[newlib-cygwin] Cygwin: pty: Fix nat pipe hand-over when pcon is disabled

[Takashi Yano]

https://sourceware.org/git/gitweb.cgi?p=newlib-cygwin.git;h=699c6892f10371cda7ada5eb68e684363a3d8ee1

commit 699c6892f10371cda7ada5eb68e684363a3d8ee1
Author: Takashi Yano <takashi.yano@nifty.ne.jp>
Date:   Tue Mar 3 22:18:22 2026 +0900

    Cygwin: pty: Fix nat pipe hand-over when pcon is disabled
    
    The nat pipe ownership hand-over mechanism relies on the console
    process list - the set of processes attached to a console, enumerable
    via `GetConsoleProcessList()`. For non-cygwin process in pcon_activated
    case, this list contains all processes attached to the pseudo console.
    Otherwise, it contains all processes attached to the invisible console.
    
    04f386e9af (Cygwin: console: Inherit pcon hand over from parent pty,
    2024-10-31) added a last-resort fallback in `get_winpid_to_hand_over()`
    that hands nat pipe ownership to any process in the console process
    list, including Cygwin processes. This fallback is needed when a
    Cygwin process on the pseudo console (that might be exec'ed from non-
    cygwin process) must take over management of an active pseudo console
    after the original owner exits.
    
    When the pseudo console is disabled, this fallback incorrectly finds a
    Cygwin process (such as the shell) and assigns it nat pipe ownership,
    because both the original nat pipe owner and the shell are assosiated
    with the same invisible console. Since there is no console for that
    process to manage, ownership never gets released, input stays stuck on
    the nat pipe.
    
    Only the third (last-resort) call in the cascade needs guarding: the
    first two calls filter for native (non-Cygwin) processes via the `nat`
    parameter, and handing ownership to another native process is fine
    regardless of pcon state. It is only the fallback to Cygwin processes
    that is dangerous without an active pseudo console.
    
    Guard the fallback with a `pcon_activated` check, since handing nat
    pipe ownership to a Cygwin process only makes sense when there is an
    active pseudo console for it to manage.
    
    Fixes: 04f386e9af99 ("Cygwin: console: Inherit pcon hand over from parent pty")
    Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>
    Reviewed-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>

Diff:
---
 winsup/cygwin/fhandler/pty.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/winsup/cygwin/fhandler/pty.cc b/winsup/cygwin/fhandler/pty.cc
index 3c8fb76c0..9868e88e5 100644
--- a/winsup/cygwin/fhandler/pty.cc
+++ b/winsup/cygwin/fhandler/pty.cc
@@ -3596,7 +3596,7 @@ fhandler_pty_slave::get_winpid_to_hand_over (tty *ttyp,
       if (!switch_to)
 	switch_to = get_console_process_id (current_pid,
 					    false, true, false, true);
-      if (!switch_to)
+      if (!switch_to && ttyp->pcon_activated)
 	switch_to = get_console_process_id (current_pid,
 					    false, false, false, false);
     }