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

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:

quoted

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