NDP Neighbor Solicitations sent during DAD must have an IP hop limit of 255

NDP Neighbor Solicitations sent during Duplicate Address Detection must have an
IP hop limit of 255, as all NDP Neighbor Solicitations should have.

Test: Test that DAD messages have the IPv6 hop limit field set to 255.
PiperOrigin-RevId: 275321680

3 files changed, 6 insertions, 15 deletions

diff --git a/pkg/tcpip/network/ipv6/icmp.go b/pkg/tcpip/network/ipv6/icmp.go
index 7b638e9d0..6c14b4aae 100644
--- a/pkg/tcpip/network/ipv6/icmp.go
+++ b/pkg/tcpip/network/ipv6/icmp.go
@@ -21,15 +21,6 @@ import (
 	"gvisor.dev/gvisor/pkg/tcpip/stack"
 )
 
-const (
-	// ndpHopLimit is the expected IP hop limit value of 255 for received
-	// NDP packets, as per RFC 4861 sections 4.1 - 4.5, 6.1.1, 6.1.2, 7.1.1,
-	// 7.1.2 and 8.1. If the hop limit value is not 255, nodes MUST silently
-	// drop the NDP packet. All outgoing NDP packets must use this value for
-	// its IP hop limit field.
-	ndpHopLimit = 255
-)
-
 // handleControl handles the case when an ICMP packet contains the headers of
 // the original packet that caused the ICMP one to be sent. This information is
 // used to find out which transport endpoint must be notified about the ICMP
@@ -90,7 +81,7 @@ func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.V
 		header.ICMPv6RouterSolicit,
 		header.ICMPv6RouterAdvert,
 		header.ICMPv6RedirectMsg:
-		if iph.HopLimit() != ndpHopLimit {
+		if iph.HopLimit() != header.NDPHopLimit {
 			received.Invalid.Increment()
 			return
 		}
@@ -217,7 +208,7 @@ func (e *endpoint) handleICMP(r *stack.Route, netHeader buffer.View, vv buffer.V
 		//
 		// The IP Hop Limit field has a value of 255, i.e., the packet
 		// could not possibly have been forwarded by a router.
-		if err := r.WritePacket(nil /* gso */, hdr, buffer.VectorisedView{}, stack.NetworkHeaderParams{Protocol: header.ICMPv6ProtocolNumber, TTL: ndpHopLimit, TOS: stack.DefaultTOS}); err != nil {
+		if err := r.WritePacket(nil /* gso */, hdr, buffer.VectorisedView{}, stack.NetworkHeaderParams{Protocol: header.ICMPv6ProtocolNumber, TTL: header.NDPHopLimit, TOS: stack.DefaultTOS}); err != nil {
 			sent.Dropped.Increment()
 			return
 		}
@@ -359,7 +350,7 @@ func (*protocol) LinkAddressRequest(addr, localAddr tcpip.Address, linkEP stack.
 	ip.Encode(&header.IPv6Fields{
 		PayloadLength: length,
 		NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-		HopLimit:      ndpHopLimit,
+		HopLimit:      header.NDPHopLimit,
 		SrcAddr:       r.LocalAddress,
 		DstAddr:       r.RemoteAddress,
 	})
diff --git a/pkg/tcpip/network/ipv6/icmp_test.go b/pkg/tcpip/network/ipv6/icmp_test.go
index dd3c4d7c4..7c11dde55 100644
--- a/pkg/tcpip/network/ipv6/icmp_test.go
+++ b/pkg/tcpip/network/ipv6/icmp_test.go
@@ -143,7 +143,7 @@ func TestICMPCounts(t *testing.T) {
 		ip.Encode(&header.IPv6Fields{
 			PayloadLength: uint16(payloadLength),
 			NextHeader:    uint8(header.ICMPv6ProtocolNumber),
-			HopLimit:      ndpHopLimit,
+			HopLimit:      header.NDPHopLimit,
 			SrcAddr:       r.LocalAddress,
 			DstAddr:       r.RemoteAddress,
 		})
diff --git a/pkg/tcpip/network/ipv6/ndp_test.go b/pkg/tcpip/network/ipv6/ndp_test.go
index e30791fe3..c32716f2e 100644
--- a/pkg/tcpip/network/ipv6/ndp_test.go
+++ b/pkg/tcpip/network/ipv6/ndp_test.go
@@ -150,7 +150,7 @@ func TestHopLimitValidation(t *testing.T) {
 
 			// Receive the NDP packet with an invalid hop limit
 			// value.
-			handleIPv6Payload(hdr, ndpHopLimit-1, ep, &r)
+			handleIPv6Payload(hdr, header.NDPHopLimit-1, ep, &r)
 
 			// Invalid count should have increased.
 			if got := invalid.Value(); got != 1 {
@@ -164,7 +164,7 @@ func TestHopLimitValidation(t *testing.T) {
 			}
 
 			// Receive the NDP packet with a valid hop limit value.
-			handleIPv6Payload(hdr, ndpHopLimit, ep, &r)
+			handleIPv6Payload(hdr, header.NDPHopLimit, ep, &r)
 
 			// Rx count of NDP packet of type typ.typ should have
 			// increased.