gh-154225: Fix os.openpty() acquiring a controlling terminal on Solaris (GH-154229)

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

Author: serhiy-storchaka

Misc/NEWS.d/next/Library/2026-07-20-14-10-00.gh-issue-154225.openpty.rst

@@ -0,0 +1,2 @@
+Fix :func:`os.openpty` on Solaris and illumos: it no longer leaves the
+pseudo-terminal as the controlling terminal of the calling process.

Modules/posixmodule.c

@@ -9431,11 +9431,30 @@ os_openpty_impl(PyObject *module)
         goto posix_error;
 
 #if defined(HAVE_STROPTS_H) && !defined(HAVE_DEV_PTC)
+    // Pushing "ptem" makes the slave a terminal, which a session leader
+    // without a controlling terminal then acquires as one despite O_NOCTTY.
+    // Note whether we already had one, so a new one can be disowned below.
+    int had_ctty = 0;
+#ifdef TIOCNOTTY
+    int tty_fd = open("/dev/tty", O_RDONLY | O_NOCTTY);
+    if (tty_fd >= 0) {
+        had_ctty = 1;
+        close(tty_fd);
+    }
+#endif
     ioctl(slave_fd, I_PUSH, "ptem"); /* push ptem */
     ioctl(slave_fd, I_PUSH, "ldterm"); /* push ldterm */
 #ifndef __hpux
     ioctl(slave_fd, I_PUSH, "ttcompat"); /* push ttcompat */
 #endif /* __hpux */
+#ifdef TIOCNOTTY
+    if (!had_ctty && getsid(0) == getpid()) {
+        // Disown it; TIOCNOTTY sends SIGHUP to the session leader.
+        PyOS_sighandler_t sig_saved = PyOS_setsig(SIGHUP, SIG_IGN);
+        ioctl(slave_fd, TIOCNOTTY);
+        PyOS_setsig(SIGHUP, sig_saved);
+    }
+#endif
 #endif /* defined(HAVE_STROPTS_H) && !defined(HAVE_DEV_PTC) */
 #endif /* HAVE_OPENPTY */