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

[Al Viro <viro@ftp.linux.org.uk>]

On Wed, Oct 03, 2007 at 12:51:08PM -0700, Casey Schaufler wrote:
> > > 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.

And your point is?  If you don't use it, you get exact same complexity
in both setups.
 
> > _What_ userland intervention?  Mounting stuff under /smack/tmp and not under
> > your /moldy?
> 
> Who said anything about mounting under /moldy? I never did.

Sigh...  So put the binding into fstab and be done with that.
 
> > 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?

Right now the main objection is about your lack of ability to read.  Which
part of "it can be mounted in different chroots/namespaces, therefore
having absolute paths doesn't work" is too hard to understand?

No, it's not about having a default.  It's about keeping an absolute pathname
in virtual fs, having all instances autosoddingmatically sharing it _and_
having change attempt in any instance automatically affect all of them.
If you have that kind of sharing, don't pretend that your mechanism really
allows absolute pathnames.