Fix panic during Address Resolution of neighbor entry created by NS

When a Neighbor Solicitation is received, a neighbor entry is created with the
remote host's link layer address, but without a link layer address resolver. If
the host decides to send a packet addressed to the IP address of that neighbor
entry, Address Resolution starts with a nil pointer to the link layer address
resolver. This causes the netstack to panic and crash.

This change ensures that when a packet is sent in that situation, the link
layer address resolver will be set before Address Resolution begins.

Tests:
 pkg/tcpip/stack:stack_test
 + TestEntryUnknownToStaleToProbeToReachable
 - TestNeighborCacheEntryNoLinkAddress

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

PiperOrigin-RevId: 325516471

1 files changed, 1 insertions, 1 deletions

diff --git a/pkg/tcpip/stack/nud.go b/pkg/tcpip/stack/nud.go
index f848d50ad..e1ec15487 100644
--- a/pkg/tcpip/stack/nud.go
+++ b/pkg/tcpip/stack/nud.go
@@ -177,7 +177,7 @@ type NUDHandler interface {
 	// Neighbor Solicitation for ARP or NDP, respectively). Validation of the
 	// probe needs to be performed before calling this function since the
 	// Neighbor Cache doesn't have access to view the NIC's assigned addresses.
-	HandleProbe(remoteAddr, localAddr tcpip.Address, protocol tcpip.NetworkProtocolNumber, remoteLinkAddr tcpip.LinkAddress)
+	HandleProbe(remoteAddr, localAddr tcpip.Address, protocol tcpip.NetworkProtocolNumber, remoteLinkAddr tcpip.LinkAddress, linkRes LinkAddressResolver)
 
 	// HandleConfirmation processes an incoming neighbor confirmation (e.g. ARP
 	// reply or Neighbor Advertisement for ARP or NDP, respectively).