bpo-36346: Do not use legacy Unicode C API in ctypes. (python#21429)

Modules/_ctypes/_ctypes.c

@@ -1366,8 +1366,6 @@ WCharArray_get_value(CDataObject *self, void *Py_UNUSED(ignored))
 static int
 WCharArray_set_value(CDataObject *self, PyObject *value, void *Py_UNUSED(ignored))
 {
-    Py_ssize_t result = 0;
-
     if (value == NULL) {
         PyErr_SetString(PyExc_TypeError,
                         "can't delete attribute");
@@ -1378,29 +1376,24 @@ WCharArray_set_value(CDataObject *self, PyObject *value, void *Py_UNUSED(ignored
                         "unicode string expected instead of %s instance",
                         Py_TYPE(value)->tp_name);
         return -1;
-    } else
-        Py_INCREF(value);
+    }
 
+    Py_ssize_t size = self->b_size / sizeof(wchar_t);
     Py_ssize_t len = PyUnicode_AsWideChar(value, NULL, 0);
     if (len < 0) {
         return -1;
     }
     // PyUnicode_AsWideChar() returns number of wchars including trailing null byte,
     // when it is called with NULL.
-    if (((size_t)len-1) > self->b_size/sizeof(wchar_t)) {
+    assert(len > 0);
+    if (len - 1 > size) {
         PyErr_SetString(PyExc_ValueError, "string too long");
-        result = -1;
-        goto done;
-    }
-    result = PyUnicode_AsWideChar(value,
-                                  (wchar_t *)self->b_ptr,
-                                  self->b_size/sizeof(wchar_t));
-    if (result >= 0 && (size_t)result < self->b_size/sizeof(wchar_t))
-        ((wchar_t *)self->b_ptr)[result] = (wchar_t)0;
-  done:
-    Py_DECREF(value);
-
-    return result >= 0 ? 0 : -1;
+        return -1;
+    }
+    if (PyUnicode_AsWideChar(value, (wchar_t *)self->b_ptr, size) < 0) {
+        return -1;
+    }
+    return 0;
 }
 
 static PyGetSetDef WCharArray_getsets[] = {
@@ -3484,10 +3477,12 @@ _validate_paramflags(PyTypeObject *type, PyObject *paramflags)
     for (i = 0; i < len; ++i) {
         PyObject *item = PyTuple_GET_ITEM(paramflags, i);
         int flag;
-        char *name;
+        PyObject *name = Py_None;
         PyObject *defval;
         PyObject *typ;
-        if (!PyArg_ParseTuple(item, "i|ZO", &flag, &name, &defval)) {
+        if (!PyArg_ParseTuple(item, "i|OO", &flag, &name, &defval) ||
+            !(name == Py_None || PyUnicode_Check(name)))
+        {
             PyErr_SetString(PyExc_TypeError,
                    "paramflags must be a sequence of (int [,string [,value]]) tuples");
             return 0;

Modules/_ctypes/callproc.c

@@ -1300,7 +1300,6 @@ module. load_flags are as defined for LoadLibraryEx in the\n\
 Windows API.\n";
 static PyObject *load_library(PyObject *self, PyObject *args)
 {
-    const WCHAR *name;
     PyObject *nameobj;
     int load_flags = 0;
     HMODULE hMod;
@@ -1309,14 +1308,14 @@ static PyObject *load_library(PyObject *self, PyObject *args)
     if (!PyArg_ParseTuple(args, "U|i:LoadLibrary", &nameobj, &load_flags))
         return NULL;
 
-    name = _PyUnicode_AsUnicode(nameobj);
-    if (!name)
-        return NULL;
-
     if (PySys_Audit("ctypes.dlopen", "O", nameobj) < 0) {
         return NULL;
     }
 
+    WCHAR *name = PyUnicode_AsWideCharString(nameobj, NULL);
+    if (!name)
+        return NULL;
+
     Py_BEGIN_ALLOW_THREADS
     /* bpo-36085: Limit DLL search directories to avoid pre-loading
      * attacks and enable use of the AddDllDirectory function.
@@ -1325,6 +1324,7 @@ static PyObject *load_library(PyObject *self, PyObject *args)
     err = hMod ? 0 : GetLastError();
     Py_END_ALLOW_THREADS
 
+    PyMem_Free(name);
     if (err == ERROR_MOD_NOT_FOUND) {
         PyErr_Format(PyExc_FileNotFoundError,
                      ("Could not find module '%.500S' (or one of its "

Modules/_ctypes/cfield.c

@@ -1220,11 +1220,8 @@ U_set(void *ptr, PyObject *value, Py_ssize_t length)
                      "string too long (%zd, maximum length %zd)",
                      size, length);
         return NULL;
-    } else if (size < length-1)
-        /* copy terminating NUL character if there is space */
-        size += 1;
-
-    if (PyUnicode_AsWideChar(value, (wchar_t *)ptr, size) == -1) {
+    }
+    if (PyUnicode_AsWideChar(value, (wchar_t *)ptr, length) == -1) {
         return NULL;
     }