crypto: gcm - simplify error handling in crypto_rfc4106_create()

Simplify the error handling in crypto_rfc4106_create() by taking
advantage of crypto_grab_aead() now handling an ERR_PTR() name and by
taking advantage of crypto_drop_aead() now accepting (as a no-op) a
spawn that hasn't been grabbed yet.

Conveniently, this eliminates the 'ccm_name' variable which was
incorrectly named (it should have been 'gcm_name').
Signed-off-by: NEric Biggers <ebiggers@google.com>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

crypto/gcm.c

@@ -840,7 +840,6 @@ static int crypto_rfc4106_create(struct crypto_template *tmpl,
 	struct aead_instance *inst;
 	struct crypto_aead_spawn *spawn;
 	struct aead_alg *alg;
-	const char *ccm_name;
 	int err;
 
 	algt = crypto_get_attr_type(tb);
@@ -852,19 +851,15 @@ static int crypto_rfc4106_create(struct crypto_template *tmpl,
 
 	mask = crypto_requires_sync(algt->type, algt->mask);
 
-	ccm_name = crypto_attr_alg_name(tb[1]);
-	if (IS_ERR(ccm_name))
-		return PTR_ERR(ccm_name);
-
 	inst = kzalloc(sizeof(*inst) + sizeof(*spawn), GFP_KERNEL);
 	if (!inst)
 		return -ENOMEM;
 
 	spawn = aead_instance_ctx(inst);
 	err = crypto_grab_aead(spawn, aead_crypto_instance(inst),
-			       ccm_name, 0, mask);
+			       crypto_attr_alg_name(tb[1]), 0, mask);
 	if (err)
-		goto out_free_inst;
+		goto err_free_inst;
 
 	alg = crypto_spawn_aead_alg(spawn);
 
@@ -872,11 +867,11 @@ static int crypto_rfc4106_create(struct crypto_template *tmpl,
 
 	/* Underlying IV size must be 12. */
 	if (crypto_aead_alg_ivsize(alg) != GCM_AES_IV_SIZE)
-		goto out_drop_alg;
+		goto err_free_inst;
 
 	/* Not a stream cipher? */
 	if (alg->base.cra_blocksize != 1)
-		goto out_drop_alg;
+		goto err_free_inst;
 
 	err = -ENAMETOOLONG;
 	if (snprintf(inst->alg.base.cra_name, CRYPTO_MAX_ALG_NAME,
@@ -885,7 +880,7 @@ static int crypto_rfc4106_create(struct crypto_template *tmpl,
 	    snprintf(inst->alg.base.cra_driver_name, CRYPTO_MAX_ALG_NAME,
 		     "rfc4106(%s)", alg->base.cra_driver_name) >=
 	    CRYPTO_MAX_ALG_NAME)
-		goto out_drop_alg;
+		goto err_free_inst;
 
 	inst->alg.base.cra_flags = alg->base.cra_flags & CRYPTO_ALG_ASYNC;
 	inst->alg.base.cra_priority = alg->base.cra_priority;
@@ -909,17 +904,11 @@ static int crypto_rfc4106_create(struct crypto_template *tmpl,
 	inst->free = crypto_rfc4106_free;
 
 	err = aead_register_instance(tmpl, inst);
-	if (err)
-		goto out_drop_alg;
-
-out:
+	if (err) {
+err_free_inst:
+		crypto_rfc4106_free(inst);
+	}
 	return err;
-
-out_drop_alg:
-	crypto_drop_aead(spawn);
-out_free_inst:
-	kfree(inst);
-	goto out;
 }
 
 static int crypto_rfc4543_setkey(struct crypto_aead *parent, const u8 *key,