gh-116510: Fix crash due to shared immortal interned strings. (gh-124646

)

Misc/NEWS.d/next/Core_and_Builtins/2024-09-26-18-21-06.gh-issue-116510.FacUWO.rst

@@ -0,0 +1,5 @@
+Fix a crash caused by immortal interned strings being shared between
+sub-interpreters that use basic single-phase init. In that case, the string
+can be used by an interpreter that outlives the interpreter that created and
+interned it. For interpreters that share obmalloc state, also share the
+interned dict with the main interpreter.

Objects/unicodeobject.c

@@ -282,13 +282,37 @@ hashtable_unicode_compare(const void *key1, const void *key2)
  }
 }
 
+/* Return true if this interpreter should share the main interpreter's
+ intern_dict. That's important for interpreters which load basic
+ single-phase init extension modules (m_size == -1). There could be interned
+ immortal strings that are shared between interpreters, due to the
+ PyDict_Update(mdict, m_copy) call in import_find_extension().
+
+ It's not safe to deallocate those strings until all interpreters that
+ potentially use them are freed. By storing them in the main interpreter, we
+ ensure they get freed after all other interpreters are freed.
+*/
+static bool
+has_shared_intern_dict(PyInterpreterState *interp)
+{
+ PyInterpreterState *main_interp = _PyInterpreterState_Main();
+ return interp != main_interp && interp->feature_flags & Py_RTFLAGS_USE_MAIN_OBMALLOC;
+}
+
 static int
 init_interned_dict(PyInterpreterState *interp)
 {
  assert(get_interned_dict(interp) == NULL);
- PyObject *interned = interned = PyDict_New();
- if (interned == NULL) {
- return -1;
+ PyObject *interned;
+ if (has_shared_intern_dict(interp)) {
+ interned = get_interned_dict(_PyInterpreterState_Main());
+ Py_INCREF(interned);
+ }
+ else {
+ interned = PyDict_New();
+ if (interned == NULL) {
+ return -1;
+ }
  }
  _Py_INTERP_CACHED_OBJECT(interp, interned_strings) = interned;
  return 0;
@@ -299,7 +323,10 @@ clear_interned_dict(PyInterpreterState *interp)
 {
  PyObject *interned = get_interned_dict(interp);
  if (interned != NULL) {
- PyDict_Clear(interned);
+ if (!has_shared_intern_dict(interp)) {
+ // only clear if the dict belongs to this interpreter
+ PyDict_Clear(interned);
+ }
  Py_DECREF(interned);
  _Py_INTERP_CACHED_OBJECT(interp, interned_strings) = NULL;
  }
@@ -15618,6 +15645,13 @@ _PyUnicode_ClearInterned(PyInterpreterState *interp)
  }
  assert(PyDict_CheckExact(interned));
 
+ if (has_shared_intern_dict(interp)) {
+ // the dict doesn't belong to this interpreter, skip the debug
+ // checks on it and just clear the pointer to it
+ clear_interned_dict(interp);
+ return;
+ }
+
 #ifdef INTERNED_STATS
  fprintf(stderr, "releasing %zd interned strings\n",
  PyDict_GET_SIZE(interned));
@@ -16126,8 +16160,10 @@ _PyUnicode_Fini(PyInterpreterState *interp)
 {
  struct _Py_unicode_state *state = &interp->unicode;
 
- // _PyUnicode_ClearInterned() must be called before _PyUnicode_Fini()
- assert(get_interned_dict(interp) == NULL);
+ if (!has_shared_intern_dict(interp)) {
+ // _PyUnicode_ClearInterned() must be called before _PyUnicode_Fini()
+ assert(get_interned_dict(interp) == NULL);
+ }
 
  _PyUnicode_FiniEncodings(&state->fs_codec);