Re: chroot issues and http://tri-ceps.blogspot.com/2007/07/theory-of-filesystem-relativity.html

[Michael Casadevall]

On Mon, 2007-09-10 at 19:55 -0400, Richard Stallman wrote:
> * Simply don't allow setting passive translators inside a chroot at
>        all. After all, chroot is only for UNIX compatibility, and
>        translators are not a UNIX concept...
> 
> This doesn't do the job.  Suppose someone creates the passive translator
> or firmlink in the directory, and later you do a chroot to that directory.
> The problem will happen.
> 

In addition, firmlinks are needed for full support for features like
networking in chroots. You need to make a firmlink
from /server/sockets/2 to *chroot*/server/sockets/2 if you want the
network to work. In addition, due to Hurd architecture, if we want full
network support inside a chroot, we'll need to either redo how
networking is done in heard (get rid of /server/sockets/2), or provide a
mechanism to share servers/sockets/etc, between the chroot jail and the
base system. I think the same problem exists in sub-Hurds, although
someone with more experience will have to comment.

> In other words, this is not about creating a firmlink while chrooted,
> it is about the existence of a firmlink inside the chroot directory.
> 
>      * Allow setting passive translators, but only temporarily, not
>        storing them in the underlying filesystem. When accessing the
>        translated node, the translator is started by the chroot.
> 
> I don't really follow that.
> 
>      * Store the passive translator, but also store the chroot
>        information; and only start the translator if the node is accessed
>        from within the same chroot.
> 
> The next one is clearly better than this one.
> 
>      * Store the passive translator and the chroot, and whenever the node
>        is accessed, run the translator in a matching chroot. This might be
>        the most elegant solution.

> 
> This doesn't seem to address the case that someone else makes a
> firmlink in the directory that you are chrooted to.
> 
>      * Last but not least, we could simply allow setting passive
>        translators from within a chroot normally like it happens now, but
>        when a translated node is accessed, the translator started would
>        run in the context of the process accessing it -- which is
>        different for a chrooted process than for a normal one.
> 
> That one makes sense.  I see another that also makes sense:
> 
>      * If a firmlink points to a place outside the chroot, treat it as if
>        it pointed to a nonexistent file.

This should only be the case for passive instances of the firmlink
translator. The active one should be allowed to point outside the jail
if needed.

> 
> That way, it can never point to the "wrong" file.
> 
> 
> The main question is, does anyone know of any flaws in these solutions?
> 
>