482 lines
19 KiB
Go
482 lines
19 KiB
Go
// Copyright 2017 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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//
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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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"github.com/google/gopacket"
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)
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// BFD Control Packet Format
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// -------------------------
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// The current version of BFD's RFC (RFC 5880) contains the following
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// diagram for the BFD Control packet format:
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//
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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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// |Vers | Diag |Sta|P|F|C|A|D|M| Detect Mult | Length |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | My Discriminator |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Your Discriminator |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Desired Min TX Interval |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Required Min RX Interval |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Required Min Echo RX Interval |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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// An optional Authentication Section MAY be present:
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//
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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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// | Auth Type | Auth Len | Authentication Data... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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//
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// Simple Password Authentication Section Format
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// ---------------------------------------------
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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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// | Auth Type | Auth Len | Auth Key ID | Password... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | ... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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//
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// Keyed MD5 and Meticulous Keyed MD5 Authentication Section Format
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// ----------------------------------------------------------------
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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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// | Auth Type | Auth Len | Auth Key ID | Reserved |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Sequence Number |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Auth Key/Digest... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | ... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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//
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// Keyed SHA1 and Meticulous Keyed SHA1 Authentication Section Format
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// ------------------------------------------------------------------
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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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// | Auth Type | Auth Len | Auth Key ID | Reserved |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Sequence Number |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | Auth Key/Hash... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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// | ... |
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// +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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//
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// From https://tools.ietf.org/rfc/rfc5880.txt
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const bfdMinimumRecordSizeInBytes int = 24
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// BFDVersion represents the version as decoded from the BFD control message
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type BFDVersion uint8
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// BFDDiagnostic represents diagnostic infomation about a BFD session
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type BFDDiagnostic uint8
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// constants that define BFDDiagnostic flags
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const (
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BFDDiagnosticNone BFDDiagnostic = 0 // No Diagnostic
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BFDDiagnosticTimeExpired BFDDiagnostic = 1 // Control Detection Time Expired
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BFDDiagnosticEchoFailed BFDDiagnostic = 2 // Echo Function Failed
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BFDDiagnosticNeighborSignalDown BFDDiagnostic = 3 // Neighbor Signaled Session Down
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BFDDiagnosticForwardPlaneReset BFDDiagnostic = 4 // Forwarding Plane Reset
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BFDDiagnosticPathDown BFDDiagnostic = 5 // Path Down
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BFDDiagnosticConcatPathDown BFDDiagnostic = 6 // Concatenated Path Down
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BFDDiagnosticAdminDown BFDDiagnostic = 7 // Administratively Down
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BFDDiagnosticRevConcatPathDown BFDDiagnostic = 8 // Reverse Concatenated Path Dow
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)
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// String returns a string version of BFDDiagnostic
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func (bd BFDDiagnostic) String() string {
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switch bd {
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default:
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return "Unknown"
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case BFDDiagnosticNone:
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return "None"
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case BFDDiagnosticTimeExpired:
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return "Control Detection Time Expired"
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case BFDDiagnosticEchoFailed:
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return "Echo Function Failed"
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case BFDDiagnosticNeighborSignalDown:
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return "Neighbor Signaled Session Down"
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case BFDDiagnosticForwardPlaneReset:
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return "Forwarding Plane Reset"
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case BFDDiagnosticPathDown:
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return "Path Down"
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case BFDDiagnosticConcatPathDown:
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return "Concatenated Path Down"
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case BFDDiagnosticAdminDown:
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return "Administratively Down"
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case BFDDiagnosticRevConcatPathDown:
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return "Reverse Concatenated Path Down"
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}
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}
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// BFDState represents the state of a BFD session
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type BFDState uint8
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// constants that define BFDState
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const (
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BFDStateAdminDown BFDState = 0
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BFDStateDown BFDState = 1
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BFDStateInit BFDState = 2
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BFDStateUp BFDState = 3
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)
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// String returns a string version of BFDState
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func (s BFDState) String() string {
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switch s {
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default:
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return "Unknown"
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case BFDStateAdminDown:
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return "Admin Down"
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case BFDStateDown:
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return "Down"
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case BFDStateInit:
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return "Init"
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case BFDStateUp:
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return "Up"
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}
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}
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// BFDDetectMultiplier represents the negotiated transmit interval,
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// multiplied by this value, provides the Detection Time for the
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// receiving system in Asynchronous mode.
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type BFDDetectMultiplier uint8
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// BFDDiscriminator is a unique, nonzero discriminator value used
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// to demultiplex multiple BFD sessions between the same pair of systems.
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type BFDDiscriminator uint32
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// BFDTimeInterval represents a time interval in microseconds
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type BFDTimeInterval uint32
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// BFDAuthType represents the authentication used in the BFD session
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type BFDAuthType uint8
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// constants that define the BFDAuthType
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const (
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BFDAuthTypeNone BFDAuthType = 0 // No Auth
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BFDAuthTypePassword BFDAuthType = 1 // Simple Password
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BFDAuthTypeKeyedMD5 BFDAuthType = 2 // Keyed MD5
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BFDAuthTypeMeticulousKeyedMD5 BFDAuthType = 3 // Meticulous Keyed MD5
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BFDAuthTypeKeyedSHA1 BFDAuthType = 4 // Keyed SHA1
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BFDAuthTypeMeticulousKeyedSHA1 BFDAuthType = 5 // Meticulous Keyed SHA1
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)
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// String returns a string version of BFDAuthType
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func (at BFDAuthType) String() string {
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switch at {
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default:
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return "Unknown"
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case BFDAuthTypeNone:
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return "No Authentication"
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case BFDAuthTypePassword:
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return "Simple Password"
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case BFDAuthTypeKeyedMD5:
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return "Keyed MD5"
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case BFDAuthTypeMeticulousKeyedMD5:
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return "Meticulous Keyed MD5"
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case BFDAuthTypeKeyedSHA1:
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return "Keyed SHA1"
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case BFDAuthTypeMeticulousKeyedSHA1:
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return "Meticulous Keyed SHA1"
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}
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}
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// BFDAuthKeyID represents the authentication key ID in use for
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// this packet. This allows multiple keys to be active simultaneously.
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type BFDAuthKeyID uint8
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// BFDAuthSequenceNumber represents the sequence number for this packet.
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// For Keyed Authentication, this value is incremented occasionally. For
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// Meticulous Keyed Authentication, this value is incremented for each
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// successive packet transmitted for a session. This provides protection
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// against replay attacks.
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type BFDAuthSequenceNumber uint32
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// BFDAuthData represents the authentication key or digest
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type BFDAuthData []byte
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// BFDAuthHeader represents authentication data used in the BFD session
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type BFDAuthHeader struct {
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AuthType BFDAuthType
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KeyID BFDAuthKeyID
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SequenceNumber BFDAuthSequenceNumber
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Data BFDAuthData
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}
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// Length returns the data length of the BFDAuthHeader based on the
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// authentication type
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func (h *BFDAuthHeader) Length() int {
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switch h.AuthType {
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case BFDAuthTypePassword:
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return 3 + len(h.Data)
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case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5:
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return 8 + len(h.Data)
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case BFDAuthTypeKeyedSHA1, BFDAuthTypeMeticulousKeyedSHA1:
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return 8 + len(h.Data)
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default:
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return 0
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}
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}
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// BFD represents a BFD control message packet whose payload contains
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// the control information required to for a BFD session.
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//
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// References
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// ----------
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//
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// Wikipedia's BFD entry:
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// https://en.wikipedia.org/wiki/Bidirectional_Forwarding_Detection
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// This is the best place to get an overview of BFD.
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//
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// RFC 5880 "Bidirectional Forwarding Detection (BFD)" (2010)
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// https://tools.ietf.org/html/rfc5880
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// This is the original BFD specification.
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//
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// RFC 5881 "Bidirectional Forwarding Detection (BFD) for IPv4 and IPv6 (Single Hop)" (2010)
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// https://tools.ietf.org/html/rfc5881
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// Describes the use of the Bidirectional Forwarding Detection (BFD)
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// protocol over IPv4 and IPv6 for single IP hops.
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type BFD struct {
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BaseLayer // Stores the packet bytes and payload bytes.
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Version BFDVersion // Version of the BFD protocol.
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Diagnostic BFDDiagnostic // Diagnostic code for last state change
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State BFDState // Current state
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Poll bool // Requesting verification
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Final bool // Responding to a received BFD Control packet that had the Poll (P) bit set.
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ControlPlaneIndependent bool // BFD implementation does not share fate with its control plane
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AuthPresent bool // Authentication Section is present and the session is to be authenticated
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Demand bool // Demand mode is active
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Multipoint bool // For future point-to-multipoint extensions. Must always be zero
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DetectMultiplier BFDDetectMultiplier // Detection time multiplier
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MyDiscriminator BFDDiscriminator // A unique, nonzero discriminator value
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YourDiscriminator BFDDiscriminator // discriminator received from the remote system.
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DesiredMinTxInterval BFDTimeInterval // Minimum interval, in microseconds, the local system would like to use when transmitting BFD Control packets
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RequiredMinRxInterval BFDTimeInterval // Minimum interval, in microseconds, between received BFD Control packets that this system is capable of supporting
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RequiredMinEchoRxInterval BFDTimeInterval // Minimum interval, in microseconds, between received BFD Echo packets that this system is capable of supporting
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AuthHeader *BFDAuthHeader // Authentication data, variable length.
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}
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// Length returns the data length of a BFD Control message which
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// changes based on the presence and type of authentication
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// contained in the message
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func (d *BFD) Length() int {
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if d.AuthPresent && (d.AuthHeader != nil) {
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return bfdMinimumRecordSizeInBytes + d.AuthHeader.Length()
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}
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return bfdMinimumRecordSizeInBytes
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}
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// LayerType returns the layer type of the BFD object, which is LayerTypeBFD.
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func (d *BFD) LayerType() gopacket.LayerType {
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return LayerTypeBFD
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}
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// decodeBFD analyses a byte slice and attempts to decode it as a BFD
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// control packet
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//
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// If it succeeds, it loads p with information about the packet and returns nil.
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// If it fails, it returns an error (non nil).
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//
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// This function is employed in layertypes.go to register the BFD layer.
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func decodeBFD(data []byte, p gopacket.PacketBuilder) error {
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// Attempt to decode the byte slice.
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d := &BFD{}
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err := d.DecodeFromBytes(data, p)
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if err != nil {
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return err
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}
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// If the decoding worked, add the layer to the packet and set it
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// as the application layer too, if there isn't already one.
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p.AddLayer(d)
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p.SetApplicationLayer(d)
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return nil
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}
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// DecodeFromBytes analyses a byte slice and attempts to decode it as a BFD
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// control packet.
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//
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// Upon succeeds, it loads the BFD object with information about the packet
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// and returns nil.
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// Upon failure, it returns an error (non nil).
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func (d *BFD) DecodeFromBytes(data []byte, df gopacket.DecodeFeedback) error {
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// If the data block is too short to be a BFD record, then return an error.
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if len(data) < bfdMinimumRecordSizeInBytes {
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df.SetTruncated()
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return errors.New("BFD packet too short")
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}
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pLen := uint8(data[3])
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if len(data) != int(pLen) {
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return errors.New("BFD packet length does not match")
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}
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// BFD type embeds type BaseLayer which contains two fields:
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// Contents is supposed to contain the bytes of the data at this level.
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// Payload is supposed to contain the payload of this level.
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// Here we set the baselayer to be the bytes of the BFD record.
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d.BaseLayer = BaseLayer{Contents: data[:len(data)]}
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// Extract the fields from the block of bytes.
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// To make sense of this, refer to the packet diagram
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// above and the section on endian conventions.
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// The first few fields are all packed into the first 32 bits. Unpack them.
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d.Version = BFDVersion(((data[0] & 0xE0) >> 5))
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d.Diagnostic = BFDDiagnostic(data[0] & 0x1F)
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data = data[1:]
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d.State = BFDState((data[0] & 0xC0) >> 6)
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d.Poll = data[0]&0x20 != 0
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d.Final = data[0]&0x10 != 0
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d.ControlPlaneIndependent = data[0]&0x08 != 0
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d.AuthPresent = data[0]&0x04 != 0
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d.Demand = data[0]&0x02 != 0
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d.Multipoint = data[0]&0x01 != 0
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data = data[1:]
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data, d.DetectMultiplier = data[1:], BFDDetectMultiplier(data[0])
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data, _ = data[1:], uint8(data[0]) // Consume length
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// The remaining fields can just be copied in big endian order.
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data, d.MyDiscriminator = data[4:], BFDDiscriminator(binary.BigEndian.Uint32(data[:4]))
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data, d.YourDiscriminator = data[4:], BFDDiscriminator(binary.BigEndian.Uint32(data[:4]))
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data, d.DesiredMinTxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))
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data, d.RequiredMinRxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))
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data, d.RequiredMinEchoRxInterval = data[4:], BFDTimeInterval(binary.BigEndian.Uint32(data[:4]))
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if d.AuthPresent && (len(data) > 2) {
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d.AuthHeader = &BFDAuthHeader{}
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data, d.AuthHeader.AuthType = data[1:], BFDAuthType(data[0])
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data, _ = data[1:], uint8(data[0]) // Consume length
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data, d.AuthHeader.KeyID = data[1:], BFDAuthKeyID(data[0])
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switch d.AuthHeader.AuthType {
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case BFDAuthTypePassword:
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d.AuthHeader.Data = BFDAuthData(data)
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case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5:
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// Skipped reserved byte
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data, d.AuthHeader.SequenceNumber = data[5:], BFDAuthSequenceNumber(binary.BigEndian.Uint32(data[1:5]))
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d.AuthHeader.Data = BFDAuthData(data)
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case BFDAuthTypeKeyedSHA1, BFDAuthTypeMeticulousKeyedSHA1:
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// Skipped reserved byte
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data, d.AuthHeader.SequenceNumber = data[5:], BFDAuthSequenceNumber(binary.BigEndian.Uint32(data[1:5]))
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d.AuthHeader.Data = BFDAuthData(data)
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}
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}
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return nil
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}
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// SerializeTo writes the serialized form of this layer into the
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// SerializationBuffer, implementing gopacket.SerializableLayer.
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// See the docs for gopacket.SerializableLayer for more info.
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func (d *BFD) SerializeTo(b gopacket.SerializeBuffer, opts gopacket.SerializeOptions) error {
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data, err := b.PrependBytes(bfdMinimumRecordSizeInBytes)
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if err != nil {
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return err
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}
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// Pack the first few fields into the first 32 bits.
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data[0] = byte(byte(d.Version<<5) | byte(d.Diagnostic))
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h := uint8(0)
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h |= (uint8(d.State) << 6)
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h |= (uint8(bool2uint8(d.Poll)) << 5)
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h |= (uint8(bool2uint8(d.Final)) << 4)
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h |= (uint8(bool2uint8(d.ControlPlaneIndependent)) << 3)
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h |= (uint8(bool2uint8(d.AuthPresent)) << 2)
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h |= (uint8(bool2uint8(d.Demand)) << 1)
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h |= uint8(bool2uint8(d.Multipoint))
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data[1] = byte(h)
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data[2] = byte(d.DetectMultiplier)
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data[3] = byte(d.Length())
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// The remaining fields can just be copied in big endian order.
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binary.BigEndian.PutUint32(data[4:], uint32(d.MyDiscriminator))
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binary.BigEndian.PutUint32(data[8:], uint32(d.YourDiscriminator))
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binary.BigEndian.PutUint32(data[12:], uint32(d.DesiredMinTxInterval))
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binary.BigEndian.PutUint32(data[16:], uint32(d.RequiredMinRxInterval))
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binary.BigEndian.PutUint32(data[20:], uint32(d.RequiredMinEchoRxInterval))
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if d.AuthPresent && (d.AuthHeader != nil) {
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auth, err := b.AppendBytes(int(d.AuthHeader.Length()))
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if err != nil {
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return err
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}
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auth[0] = byte(d.AuthHeader.AuthType)
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auth[1] = byte(d.AuthHeader.Length())
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auth[2] = byte(d.AuthHeader.KeyID)
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switch d.AuthHeader.AuthType {
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case BFDAuthTypePassword:
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copy(auth[3:], d.AuthHeader.Data)
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case BFDAuthTypeKeyedMD5, BFDAuthTypeMeticulousKeyedMD5:
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auth[3] = byte(0)
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binary.BigEndian.PutUint32(auth[4:], uint32(d.AuthHeader.SequenceNumber))
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copy(auth[8:], d.AuthHeader.Data)
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case BFDAuthTypeKeyedSHA1, BFDAuthTypeMeticulousKeyedSHA1:
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auth[3] = byte(0)
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binary.BigEndian.PutUint32(auth[4:], uint32(d.AuthHeader.SequenceNumber))
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copy(auth[8:], d.AuthHeader.Data)
|
|
}
|
|
}
|
|
|
|
return nil
|
|
}
|
|
|
|
// CanDecode returns a set of layers that BFD objects can decode.
|
|
// As BFD objects can only decide the BFD layer, we can return just that layer.
|
|
// Apparently a single layer type implements LayerClass.
|
|
func (d *BFD) CanDecode() gopacket.LayerClass {
|
|
return LayerTypeBFD
|
|
}
|
|
|
|
// NextLayerType specifies the next layer that GoPacket should attempt to
|
|
// analyse after this (BFD) layer. As BFD packets do not contain any payload
|
|
// bytes, there are no further layers to analyse.
|
|
func (d *BFD) NextLayerType() gopacket.LayerType {
|
|
return gopacket.LayerTypeZero
|
|
}
|
|
|
|
// Payload returns an empty byte slice as BFD packets do not carry a payload
|
|
func (d *BFD) Payload() []byte {
|
|
return nil
|
|
}
|
|
|
|
// bool2uint8 converts a bool to uint8
|
|
func bool2uint8(b bool) uint8 {
|
|
if b {
|
|
return 1
|
|
}
|
|
return 0
|
|
}
|