[PATCH 05/11] crypto alg: Introduce max blocksize and alignmask

Kees Cook
2018-06-20T19:06:38Z

In the quest to remove all stack VLA usage from the kernel[1], this
exposes the existing upper bound on crypto block sizes for VLA removal,
and introduces a new check for alignmask (current maximum in the kernel
is 63 from manual inspection of all cra_alignmask settings).

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

Signed-off-by: Kees Cook <keescook@chromium.org>
---
crypto/algapi.c | 5 ++++-
include/linux/crypto.h | 4 ++++
2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/crypto/algapi.c b/crypto/algapi.c
index c0755cf4f53f..760a412b059c 100644
--- a/crypto/algapi.c
+++ b/crypto/algapi.c
@@ -57,7 +57,10 @@ 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)
+ if (alg->cra_blocksize > CRYPTO_ALG_MAX_BLOCKSIZE)
+ return -EINVAL;
+
+ if (alg->cra_alignmask > CRYPTO_ALG_MAX_ALIGNMASK)
return -EINVAL;

if (!alg->cra_type && (alg->cra_flags & CRYPTO_ALG_TYPE_MASK) ==
diff --git a/include/linux/crypto.h b/include/linux/crypto.h
index 6eb06101089f..e76ffcbd5aa6 100644
--- a/include/linux/crypto.h
+++ b/include/linux/crypto.h
@@ -134,6 +134,10 @@
*/
#define CRYPTO_MAX_ALG_NAME 128

+/* Maximum values for registered algorithms. */
+#define CRYPTO_ALG_MAX_BLOCKSIZE (PAGE_SIZE / 8)
+#define CRYPTO_ALG_MAX_ALIGNMASK 63
+
/*
* The macro CRYPTO_MINALIGN_ATTR (along with the void * type in the actual
* declaration) is used to ensure that the crypto_tfm context structure is
--
2.17.1