Cygwin: console: Fix the console states after the console is closed

Due to a bug introduced by the commit 3312f2d, when the parent
process exits before the child process exits, disable_master_thread
is wrongly set to true, that disables special key handling such as
Ctrl-C. With this patch, the disable_master_thread is set to true if
any of the following conditions is met.
  - The parent process is not a cygwin process.
  - The master process already died.
  - The current process is the master process.
Otherwise, disable_master_thread remains false to keep special key
handling enabled.

Addresses: https://cygwin.com/pipermail/cygwin/2025-April/257909.html
Fixed: 3312f2d ("Cygwin: console: Redesign mode set strategy on close().")
Reported-by: Jeremy Drake <[email protected]>
Signed-off-by: Takashi Yano <[email protected]>

Author: tyan0

winsup/cygwin/fhandler/console.cc

@@ -932,7 +932,7 @@ fhandler_console::cleanup_for_non_cygwin_app (handle_set_t *p)
   /* Cleaning-up console mode for non-cygwin app. */
   /* conmode can be tty::restore when non-cygwin app is
      exec'ed from login shell. */
-  tty::cons_mode conmode = cons_mode_on_close ();
+  tty::cons_mode conmode = cons_mode_on_close (p);
   set_output_mode (conmode, ti, p);
   set_input_mode (conmode, ti, p);
   set_disable_master_thread (con.owner == GetCurrentProcessId ());
@@ -1991,8 +1991,9 @@ fhandler_console::close (int flag)
 
   acquire_output_mutex (mutex_timeout);
 
-  if (shared_console_info[unit] && myself->ppid == 1
-      && (dev_t) myself->ctty == get_device ())
+  if (shared_console_info[unit] && con.curr_input_mode != tty::restore
+      && (dev_t) myself->ctty == get_device ()
+      && cons_mode_on_close (&handle_set) == tty::restore)
     {
       set_output_mode (tty::restore, &get_ttyp ()->ti, &handle_set);
       set_input_mode (tty::restore, &get_ttyp ()->ti, &handle_set);
@@ -4704,10 +4705,25 @@ fhandler_console::fstat (struct stat *st)
 }
 
 tty::cons_mode
-fhandler_console::cons_mode_on_close ()
+fhandler_console::cons_mode_on_close (handle_set_t *p)
 {
+  int unit = p->unit;
   if (myself->ppid != 1) /* Execed from normal cygwin process. */
     return tty::cygwin;
 
+  if (!process_alive (con.owner)) /* The Master process already died. */
+    return tty::restore;
+  if (con.owner == GetCurrentProcessId ()) /* Master process */
+    return tty::restore;
+
+  PROCESS_BASIC_INFORMATION pbi;
+  NTSTATUS status =
+    NtQueryInformationProcess (GetCurrentProcess (), ProcessBasicInformation,
+			       &pbi, sizeof (pbi), NULL);
+  if (NT_SUCCESS (status)
+      && !process_alive ((DWORD) pbi.InheritedFromUniqueProcessId))
+    /* Execed from normal cygwin process and the parent has been exited. */
+    return tty::cygwin;
+
   return tty::restore; /* otherwise, restore */
 }

winsup/cygwin/local_includes/fhandler.h

@@ -2368,7 +2368,7 @@ class fhandler_console: public fhandler_termios
 
   void setup_pcon_hand_over ();
   static void pcon_hand_over_proc ();
-  static tty::cons_mode cons_mode_on_close ();
+  static tty::cons_mode cons_mode_on_close (handle_set_t *);
 
   friend tty_min * tty_list::get_cttyp ();
 };