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Commit 69aafa11 authored by Kees Cook's avatar Kees Cook Committed by Rishabh Bhatnagar
Browse files

crypto: api - Introduce generic max blocksize and alignmask 

In the quest to remove all stack VLA usage from the kernel[1], this
exposes a new general upper bound on crypto blocksize and alignmask
(higher than for the existing cipher limits) for VLA removal,
and introduces new checks.

At present, the highest cra_alignmask in the kernel is 63. The highest
cra_blocksize is 144 (SHA3_224_BLOCK_SIZE, 18 8-byte words). For the
new blocksize limit, I went with 160 (20 8-byte words).

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com



Change-Id: Icee27c45f542a9de25310b193c5bd08bc236996e
Signed-off-by: default avatarKees Cook <keescook@chromium.org>
Signed-off-by: default avatarHerbert Xu <herbert@gondor.apana.org.au>
Git-Repo: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Git-Commit: a9f7f88a12f1494deca1fd9e173c7ae886d14f91
Signed-off-by: default avatarRishabh Bhatnagar <rishabhb@codeaurora.org>
parent 3f66393f

crypto/algapi.c

+6 −1
Original line number Diff line number Diff line
@@ -57,9 +57,14 @@ static int crypto_check_alg(struct crypto_alg *alg) 
	if (alg->cra_alignmask & (alg->cra_alignmask + 1))

		return -EINVAL;



	if (alg->cra_blocksize > PAGE_SIZE / 8)

	/* General maximums for all algs. */

	if (alg->cra_alignmask > MAX_ALGAPI_ALIGNMASK)

		return -EINVAL;



	if (alg->cra_blocksize > MAX_ALGAPI_BLOCKSIZE)

		return -EINVAL;



	/* Lower maximums for specific alg types. */

	if (!alg->cra_type && (alg->cra_flags & CRYPTO_ALG_TYPE_MASK) ==

			       CRYPTO_ALG_TYPE_CIPHER) {

		if (alg->cra_alignmask > MAX_CIPHER_ALIGNMASK)

include/crypto/algapi.h

+3 −1
Original line number Diff line number Diff line
@@ -20,8 +20,10 @@ 
/*

 * Maximum values for blocksize and alignmask, used to allocate

 * static buffers that are big enough for any combination of

 * ciphers and architectures.

 * algs and architectures. Ciphers have a lower maximum size.

 */

#define MAX_ALGAPI_BLOCKSIZE		160

#define MAX_ALGAPI_ALIGNMASK		63

#define MAX_CIPHER_BLOCKSIZE		16

#define MAX_CIPHER_ALIGNMASK		15