linux-kernel - Re: symlinks with permissions (fwd)

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Message-ID: <20091029203500.GB30747@elf.ucw.cz>
Date:	Thu, 29 Oct 2009 21:35:00 +0100
From:	Pavel Machek <pavel@....cz>
To:	Casey Schaufler <casey@...aufler-ca.com>
Cc:	kernel list <linux-kernel@...r.kernel.org>
Subject: Re: symlinks with permissions (fwd)

Hi!

> >> Do you know of any cases where this difference matters in practice?
> >>     
> >
> > Actually yes, see the bugtraq post. guest was able to write to my file
> > when I expected that file to be protected.
> >
> > According to the bugtraq discussion, people expect directory
> > permissions to work.
> 
> Gawd, I hate to say this, but people have been improperly educated
> if they expect directory permissions to behave thusly. You can not
> count on the permissions on a directory to protect access on a file
> that the directory contains a reference to. Hard links. Mount points.
> /proc/8675309/fd. Passing file descriptors over sockets. Fork, for
> heaven's sake. That's not how Linux directories really work.

Actually it was how Unix directories really worked, before Linux /proc
came around and broke it.

See the bugtraq; yes, hardlinks are similar, but at least you see them
on ls -l. Mount points are root-only. And you can't use fork to
upgrade "read-only" filedescriptor to read write. 

										Pavel

-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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