> > +	/*
> > +	 * For unprivileged mounts use current uid/gid.  Still allow
> > +	 * "user_id" and "group_id" options for compatibility, but
> > +	 * only if they match these values.
> > +	 */
> > +	if (!capable(CAP_SYS_ADMIN)) {
> > +		d->user_id = current->uid;
> > +		d->user_id_present = 1;
> > +		d->group_id = current->gid;
> > +		d->group_id_present = 1;
> > +
> > +	}
> 
> CAP_SETUID is the appropriate capability...
> 
> This is not a dimension we have not fully explored.
> What is the problem with a user controlled mount having different
> uid and gid values.
> 
> Yes they map into different users but how is this a problem.
> The only problem that I can recall is the historic chown problem
> where you could give files to other users and mess up their quotas.
> 
> Or is the problem other users writing to this user controlled
> filesystem?

Yes.  Or even just a suid process trying to access the user controlled
filesystem.  See Documentation/filesystems/fuse.txt for the gory
details.

Eric, thanks for the detailed review :)

Miklos
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