[CRYPTO] api: Require block size to be less than PAGE_SIZE/8

The cipher code path may allocate up to two blocks of data on the stack.
Therefore we need to place limits on the maximum block size.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/api.c

@@ -251,7 +251,7 @@ int crypto_register_alg(struct crypto_alg *alg)
 	if (alg->cra_alignmask & alg->cra_blocksize)
 		return -EINVAL;
 
-	if (alg->cra_blocksize > PAGE_SIZE)
+	if (alg->cra_blocksize > PAGE_SIZE / 8)
 		return -EINVAL;
 
 	if (alg->cra_priority < 0)