crypto: xts - Propagate NEED_FALLBACK bit

When we're used as a fallback algorithm, we should propagate
the NEED_FALLBACK bit when searching for the underlying ECB mode.

This just happens to fix a hang too because otherwise the search
may end up loading the same module that triggered this XTS creation.

Cc: stable@vger.kernel.org #4.10
Fixes: f1c131b45410 ("crypto: xts - Convert to skcipher")
Reported-by: Harald Freudenberger <freude@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/xts.c

@@ -463,6 +463,7 @@ static int create(struct crypto_template *tmpl, struct rtattr **tb)
 	struct xts_instance_ctx *ctx;
 	struct skcipher_alg *alg;
 	const char *cipher_name;
+	u32 mask;
 	int err;
 
 	algt = crypto_get_attr_type(tb);
@@ -483,18 +484,19 @@ static int create(struct crypto_template *tmpl, struct rtattr **tb)
 	ctx = skcipher_instance_ctx(inst);
 
 	crypto_set_skcipher_spawn(&ctx->spawn, skcipher_crypto_instance(inst));
-	err = crypto_grab_skcipher(&ctx->spawn, cipher_name, 0,
-				   crypto_requires_sync(algt->type,
-							algt->mask));
+
+	mask = crypto_requires_off(algt->type, algt->mask,
+				   CRYPTO_ALG_NEED_FALLBACK |
+				   CRYPTO_ALG_ASYNC);
+
+	err = crypto_grab_skcipher(&ctx->spawn, cipher_name, 0, mask);
 	if (err == -ENOENT) {
 		err = -ENAMETOOLONG;
 		if (snprintf(ctx->name, CRYPTO_MAX_ALG_NAME, "ecb(%s)",
 			     cipher_name) >= CRYPTO_MAX_ALG_NAME)
 			goto err_free_inst;
 
-		err = crypto_grab_skcipher(&ctx->spawn, ctx->name, 0,
-					   crypto_requires_sync(algt->type,
-								algt->mask));
+		err = crypto_grab_skcipher(&ctx->spawn, ctx->name, 0, mask);
 	}
 
 	if (err)