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Re: Hurdish applications for persistence

From: Jonathan S. Shapiro
Subject: Re: Hurdish applications for persistence
Date: Fri, 14 Oct 2005 10:14:17 -0400

On Fri, 2005-10-14 at 15:19 +0200, Marcus Brinkmann wrote:
> At Fri, 14 Oct 2005 14:44:49 +0200,
> Bas Wijnen <address@hidden> wrote:
> > If the chrooted filesystem contains an active translator, it will 
> > (correctly)
> > have a different root.  This can be used to construct communication 
> > channels,
> > but I feel it would also generate accidental channels.
> This is always true.  If you give somebody a capability that allows
> you to retrieve further capabilities, then yes, you give potentially
> all those other capabilities to the process as well.
> But note that if the task is confined, it can not get such a
> capability from the constructor.  So, the instantiator would
> explicitely give it such a capability.  You can shoot yourself in the
> foot.

Marcus has it, but here is a more precise way to state what he says:

The purpose of a chroot environment is to prevent escape. If there
existed some way to accomplish it, we would usually be happy to let the
chroot environment share **purely read only** state with our larger
environment. For example, it is silly to make multiple copies
of /bin/ls.

The only catch with purely read-only sharing is that, of course, there
will be *some* content that we do *not* want to put in the chroot
environment. So we simply shouldn't do that.

In practice, I suggest that this is a matter of configuration.


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