Re: [PATCH] 1/2 SELinux: Add get, set, and cloning of superblock security information

[Eric Paris <eparis@redhat.com>]

On Thu, 2007-09-06 at 09:28 -0700, Casey Schaufler wrote:
> --- Eric Paris <eparis@redhat.com> wrote:
> 
> > On Thu, 2007-09-06 at 08:59 -0700, Casey Schaufler wrote:
> > > --- Eric Paris <eparis@redhat.com> wrote:
> > > 
> > > > Adds security_get_sb_mnt_opts, security_set_sb_mnt_opts, and
> > > > security_clont_sb_mnt_opts to the LSM and to SELinux.  This is in
> > > > preparation for NFS to be able to own its own mount options and remove
> > > > the NFS specific code from SELinux.
> > > 
> > > What is the purpose of security_clone_sb_mnt_opts? I see where it is
> > > being used, but it's not clear to me why it is necessary. The old SELinux
> > > code doesn't clone the options, it filters out the ones it cares about.
> > > If that is the behavior you'd expect of this hook, I suggest the name
> > > reflect that, perhaps security_filter_sb_mnt_opts.
> > 
> > I'm not sure what you mean by filter and I don't know which code you are
> > referring to.
> > 
> > At the moment the only user of clone is nfs nohide mounts.  Given an
> > exports list like
> > 
> > /export *()
> > /export/nohide *(nohide)
> > 
> > where /export/nohide actually crosses a filesystem boundry the nfs
> > client will quietly mount the new export on your machine as soon as you
> > enter that directory.  Assuming the user originally mounted /export with
> > some security options when nfs mounts this new export there needs to be
> > some way to propogate those security options forward to this new mount.
> > So the one usage of clone simply takes the security options from the
> > superblock related to /export and applies those to the new security
> > block related to /export/nohide
> 
> That is perfectly sensible. Is the intent to clone all the mount options
> or just the security mount options? Inquiring LSM writers want to know.

I'd have to say the security ones.  It is NFS's problem to make sure
that the options they understand are being handled correctly and I think
it is the security layers problem to make sure the options they
understand are being cloned.  (I tried to make these pretty generic and
extensible for other LSM writers, especially get/set if anyone else
someday makes use of mount options....)

-Eric


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