Re: [PATCH v2 11/11] crypto: skcipher: Remove VLA usage for SKCIPHER_REQUEST_ON_STACK

Herbert Xu
2018-06-27T22:28:28Z

On Wed, Jun 27, 2018 at 11:31:09AM -0700, Kees Cook wrote:
>
> I might be catching on... so from this list, I should only "count" the
> synchronous ones as being wrappable? The skcipher list is actually
> pretty short:
>
> crypto/cryptd.c: crypto_skcipher_set_reqsize(
> crypto/cryptd.c- tfm, sizeof(struct
> cryptd_skcipher_request_ctx));

cryptd is async so you don't have to include it.

> These are "simple" wrappers:
>
> crypto/lrw.c: crypto_skcipher_set_reqsize(tfm,
> crypto_skcipher_reqsize(cipher) +
> crypto/lrw.c- sizeof(struct rctx));
>
> crypto/simd.c- reqsize = sizeof(struct skcipher_request);
> crypto/simd.c- reqsize += crypto_skcipher_reqsize(&cryptd_tfm->base);
> crypto/simd.c: crypto_skcipher_set_reqsize(tfm, reqsize);

simd is async.

> crypto/xts.c: crypto_skcipher_set_reqsize(tfm,
> crypto_skcipher_reqsize(child) +
> crypto/xts.c- sizeof(struct rctx));
>
> But what are the "legitimate" existing crypto_skcipher_reqsize() values here?
>
> These are "complex" wrappers, with cts even adding blocksize to the mix...
>
> crypto/ctr.c- align = crypto_skcipher_alignmask(tfm);
> crypto/ctr.c- align &= ~(crypto_tfm_ctx_alignment() - 1);
> crypto/ctr.c- reqsize = align + sizeof(struct crypto_rfc3686_req_ctx) +
> crypto/ctr.c- crypto_skcipher_reqsize(cipher);
> crypto/ctr.c: crypto_skcipher_set_reqsize(tfm, reqsize);
>
> crypto/cts.c- align = crypto_skcipher_alignmask(tfm);
> crypto/cts.c- bsize = crypto_skcipher_blocksize(cipher);
> crypto/cts.c- reqsize = ALIGN(sizeof(struct crypto_cts_reqctx) +
> crypto/cts.c- crypto_skcipher_reqsize(cipher),
> crypto/cts.c- crypto_tfm_ctx_alignment()) +
> crypto/cts.c- (align & ~(crypto_tfm_ctx_alignment() - 1)) + bsize;
> crypto/cts.c-
> crypto/cts.c: crypto_skcipher_set_reqsize(tfm, reqsize);
>
> What values might be expected here? It seems the entire blocksize
> needs to be included as well...

But otherwise yes these are the ones that count.

Cheers,
--
Email: Herbert Xu <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
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