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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

Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
This commit is contained in:
Kees Cook 2018-08-07 14:18:40 -07:00 committed by Herbert Xu
parent b68a7ec1e9
commit a9f7f88a12
2 changed files with 9 additions and 2 deletions
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7
crypto/algapi.c
View File

@ -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)

4
include/crypto/algapi.h
View File

@ -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