bugtraq - Re: /proc filesystem allows bypassing directory permissions on Linux

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Date: Mon, 26 Oct 2009 13:42:17 +0300
From: Dan Yefimov <dan@...htwave.net.ru>
To: psz@...hs.usyd.edu.au
Cc: Pavel Machek <pavel@....cz>, bugtraq@...urityfocus.com
Subject: Re: /proc filesystem allows bypassing directory permissions on Linux

On 25.10.2009 2:40, psz@...hs.usyd.edu.au wrote:
> Dear Pavel,
>
>> ... that's exactly the problem.
>
> I see, the /proc/*/fd/* objects seem "confused": are they symlinks,
> hardlinks, or open file descriptors? I guess should always act as
> the latter, where access mode flags (O_RDONLY or O_RDWR) are set at
> open() and not changeable afterwards in fcntl(). Any open() on them
> should behave as a dup().
>
Paul, in authentic kernels /proc/<PID>/fd/<FD> are symlinks, not anything other. 
There're no such publicly accessible file objects, as file descriptors, there're 
only files (including special ones), directories and symlinks. But the above 
words don't necessary relate to patched kernels like distributed by third parties.
-- 

Sincerely Your, Dan.