[3.13] bpo-44172: Keep reference to original window in curses subwindow objects (GH-26226) (GH-133370)

serhiy-storchaka · michaelforney · web-flow · commit 3c9d1778ef73 · 2025-05-04T11:15:43.000Z
The X/Open curses specification[0] and ncurses documentation[1] both state that subwindows must be deleted before the main window. Deleting the windows in the wrong order causes a double-free with NetBSD's curses implementation. To fix this, keep track of the original window object in the subwindow object, and keep a reference to the original for the lifetime of the subwindow. [0] https://pubs.opengroup.org/onlinepubs/7908799/xcurses/delwin.html [1] https://invisible-island.net/ncurses/man/curs_window.3x.html (cherry picked from commit 0af61fe) Co-authored-by: Michael Forney <mforney@mforney.org>
diff --git a/Include/py_curses.h b/Include/py_curses.h
@@ -75,10 +75,11 @@ extern "C" {
 
 /* Type declarations */
 
-typedef struct {
+typedef struct PyCursesWindowObject {
     PyObject_HEAD
     WINDOW *win;
     char *encoding;
+    struct PyCursesWindowObject *orig;
 } PyCursesWindowObject;
 
 #define PyCursesWindow_Check(v) Py_IS_TYPE((v), &PyCursesWindow_Type)
diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
@@ -8,7 +8,8 @@
 from unittest.mock import MagicMock
 
 from test.support import (requires, verbose, SaveSignals, cpython_only,
-                          check_disallow_instantiation, MISSING_C_DOCSTRINGS)
+                          check_disallow_instantiation, MISSING_C_DOCSTRINGS,
+                          gc_collect)
 from test.support.import_helper import import_module
 
 # Optionally test curses module.  This currently requires that the
@@ -187,6 +188,14 @@ def test_create_windows(self):
         self.assertEqual(win3.getparyx(), (2, 1))
         self.assertEqual(win3.getmaxyx(), (6, 11))
 
+    def test_subwindows_references(self):
+        win = curses.newwin(5, 10)
+        win2 = win.subwin(3, 7)
+        del win
+        gc_collect()
+        del win2
+        gc_collect()
+
     def test_move_cursor(self):
         stdscr = self.stdscr
         win = stdscr.subwin(10, 15, 2, 5)
diff --git a/Misc/NEWS.d/next/Library/2021-05-18-19-12-58.bpo-44172.rJ_-CI.rst b/Misc/NEWS.d/next/Library/2021-05-18-19-12-58.bpo-44172.rJ_-CI.rst
@@ -0,0 +1,2 @@
+Keep a reference to original :mod:`curses` windows in subwindows so
+that the original window does not get deleted before subwindows.
diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
@@ -666,7 +666,8 @@ Window_TwoArgNoReturnFunction(wresize, int, "ii;lines,columns")
 /* Allocation and deallocation of Window Objects */
 
 static PyObject *
-PyCursesWindow_New(WINDOW *win, const char *encoding)
+PyCursesWindow_New(WINDOW *win, const char *encoding,
+                   PyCursesWindowObject *orig)
 {
     PyCursesWindowObject *wo;
 
@@ -697,6 +698,8 @@ PyCursesWindow_New(WINDOW *win, const char *encoding)
         PyErr_NoMemory();
         return NULL;
     }
+    wo->orig = orig;
+    Py_XINCREF(orig);
     return (PyObject *)wo;
 }
 
@@ -706,6 +709,7 @@ PyCursesWindow_Dealloc(PyCursesWindowObject *wo)
     if (wo->win != stdscr) delwin(wo->win);
     if (wo->encoding != NULL)
         PyMem_Free(wo->encoding);
+    Py_XDECREF(wo->orig);
     PyObject_Free(wo);
 }
 
@@ -1309,7 +1313,7 @@ _curses_window_derwin_impl(PyCursesWindowObject *self, int group_left_1,
         return NULL;
     }
 
-    return (PyObject *)PyCursesWindow_New(win, NULL);
+    return (PyObject *)PyCursesWindow_New(win, NULL, self);
 }
 
 /*[clinic input]
@@ -2336,7 +2340,7 @@ _curses_window_subwin_impl(PyCursesWindowObject *self, int group_left_1,
         return NULL;
     }
 
-    return (PyObject *)PyCursesWindow_New(win, self->encoding);
+    return (PyObject *)PyCursesWindow_New(win, self->encoding, self);
 }
 
 /*[clinic input]
@@ -3084,7 +3088,7 @@ _curses_getwin(PyObject *module, PyObject *file)
         PyErr_SetString(PyCursesError, catchall_NULL);
         goto error;
     }
-    res = PyCursesWindow_New(win, NULL);
+    res = PyCursesWindow_New(win, NULL, NULL);
 
 error:
     fclose(fp);
@@ -3257,7 +3261,7 @@ _curses_initscr_impl(PyObject *module)
 
     if (initialised) {
         wrefresh(stdscr);
-        return (PyObject *)PyCursesWindow_New(stdscr, NULL);
+        return (PyObject *)PyCursesWindow_New(stdscr, NULL, NULL);
     }
 
     win = initscr();
@@ -3349,7 +3353,7 @@ _curses_initscr_impl(PyObject *module)
     SetDictInt("LINES", LINES);
     SetDictInt("COLS", COLS);
 
-    winobj = (PyCursesWindowObject *)PyCursesWindow_New(win, NULL);
+    winobj = (PyCursesWindowObject *)PyCursesWindow_New(win, NULL, NULL);
     screen_encoding = winobj->encoding;
     return (PyObject *)winobj;
 }
@@ -3728,7 +3732,7 @@ _curses_newpad_impl(PyObject *module, int nlines, int ncols)
         return NULL;
     }
 
-    return (PyObject *)PyCursesWindow_New(win, NULL);
+    return (PyObject *)PyCursesWindow_New(win, NULL, NULL);
 }
 
 /*[clinic input]
@@ -3767,7 +3771,7 @@ _curses_newwin_impl(PyObject *module, int nlines, int ncols,
         return NULL;
     }
 
-    return (PyObject *)PyCursesWindow_New(win, NULL);
+    return (PyObject *)PyCursesWindow_New(win, NULL, NULL);
 }
 
 /*[clinic input]

Original file line number	Diff line number	Diff line change
`@@ -0,0 +1,2 @@`
	`1`	+Keep a reference to original :mod:`curses` windows in subwindows so
	`2`	`+that the original window does not get deleted before subwindows.`
Original file line number	Diff line number	Diff line change
`@@ -666,7 +666,8 @@ Window_TwoArgNoReturnFunction(wresize, int, "ii;lines,columns")`
`666`	`666`	`/* Allocation and deallocation of Window Objects */`
`667`	`667`
`668`	`668`	`static PyObject *`
`669`		`-PyCursesWindow_New(WINDOW win, const char encoding)`
	`669`	`+PyCursesWindow_New(WINDOW win, const char encoding,`
	`670`	`+ PyCursesWindowObject *orig)`
`670`	`671`	`{`
`671`	`672`	`PyCursesWindowObject *wo;`
`672`	`673`
`@@ -697,6 +698,8 @@ PyCursesWindow_New(WINDOW win, const char encoding)`
`697`	`698`	`PyErr_NoMemory();`
`698`	`699`	`return NULL;`
`699`	`700`	`}`
	`701`	`+ wo->orig = orig;`
	`702`	`+ Py_XINCREF(orig);`
`700`	`703`	`return (PyObject *)wo;`
`701`	`704`	`}`
`702`	`705`
`@@ -706,6 +709,7 @@ PyCursesWindow_Dealloc(PyCursesWindowObject *wo)`
`706`	`709`	`if (wo->win != stdscr) delwin(wo->win);`
`707`	`710`	`if (wo->encoding != NULL)`
`708`	`711`	`PyMem_Free(wo->encoding);`
	`712`	`+ Py_XDECREF(wo->orig);`
`709`	`713`	`PyObject_Free(wo);`
`710`	`714`	`}`
`711`	`715`
`@@ -1309,7 +1313,7 @@ _curses_window_derwin_impl(PyCursesWindowObject *self, int group_left_1,`
`1309`	`1313`	`return NULL;`
`1310`	`1314`	`}`
`1311`	`1315`
`1312`		`- return (PyObject *)PyCursesWindow_New(win, NULL);`
	`1316`	`+ return (PyObject *)PyCursesWindow_New(win, NULL, self);`
`1313`	`1317`	`}`
`1314`	`1318`
`1315`	`1319`	`/*[clinic input]`
`@@ -2336,7 +2340,7 @@ _curses_window_subwin_impl(PyCursesWindowObject *self, int group_left_1,`
`2336`	`2340`	`return NULL;`
`2337`	`2341`	`}`
`2338`	`2342`
`2339`		`- return (PyObject *)PyCursesWindow_New(win, self->encoding);`
	`2343`	`+ return (PyObject *)PyCursesWindow_New(win, self->encoding, self);`
`2340`	`2344`	`}`
`2341`	`2345`
`2342`	`2346`	`/*[clinic input]`
`@@ -3084,7 +3088,7 @@ _curses_getwin(PyObject module, PyObject file)`
`3084`	`3088`	`PyErr_SetString(PyCursesError, catchall_NULL);`
`3085`	`3089`	`goto error;`
`3086`	`3090`	`}`
`3087`		`- res = PyCursesWindow_New(win, NULL);`
	`3091`	`+ res = PyCursesWindow_New(win, NULL, NULL);`
`3088`	`3092`
`3089`	`3093`	`error:`
`3090`	`3094`	`fclose(fp);`
`@@ -3257,7 +3261,7 @@ _curses_initscr_impl(PyObject *module)`
`3257`	`3261`
`3258`	`3262`	`if (initialised) {`
`3259`	`3263`	`wrefresh(stdscr);`
`3260`		`- return (PyObject *)PyCursesWindow_New(stdscr, NULL);`
	`3264`	`+ return (PyObject *)PyCursesWindow_New(stdscr, NULL, NULL);`
`3261`	`3265`	`}`
`3262`	`3266`
`3263`	`3267`	`win = initscr();`
`@@ -3349,7 +3353,7 @@ _curses_initscr_impl(PyObject *module)`
`3349`	`3353`	`SetDictInt("LINES", LINES);`
`3350`	`3354`	`SetDictInt("COLS", COLS);`
`3351`	`3355`
`3352`		`- winobj = (PyCursesWindowObject *)PyCursesWindow_New(win, NULL);`
	`3356`	`+ winobj = (PyCursesWindowObject *)PyCursesWindow_New(win, NULL, NULL);`
`3353`	`3357`	`screen_encoding = winobj->encoding;`
`3354`	`3358`	`return (PyObject *)winobj;`
`3355`	`3359`	`}`
`@@ -3728,7 +3732,7 @@ _curses_newpad_impl(PyObject *module, int nlines, int ncols)`
`3728`	`3732`	`return NULL;`
`3729`	`3733`	`}`
`3730`	`3734`
`3731`		`- return (PyObject *)PyCursesWindow_New(win, NULL);`
	`3735`	`+ return (PyObject *)PyCursesWindow_New(win, NULL, NULL);`
`3732`	`3736`	`}`
`3733`	`3737`
`3734`	`3738`	`/*[clinic input]`
`@@ -3767,7 +3771,7 @@ _curses_newwin_impl(PyObject *module, int nlines, int ncols,`
`3767`	`3771`	`return NULL;`
`3768`	`3772`	`}`
`3769`	`3773`
`3770`		`- return (PyObject *)PyCursesWindow_New(win, NULL);`
	`3774`	`+ return (PyObject *)PyCursesWindow_New(win, NULL, NULL);`
`3771`	`3775`	`}`
`3772`	`3776`
`3773`	`3777`	`/*[clinic input]`