Issue #17223: Fix PyUnicode_FromUnicode() on Windows (16-bit wchar_t type)

to reject invalid UTF-16 surrogate.

Misc/NEWS

@@ -10,6 +10,9 @@ What's New in Python 3.4.0 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #17223: Fix PyUnicode_FromUnicode() on Windows (16-bit wchar_t type)
+  to reject invalid UTF-16 surrogate.
+
 - Issue #17032: The "global" in the "NameError: global name 'x' is not defined"
   error message has been removed.  Patch by Ram Rachum.
 

Objects/unicodeobject.c

@@ -1384,14 +1384,19 @@ find_maxchar_surrogates(const wchar_t *begin, const wchar_t *end,
 
     for (iter = begin; iter < end; ) {
 #if SIZEOF_WCHAR_T == 2
-        if (Py_UNICODE_IS_HIGH_SURROGATE(iter[0])
-            && (iter+1) < end
+        if (Py_UNICODE_IS_HIGH_SURROGATE(iter[0])) {
+            if ((iter+1) < end
                 && Py_UNICODE_IS_LOW_SURROGATE(iter[1]))
             {
                 ch = Py_UNICODE_JOIN_SURROGATES(iter[0], iter[1]);
                 ++(*num_surrogates);
                 iter += 2;
             }
+            else {
+                PyErr_SetString(PyExc_ValueError, "illegal UTF-16 surrogate");
+                return -1;
+            }
+        }
         else
 #endif
         {