linux-kernel - Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks and file bind mounts (try #5)

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Message-ID: <20091130122851.GF13328@elf.ucw.cz>
Date:	Mon, 30 Nov 2009 13:28:51 +0100
From:	Pavel Machek <pavel@....cz>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	jlayton@...hat.com, jamie@...reable.org, ebiederm@...ssion.com,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	viro@...IV.linux.org.uk
Subject: Re: [PATCH 0/3] vfs: plug some holes involving LAST_BIND symlinks
 and file bind mounts (try #5)

On Tue 2009-11-24 13:59:06, Miklos Szeredi wrote:
> On Tue, 24 Nov 2009, Pavel Machek wrote:
> > I believe that current semantics is ugly enough that 'documenting' it
> > is not enough... and people want to port from other systems, too, not
> > expecting nasty surprises like this...
> 
> This hasn't been a problem for the last 12 years, and still we don't
> see script kiddies exploiting this hole and sysadmins hurrying to
> secure their system, even though it has been public for quite a while.
> 
> Why?

Because condition when it hits are quite unusual?

> The reason might be, that there *is no* violation of security.

Well, security people disagree with you.

> See this: the surprise isn't that an inode can be reached from
> multiple paths, that has been possible with hard links for as long as
> unix lived.  The suprise is that the inode can be reached through
> proc.  So this "hole" that has been opened about 12 years ago in linux
> is quite well known.  Only this particular aspect of it isn't well
> known, but that doesn't mean it's not right, does it?

It does. Bypassing checks on read-only file descriptors is design
misfeature, and users are clearly unaware. (See bugtraq). Being "old"
does not mean it is right.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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