Re: [PATCH 01/11] crypto: shash: Remove VLA usage

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On 06/20/2018 07:03 PM, Kees Cook wrote:
In the quest to remove all stack VLA usage from the kernel[1], this
removes the VLAs in SHASH_DESC_ON_STACK (via crypto_shash_descsize())
by using the maximum allowable size (which is now more clearly captured
in a macro). Similar limits are turned into macros as well.

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

Signed-off-by: Kees Cook <keescook@xxxxxxxxxxxx>

Got the following warnings:

crypto/testmgr.c: In function ‘alg_test_crc32c.part.4’:
crypto/testmgr.c:1896:1: warning: the frame size of 2088 bytes is larger than 1024 bytes [-Wframe-larger-than=]
crypto/hmac.c: In function ‘hmac_setkey’:
crypto/hmac.c:88:1: warning: the frame size of 2088 bytes is larger than 1024 bytes [-Wframe-larger-than=]

Christophe

---
  crypto/shash.c        | 6 +++---
  include/crypto/hash.h | 6 +++++-
  2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/crypto/shash.c b/crypto/shash.c
index 5d732c6bb4b2..ab6902c6dae7 100644
--- a/crypto/shash.c
+++ b/crypto/shash.c
@@ -458,9 +458,9 @@ static int shash_prepare_alg(struct shash_alg *alg)
  {
  	struct crypto_alg *base = &alg->base;
- if (alg->digestsize > PAGE_SIZE / 8 ||
-	    alg->descsize > PAGE_SIZE / 8 ||
-	    alg->statesize > PAGE_SIZE / 8)
+	if (alg->digestsize > SHASH_MAX_DIGESTSIZE ||
+	    alg->descsize > SHASH_MAX_DESCSIZE ||
+	    alg->statesize > SHASH_MAX_STATESIZE)
  		return -EINVAL;
base->cra_type = &crypto_shash_type;
diff --git a/include/crypto/hash.h b/include/crypto/hash.h
index 76e432cab75d..308aad8bf523 100644
--- a/include/crypto/hash.h
+++ b/include/crypto/hash.h
@@ -151,9 +151,13 @@ struct shash_desc {
  	void *__ctx[] CRYPTO_MINALIGN_ATTR;
  };
+#define SHASH_MAX_DIGESTSIZE (PAGE_SIZE / 8)
+#define SHASH_MAX_DESCSIZE      (PAGE_SIZE / 8)
+#define SHASH_MAX_STATESIZE     (PAGE_SIZE / 8)
+
  #define SHASH_DESC_ON_STACK(shash, ctx)				  \
  	char __##shash##_desc[sizeof(struct shash_desc) +	  \
-		crypto_shash_descsize(ctx)] CRYPTO_MINALIGN_ATTR; \
+		SHASH_MAX_DESCSIZE] CRYPTO_MINALIGN_ATTR; \
  	struct shash_desc *shash = (struct shash_desc *)__##shash##_desc
/**


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