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

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Message-Id: <1256464016.4005.21.camel@nepomuk.localdomain>
Date: Sun, 25 Oct 2009 10:46:56 +0100
From: Klaus Lichtenwalder <k.lichtenwalder@...puter.org>
To: bugtraq@...urityfocus.com
Subject: Re: /proc filesystem allows bypassing directory permissions on
 Linux

Am Samstag, den 24.10.2009, 01:12 +0400 schrieb Dan Yefimov:
> On 24.10.2009 0:35, Matthew Bergin wrote:
> > doesnt look like the original owner is trying to write to it. Shows it
> > cant, it had guest write to it via the proc folders bad permissions.
> > Looks legitimate
> >
> Please tell me, who issued 'chmod 0666 unwritable_file'? Was that an attacker? 
> No, that was the owner of 'unwritable_file', nobody else. What the 0666 file 
> mode means? It means, that everybody can write to the file, can't he? So why do 
> you believe that pretension legitimate?

Well, at first I would say this might definitely somewhat unexpected.
It's correct otoh, that you shouldn't be too lax with files when you
think you "secured" them somewhere in the path... 
But if you think of /proc/x/fd as *hard* links to the files, then the
behavior would not be surprising, which might help...

(You might have this as a "real world scenario" if you have some brain
dead application which you try to secure in this way...)

Klaus

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