Re: [PATCH 1/1] Cygwin: console: Maintain EXTENDED_FLAGS state

[Takashi Yano <takashi.yano@nifty.ne.jp>]

On Wed, 9 Feb 2022 19:09:02 -0500
Mitchell Hentges wrote:
> As well-described over in this post [1], it's possible for
> the active console mode to be impossible to correctly determine.
> Specifically, if ENABLE_EXTENDED_FLAGS is at any point unset,
> then the flags it's associated with (ENABLE_INSERT_MODE,
> ENABLE_QUICK_EDIT_MODE) will no longer be discoverable - they'll
> always show up as unset, regardless of real console state.
> 
> It's not possible to work around this by setting
> ENABLE_EXTENDED_FLAGS once then re-querying, because setting
> ENABLE_EXTENDED_FLAGS on it's own will *disable* its related
> flags.
> 
> Anyways, to avoid this case, all programs doing SetConsoleMode()
> must be good community citizens and carefully maintain its state.
> Unfortunately, we're accidentally stepping on this in
> fhandler_console::set_input_mode().
> 
> This patch solves this by carrying forward ENABLED_EXTENDED_FLAGS
> (and friends) in the only place where it had been ignored: set_input_mode()
> Since the previous behaviour of leaving all three flags unset would
> essentially maintain their existing state (except for the footgun
> being worked around here), *adding* the carry-over of the flags now
> should not alter console behaviour.
> 
> [1] https://www.os2museum.com/wp/disabling-quick-edit-mode/
> ---
>  winsup/cygwin/fhandler_console.cc | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/winsup/cygwin/fhandler_console.cc
> b/winsup/cygwin/fhandler_console.cc
> index 7a1a45bc1..b2554c3ba 100644
> --- a/winsup/cygwin/fhandler_console.cc
> +++ b/winsup/cygwin/fhandler_console.cc
> @@ -458,16 +458,18 @@ void
>  fhandler_console::set_input_mode (tty::cons_mode m, const termios *t,
>                                   const handle_set_t *p)
>  {
> -  DWORD flags = 0, oflags;
> +  DWORD oflags;
>    WaitForSingleObject (p->input_mutex, mutex_timeout);
>    GetConsoleMode (p->input_handle, &oflags);
> +  DWORD flags = oflags
> +      & (ENABLE_EXTENDED_FLAGS | ENABLE_INSERT_MODE |
> ENABLE_QUICK_EDIT_MODE);
>    switch (m)
>      {
>      case tty::restore:
> -      flags = ENABLE_ECHO_INPUT | ENABLE_LINE_INPUT |
> ENABLE_PROCESSED_INPUT;
> +      flags |= ENABLE_ECHO_INPUT | ENABLE_LINE_INPUT |
> ENABLE_PROCESSED_INPUT;
>        break;
>      case tty::cygwin:
> -      flags = ENABLE_WINDOW_INPUT;
> +      flags |= ENABLE_WINDOW_INPUT;
>        if (wincap.has_con_24bit_colors () && !con_is_legacy)
>         flags |= ENABLE_VIRTUAL_TERMINAL_INPUT;
>        else
> --
> 2.35.1

Thanks for the patch. The patch looks good, however, it is
malformed, probably due to your mailer. (e.g. Sprious new
line inserted, and tab not preserved.)

Could you please resend it?

-- 
Takashi Yano <takashi.yano@nifty.ne.jp>