linux-kernel - Re: [PATCH 2/2] keys, trusted: seal with a policy

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Date:	Wed, 09 Dec 2015 11:10:38 -0500
From:	Mimi Zohar <zohar@...ux.vnet.ibm.com>
To:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
Cc:	David Howells <dhowells@...hat.com>,
	Peter Huewe <peterhuewe@....de>,
	Marcel Selhorst <tpmdd@...horst.net>,
	Jonathan Corbet <corbet@....net>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	James Morris <james.l.morris@...cle.com>,
	"Serge E. Hallyn" <serge@...lyn.com>,
	"open list:KEYS-ENCRYPTED" <linux-security-module@...r.kernel.org>,
	"open list:KEYS-ENCRYPTED" <keyrings@...r.kernel.org>,
	"open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
	open list <linux-kernel@...r.kernel.org>,
	"moderated list:TPM DEVICE DRIVER" 
	<tpmdd-devel@...ts.sourceforge.net>
Subject: Re: [PATCH 2/2] keys, trusted: seal with a policy

On Wed, 2015-12-09 at 16:24 +0200, Jarkko Sakkinen wrote:
> On Tue, Dec 08, 2015 at 06:56:17PM -0500, Mimi Zohar wrote:
> > On Tue, 2015-12-08 at 22:24 +0200, Jarkko Sakkinen wrote:
> > > On Tue, Dec 08, 2015 at 01:01:02PM +0200, Jarkko Sakkinen wrote:
> > > > On Tue, Dec 08, 2015 at 09:35:05AM +1100, James Morris wrote:
> > > > > On Mon, 7 Dec 2015, Jarkko Sakkinen wrote:
> > > > > 
> > > > > > On Fri, Nov 20, 2015 at 01:34:35PM +1100, James Morris wrote:
> > > > > > > On Wed, 18 Nov 2015, Jarkko Sakkinen wrote:
> > > > > > > 
> > > > > > > > On Wed, Nov 18, 2015 at 11:21:01AM +1100, James Morris wrote:
> > > > > > > > > On Tue, 17 Nov 2015, Jarkko Sakkinen wrote:
> > > > > > > > > 
> > > > > > > > > >  			}
> > > > > > > > > >  			break;
> > > > > > > > > > +		case Opt_policydigest:
> > > > > > > > > > +			if (!tpm2 ||
> > > > > > > > > > +			    strlen(args[0].from) != (2 * opt->digest_len))
> > > > > > > > > > +				return -EINVAL;
> > > > > > > > > > +			kfree(opt->policydigest);
> > > > > > > > > > +			opt->policydigest = kzalloc(opt->digest_len,
> > > > > > > > > > +						    GFP_KERNEL);
> > 
> > You're allocating the exact amount of storage needed.  There's no reason
> > to use kzalloc here or elsewhere in the patch.
> 
> Yup. I'll change this.
> 
> > > > > > > > > 
> > > > > > > > > Is it correct to kfree opt->policydigest here before allocating it?
> > > > > > > > 
> > > > > > > > I think so. The same option might be encountered multiple times.
> > > > > > > 
> > > > > > > This would surely signify an error?
> > > > > > 
> > > > > > I'm following the semantics of other options. That's why I implemented
> > > > > > it that way for example:
> > > > > > 
> > > > > > keyctl add trusted kmk "new 32 keyhandle=0x80000000 keyhandle=0x80000000"
> > > > > > 
> > > > > > is perfectly OK. I just thought that it'd be more odd if this option
> > > > > > behaved in a different way...
> > > > > 
> > > > > It seems broken to me -- if you're messing up keyctl commands you might 
> > > > > want to know about it, but we should remain consistent.
> > > > 
> > > > So should I return error if policyhandle/digest appears a second time? I
> > > > agree that it'd be better to return -EINVAL.
> > > > 
> > > > The existing behavior is such that any option can appear multiple times
> > > > and I chose to be consistent with that.
> > > 
> > > Mimi, David?
> > 
> > I don't have a problem with changing the existing behavior to allow the
> > options to be specified only once.
> 
> I don't think this patch is right place to change the behavior as it
> should be done for other options too.

I think the easiest way of checking if a token has already been seen
would be to define
 a flag and use test_and_set_bit(token, <flag>) after the following code
snippet.

          while ((p = strsep(&c, " \t"))) {
                if (*p == '\0' || *p == ' ' || *p == '\t')
                        continue;
                token = match_token(p, key_tokens, args);

Having a separate patch is probably a good idea.

Mimi

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