[security] bpo-13617: Reject embedded null characters in wchar* strings. (#2302)

Based on patch by Victor Stinner.

Add private C API function _PyUnicode_AsUnicode() which is similar to
PyUnicode_AsUnicode(), but checks for null characters.

1 files changed, 10 insertions, 0 deletions

diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
index 5dc0865c1c..a70915143c 100644
--- a/Modules/_cursesmodule.c
+++ b/Modules/_cursesmodule.c
@@ -341,9 +341,11 @@ static int
 PyCurses_ConvertToString(PyCursesWindowObject *win, PyObject *obj,
                          PyObject **bytes, wchar_t **wstr)
 {
+    char *str;
     if (PyUnicode_Check(obj)) {
 #ifdef HAVE_NCURSESW
         assert (wstr != NULL);
+
         *wstr = PyUnicode_AsWideCharString(obj, NULL);
         if (*wstr == NULL)
             return 0;
@@ -353,12 +355,20 @@ PyCurses_ConvertToString(PyCursesWindowObject *win, PyObject *obj,
         *bytes = PyUnicode_AsEncodedString(obj, win->encoding, NULL);
         if (*bytes == NULL)
             return 0;
+        /* check for embedded null bytes */
+        if (PyBytes_AsStringAndSize(*bytes, &str, NULL) < 0) {
+            return 0;
+        }
         return 1;
 #endif
     }
     else if (PyBytes_Check(obj)) {
         Py_INCREF(obj);
         *bytes = obj;
+        /* check for embedded null bytes */
+        if (PyBytes_AsStringAndSize(*bytes, &str, NULL) < 0) {
+            return 0;
+        }
         return 1;
     }