dhcpv6/ztpv6: avoid panic in ParseVendorData on non-Message packets

The Ciena branch of ParseVendorData unconditionally type-asserted the
DHCPv6 packet to *dhcpv6.Message to read the client identifier. Because
ParseVendorData accepts the dhcpv6.DHCPv6 interface and the ztpv6
helpers are documented to run on relayed packets, passing a
*dhcpv6.RelayMessage carrying a Ciena vendor class option panicked with
'interface conversion: dhcpv6.DHCPv6 is *dhcpv6.RelayMessage, not
*dhcpv6.Message'.

Guard the assertion with the comma-ok form so a non-Message packet
simply skips the serial-number lookup instead of crashing. Behavior for
*dhcpv6.Message inputs is unchanged. Adds a regression test.

Signed-off-by: Chris (ChrisJr404) <11917633+ChrisJr404@users.noreply.github.com>

Author: ChrisJr404

dhcpv6/ztpv6/parse_vendor_options.go

@@ -118,9 +118,10 @@ func ParseVendorData(packet dhcpv6.DHCPv6) (*VendorData, error) {
 			}
 			vd.VendorName = iana.EnterpriseIDCienaCorporation.String()
 			vd.Model = v[1] + "-" + v[2]
-			duid := packet.(*dhcpv6.Message).Options.ClientID()
-			if enterpriseDUID, ok := duid.(*dhcpv6.DUIDEN); ok {
-				vd.Serial = string(enterpriseDUID.EnterpriseIdentifier)
+			if msg, ok := packet.(*dhcpv6.Message); ok {
+				if enterpriseDUID, ok := msg.Options.ClientID().(*dhcpv6.DUIDEN); ok {
+					vd.Serial = string(enterpriseDUID.EnterpriseIdentifier)
+				}
 			}
 			return &vd, nil
 		}

dhcpv6/ztpv6/parse_vendor_options_test.go

@@ -128,3 +128,24 @@ func TestParseVendorDataWithVendorClass(t *testing.T) {
 		})
 	}
 }
+
+// TestParseVendorDataCienaRelayMessage ensures ParseVendorData does not panic
+// when handed a RelayMessage (rather than a *Message) carrying a Ciena vendor
+// class option. The ztpv6 helpers are documented to run on relayed packets, so
+// a *RelayMessage is a legitimate input.
+func TestParseVendorDataCienaRelayMessage(t *testing.T) {
+	relay := &dhcpv6.RelayMessage{
+		MessageType: dhcpv6.MessageTypeRelayForward,
+	}
+	relay.Options.Add(&dhcpv6.OptVendorClass{
+		EnterpriseNumber: uint32(iana.EnterpriseIDCienaCorporation),
+		Data:             [][]byte{[]byte("1271-23422Z11-123")},
+	})
+
+	vd, err := ParseVendorData(relay)
+	require.NoError(t, err)
+	require.Equal(t, &VendorData{
+		VendorName: iana.EnterpriseIDCienaCorporation.String(),
+		Model:      "23422Z11-123",
+	}, vd)
+}