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// Copyright 2011 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 ssh
import (
"bytes"
"encoding/binary"
"errors"
"fmt"
"io"
"math/big"
"reflect"
"strconv"
"strings"
)
// These are SSH message type numbers. They are scattered around several
// documents but many were taken from [SSH-PARAMETERS].
const (
msgIgnore = 2
msgUnimplemented = 3
msgDebug = 4
msgNewKeys = 21
)
// SSH messages:
//
// These structures mirror the wire format of the corresponding SSH messages.
// They are marshaled using reflection with the marshal and unmarshal functions
// in this file. The only wrinkle is that a final member of type []byte with a
// ssh tag of "rest" receives the remainder of a packet when unmarshaling.
// See RFC 4253, section 11.1.
const msgDisconnect = 1
// disconnectMsg is the message that signals a disconnect. It is also
// the error type returned from mux.Wait()
type disconnectMsg struct {
Reason uint32 `sshtype:"1"`
Message string
Language string
}
func (d *disconnectMsg) Error() string {
return fmt.Sprintf("ssh: disconnect, reason %d: %s", d.Reason, d.Message)
}
// See RFC 4253, section 7.1.
const msgKexInit = 20
type kexInitMsg struct {
Cookie [16]byte `sshtype:"20"`
KexAlgos []string
ServerHostKeyAlgos []string
CiphersClientServer []string
CiphersServerClient []string
MACsClientServer []string
MACsServerClient []string
CompressionClientServer []string
CompressionServerClient []string
LanguagesClientServer []string
LanguagesServerClient []string
FirstKexFollows bool
Reserved uint32
}
// See RFC 4253, section 8.
// Diffie-Helman
const msgKexDHInit = 30
type kexDHInitMsg struct {
X *big.Int `sshtype:"30"`
}
const msgKexECDHInit = 30
type kexECDHInitMsg struct {
ClientPubKey []byte `sshtype:"30"`
}
const msgKexECDHReply = 31
type kexECDHReplyMsg struct {
HostKey []byte `sshtype:"31"`
EphemeralPubKey []byte
Signature []byte
}
const msgKexDHReply = 31
type kexDHReplyMsg struct {
HostKey []byte `sshtype:"31"`
Y *big.Int
Signature []byte
}
// See RFC 4253, section 10.
const msgServiceRequest = 5
type serviceRequestMsg struct {
Service string `sshtype:"5"`
}
// See RFC 4253, section 10.
const msgServiceAccept = 6
type serviceAcceptMsg struct {
Service string `sshtype:"6"`
}
// See RFC 4252, section 5.
const msgUserAuthRequest = 50
type userAuthRequestMsg struct {
User string `sshtype:"50"`
Service string
Method string
Payload []byte `ssh:"rest"`
}
// Used for debug printouts of packets.
type userAuthSuccessMsg struct {
}
// See RFC 4252, section 5.1
const msgUserAuthFailure = 51
type userAuthFailureMsg struct {
Methods []string `sshtype:"51"`
PartialSuccess bool
}
// See RFC 4252, section 5.1
const msgUserAuthSuccess = 52
// See RFC 4252, section 5.4
const msgUserAuthBanner = 53
type userAuthBannerMsg struct {
Message string `sshtype:"53"`
// unused, but required to allow message parsing
Language string
}
// See RFC 4256, section 3.2
const msgUserAuthInfoRequest = 60
const msgUserAuthInfoResponse = 61
type userAuthInfoRequestMsg struct {
User string `sshtype:"60"`
Instruction string
DeprecatedLanguage string
NumPrompts uint32
Prompts []byte `ssh:"rest"`
}
// See RFC 4254, section 5.1.
const msgChannelOpen = 90
type channelOpenMsg struct {
ChanType string `sshtype:"90"`
PeersID uint32
PeersWindow uint32
MaxPacketSize uint32
TypeSpecificData []byte `ssh:"rest"`
}
const msgChannelExtendedData = 95
const msgChannelData = 94
// Used for debug print outs of packets.
type channelDataMsg struct {
PeersID uint32 `sshtype:"94"`
Length uint32
Rest []byte `ssh:"rest"`
}
// See RFC 4254, section 5.1.
const msgChannelOpenConfirm = 91
type channelOpenConfirmMsg struct {
PeersID uint32 `sshtype:"91"`
MyID uint32
MyWindow uint32
MaxPacketSize uint32
TypeSpecificData []byte `ssh:"rest"`
}
// See RFC 4254, section 5.1.
const msgChannelOpenFailure = 92
type channelOpenFailureMsg struct {
PeersID uint32 `sshtype:"92"`
Reason RejectionReason
Message string
Language string
}
const msgChannelRequest = 98
type channelRequestMsg struct {
PeersID uint32 `sshtype:"98"`
Request string
WantReply bool
RequestSpecificData []byte `ssh:"rest"`
}
// See RFC 4254, section 5.4.
const msgChannelSuccess = 99
type channelRequestSuccessMsg struct {
PeersID uint32 `sshtype:"99"`
}
// See RFC 4254, section 5.4.
const msgChannelFailure = 100
type channelRequestFailureMsg struct {
PeersID uint32 `sshtype:"100"`
}
// See RFC 4254, section 5.3
const msgChannelClose = 97
type channelCloseMsg struct {
PeersID uint32 `sshtype:"97"`
}
// See RFC 4254, section 5.3
const msgChannelEOF = 96
type channelEOFMsg struct {
PeersID uint32 `sshtype:"96"`
}
// See RFC 4254, section 4
const msgGlobalRequest = 80
type globalRequestMsg struct {
Type string `sshtype:"80"`
WantReply bool
Data []byte `ssh:"rest"`
}
// See RFC 4254, section 4
const msgRequestSuccess = 81
type globalRequestSuccessMsg struct {
Data []byte `ssh:"rest" sshtype:"81"`
}
// See RFC 4254, section 4
const msgRequestFailure = 82
type globalRequestFailureMsg struct {
Data []byte `ssh:"rest" sshtype:"82"`
}
// See RFC 4254, section 5.2
const msgChannelWindowAdjust = 93
type windowAdjustMsg struct {
PeersID uint32 `sshtype:"93"`
AdditionalBytes uint32
}
// See RFC 4252, section 7
const msgUserAuthPubKeyOk = 60
type userAuthPubKeyOkMsg struct {
Algo string `sshtype:"60"`
PubKey []byte
}
// typeTags returns the possible type bytes for the given reflect.Type, which
// should be a struct. The possible values are separated by a '|' character.
func typeTags(structType reflect.Type) (tags []byte) {
tagStr := structType.Field(0).Tag.Get("sshtype")
for _, tag := range strings.Split(tagStr, "|") {
i, err := strconv.Atoi(tag)
if err == nil {
tags = append(tags, byte(i))
}
}
return tags
}
func fieldError(t reflect.Type, field int, problem string) error {
if problem != "" {
problem = ": " + problem
}
return fmt.Errorf("ssh: unmarshal error for field %s of type %s%s", t.Field(field).Name, t.Name(), problem)
}
var errShortRead = errors.New("ssh: short read")
// Unmarshal parses data in SSH wire format into a structure. The out
// argument should be a pointer to struct. If the first member of the
// struct has the "sshtype" tag set to a '|'-separated set of numbers
// in decimal, the packet must start with one of those numbers. In
// case of error, Unmarshal returns a ParseError or
// UnexpectedMessageError.
func Unmarshal(data []byte, out interface{}) error {
v := reflect.ValueOf(out).Elem()
structType := v.Type()
expectedTypes := typeTags(structType)
var expectedType byte
if len(expectedTypes) > 0 {
expectedType = expectedTypes[0]
}
if len(data) == 0 {
return parseError(expectedType)
}
if len(expectedTypes) > 0 {
goodType := false
for _, e := range expectedTypes {
if e > 0 && data[0] == e {
goodType = true
break
}
}
if !goodType {
return fmt.Errorf("ssh: unexpected message type %d (expected one of %v)", data[0], expectedTypes)
}
data = data[1:]
}
var ok bool
for i := 0; i < v.NumField(); i++ {
field := v.Field(i)
t := field.Type()
switch t.Kind() {
case reflect.Bool:
if len(data) < 1 {
return errShortRead
}
field.SetBool(data[0] != 0)
data = data[1:]
case reflect.Array:
if t.Elem().Kind() != reflect.Uint8 {
return fieldError(structType, i, "array of unsupported type")
}
if len(data) < t.Len() {
return errShortRead
}
for j, n := 0, t.Len(); j < n; j++ {
field.Index(j).Set(reflect.ValueOf(data[j]))
}
data = data[t.Len():]
case reflect.Uint64:
var u64 uint64
if u64, data, ok = parseUint64(data); !ok {
return errShortRead
}
field.SetUint(u64)
case reflect.Uint32:
var u32 uint32
if u32, data, ok = parseUint32(data); !ok {
return errShortRead
}
field.SetUint(uint64(u32))
case reflect.Uint8:
if len(data) < 1 {
return errShortRead
}
field.SetUint(uint64(data[0]))
data = data[1:]
case reflect.String:
var s []byte
if s, data, ok = parseString(data); !ok {
return fieldError(structType, i, "")
}
field.SetString(string(s))
case reflect.Slice:
switch t.Elem().Kind() {
case reflect.Uint8:
if structType.Field(i).Tag.Get("ssh") == "rest" {
field.Set(reflect.ValueOf(data))
data = nil
} else {
var s []byte
if s, data, ok = parseString(data); !ok {
return errShortRead
}
field.Set(reflect.ValueOf(s))
}
case reflect.String:
var nl []string
if nl, data, ok = parseNameList(data); !ok {
return errShortRead
}
field.Set(reflect.ValueOf(nl))
default:
return fieldError(structType, i, "slice of unsupported type")
}
case reflect.Ptr:
if t == bigIntType {
var n *big.Int
if n, data, ok = parseInt(data); !ok {
return errShortRead
}
field.Set(reflect.ValueOf(n))
} else {
return fieldError(structType, i, "pointer to unsupported type")
}
default:
return fieldError(structType, i, fmt.Sprintf("unsupported type: %v", t))
}
}
if len(data) != 0 {
return parseError(expectedType)
}
return nil
}
// Marshal serializes the message in msg to SSH wire format. The msg
// argument should be a struct or pointer to struct. If the first
// member has the "sshtype" tag set to a number in decimal, that
// number is prepended to the result. If the last of member has the
// "ssh" tag set to "rest", its contents are appended to the output.
func Marshal(msg interface{}) []byte {
out := make([]byte, 0, 64)
return marshalStruct(out, msg)
}
func marshalStruct(out []byte, msg interface{}) []byte {
v := reflect.Indirect(reflect.ValueOf(msg))
msgTypes := typeTags(v.Type())
if len(msgTypes) > 0 {
out = append(out, msgTypes[0])
}
for i, n := 0, v.NumField(); i < n; i++ {
field := v.Field(i)
switch t := field.Type(); t.Kind() {
case reflect.Bool:
var v uint8
if field.Bool() {
v = 1
}
out = append(out, v)
case reflect.Array:
if t.Elem().Kind() != reflect.Uint8 {
panic(fmt.Sprintf("array of non-uint8 in field %d: %T", i, field.Interface()))
}
for j, l := 0, t.Len(); j < l; j++ {
out = append(out, uint8(field.Index(j).Uint()))
}
case reflect.Uint32:
out = appendU32(out, uint32(field.Uint()))
case reflect.Uint64:
out = appendU64(out, uint64(field.Uint()))
case reflect.Uint8:
out = append(out, uint8(field.Uint()))
case reflect.String:
s := field.String()
out = appendInt(out, len(s))
out = append(out, s...)
case reflect.Slice:
switch t.Elem().Kind() {
case reflect.Uint8:
if v.Type().Field(i).Tag.Get("ssh") != "rest" {
out = appendInt(out, field.Len())
}
out = append(out, field.Bytes()...)
case reflect.String:
offset := len(out)
out = appendU32(out, 0)
if n := field.Len(); n > 0 {
for j := 0; j < n; j++ {
f := field.Index(j)
if j != 0 {
out = append(out, ',')
}
out = append(out, f.String()...)
}
// overwrite length value
binary.BigEndian.PutUint32(out[offset:], uint32(len(out)-offset-4))
}
default:
panic(fmt.Sprintf("slice of unknown type in field %d: %T", i, field.Interface()))
}
case reflect.Ptr:
if t == bigIntType {
var n *big.Int
nValue := reflect.ValueOf(&n)
nValue.Elem().Set(field)
needed := intLength(n)
oldLength := len(out)
if cap(out)-len(out) < needed {
newOut := make([]byte, len(out), 2*(len(out)+needed))
copy(newOut, out)
out = newOut
}
out = out[:oldLength+needed]
marshalInt(out[oldLength:], n)
} else {
panic(fmt.Sprintf("pointer to unknown type in field %d: %T", i, field.Interface()))
}
}
}
return out
}
var bigOne = big.NewInt(1)
func parseString(in []byte) (out, rest []byte, ok bool) {
if len(in) < 4 {
return
}
length := binary.BigEndian.Uint32(in)
in = in[4:]
if uint32(len(in)) < length {
return
}
out = in[:length]
rest = in[length:]
ok = true
return
}
var (
comma = []byte{','}
emptyNameList = []string{}
)
func parseNameList(in []byte) (out []string, rest []byte, ok bool) {
contents, rest, ok := parseString(in)
if !ok {
return
}
if len(contents) == 0 {
out = emptyNameList
return
}
parts := bytes.Split(contents, comma)
out = make([]string, len(parts))
for i, part := range parts {
out[i] = string(part)
}
return
}
func parseInt(in []byte) (out *big.Int, rest []byte, ok bool) {
contents, rest, ok := parseString(in)
if !ok {
return
}
out = new(big.Int)
if len(contents) > 0 && contents[0]&0x80 == 0x80 {
// This is a negative number
notBytes := make([]byte, len(contents))
for i := range notBytes {
notBytes[i] = ^contents[i]
}
out.SetBytes(notBytes)
out.Add(out, bigOne)
out.Neg(out)
} else {
// Positive number
out.SetBytes(contents)
}
ok = true
return
}
func parseUint32(in []byte) (uint32, []byte, bool) {
if len(in) < 4 {
return 0, nil, false
}
return binary.BigEndian.Uint32(in), in[4:], true
}
func parseUint64(in []byte) (uint64, []byte, bool) {
if len(in) < 8 {
return 0, nil, false
}
return binary.BigEndian.Uint64(in), in[8:], true
}
func intLength(n *big.Int) int {
length := 4 /* length bytes */
if n.Sign() < 0 {
nMinus1 := new(big.Int).Neg(n)
nMinus1.Sub(nMinus1, bigOne)
bitLen := nMinus1.BitLen()
if bitLen%8 == 0 {
// The number will need 0xff padding
length++
}
length += (bitLen + 7) / 8
} else if n.Sign() == 0 {
// A zero is the zero length string
} else {
bitLen := n.BitLen()
if bitLen%8 == 0 {
// The number will need 0x00 padding
length++
}
length += (bitLen + 7) / 8
}
return length
}
func marshalUint32(to []byte, n uint32) []byte {
binary.BigEndian.PutUint32(to, n)
return to[4:]
}
func marshalUint64(to []byte, n uint64) []byte {
binary.BigEndian.PutUint64(to, n)
return to[8:]
}
func marshalInt(to []byte, n *big.Int) []byte {
lengthBytes := to
to = to[4:]
length := 0
if n.Sign() < 0 {
// A negative number has to be converted to two's-complement
// form. So we'll subtract 1 and invert. If the
// most-significant-bit isn't set then we'll need to pad the
// beginning with 0xff in order to keep the number negative.
nMinus1 := new(big.Int).Neg(n)
nMinus1.Sub(nMinus1, bigOne)
bytes := nMinus1.Bytes()
for i := range bytes {
bytes[i] ^= 0xff
}
if len(bytes) == 0 || bytes[0]&0x80 == 0 {
to[0] = 0xff
to = to[1:]
length++
}
nBytes := copy(to, bytes)
to = to[nBytes:]
length += nBytes
} else if n.Sign() == 0 {
// A zero is the zero length string
} else {
bytes := n.Bytes()
if len(bytes) > 0 && bytes[0]&0x80 != 0 {
// We'll have to pad this with a 0x00 in order to
// stop it looking like a negative number.
to[0] = 0
to = to[1:]
length++
}
nBytes := copy(to, bytes)
to = to[nBytes:]
length += nBytes
}
lengthBytes[0] = byte(length >> 24)
lengthBytes[1] = byte(length >> 16)
lengthBytes[2] = byte(length >> 8)
lengthBytes[3] = byte(length)
return to
}
func writeInt(w io.Writer, n *big.Int) {
length := intLength(n)
buf := make([]byte, length)
marshalInt(buf, n)
w.Write(buf)
}
func writeString(w io.Writer, s []byte) {
var lengthBytes [4]byte
lengthBytes[0] = byte(len(s) >> 24)
lengthBytes[1] = byte(len(s) >> 16)
lengthBytes[2] = byte(len(s) >> 8)
lengthBytes[3] = byte(len(s))
w.Write(lengthBytes[:])
w.Write(s)
}
func stringLength(n int) int {
return 4 + n
}
func marshalString(to []byte, s []byte) []byte {
to[0] = byte(len(s) >> 24)
to[1] = byte(len(s) >> 16)
to[2] = byte(len(s) >> 8)
to[3] = byte(len(s))
to = to[4:]
copy(to, s)
return to[len(s):]
}
var bigIntType = reflect.TypeOf((*big.Int)(nil))
// Decode a packet into its corresponding message.
func decode(packet []byte) (interface{}, error) {
var msg interface{}
switch packet[0] {
case msgDisconnect:
msg = new(disconnectMsg)
case msgServiceRequest:
msg = new(serviceRequestMsg)
case msgServiceAccept:
msg = new(serviceAcceptMsg)
case msgKexInit:
msg = new(kexInitMsg)
case msgKexDHInit:
msg = new(kexDHInitMsg)
case msgKexDHReply:
msg = new(kexDHReplyMsg)
case msgUserAuthRequest:
msg = new(userAuthRequestMsg)
case msgUserAuthSuccess:
return new(userAuthSuccessMsg), nil
case msgUserAuthFailure:
msg = new(userAuthFailureMsg)
case msgUserAuthPubKeyOk:
msg = new(userAuthPubKeyOkMsg)
case msgGlobalRequest:
msg = new(globalRequestMsg)
case msgRequestSuccess:
msg = new(globalRequestSuccessMsg)
case msgRequestFailure:
msg = new(globalRequestFailureMsg)
case msgChannelOpen:
msg = new(channelOpenMsg)
case msgChannelData:
msg = new(channelDataMsg)
case msgChannelOpenConfirm:
msg = new(channelOpenConfirmMsg)
case msgChannelOpenFailure:
msg = new(channelOpenFailureMsg)
case msgChannelWindowAdjust:
msg = new(windowAdjustMsg)
case msgChannelEOF:
msg = new(channelEOFMsg)
case msgChannelClose:
msg = new(channelCloseMsg)
case msgChannelRequest:
msg = new(channelRequestMsg)
case msgChannelSuccess:
msg = new(channelRequestSuccessMsg)
case msgChannelFailure:
msg = new(channelRequestFailureMsg)
default:
return nil, unexpectedMessageError(0, packet[0])
}
if err := Unmarshal(packet, msg); err != nil {
return nil, err
}
return msg, nil
}