Re: [PATCH 4/4] KEYS: Add keyctl function to get a security label

[David Howells <dhowells@redhat.com>]

Andrew Morton <akpm@linux-foundation.org> wrote:

> > +	key_ref = lookup_user_key(NULL, keyid, 0, 1, KEY_VIEW);
> > +	if (IS_ERR(key_ref)) {
> > +		if (PTR_ERR(key_ref) != -EACCES)
> > +			return PTR_ERR(key_ref);
> > +
> > +		/* viewing a key under construction is also permitted if we
> > +		 * have the authorisation token handy */
> > +		instkey = key_get_instantiation_authkey(keyid);
> > +		if (IS_ERR(instkey))
> > +			return PTR_ERR(key_ref);
> > +		key_put(instkey);
> 
> This check looks a wee bit racy?

It's not particularly racy.  Admittedly there's a tiny window in which we can
retrieve the security label of a key for which we had an authorisation token
that got revoked just as we completed our access checks on it.  Does this
matter?

David