From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5F95FC433EF for ; Wed, 27 Apr 2022 06:53:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1358467AbiD0G5H (ORCPT ); Wed, 27 Apr 2022 02:57:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49218 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1358404AbiD0G4u (ORCPT ); Wed, 27 Apr 2022 02:56:50 -0400 Received: from 1wt.eu (wtarreau.pck.nerim.net [62.212.114.60]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id BE2A7156E03; Tue, 26 Apr 2022 23:53:40 -0700 (PDT) Received: (from willy@localhost) by pcw.home.local (8.15.2/8.15.2/Submit) id 23R6qpH8002131; Wed, 27 Apr 2022 08:52:51 +0200 From: Willy Tarreau To: netdev@vger.kernel.org Cc: David Miller , Jakub Kicinski , Eric Dumazet , Moshe Kol , Yossi Gilad , Amit Klein , linux-kernel@vger.kernel.org, Willy Tarreau Subject: [PATCH net 7/7] tcp: drop the hash_32() part from the index calculation Date: Wed, 27 Apr 2022 08:52:33 +0200 Message-Id: <20220427065233.2075-8-w@1wt.eu> X-Mailer: git-send-email 2.17.5 In-Reply-To: <20220427065233.2075-1-w@1wt.eu> References: <20220427065233.2075-1-w@1wt.eu> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In commit 190cc82489f4 ("tcp: change source port randomizarion at connect() time"), the table_perturb[] array was introduced and an index was taken from the port_offset via hash_32(). But it turns out that hash_32() performs a multiplication while the input here comes from the output of SipHash in secure_seq, that is well distributed enough to avoid the need for yet another hash. Suggested-by: Amit Klein Reviewed-by: Eric Dumazet Signed-off-by: Willy Tarreau --- net/ipv4/inet_hashtables.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index f30c50aaf8e2..a75e66d7eee6 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -778,7 +778,7 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, net_get_random_once(table_perturb, INET_TABLE_PERTURB_SIZE * sizeof(*table_perturb)); - index = hash_32(port_offset, INET_TABLE_PERTURB_SHIFT); + index = port_offset & (INET_TABLE_PERTURB_SIZE - 1); offset = (READ_ONCE(table_perturb[index]) + (port_offset >> 32)) % remaining; /* In first pass we try ports of @low parity. -- 2.17.5