mirror of
https://github.com/tailscale/tailscale.git
synced 2024-12-04 23:45:34 +00:00
158 lines
4.2 KiB
Go
158 lines
4.2 KiB
Go
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package ssh
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import (
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"crypto/rand"
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"crypto/rsa"
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"encoding/binary"
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"github.com/tailscale/golang-x-crypto/ssh"
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)
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func generateSigner() (ssh.Signer, error) {
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key, err := rsa.GenerateKey(rand.Reader, 2048)
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if err != nil {
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return nil, err
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}
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return ssh.NewSignerFromKey(key)
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}
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func parsePtyRequest(payload []byte) (pty Pty, ok bool) {
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// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.2
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// 6.2. Requesting a Pseudo-Terminal
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// A pseudo-terminal can be allocated for the session by sending the
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// following message.
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// byte SSH_MSG_CHANNEL_REQUEST
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// uint32 recipient channel
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// string "pty-req"
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// boolean want_reply
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// string TERM environment variable value (e.g., vt100)
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// uint32 terminal width, characters (e.g., 80)
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// uint32 terminal height, rows (e.g., 24)
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// uint32 terminal width, pixels (e.g., 640)
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// uint32 terminal height, pixels (e.g., 480)
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// string encoded terminal modes
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// The payload starts from the TERM variable.
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term, rem, ok := parseString(payload)
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if !ok {
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return
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}
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win, rem, ok := parseWindow(rem)
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if !ok {
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return
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}
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modes, ok := parseTerminalModes(rem)
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if !ok {
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return
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}
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pty = Pty{
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Term: term,
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Window: win,
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Modes: modes,
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}
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return
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}
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func parseTerminalModes(in []byte) (modes ssh.TerminalModes, ok bool) {
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// See https://datatracker.ietf.org/doc/html/rfc4254#section-8
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// 8. Encoding of Terminal Modes
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//
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// All 'encoded terminal modes' (as passed in a pty request) are encoded
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// into a byte stream. It is intended that the coding be portable
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// across different environments. The stream consists of opcode-
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// argument pairs wherein the opcode is a byte value. Opcodes 1 to 159
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// have a single uint32 argument. Opcodes 160 to 255 are not yet
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// defined, and cause parsing to stop (they should only be used after
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// any other data). The stream is terminated by opcode TTY_OP_END
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// (0x00).
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//
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// The client SHOULD put any modes it knows about in the stream, and the
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// server MAY ignore any modes it does not know about. This allows some
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// degree of machine-independence, at least between systems that use a
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// POSIX-like tty interface. The protocol can support other systems as
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// well, but the client may need to fill reasonable values for a number
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// of parameters so the server pty gets set to a reasonable mode (the
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// server leaves all unspecified mode bits in their default values, and
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// only some combinations make sense).
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_, rem, ok := parseUint32(in)
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if !ok {
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return
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}
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const ttyOpEnd = 0
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for len(rem) > 0 {
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if modes == nil {
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modes = make(ssh.TerminalModes)
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}
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code := uint8(rem[0])
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rem = rem[1:]
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if code == ttyOpEnd || code > 160 {
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break
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}
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var val uint32
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val, rem, ok = parseUint32(rem)
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if !ok {
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return
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}
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modes[code] = val
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}
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ok = true
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return
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}
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func parseWindow(s []byte) (win Window, rem []byte, ok bool) {
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// See https://datatracker.ietf.org/doc/html/rfc4254#section-6.7
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// 6.7. Window Dimension Change Message
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// When the window (terminal) size changes on the client side, it MAY
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// send a message to the other side to inform it of the new dimensions.
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// byte SSH_MSG_CHANNEL_REQUEST
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// uint32 recipient channel
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// string "window-change"
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// boolean FALSE
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// uint32 terminal width, columns
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// uint32 terminal height, rows
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// uint32 terminal width, pixels
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// uint32 terminal height, pixels
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wCols, rem, ok := parseUint32(s)
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if !ok {
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return
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}
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hRows, rem, ok := parseUint32(rem)
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if !ok {
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return
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}
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wPixels, rem, ok := parseUint32(rem)
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if !ok {
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return
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}
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hPixels, rem, ok := parseUint32(rem)
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if !ok {
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return
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}
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win = Window{
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Width: int(wCols),
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Height: int(hRows),
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WidthPixels: int(wPixels),
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HeightPixels: int(hPixels),
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}
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return
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}
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func parseString(in []byte) (out string, rem []byte, ok bool) {
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length, rem, ok := parseUint32(in)
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if uint32(len(rem)) < length || !ok {
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ok = false
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return
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}
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out, rem = string(rem[:length]), rem[length:]
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ok = true
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return
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}
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func parseUint32(in []byte) (uint32, []byte, bool) {
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if len(in) < 4 {
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return 0, nil, false
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}
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return binary.BigEndian.Uint32(in), in[4:], true
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}
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