linux-kernel - Re: BUG: Securityfs and bind mounts (2.6.34)

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Message-ID: <20100708154648.GA13923@kroah.com>
Date:	Thu, 8 Jul 2010 08:46:48 -0700
From:	Greg KH <greg@...ah.com>
To:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: BUG: Securityfs and bind mounts (2.6.34)

On Thu, Jul 08, 2010 at 04:32:42PM +0100, Tvrtko Ursulin wrote:
> On Thursday 08 Jul 2010 16:20:59 Greg KH wrote:
> > > :) Well I do not know, but, it kind of smelled like a bug in the
> > > : vfs/mount
> > >
> > > handling/securityfs area so I thought to let experts know. I _think_ I
> > > did nothing that much wrong. Just used the exposed API
> > > (securityfs_remove) and some bind mount shuffling from userspace.
> >
> > securitfs just uses libfs underneath it, and really doesn't have any
> > bindings for module ownerships, so I wouldn't recommend doing what you
> > just did.
> 
> Just do double check what you are saying, securityfs is not safe for use from
> modules? If so I would then recommend removing the exports otherwise it is an
> invitation to shoot yourself into the foot.

Hm, did you properly set the module owner of the file_operations that
you passed to securityfs?  That should protect if you have an open file,
but I doubt anyone thought you would do crazy things like bind mounts on
top of a ramfs and then think it was safe to unload a lower module :)

> Also, in-three TPM driver can be built as a module so how does that
> work?

You have to be root to unload modules, and if you are that, you can do
worse things than this.

thanks,

greg k-h
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