linux-kernel - Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

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Date:	Wed, 19 Dec 2007 08:13:30 -0600
From:	"Serge E. Hallyn" <serue@...ibm.com>
To:	Oren Laadan <orenl@...columbia.edu>
Cc:	"Serge E. Hallyn" <serue@...ibm.com>,
	Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
	linux-fsdevel@...r.kernel.org,
	Linux Containers <containers@...ts.osdl.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 1/2] [RFC] Simple tamper-proof device filesystem.

Quoting Oren Laadan (orenl@...columbia.edu):
> 
> Serge E. Hallyn wrote:
> > Quoting Oren Laadan (orenl@...columbia.edu):
> >> I hate to bring this again, but what if the admin in the container
> >> mounts an external file system (eg. nfs, usb, loop mount from a file,
> >> or via fuse), and that file system already has a device that we would
> >> like to ban inside that container ?
> > 
> > Miklos' user mount patches enforced that if !capable(CAP_MKNOD),
> > then mnt->mnt_flags |= MNT_NODEV.  So that's no problem.
> 
> Yes, that works to disallow all device files from a mounted file system.
> 
> But it's a black and white thing: either they are all banned or allowed;
> you can't have some devices allowed and others not, depending on type
> A scenario where this may be useful is, for instance, if we some apps in
> the container to execute withing a pre-made chroot (sub)tree within that
> container.

Yes, it's workable short-term, and we've always said that a more
complete solution would be worked on later, as people have time.

> > But that's been pulled out of -mm! ?  Crap.
> > 
> >> Since anyway we will have to keep a white- (or black-) list of devices
> >> that are permitted in a container, and that list may change even change
> >> per container -- why not enforce the access control at the VFS layer ?
> >> It's safer in the long run.
> > 
> > By that you mean more along the lines of Pavel's patch than my whitelist
> > LSM, or you actually mean Tetsuo's filesystem (i assume you don't mean that
> > by 'vfs layer' :), or something different entirely?
> 
> :)
> 
> By 'vfs' I mean at open() time, and not at mount(), or mknod() time.
> Either yours or Pavel's; I tend to prefer not to use LSM as it may
> collide with future security modules.

Yeah I keep waffling.  The LSM is so simple...  but i do prefer Pavel's
patch.  Let's keep pursuing that.

-serge
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