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

[Kees Cook]

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 at 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