linux-kernel - Re: [PATCH v7 1/2] crypto: AF

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Date:	Mon, 05 Jan 2015 11:46:50 +0100
From:	Stephan Mueller <smueller@...onox.de>
To:	Herbert Xu <herbert@...dor.apana.org.au>
Cc:	Daniel Borkmann <dborkman@...hat.com>,
	'Quentin Gouchet' <quentin.gouchet@...il.com>,
	linux-kernel@...r.kernel.org, linux-crypto@...r.kernel.org,
	ABI/API <linux-api@...r.kernel.org>
Subject: Re: [PATCH v7 1/2] crypto: AF_ALG: add AEAD support

Am Montag, 5. Januar 2015, 21:31:59 schrieb Herbert Xu:

Hi Herbert,

> On Fri, Jan 02, 2015 at 03:41:33PM +0100, Stephan Mueller wrote:
> > +		if (!con.aead_assoclen)
> > +			return -EINVAL;
> 
> AD being zero should be fine.

Ok, removed.
> 
> > +		/* aead_recvmsg limits the maximum AD size to one page */
> > +		if (con.aead_assoclen > PAGE_SIZE)
> > +			return -E2BIG;
> 
> I don't see any need to limit the size of the AD.

The need for that check lies in aead_recvmsg:

        /*
         * first chunk of input is AD -- one scatterlist entry is one page,
         * and we process only one scatterlist, the maximum size of AD is
         * one page
         */
        sg_init_table(&assoc, 1);
        sg_set_page(&assoc, sg_page(sg), ctx->aead_assoclen, sg->offset);
        aead_request_set_assoc(&ctx->aead_req, &assoc, ctx->aead_assoclen);

There you see that I only create an sg table with one entry for the AD. If we 
would allow an arbitrary AD size, I would see the need of a for loop in 
addition to the one directly beneath this AD scatterlist setting: one for 
identifying how many sg entries I need to allocate and one for the actual 
assignment.

As I felt that one page should be sufficient for the AD, I wanted to avoid the 
extra overhead for another for loop.
> 
> Cheers,


-- 
Ciao
Stephan
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