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ssh/tailssh: make pty termios options match OpenSSH

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Still not sure the exact rules of how/when/who's supposed to set
these, but this works for now on making them match. Baby steps.
Will research more and adjust later.

Updates #4146 (but not enough to fix it, something's still wrong)
Updates #3802

Change-Id: I496d8cd7e31d45fe9ede88fc8894f35dc096de67
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2022-03-11 11:19:55 -08:00
committed by Brad Fitzpatrick
parent 1dd5cf62a5
commit ba1adf6c24
4 changed files with 91 additions and 8 deletions
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49
ssh/tailssh/incubator.go
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@ -28,6 +28,7 @@ import (
"github.com/creack/pty"
"github.com/gliderlabs/ssh"
"github.com/u-root/u-root/pkg/termios"
"golang.org/x/sys/unix"
"tailscale.com/cmd/tailscaled/childproc"
"tailscale.com/types/logger"
@ -209,12 +210,50 @@ func startWithPTY(cmd *exec.Cmd, ptyReq ssh.Pty) (ptyFile *os.File, err error) {
tty.Close()
}
}()
if err = pty.Setsize(ptyFile, &pty.Winsize{
Rows: uint16(ptyReq.Window.Height),
Cols: uint16(ptyReq.Window.Width),
ptyRawConn, err := ptyFile.SyscallConn()
if err != nil {
return nil, fmt.Errorf("SyscallConn: %w", err)
}
var ctlErr error
if err := ptyRawConn.Control(func(fd uintptr) {
// Load existing PTY settings to modify them & save them back.
tios, err := termios.GTTY(int(fd))
if err != nil {
ctlErr = fmt.Errorf("GTTY: %w", err)
return
}
// Set the rows & cols to those advertised from the ptyReq frame
// received over SSH.
tios.Row = int(ptyReq.Window.Height)
tios.Col = int(ptyReq.Window.Width)
// And these are just stumbling around in the dark temporarily
// while we try to match OpenSSH settings. Empirically this makes
// stty -a output be the same, but we're still having problems:
// https://github.com/tailscale/tailscale/issues/4146
// TODO(bradfitz): figure all this out and do something more principled
// and confident and documented, once we have a clue.
tios.Ispeed = 9600
tios.Ospeed = 9600
tios.CC["eol"] = 255
tios.CC["eol2"] = 255
tios.Opts["echok"] = false
tios.Opts["imaxbel"] = true
tios.Opts["iutf8"] = true
tios.Opts["ixany"] = true
tios.Opts["pendin"] = true
// Save PTY settings.
if _, err := tios.STTY(int(fd)); err != nil {
ctlErr = fmt.Errorf("STTY: %w", err)
return
}
}); err != nil {
err = fmt.Errorf("pty.Setsize: %w", err)
return
return nil, fmt.Errorf("ptyRawConn.Control: %w", err)
}
if ctlErr != nil {
return nil, fmt.Errorf("ptyRawConn.Control func: %w", ctlErr)
}
cmd.SysProcAttr = &syscall.SysProcAttr{
Setctty: true,