messages that do not satisfy all of the following validity checks:
+		//    ...
+		//    - If the IP source address is the unspecified address, the IP
+		//      destination address is a solicited-node multicast address.
+		if unspecifiedSource && !header.IsSolicitedNodeAddr(r.LocalAddress) {
+			received.Invalid.Increment()
+			return
+		}
+
 		// ICMPv6 Neighbor Solicit messages are always sent to
 		// specially crafted IPv6 multicast addresses. As a result, the
 		// route we end up with here has as its LocalAddress such a

pkg/tcpip/network/ipv6/ndp_test.go

@@ -410,7 +410,7 @@ func TestNeighorSolicitationResponse(t *testing.T) {
 		naDst         tcpip.Address
 	}{
 		{
-			name:          "Unspecified source to multicast destination",
+			name:          "Unspecified source to solicited-node multicast destination",
 			nsOpts:        nil,
 			nsSrcLinkAddr: remoteLinkAddr0,
 			nsSrc:         header.IPv6Any,
@@ -437,11 +437,7 @@ func TestNeighorSolicitationResponse(t *testing.T) {
 			nsSrcLinkAddr: remoteLinkAddr0,
 			nsSrc:         header.IPv6Any,
 			nsDst:         nicAddr,
-			nsInvalid:     false,
-			naDstLinkAddr: remoteLinkAddr0,
-			naSolicited:   false,
-			naSrc:         nicAddr,
-			naDst:         header.IPv6AllNodesMulticastAddress,
+			nsInvalid:     true,
 		},
 		{
 			name: "Unspecified source with source ll option to unicast destination",