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// Copyright 2015 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package icmp
import (
"encoding/binary"
"golang.org/x/net/ipv4"
"golang.org/x/net/ipv6"
)
// An Extension represents an ICMP extension.
type Extension interface {
// Len returns the length of ICMP extension.
// The provided proto must be either the ICMPv4 or ICMPv6
// protocol number.
Len(proto int) int
// Marshal returns the binary encoding of ICMP extension.
// The provided proto must be either the ICMPv4 or ICMPv6
// protocol number.
Marshal(proto int) ([]byte, error)
}
const extensionVersion = 2
func validExtensionHeader(b []byte) bool {
v := int(b[0]&0xf0) >> 4
s := binary.BigEndian.Uint16(b[2:4])
if s != 0 {
s = checksum(b)
}
if v != extensionVersion || s != 0 {
return false
}
return true
}
// parseExtensions parses b as a list of ICMP extensions.
// The length attribute l must be the length attribute field in
// received icmp messages.
//
// It will return a list of ICMP extensions and an adjusted length
// attribute that represents the length of the padded original
// datagram field. Otherwise, it returns an error.
func parseExtensions(typ Type, b []byte, l int) ([]Extension, int, error) {
// Still a lot of non-RFC 4884 compliant implementations are
// out there. Set the length attribute l to 128 when it looks
// inappropriate for backwards compatibility.
//
// A minimal extension at least requires 8 octets; 4 octets
// for an extension header, and 4 octets for a single object
// header.
//
// See RFC 4884 for further information.
switch typ {
case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
if len(b) < 8 || !validExtensionHeader(b) {
return nil, -1, errNoExtension
}
l = 0
default:
if 128 > l || l+8 > len(b) {
l = 128
}
if l+8 > len(b) {
return nil, -1, errNoExtension
}
if !validExtensionHeader(b[l:]) {
if l == 128 {
return nil, -1, errNoExtension
}
l = 128
if !validExtensionHeader(b[l:]) {
return nil, -1, errNoExtension
}
}
}
var exts []Extension
for b = b[l+4:]; len(b) >= 4; {
ol := int(binary.BigEndian.Uint16(b[:2]))
if 4 > ol || ol > len(b) {
break
}
switch b[2] {
case classMPLSLabelStack:
ext, err := parseMPLSLabelStack(b[:ol])
if err != nil {
return nil, -1, err
}
exts = append(exts, ext)
case classInterfaceInfo:
ext, err := parseInterfaceInfo(b[:ol])
if err != nil {
return nil, -1, err
}
exts = append(exts, ext)
case classInterfaceIdent:
ext, err := parseInterfaceIdent(b[:ol])
if err != nil {
return nil, -1, err
}
exts = append(exts, ext)
default:
ext := &RawExtension{Data: make([]byte, ol)}
copy(ext.Data, b[:ol])
exts = append(exts, ext)
}
b = b[ol:]
}
return exts, l, nil
}
func validExtensions(typ Type, exts []Extension) bool {
switch typ {
case ipv4.ICMPTypeDestinationUnreachable, ipv4.ICMPTypeTimeExceeded, ipv4.ICMPTypeParameterProblem,
ipv6.ICMPTypeDestinationUnreachable, ipv6.ICMPTypeTimeExceeded:
for i := range exts {
switch exts[i].(type) {
case *MPLSLabelStack, *InterfaceInfo, *RawExtension:
default:
return false
}
}
return true
case ipv4.ICMPTypeExtendedEchoRequest, ipv6.ICMPTypeExtendedEchoRequest:
var n int
for i := range exts {
switch exts[i].(type) {
case *InterfaceIdent:
n++
case *RawExtension:
default:
return false
}
}
// Not a single InterfaceIdent object or a combo of
// RawExtension and InterfaceIdent objects is not
// allowed.
if n == 1 && len(exts) > 1 {
return false
}
return true
default:
return false
}
}
// A RawExtension represents a raw extension.
//
// A raw extension is excluded from message processing and can be used
// to construct applications such as protocol conformance testing.
type RawExtension struct {
Data []byte // data
}
// Len implements the Len method of Extension interface.
func (p *RawExtension) Len(proto int) int {
if p == nil {
return 0
}
return len(p.Data)
}
// Marshal implements the Marshal method of Extension interface.
func (p *RawExtension) Marshal(proto int) ([]byte, error) {
return p.Data, nil
}
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