[PATCH 10/11] crypto: ahash: Remove VLA usage for AHASH_REQUEST_ON_STACK

Kees Cook
2018-06-20T19:06:37Z

In the quest to remove all stack VLA usage from the kernel[1], this caps
the ahash request size similar to the other limits and adds a sanity
check at registration.

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

Signed-off-by: Kees Cook <keescook@chromium.org>
---
include/crypto/hash.h | 3 ++-
include/crypto/internal/hash.h | 1 +
2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index b9df568dc98e..7d62309baf0b 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -66,10 +66,11 @@ struct ahash_request {

#define AHASH_MAX_DIGESTSIZE (PAGE_SIZE / 8)
#define AHASH_MAX_STATESIZE (PAGE_SIZE / 8)
+#define AHASH_MAX_REQSIZE (PAGE_SIZE / 8)

#define AHASH_REQUEST_ON_STACK(name, ahash) \
char __##name##_desc[sizeof(struct ahash_request) + \
- crypto_ahash_reqsize(ahash)] CRYPTO_MINALIGN_ATTR; \
+ AHASH_MAX_REQSIZE] CRYPTO_MINALIGN_ATTR; \
struct ahash_request *name = (void *)__##name##_desc

/**
diff --git a/include/crypto/internal/hash.h b/include/crypto/internal/hash.h
index a0b0ad9d585e..d96ae5f52125 100644
--- a/include/crypto/internal/hash.h
+++ b/include/crypto/internal/hash.h
@@ -142,6 +142,7 @@ static inline struct ahash_alg *__crypto_ahash_alg(struct crypto_alg *alg)
static inline void crypto_ahash_set_reqsize(struct crypto_ahash *tfm,
unsigned int reqsize)
{
+ BUG_ON(reqsize > AHASH_MAX_REQSIZE);
tfm->reqsize = reqsize;
}

--
2.17.1