[New-bugs-announce] [issue30708] Ensure that the result of PyUnicode_AsWideCharString() doesn't contain null characters if size is not returned

[Serhiy Storchaka]

New submission from Serhiy Storchaka:

The second parameter of the PyUnicode_AsWideCharString() function

    wchar_t* PyUnicode_AsWideCharString(PyObject *unicode, Py_ssize_t *size)

is a pointer to Py_ssize_t. The size of created wchar_t array is saved on this pointer if it is not NULL. If NULL is passed as the second argument, the only way to determine the size of the wchar_t string is using wcslen(). But if the string contains the null characters, it looks truncated for wcslen() and other C API functions.

Reliable code should always pass the non-NULL second argument and check that wcslen() is equal to the returned string size. See for example the code in Modules/_io/winconsoleio.c. Passing NULL as the second argument is unsafe. But most code doesn't do such check (see all other usages of PyUnicode_AsWideCharString(..., NULL)). And this check complicates the callers code.

I propose to make the check for null characters inside of PyUnicode_AsWideCharString() if NULL is passes as the second argument. This will fix all unsafe usages of PyUnicode_AsWideCharString() and allow to simplify the reliable code.

This issue fixes the part of issue13617.

----------
components: Interpreter Core, Unicode
messages: 296401
nosy: ezio.melotti, haypo, serhiy.storchaka, steve.dower
priority: normal
severity: normal
stage: patch review
status: open
title: Ensure that the result of PyUnicode_AsWideCharString() doesn't contain null characters if size is not returned
type: enhancement
versions: Python 3.7

_______________________________________
Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue30708>
_______________________________________