#18113: avoid segfault if Py_XDECREF triggers code that calls set_panel_userptr again

Problem noted & original patch by Serhiy Storchaka; I tweaked the patch a bit.

2 files changed, 17 insertions, 3 deletions

diff --git a/Lib/test/test_curses.py b/Lib/test/test_curses.py
index 76812b7..7310afc 100644
--- a/Lib/test/test_curses.py
+++ b/Lib/test/test_curses.py
@@ -264,6 +264,14 @@ def test_userptr_memory_leak(stdscr):
     if sys.getrefcount(obj) != nrefs:
         raise RuntimeError("set_userptr leaked references")
 
+def test_userptr_segfault(stdscr):
+    panel = curses.panel.new_panel(stdscr)
+    class A:
+        def __del__(self):
+            panel.set_userptr(None)
+    panel.set_userptr(A())
+    panel.set_userptr(None)
+
 def test_resize_term(stdscr):
     if hasattr(curses, 'resizeterm'):
         lines, cols = curses.LINES, curses.COLS
@@ -330,6 +338,7 @@ def main(stdscr):
         window_funcs(stdscr)
         test_userptr_without_set(stdscr)
         test_userptr_memory_leak(stdscr)
+        test_userptr_segfault(stdscr)
         test_resize_term(stdscr)
         test_issue6243(stdscr)
         test_unget_wch(stdscr)
diff --git a/Modules/_curses_panel.c b/Modules/_curses_panel.c
index c11f3d8..f560702 100644
--- a/Modules/_curses_panel.c
+++ b/Modules/_curses_panel.c
@@ -323,12 +323,17 @@ static PyObject *
 PyCursesPanel_set_panel_userptr(PyCursesPanelObject *self, PyObject *obj)
 {
     PyObject *oldobj;
+    int rc;
     PyCursesInitialised;
+    Py_INCREF(obj);
     oldobj = (PyObject *) panel_userptr(self->pan);
+    rc = set_panel_userptr(self->pan, (void*)obj);
+    if (rc == ERR) {
+        /* In case of an ncurses error, decref the new object again */
+        Py_DECREF(obj);
+    }
     Py_XDECREF(oldobj);
-    Py_INCREF(obj);
-    return PyCursesCheckERR(set_panel_userptr(self->pan, (void*)obj),
-                            "set_panel_userptr");
+    return PyCursesCheckERR(rc, "set_panel_userptr");
 }
 
 static PyObject *