157 lines
5.6 KiB
Go
157 lines
5.6 KiB
Go
// Copyright 2016 Google, Inc. All rights reserved.
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//
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// Use of this source code is governed by a BSD-style license
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// that can be found in the LICENSE file in the root of the source
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// tree.
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package layers
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import (
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"encoding/binary"
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"errors"
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"net"
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"github.com/google/gopacket"
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)
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/*
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This layer provides decoding for Virtual Router Redundancy Protocol (VRRP) v2.
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https://tools.ietf.org/html/rfc3768#section-5
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0 1 2 3
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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|Version| Type | Virtual Rtr ID| Priority | Count IP Addrs|
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Auth Type | Adver Int | Checksum |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| IP Address (1) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| . |
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| . |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| IP Address (n) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Authentication Data (1) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| Authentication Data (2) |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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*/
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type VRRPv2Type uint8
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type VRRPv2AuthType uint8
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const (
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VRRPv2Advertisement VRRPv2Type = 0x01 // router advertisement
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)
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// String conversions for VRRP message types
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func (v VRRPv2Type) String() string {
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switch v {
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case VRRPv2Advertisement:
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return "VRRPv2 Advertisement"
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default:
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return ""
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}
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}
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const (
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VRRPv2AuthNoAuth VRRPv2AuthType = 0x00 // No Authentication
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VRRPv2AuthReserved1 VRRPv2AuthType = 0x01 // Reserved field 1
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VRRPv2AuthReserved2 VRRPv2AuthType = 0x02 // Reserved field 2
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)
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func (v VRRPv2AuthType) String() string {
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switch v {
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case VRRPv2AuthNoAuth:
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return "No Authentication"
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case VRRPv2AuthReserved1:
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return "Reserved"
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case VRRPv2AuthReserved2:
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return "Reserved"
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default:
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return ""
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}
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}
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// VRRPv2 represents an VRRP v2 message.
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type VRRPv2 struct {
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BaseLayer
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Version uint8 // The version field specifies the VRRP protocol version of this packet (v2)
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Type VRRPv2Type // The type field specifies the type of this VRRP packet. The only type defined in v2 is ADVERTISEMENT
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VirtualRtrID uint8 // identifies the virtual router this packet is reporting status for
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Priority uint8 // specifies the sending VRRP router's priority for the virtual router (100 = default)
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CountIPAddr uint8 // The number of IP addresses contained in this VRRP advertisement.
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AuthType VRRPv2AuthType // identifies the authentication method being utilized
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AdverInt uint8 // The Advertisement interval indicates the time interval (in seconds) between ADVERTISEMENTS. The default is 1 second
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Checksum uint16 // used to detect data corruption in the VRRP message.
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IPAddress []net.IP // one or more IP addresses associated with the virtual router. Specified in the CountIPAddr field.
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}
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// LayerType returns LayerTypeVRRP for VRRP v2 message.
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func (v *VRRPv2) LayerType() gopacket.LayerType { return LayerTypeVRRP }
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func (v *VRRPv2) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
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v.BaseLayer = BaseLayer{Contents: data[:len(data)]}
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v.Version = data[0] >> 4 // high nibble == VRRP version. We're expecting v2
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v.Type = VRRPv2Type(data[0] & 0x0F) // low nibble == VRRP type. Expecting 1 (advertisement)
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if v.Type != 1 {
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// rfc3768: A packet with unknown type MUST be discarded.
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return errors.New("Unrecognized VRRPv2 type field.")
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}
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v.VirtualRtrID = data[1]
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v.Priority = data[2]
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v.CountIPAddr = data[3]
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if v.CountIPAddr < 1 {
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return errors.New("VRRPv2 number of IP addresses is not valid.")
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}
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v.AuthType = VRRPv2AuthType(data[4])
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v.AdverInt = uint8(data[5])
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v.Checksum = binary.BigEndian.Uint16(data[6:8])
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// populate the IPAddress field. The number of addresses is specified in the v.CountIPAddr field
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// offset references the starting byte containing the list of ip addresses
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offset := 8
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for i := uint8(0); i < v.CountIPAddr; i++ {
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v.IPAddress = append(v.IPAddress, data[offset:offset+4])
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offset += 4
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}
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// any trailing packets here may be authentication data and *should* be ignored in v2 as per RFC
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//
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// 5.3.10. Authentication Data
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//
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// The authentication string is currently only used to maintain
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// backwards compatibility with RFC 2338. It SHOULD be set to zero on
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// transmission and ignored on reception.
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return nil
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}
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// CanDecode specifies the layer type in which we are attempting to unwrap.
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func (v *VRRPv2) CanDecode() gopacket.LayerClass {
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return LayerTypeVRRP
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}
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// NextLayerType specifies the next layer that should be decoded. VRRP does not contain any further payload, so we set to 0
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func (v *VRRPv2) NextLayerType() gopacket.LayerType {
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return gopacket.LayerTypeZero
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}
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// The VRRP packet does not include payload data. Setting byte slice to nil
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func (v *VRRPv2) Payload() []byte {
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return nil
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}
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// decodeVRRP will parse VRRP v2
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func decodeVRRP(data []byte, p gopacket.PacketBuilder) error {
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if len(data) < 8 {
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return errors.New("Not a valid VRRP packet. Packet length is too small.")
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}
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v := &VRRPv2{}
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return decodingLayerDecoder(v, data, p)
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}
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