Cygwin: console, pty: Fix segfault in child_info_spawn::worker().

- After the commit "Cygwin: pty, console: Fix handle leak which
  occurs on exec() error.", startxwin cannot start X due to the
  error "Failed to activate virtual core keyboard: 2". The problem
  is access violation in the code retrieving the pgid of the ctty.
  This patch fixes the issue.

  Addresses: https://cygwin.com/pipermail/cygwin/2022-March/251013.html

2 files changed, 7 insertions, 3 deletions

diff --git a/winsup/cygwin/fhandler.h b/winsup/cygwin/fhandler.h
index e7cf17d..b87160e 100644
--- a/winsup/cygwin/fhandler.h
+++ b/winsup/cygwin/fhandler.h
@@ -1915,6 +1915,7 @@ class fhandler_termios: public fhandler_base
   };
 
  public:
+  virtual pid_t tc_getpgid () { return 0; };
   tty_min*& tc () {return _tc;}
   fhandler_termios () :
   fhandler_base ()
@@ -2158,9 +2159,10 @@ private:
 			       const handle_set_t *p);
 
  public:
-  static pid_t tc_getpgid ()
+  pid_t tc_getpgid ()
   {
-    return shared_console_info ? shared_console_info->tty_min_state.getpgid () : myself->pgid;
+    return shared_console_info ?
+      shared_console_info->tty_min_state.getpgid () : 0;
   }
   fhandler_console (fh_devices);
   static console_state *open_shared_console (HWND hw, HANDLE& h)
@@ -2343,6 +2345,8 @@ class fhandler_pty_slave: public fhandler_pty_common
   void fch_close_handles ();
 
  public:
+  pid_t tc_getpgid () { return _tc ? _tc->pgid : 0; }
+
   struct handle_set_t
   {
     HANDLE from_master_nat;
diff --git a/winsup/cygwin/spawn.cc b/winsup/cygwin/spawn.cc
index 3b54309..fb3d09d 100644
--- a/winsup/cygwin/spawn.cc
+++ b/winsup/cygwin/spawn.cc
@@ -564,7 +564,7 @@ child_info_spawn::worker (const char *prog_arg, const char *const *argv,
 	 because the Ctrl-C event is sent to all processes in the console, unless
 	 they ignore it explicitely.  CREATE_NEW_PROCESS_GROUP does that for us. */
       pid_t ctty_pgid =
-	::cygheap->ctty ? ::cygheap->ctty->tc ()->getpgid () : 0;
+	::cygheap->ctty ? ::cygheap->ctty->tc_getpgid () : 0;
       if (!iscygwin () && ctty_pgid && ctty_pgid != myself->pgid)
 	c_flags |= CREATE_NEW_PROCESS_GROUP;
       refresh_cygheap ();