[New-bugs-announce] [issue36311] Flaw in Windows code page decoder for large input

[Serhiy Storchaka]

New submission from Serhiy Storchaka <storchaka+cpython at gmail.com>:

There is a flaw in PyUnicode_DecodeCodePageStateful() (exposed as _codecs.code_page_decode() at Python level). Since MultiByteToWideChar() takes the size of the input as C int, it can not be used for decoding more than 2 GiB. Large input is split on chunks of size 2 GiB which are decoded separately. The problem is if it split in the middle of a multibyte character. In this case decoding chunks will always fail or replace incomplete parts of the multibyte character at both ends with what the error handler returns.

It is hard to reproduce this bug, because you need to decode more than 2 GiB, and you will need at least 14 GiB of RAM for this (maybe more).

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components: Interpreter Core, Windows
messages: 338061
nosy: doerwalter, lemburg, paul.moore, serhiy.storchaka, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
status: open
title: Flaw in Windows code page decoder for large input
type: behavior
versions: Python 2.7, Python 3.7, Python 3.8

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue36311>
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