crypto: hash - Remove VLA usage

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), along with a few other cases. Similar limits are turned into
macros as well.

A review of existing sizes shows that SHA512_DIGEST_SIZE (64) is the
largest digest size and that sizeof(struct sha3_state) (360) is the
largest descriptor size. The corresponding maximums are reduced.

[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>

1 files changed, 3 insertions, 3 deletions

diff --git a/crypto/shash.c b/crypto/shash.c
index 5d732c6bb4b2..86d76b5c626c 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 > HASH_MAX_DIGESTSIZE ||
+            alg->descsize > HASH_MAX_DESCSIZE ||
+            alg->statesize > HASH_MAX_STATESIZE)
                 return -EINVAL;
 
         base->cra_type = &crypto_shash_type;