Re: [Keyrings] [PATCH] Keys: Add LSM hooks for key management

[James Morris <jmorris@namei.org>]

On Thu, 6 Oct 2005, David Howells wrote:

> James Morris <jmorris@namei.org> wrote:
> 
> > I think this looks ok from an SELinux point of view if keys are treated as 
> > opaque objects, i.e. like files.
> 
> I'll make some changes based on the suggestions I've received. Those who
> request the return of keyfs can go boil their heads.

You know, I was thinking, ext3 could be much more compact if it was just a 
set of custom syscalls and had no VFS representation.

What about a per process /proc/pid/keys, which contains keyrings and keys, 
which can be opened, closed, use xattrs for any special access control 
etc. ?

> > We could do something like create a new object class (kernkey or 
> > something) and implement SELinux permissions for the class such as read, 
> > write, search, link, setattr and getattr.  Your KEY_VIEW perm could be 
> > translated to SELinux getattr.
> 
> Should I expand the permissions mask to include a setattr?

Possibly for setperm and chown.

> > I'm not sure if we need user-level labeling of keys via the set & get 
> > security ops, although LSPP may require some form of get_security. If we 
> > don't need to manually set security attributes but still view them, they 
> > could be displayed via /proc/keys rather than implementing a separate 
> > multiplexed syscall.
> 
> Would it be worth me adding a key type op by which a security module can ask
> the type its opinion (or by which key_alloc() can ask the type to give the
> security module an earful)?

Well, SELinux is the only significant LSM in the tree and I don't think it 
needs to set the labels.  So, no.

> >   keyctl_chown_key()
> >   keyctl_setperm_key()
> 
> Okay.
> 
> >   keyctl_set_reqkey_keyring()
> 
> Should this really be securified? It merely controls the default destination
> for a key created by request_key(), and is limited to the keyrings the process
> is subscribed to in any case.

Ok, if needed, it can be added later.

> > All users of key_permission() need to propagate the error code from the 
> > LSM back to the user.
> 
> Really? Why?

Because the LSM has final say on the error code returned to the caller.  
If the LSM runs out of memory, for example, it's silly to return -EACCES.

> Note that the fact that key_permission() fails for a key is sometimes ignored,
> such as when I'm doing a search and one potentially matching key fails, but a
> subsequent matching key passes.

Ok, that sounds like an internal issue to be resolved, ensuring that if 
you are returning to the caller, the LSM's error code is returned.


- James
-- 
James Morris
<jmorris@namei.org>