Re: Conditional SymLinks

Adam D. Bradley (artdodge@cs.bu.edu)
Fri, 12 Dec 1997 00:33:42 -0500 (EST)

> > > There is I beleive some unix out there where one could imbed environment
> > > variables in symlinks, like:
> > >
> > > /tmp -> ${HOME}/tmp
> >
> > Yeah, I had this idea maybe ten years ago. A friend told me someone
> > (IRIX ?) has already done it. The idea of active objects in the filesystem
> > is interesting, and could make porting code from other systems easier. Of
> > course it could make debugging nearly impossible.
>
> I've seen this _many_ years ago in a BSD 4.2 (4.3?) implementation
> from Sony (NewsOS 3.x and 4.x) on their MIPS R3000 workstations.
> it was a nice feature and I really would like to see this in Linux too
> (but don't ask me how this should be done;)

I've pondered ways of going about this. The problem is, the
uid-to-home-directory is purely a userspace construct. Consider this
possibility then:

/tmp (symlink) -> /proc/uidtmp
/proc/uidtmp is an on-the-fly symlink (like /proc/self)
to -> /realtmp/<euid> (or whichever UID field is apropos)
(Where "realtmp" some directory name settable with a proc entry or
sysctl). And the /realtmp/<uid> files can actually be whatever you
like, e.g. individual symlinks to "/home/username/tmp/"

This could be done with minimal code, default to "off", and be a
useful, easy-to-tune mechanism for people who are more A.R. about
their security. It would also keep policy _out_ of the kernel.

Just an idea.

Adam

--
Things look so bad everywhere      Adam D. Bradley      artdodge@cs.bu.edu
In this whole world what is fair        Boston University Computer Science
We walk blind and we try to see             Ph.D. student and Linux hacker
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