[issue13734] Add a generic directory walker method to avoid symlink attacks

[Hynek Schlawack]

New submission from Hynek Schlawack <hs at ox.cx>:

This is an offspring of #4489 (which is a security bug). The method is AFAIU intended to be private. 

As shown in the discussion of the mentioned #4489, there is a whole family of attacks that exploit the time window between gathering path names and executing a function on them. A general description of this problem can be found in: https://www.securecoding.cert.org/confluence/display/seccode/POS35-C.+Avoid+race+conditions+while+checking+for+the+existence+of+a+symbolic+link

While the consequences in rmtree() are probably most dramatic, other recursive functions could benefit too (chmodtree() and chowntree() were mentioned) so Charles-François suggested to write a "generic walker method that would take as argument the methods to call on a directory and on a file (or link)".

Some (probably) necessary helper functions has been already implemented in #4761 (*at()) and #10755 (fdlistdir()).

Has there already been done any work? Ross mentioned he wanted to take a stab?

----------
components: Library (Lib)
messages: 150833
nosy: hynek.schlawack, neologix, pitrou, rosslagerwall, tarek
priority: normal
severity: normal
status: open
title: Add a generic directory walker method to avoid symlink attacks
type: security
versions: Python 3.3

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<http://bugs.python.org/issue13734>
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