linux-kernel - Re: [PATCH] Version 4 (2.6.23-rc8-mm2) Smack: Simplified Mandatory Access Control Kernel

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Date:	Wed, 3 Oct 2007 12:51:08 -0700 (PDT)
From:	Casey Schaufler <casey@...aufler-ca.com>
To:	Al Viro <viro@....linux.org.uk>,
	Casey Schaufler <casey@...aufler-ca.com>
Cc:	torvalds@...l.org, linux-security-module@...r.kernel.org,
	linux-kernel@...r.kernel.org, akpm@...l.org, paul.moore@...com
Subject: Re: [PATCH] Version 4 (2.6.23-rc8-mm2) Smack: Simplified Mandatory Access Control Kernel


--- Al Viro <viro@....linux.org.uk> wrote:

> On Wed, Oct 03, 2007 at 10:21:08AM -0700, Casey Schaufler wrote:
> > > what
> > > happens if we want it in two chroot jails with different layouts?
> > 
> > As you can only have /smack mounted once, this isn't an issue,
> > but it does present an interesting use case that brings the one
> > mount limitation into question. I'll add addressing this to the
> > short term todo list.
> 
> Of course you can mount it more than once.  Just bind the sucker and you
> are done.
>  
> > > I really don't get it; why not simply have something like
> > > /smack/tmp.link resolve to tmp/<label> and have userland bind or mount
> > > whatever you bloody like on /smack/tmp?
> > 
> > Because you throw "simple" out the window when you require userland
> > assistance to perform this function.
> 
> Any more than having /tmp replaced with a symlink?

Yes. By the way, there's nothing that really requires that you
use a /smack symlink if you don't want to. /tmp can still be a
real directory, a mount point, a symlink to /var/tmp, or whatever
else you want it to be if that suits your needs better. For the
simplest scenarios /tmp -> /smack/tmp -> /moldy/<label> has every
other scheme I've seen throughly beaten.

> > I'm having some trouble seeing how the 60 lines of code in
> > smackfs dealing with symlinks would be improved by your suggestions.
> > I certainly don't see how requiring userland intervention would
> > do anything but make it bigger and less reliable.
> 
> _What_ userland intervention?  Mounting stuff under /smack/tmp and not under
> your /moldy?

Who said anything about mounting under /moldy? I never did.

> Having /tmp replaced with symlink to /smack/tmp.link instead
> of replacing it with a symlink to /smack/tmp?
> 
> Absolute paths in that kind of thing are _wrong_.  You know where the things
> are on your fs.  You don't know if anything else will be visible, let alone
> whether it will be at the same place in all chroots or namespaces.  And no,
> you _can't_ make sure that fs is visible only in one place.  No fs can or
> has any business even trying.

Is the objection that there is a default value coded in?


Casey Schaufler
casey@...aufler-ca.com
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