Use-after-free for a window created inside curses.screen.use() #155864

Bug description:

screen.use() makes its screen current for the callback, but a window created there records the screen that was current before the call. The window therefore does not keep its own screen alive, and that screen can be freed while the window is still in use.

import curses, gc, pty

A = curses.newterm(None, pty.openpty()[1], pty.openpty()[1])
B = curses.newterm(None, pty.openpty()[1], pty.openpty()[1])
win = A.use(lambda s: curses.newwin(5, 5))   # a window on screen A
del A                                        # A's only window is win
gc.collect()
win.addstr(0, 0, "x")

$ TERM=xterm-256color ./python repro.py; echo "rc=$?"
Segmentation fault (core dumped)
rc=139

Expected: the window keeps the screen it belongs to alive. Doc/library/curses.rst says "Each window keeps its screen alive, so a screen remains valid as long as any of its windows does".

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-155864: Keep the module's current screen in step with use_screen() #155865