linux-kernel - Re: [PATCH] KEYS: trusted: fix -Wvarags warning

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Date:   Fri, 12 Oct 2018 08:05:51 -0700
From:   James Bottomley <jejb@...ux.ibm.com>
To:     Denis Kenzior <denkenz@...il.com>, ndesaulniers@...gle.com,
        dhowells@...hat.com
Cc:     natechancellor@...il.com, ebiggers@...gle.com,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        James Morris <jmorris@...ei.org>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        linux-integrity@...r.kernel.org, keyrings@...r.kernel.org,
        linux-security-module@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] KEYS: trusted: fix -Wvarags warning

On Fri, 2018-10-12 at 07:29 -0500, Denis Kenzior wrote:
> Hi Nick,
> 
> > @@ -123,7 +123,7 @@ static int TSS_rawhmac(unsigned char *digest,
> > const unsigned char *key,
> >    */
> >   static int TSS_authhmac(unsigned char *digest, const unsigned
> > char *key,
> >   			unsigned int keylen, unsigned char *h1,
> > -			unsigned char *h2, unsigned char h3, ...)
> > +			unsigned char h2, unsigned char *h3, ...)
> >   {
> >   	unsigned char paramdigest[SHA1_DIGEST_SIZE];
> >   	struct sdesc *sdesc;
> 
> So my concern here is that this actually breaks the natural argument 
> order compared to what the specification uses.  This in turn
> requires 
> one to perform some mental gymnastics and I'm not sure that this is
> such 
> a good idea.  Refer to 
> https://trustedcomputinggroup.org/wp-content/uploads/TPM-Main-Part-3-
> Commands_v1.2_rev116_01032011.pdf 
> for details.
> 
> Note that H3 is really the 'continueAuthSession' variable which is a 
> bool.  In the above specification BOOL has a size of 1, and
> TSS_authhmac already assigns a h3 to 'c' which is used for the actual
> hashing.
> 
> So can't we simply use 'bool' or uint32 as the type for h3 instead
> of re-ordering everything

The problem is the standard is ambiguious.  The only thing that's
guaranteed to work for all time is a char *.  If you want to keep the
order, what I'd suggest is inserting a dummy pointer argument which is
always expected to be NULL between the h3 and the varargs.

James