tailscale/tempfork/gliderlabs/ssh/util.go

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package ssh
import (
"crypto/rand"
"crypto/rsa"
"encoding/binary"
"github.com/tailscale/golang-x-crypto/ssh"
)
func generateSigner() (ssh.Signer, error) {
key, err := rsa.GenerateKey(rand.Reader, 2048)
if err != nil {
return nil, err
}
return ssh.NewSignerFromKey(key)
}
func parsePtyRequest(payload []byte) (pty Pty, ok bool) {
// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.2
// 6.2. Requesting a Pseudo-Terminal
// A pseudo-terminal can be allocated for the session by sending the
// following message.
// byte SSH_MSG_CHANNEL_REQUEST
// uint32 recipient channel
// string "pty-req"
// boolean want_reply
// string TERM environment variable value (e.g., vt100)
// uint32 terminal width, characters (e.g., 80)
// uint32 terminal height, rows (e.g., 24)
// uint32 terminal width, pixels (e.g., 640)
// uint32 terminal height, pixels (e.g., 480)
// string encoded terminal modes
// The payload starts from the TERM variable.
term, rem, ok := parseString(payload)
if !ok {
return
}
win, rem, ok := parseWindow(rem)
if !ok {
return
}
modes, ok := parseTerminalModes(rem)
if !ok {
return
}
pty = Pty{
Term: term,
Window: win,
Modes: modes,
}
return
}
func parseTerminalModes(in []byte) (modes ssh.TerminalModes, ok bool) {
// See https://datatracker.ietf.org/doc/html/rfc4254#section-8
// 8. Encoding of Terminal Modes
//
// All 'encoded terminal modes' (as passed in a pty request) are encoded
// into a byte stream. It is intended that the coding be portable
// across different environments. The stream consists of opcode-
// argument pairs wherein the opcode is a byte value. Opcodes 1 to 159
// have a single uint32 argument. Opcodes 160 to 255 are not yet
// defined, and cause parsing to stop (they should only be used after
// any other data). The stream is terminated by opcode TTY_OP_END
// (0x00).
//
// The client SHOULD put any modes it knows about in the stream, and the
// server MAY ignore any modes it does not know about. This allows some
// degree of machine-independence, at least between systems that use a
// POSIX-like tty interface. The protocol can support other systems as
// well, but the client may need to fill reasonable values for a number
// of parameters so the server pty gets set to a reasonable mode (the
// server leaves all unspecified mode bits in their default values, and
// only some combinations make sense).
_, rem, ok := parseUint32(in)
if !ok {
return
}
const ttyOpEnd = 0
for len(rem) > 0 {
if modes == nil {
modes = make(ssh.TerminalModes)
}
code := uint8(rem[0])
rem = rem[1:]
if code == ttyOpEnd || code > 160 {
break
}
var val uint32
val, rem, ok = parseUint32(rem)
if !ok {
return
}
modes[code] = val
}
ok = true
return
}
func parseWindow(s []byte) (win Window, rem []byte, ok bool) {
// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.7
// 6.7. Window Dimension Change Message
// When the window (terminal) size changes on the client side, it MAY
// send a message to the other side to inform it of the new dimensions.
// byte SSH_MSG_CHANNEL_REQUEST
// uint32 recipient channel
// string "window-change"
// boolean FALSE
// uint32 terminal width, columns
// uint32 terminal height, rows
// uint32 terminal width, pixels
// uint32 terminal height, pixels
wCols, rem, ok := parseUint32(s)
if !ok {
return
}
hRows, rem, ok := parseUint32(rem)
if !ok {
return
}
wPixels, rem, ok := parseUint32(rem)
if !ok {
return
}
hPixels, rem, ok := parseUint32(rem)
if !ok {
return
}
win = Window{
Width: int(wCols),
Height: int(hRows),
WidthPixels: int(wPixels),
HeightPixels: int(hPixels),
}
return
}
func parseString(in []byte) (out string, rem []byte, ok bool) {
length, rem, ok := parseUint32(in)
if uint32(len(rem)) < length || !ok {
ok = false
return
}
out, rem = string(rem[:length]), rem[length:]
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
}