Re: Proposal: restrict link(2)

Aaron Denney (
14 Dec 1996 20:02:49 GMT

Harald Koenig <> wrote:
> > Harald Koenig writes:
> > > * clobber other user's disk quoatas, disk usage and disk space accounting etc.
> >
> > No.
> [ nonsense example deleted ]
> > You have only a cursory understanding of how hard links work.
[Quota breaking]
> got the message?


> or other example about access restriction:
> assume: jim and joe are in (some) same group(s)
> /home/joe/project/world_shouldnt_read is a file that...
> so directory "project" can only be accesed using group permission
> (e.g. permission 770 or 750)
> now jim (how is allowed to access project and thus project/world_shouldnt_read)
> want's to make spy's life easier: he creates a hard link from the file above to
> /home/jim/donnation_to_the_world/TOP_SECRET where donnation_to_the_world
> ahs e.g. permissions 755. now world is able to access the data in the file
> "world_shouldnt_read" which wasn't planed at all from joe
> (using multiple differnet groups there are situations where you can't
> remove world acces from this file; access control is done through directories...)
> and what about the message of this case ?

In this example jim has access to the directory to link the file.
You mention that the file has world read access, so jim could just _copy_
the file and everybody could still read what is in it.

If you give somebody access to information they will be able to give
that information to whomever they want. Very simple, and no real way
around it.

I know of a cluster that solvs this problem by letting the users create
their own groups: A directory is scanned once a day, and groups are
created with their name being the file name, and the contents of the
file being the members of the group. Almost as good as ACL's.

Of course this approach does let you open to denial of service attacks,
but what doesn't?

--Aaron Denney