David K. Bainbridge | 215e024 | 2017-09-05 23:18:24 -0700 | [diff] [blame] | 1 | // Copyright 2012 The Go Authors. All rights reserved. |
| 2 | // Use of this source code is governed by a BSD-style |
| 3 | // license that can be found in the LICENSE file. |
| 4 | |
| 5 | // Package icmp provides basic functions for the manipulation of |
| 6 | // messages used in the Internet Control Message Protocols, |
| 7 | // ICMPv4 and ICMPv6. |
| 8 | // |
| 9 | // ICMPv4 and ICMPv6 are defined in RFC 792 and RFC 4443. |
| 10 | // Multi-part message support for ICMP is defined in RFC 4884. |
| 11 | // ICMP extensions for MPLS are defined in RFC 4950. |
| 12 | // ICMP extensions for interface and next-hop identification are |
| 13 | // defined in RFC 5837. |
| 14 | package icmp // import "golang.org/x/net/icmp" |
| 15 | |
| 16 | import ( |
| 17 | "encoding/binary" |
| 18 | "errors" |
| 19 | "net" |
| 20 | "syscall" |
| 21 | |
| 22 | "golang.org/x/net/internal/iana" |
| 23 | "golang.org/x/net/ipv4" |
| 24 | "golang.org/x/net/ipv6" |
| 25 | ) |
| 26 | |
| 27 | // BUG(mikio): This package is not implemented on NaCl and Plan 9. |
| 28 | |
| 29 | var ( |
| 30 | errMessageTooShort = errors.New("message too short") |
| 31 | errHeaderTooShort = errors.New("header too short") |
| 32 | errBufferTooShort = errors.New("buffer too short") |
| 33 | errOpNoSupport = errors.New("operation not supported") |
| 34 | errNoExtension = errors.New("no extension") |
| 35 | errInvalidExtension = errors.New("invalid extension") |
| 36 | ) |
| 37 | |
| 38 | func checksum(b []byte) uint16 { |
| 39 | csumcv := len(b) - 1 // checksum coverage |
| 40 | s := uint32(0) |
| 41 | for i := 0; i < csumcv; i += 2 { |
| 42 | s += uint32(b[i+1])<<8 | uint32(b[i]) |
| 43 | } |
| 44 | if csumcv&1 == 0 { |
| 45 | s += uint32(b[csumcv]) |
| 46 | } |
| 47 | s = s>>16 + s&0xffff |
| 48 | s = s + s>>16 |
| 49 | return ^uint16(s) |
| 50 | } |
| 51 | |
| 52 | // A Type represents an ICMP message type. |
| 53 | type Type interface { |
| 54 | Protocol() int |
| 55 | } |
| 56 | |
| 57 | // A Message represents an ICMP message. |
| 58 | type Message struct { |
| 59 | Type Type // type, either ipv4.ICMPType or ipv6.ICMPType |
| 60 | Code int // code |
| 61 | Checksum int // checksum |
| 62 | Body MessageBody // body |
| 63 | } |
| 64 | |
| 65 | // Marshal returns the binary encoding of the ICMP message m. |
| 66 | // |
| 67 | // For an ICMPv4 message, the returned message always contains the |
| 68 | // calculated checksum field. |
| 69 | // |
| 70 | // For an ICMPv6 message, the returned message contains the calculated |
| 71 | // checksum field when psh is not nil, otherwise the kernel will |
| 72 | // compute the checksum field during the message transmission. |
| 73 | // When psh is not nil, it must be the pseudo header for IPv6. |
| 74 | func (m *Message) Marshal(psh []byte) ([]byte, error) { |
| 75 | var mtype int |
| 76 | switch typ := m.Type.(type) { |
| 77 | case ipv4.ICMPType: |
| 78 | mtype = int(typ) |
| 79 | case ipv6.ICMPType: |
| 80 | mtype = int(typ) |
| 81 | default: |
| 82 | return nil, syscall.EINVAL |
| 83 | } |
| 84 | b := []byte{byte(mtype), byte(m.Code), 0, 0} |
| 85 | if m.Type.Protocol() == iana.ProtocolIPv6ICMP && psh != nil { |
| 86 | b = append(psh, b...) |
| 87 | } |
| 88 | if m.Body != nil && m.Body.Len(m.Type.Protocol()) != 0 { |
| 89 | mb, err := m.Body.Marshal(m.Type.Protocol()) |
| 90 | if err != nil { |
| 91 | return nil, err |
| 92 | } |
| 93 | b = append(b, mb...) |
| 94 | } |
| 95 | if m.Type.Protocol() == iana.ProtocolIPv6ICMP { |
| 96 | if psh == nil { // cannot calculate checksum here |
| 97 | return b, nil |
| 98 | } |
| 99 | off, l := 2*net.IPv6len, len(b)-len(psh) |
| 100 | binary.BigEndian.PutUint32(b[off:off+4], uint32(l)) |
| 101 | } |
| 102 | s := checksum(b) |
| 103 | // Place checksum back in header; using ^= avoids the |
| 104 | // assumption the checksum bytes are zero. |
| 105 | b[len(psh)+2] ^= byte(s) |
| 106 | b[len(psh)+3] ^= byte(s >> 8) |
| 107 | return b[len(psh):], nil |
| 108 | } |
| 109 | |
| 110 | var parseFns = map[Type]func(int, []byte) (MessageBody, error){ |
| 111 | ipv4.ICMPTypeDestinationUnreachable: parseDstUnreach, |
| 112 | ipv4.ICMPTypeTimeExceeded: parseTimeExceeded, |
| 113 | ipv4.ICMPTypeParameterProblem: parseParamProb, |
| 114 | |
| 115 | ipv4.ICMPTypeEcho: parseEcho, |
| 116 | ipv4.ICMPTypeEchoReply: parseEcho, |
| 117 | |
| 118 | ipv6.ICMPTypeDestinationUnreachable: parseDstUnreach, |
| 119 | ipv6.ICMPTypePacketTooBig: parsePacketTooBig, |
| 120 | ipv6.ICMPTypeTimeExceeded: parseTimeExceeded, |
| 121 | ipv6.ICMPTypeParameterProblem: parseParamProb, |
| 122 | |
| 123 | ipv6.ICMPTypeEchoRequest: parseEcho, |
| 124 | ipv6.ICMPTypeEchoReply: parseEcho, |
| 125 | } |
| 126 | |
| 127 | // ParseMessage parses b as an ICMP message. |
| 128 | // Proto must be either the ICMPv4 or ICMPv6 protocol number. |
| 129 | func ParseMessage(proto int, b []byte) (*Message, error) { |
| 130 | if len(b) < 4 { |
| 131 | return nil, errMessageTooShort |
| 132 | } |
| 133 | var err error |
| 134 | m := &Message{Code: int(b[1]), Checksum: int(binary.BigEndian.Uint16(b[2:4]))} |
| 135 | switch proto { |
| 136 | case iana.ProtocolICMP: |
| 137 | m.Type = ipv4.ICMPType(b[0]) |
| 138 | case iana.ProtocolIPv6ICMP: |
| 139 | m.Type = ipv6.ICMPType(b[0]) |
| 140 | default: |
| 141 | return nil, syscall.EINVAL |
| 142 | } |
| 143 | if fn, ok := parseFns[m.Type]; !ok { |
| 144 | m.Body, err = parseDefaultMessageBody(proto, b[4:]) |
| 145 | } else { |
| 146 | m.Body, err = fn(proto, b[4:]) |
| 147 | } |
| 148 | if err != nil { |
| 149 | return nil, err |
| 150 | } |
| 151 | return m, nil |
| 152 | } |