[3.6] bpo-30708: Check for null characters in PyUnicode_AsWideCharString(). (GH-2285) (#2443)

Raise a ValueError if the second argument is NULL and the wchar_t\*
string contains null characters..
(cherry picked from commit e613e6add5)

Objects/unicodeobject.c

@@ -3017,6 +3017,37 @@ PyUnicode_AsWideCharString(PyObject *unicode,
     return buffer;
 }
 
+wchar_t*
+_PyUnicode_AsWideCharString(PyObject *unicode)
+{
+    const wchar_t *wstr;
+    wchar_t *buffer;
+    Py_ssize_t buflen;
+
+    if (unicode == NULL) {
+        PyErr_BadInternalCall();
+        return NULL;
+    }
+
+    wstr = PyUnicode_AsUnicodeAndSize(unicode, &buflen);
+    if (wstr == NULL) {
+        return NULL;
+    }
+    if (wcslen(wstr) != (size_t)buflen) {
+        PyErr_SetString(PyExc_ValueError,
+                        "embedded null character");
+        return NULL;
+    }
+
+    buffer = PyMem_NEW(wchar_t, buflen + 1);
+    if (buffer == NULL) {
+        PyErr_NoMemory();
+        return NULL;
+    }
+    memcpy(buffer, wstr, (buflen + 1) * sizeof(wchar_t));
+    return buffer;
+}
+
 #endif /* HAVE_WCHAR_H */
 
 PyObject *