Re: -mm -> 2.6.13 merge status (fuse)

Eric Van Hensbergen
2005-06-22T16:52:07Z

On 6/22/05, Miklos Szeredi <miklos@szeredi.hu> wrote:
> >
> > I'm confused why everything has to be remounted nosuid. I understand
> > enforcing synthetics to be mounted nosuid, but not the rest of the
> > file systems.
>
> It's related to the problem of a suid program accessing synthetic
> filesystem, and filesystem doing something bad to suid program (make
> it hang, supply bogus data ...). This can be solved by "squashing"
> suid for the whole namespace (basically the Plan 9 solution).
> Unfortunately this is not really practical in Linux/Unix.
>

Just to make sure I understand you - if I don't squash suid for the
entire name space, a user could mount a malicious synthetic (even with
NOSUID) and then launch an SUID app from an inherited mount which
would then traverse to the malicious synthetic.

That's a nasty case I hadn't considered before -- however, what's the
potential damage there? The user could hold up progress of the SUID
app that they launched, but that wouldn't necessarily impede system
progress since system-critical suid apps wouldn't be typically
launched by a user. I suppose there is the possibility that if
multiple instances of such an SUID app share a global lock you could
get into trouble -- do we have any concrete example apps that would
exhibit this kind of behavior?

Are there other vunerabilities that I'm missing?

-eric