[PATCH 1/2] crypto: cbc - Propagate NEED_FALLBACK bit

[Marcelo Henrique Cerri]

When requesting a fallback algorithm, we should propagate the
NEED_FALLBACK bit when search for the underlying algorithm.

This will prevents drivers from allocating unnecessary fallbacks that
are never called. For instance, currently the vmx-crypto driver will use
the following chain of calls when calling the fallback implementation:

p8_aes_cbc -> cbc(p8_aes) -> aes-generic

However p8_aes will always delegate its calls to aes-generic. With this
patch, p8_aes_cbc will be able to use cbc(aes-generic) directly as its
fallback. The same applies to aes_s390.

Signed-off-by: Marcelo Henrique Cerri <marcelo.cerri@xxxxxxxxxxxxx>
---
 crypto/cbc.c | 20 ++++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/crypto/cbc.c b/crypto/cbc.c
index bc160a3..7147842 100644
--- a/crypto/cbc.c
+++ b/crypto/cbc.c
@@ -108,24 +108,32 @@ static void crypto_cbc_free(struct skcipher_instance *inst)
 static int crypto_cbc_create(struct crypto_template *tmpl, struct rtattr **tb)
 {
 	struct skcipher_instance *inst;
+	struct crypto_attr_type *algt;
 	struct crypto_spawn *spawn;
 	struct crypto_alg *alg;
+	u32 mask;
 	int err;
 
 	err = crypto_check_attr_type(tb, CRYPTO_ALG_TYPE_SKCIPHER);
 	if (err)
 		return err;
 
+	algt = crypto_get_attr_type(tb);
+	if (IS_ERR(algt))
+		return PTR_ERR(algt);
+
+	mask = CRYPTO_ALG_TYPE_MASK |
+		crypto_requires_off(algt->type, algt->mask,
+				    CRYPTO_ALG_NEED_FALLBACK);
+
+	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER, mask);
+	if (IS_ERR(alg))
+		return PTR_ERR(alg);
+
 	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 	if (!inst)
 		return -ENOMEM;
 
-	alg = crypto_get_attr_alg(tb, CRYPTO_ALG_TYPE_CIPHER,
-				  CRYPTO_ALG_TYPE_MASK);
-	err = PTR_ERR(alg);
-	if (IS_ERR(alg))
-		goto err_free_inst;
-
 	spawn = skcipher_instance_ctx(inst);
 	err = crypto_init_spawn(spawn, alg, skcipher_crypto_instance(inst),
 				CRYPTO_ALG_TYPE_MASK);
-- 
2.7.4