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transport.go
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transport.go
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package ssh
import (
"bufio"
"bytes"
"crypto/cipher"
"errors"
"hash"
"io"
)
type transport struct {
conn io.ReadWriteCloser
in *bufio.Reader
rc, wc cipher.BlockMode
rh, wh hash.Hash
rseq, wseq uint32
packets chan []byte
newkey chan int
rident string
ckex, skex, session_id []byte
}
func newTransport(conn io.ReadWriteCloser) (*transport, error) {
_, err := conn.Write([]byte(ident + "\r\n"))
if err != nil {
return nil, err
}
in := bufio.NewReader(conn)
var line []byte
var prefix bool
for {
line, prefix, err = in.ReadLine()
if err != nil {
return nil, err
}
if prefix {
return nil, errors.New("Too long identification line")
}
Log(1, "%s", line)
if bytes.HasPrefix(line, []byte("SSH-2.0-")) {
break
}
if bytes.HasPrefix(line, []byte("SSH-")) {
return nil, errors.New("Unsupported ssh version")
}
}
return &transport{conn, in, NullCrypto{}, NullCrypto{}, NullHash{}, NullHash{}, 0, 0, make(chan []byte, 512*1024), make(chan int, 1), string(line), nil, nil, nil}, nil
}
func (s *transport) readPacket() ([]byte, error) {
bs := s.rc.BlockSize()
if bs < 16 {
bs = 16
}
// read packet header
b := make([]byte, bs)
_, err := io.ReadFull(s.in, b)
if err != nil {
return nil, err
}
Log(9, "WIRE = %X", b)
// decrypt header
s.rc.CryptBlocks(b, b)
Log(9, "DEC = %X", b)
lfield := int(bigendian.Uint32(b))
lpadding := int(b[4])
// FIXME add checks here to validate packet
lhash := s.rh.Size()
lrest := 4 + lfield + lhash - len(b)
if (lrest > 12*1024*1024) || (lfield < 0) {
Log(0, "lfield %d lrest %d", lfield, lrest)
return nil, errors.New("too large packet")
}
packet := make([]byte, len(b)+lrest)
copy(packet, b)
rest := packet[len(b):]
_, err = io.ReadFull(s.in, rest)
if err != nil {
return nil, err
}
s.rc.CryptBlocks(rest[0:lrest-lhash], rest[0:lrest-lhash])
var rseqb [4]byte
bigendian.PutUint32(rseqb[:], s.rseq)
s.rseq++
s.rh.Reset()
s.rh.Write(rseqb[:])
s.rh.Write(packet[0 : len(packet)-lhash])
if !constEq(s.rh.Sum(nil), packet[len(packet)-lhash:]) {
return nil, errors.New("Invalid mac")
}
return packet[5 : 4+lfield-lpadding], nil
}
func (s *transport) Packet() *Encoder {
return s.PacketN(0)
}
func (s *transport) PacketN(n int) *Encoder {
n = (n+5+31) & (^31)
return NewEncoderWithCommit(make([]byte, 5, n), func(data []byte) (size int, err error) {
return s.write(data)
})
}
func (s *transport) write(data []byte) (size int, err error) {
bs := s.wc.BlockSize()
if bs < 16 {
bs = 16
}
padding := bs - (len(data) % bs)
if padding < 4 {
padding += bs
}
data[4] = byte(padding)
data = append(data, rand(padding)...)
bigendian.PutUint32(data, uint32(len(data)-4))
var wseqb [4]byte
bigendian.PutUint32(wseqb[:], s.wseq)
s.wh.Reset()
s.wh.Write(wseqb[:])
s.wh.Write(data)
mac := s.wh.Sum(nil)
s.wc.CryptBlocks(data, data)
data = append(data, mac...)
size, err = s.conn.Write(data)
s.wseq++
return
}
func (s *transport) writeKexInit() {
p := NewEncoder()
p.Byte(MsgKexinit).Bytes(rand(16))
p.U32String(NameListKexAlgorithms).U32String(NameListServerHostKeyAlgorithms)
p.U32String(NameListEncryptionAlgorithms1).U32String(NameListEncryptionAlgorithms2)
p.U32String(NameListMacAlgorithms1).U32String(NameListMacAlgorithms2)
p.U32String(NameListCompressionAlgorithms1).U32String(NameListCompressionAlgorithms2)
p.U32String(NameListLanguages1).U32String(NameListLanguages2)
p.Byte(0).U32(0)
s.ckex = p.Out()
s.Packet().Bytes(s.ckex).Commit()
}
type kexres struct {
Kex, Shk, EncCS, EncSC, MacCS, MacSC, ComCS, ComSC string
}
func (s *transport) parseKexinit(b []byte) (*kexres, error) {
s.skex = make([]byte, len(b))
copy(s.skex, b)
b = b[1:]
var cookie []byte
var kex, shk, ecs, esc, mcs, msc, ccs, csc, lcs, lsc string
var follows byte
var reserved uint32
p := NewDecoder(b).NBytes(16, &cookie)
p.U32String(&kex).U32String(&shk)
p.U32String(&ecs).U32String(&esc)
p.U32String(&mcs).U32String(&msc)
p.U32String(&ccs).U32String(&csc)
p.U32String(&lcs).U32String(&lsc)
p.Byte(&follows).U32(&reserved).End()
guessed := true
var r kexres
var g bool
var err error
r.Kex, g, err = namelistCheck(NameListKexAlgorithms, kex)
if err != nil {
return nil, err
}
guessed = g && guessed
r.Shk, g, err = namelistCheck(NameListServerHostKeyAlgorithms, shk)
if err != nil {
return nil, err
}
guessed = g && guessed
r.EncCS, g, err = namelistCheck(NameListEncryptionAlgorithms1, ecs)
if err != nil {
return nil, err
}
guessed = g && guessed
r.EncSC, g, err = namelistCheck(NameListEncryptionAlgorithms2, esc)
if err != nil {
return nil, err
}
guessed = g && guessed
r.MacCS, g, err = namelistCheck(NameListMacAlgorithms1, mcs)
if err != nil {
return nil, err
}
guessed = g && guessed
r.MacSC, g, err = namelistCheck(NameListMacAlgorithms2, msc)
if err != nil {
return nil, err
}
guessed = g && guessed
r.ComCS, g, err = namelistCheck(NameListCompressionAlgorithms1, ccs)
if err != nil {
return nil, err
}
guessed = g && guessed
r.ComSC, g, err = namelistCheck(NameListCompressionAlgorithms2, csc)
if err != nil {
return nil, err
}
guessed = g && guessed
if !guessed && (follows > 0) {
<-s.packets
}
return &r, nil
}