Re: [PATCH v7 1/2] crypto: AF_ALG: add AEAD support

[Stephan Mueller <smueller@chronox.de>]

Am Montag, 5. Januar 2015, 21:51:06 schrieb Herbert Xu:

Hi Herbert,

> On Mon, Jan 05, 2015 at 11:46:50AM +0100, Stephan Mueller wrote:
> > 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.
> 
> Please remove the limit as otherwise we would never be able to
> add support for this in a future kernel as appliations won't be
> able to rely on it.
> 
> There is no such limit in the kernel interface and we shouldn't
> be adding one here.

One question: are you aware of an existing mechanism to split one scatterlist 
into two at a given offset?

> 
> Cheers,


-- 
Ciao
Stephan