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

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Message-ID: <20091023223923.GB2659@elf.ucw.cz>
Date: Sat, 24 Oct 2009 00:39:24 +0200
From: Pavel Machek <pavel@....cz>
To: Dan Yefimov <dan@...htwave.net.ru>
Cc: bugtraq@...urityfocus.com
Subject: Re: /proc filesystem allows bypassing directory permissions on
 Linux

> >Original owner did chmod 666... after making sure traditional unix
> >permissions protect the file. Please look at original mail; it was
> >subtle but I believe I got it right, and file would not be writable
> >with /proc unmounted.
> >
> I remember the original mail content. You're right, you can't reach
> the file if the procfs is not mounted, but you forget about the
> race, allowing the guest to create a hardlink to the file in an
> unrestricted location before the directory access becomes
> restricted. Again, procfs is just another, specific kind of
> hardlinks.

Check it again.  There's no race; I check link count before chmod 666.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html