[issue4126] remove not decodable environment variables

[STINNER Victor]

New submission from STINNER Victor <victor.stinner at haypocalc.com>:

Python3 skips environment variables which can not be parsed and 
decoded as unicode strings. But exec*() functions keep the original 
environment and so the child process environment is different than the 
Python environement (than os.environ).

I propose to remove these variables to avoid strange behaviours, but 
also to avoid possible security issues.

The attached patch is an implementation of this idea using a custom 
implementation of unsetenv(): _Py_unsetenv() argument is not the name 
of the variable but the raw variable including the value (eg. "a=b"). 
So it's also possible to drop truncated variables like "a" (no value 
nor "=" character).

This issue also affects Python2 since Python2 does also skip variable 
with no value but the variables still exist in memory (and so child 
process get them).

----------
components: Interpreter Core
files: unsetenv.patch
keywords: patch
messages: 74784
nosy: haypo
severity: normal
status: open
title: remove not decodable environment variables
type: security
versions: Python 3.0
Added file: http://bugs.python.org/file11799/unsetenv.patch

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue4126>
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