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

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Date:	Wed, 13 Feb 2008 12:38:39 +0000
From:	David Howells <dhowells@...hat.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	dhowells@...hat.com, torvalds@...ux-foundation.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] KEYS: Add keyctl function to get a security label

Andrew Morton <akpm@...ux-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
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