gh-83004: Harden msvcrt init (#103383)

PC/msvcrtmodule.c

@@ -609,11 +609,11 @@ PyMODINIT_FUNC
 PyInit_msvcrt(void)
 {
  int st;
- PyObject *d, *version;
  PyObject *m = PyModule_Create(&msvcrtmodule);
- if (m == NULL)
+ if (m == NULL) {
  return NULL;
- d = PyModule_GetDict(m);
+ }
+ PyObject *d = PyModule_GetDict(m); // Borrowed ref.
 
  /* constants for the locking() function's mode argument */
  insertint(d, "LK_LOCK", _LK_LOCK);
@@ -644,30 +644,47 @@ PyInit_msvcrt(void)
 #ifdef _VC_ASSEMBLY_PUBLICKEYTOKEN
  st = PyModule_AddStringConstant(m, "VC_ASSEMBLY_PUBLICKEYTOKEN",
  _VC_ASSEMBLY_PUBLICKEYTOKEN);
- if (st < 0) return NULL;
+ if (st < 0) {
+ goto error;
+ }
 #endif
 #ifdef _CRT_ASSEMBLY_VERSION
  st = PyModule_AddStringConstant(m, "CRT_ASSEMBLY_VERSION",
  _CRT_ASSEMBLY_VERSION);
- if (st < 0) return NULL;
+ if (st < 0) {
+ goto error;
+ }
 #endif
 #ifdef __LIBRARIES_ASSEMBLY_NAME_PREFIX
  st = PyModule_AddStringConstant(m, "LIBRARIES_ASSEMBLY_NAME_PREFIX",
  __LIBRARIES_ASSEMBLY_NAME_PREFIX);
- if (st < 0) return NULL;
+ if (st < 0) {
+ goto error;
+ }
 #endif
 
  /* constants for the 2010 crt versions */
 #if defined(_VC_CRT_MAJOR_VERSION) && defined (_VC_CRT_MINOR_VERSION) && defined(_VC_CRT_BUILD_VERSION) && defined(_VC_CRT_RBUILD_VERSION)
- version = PyUnicode_FromFormat("%d.%d.%d.%d", _VC_CRT_MAJOR_VERSION,
- _VC_CRT_MINOR_VERSION,
- _VC_CRT_BUILD_VERSION,
- _VC_CRT_RBUILD_VERSION);
- st = PyModule_AddObject(m, "CRT_ASSEMBLY_VERSION", version);
- if (st < 0) return NULL;
+ PyObject *version = PyUnicode_FromFormat("%d.%d.%d.%d",
+ _VC_CRT_MAJOR_VERSION,
+ _VC_CRT_MINOR_VERSION,
+ _VC_CRT_BUILD_VERSION,
+ _VC_CRT_RBUILD_VERSION);
+ if (version == NULL) {
+ goto error;
+ }
+ st = PyModule_AddObjectRef(m, "CRT_ASSEMBLY_VERSION", version);
+ Py_DECREF(version);
+ if (st < 0) {
+ goto error;
+ }
 #endif
  /* make compiler warning quiet if st is unused */
  (void)st;
 
  return m;
+
+error:
+ Py_DECREF(m);
+ return NULL;
 }