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 66716C433FE for ; Mon, 16 May 2022 20:39:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1349206AbiEPUiK (ORCPT ); Mon, 16 May 2022 16:38:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55968 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1350984AbiEPUBy (ORCPT ); Mon, 16 May 2022 16:01:54 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DC5794B874; Mon, 16 May 2022 12:56:17 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id 86DDBB81607; Mon, 16 May 2022 19:56:16 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id D33D1C385AA; Mon, 16 May 2022 19:56:14 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1652730975; bh=lhW8NJEDdIn54Z0I2VF12YbCHzDA9ZNvrF4WYLJPgbY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pKdgkrMHXljk+nEMbo9Je9BbmBmQzu1LDHRZW2h9I6ox22uDbQF70zispXbnLo1pr dV9NN6sS5Qoyk27WHu39AL4+hm9aKYBSMueITSkHSQRtiwqJiZTTcpH2H064OOTm1L O187/F6y+SMIYWCdRklTO8YYUct9ITi8bOXud718= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Moshe Kol , Yossi Gilad , Amit Klein , Eric Dumazet , Willy Tarreau , Jakub Kicinski , Sasha Levin Subject: [PATCH 5.17 064/114] tcp: add small random increments to the source port Date: Mon, 16 May 2022 21:36:38 +0200 Message-Id: <20220516193627.330987514@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220516193625.489108457@linuxfoundation.org> References: <20220516193625.489108457@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Willy Tarreau [ Upstream commit ca7af0402550f9a0b3316d5f1c30904e42ed257d ] Here we're randomly adding between 0 and 7 random increments to the selected source port in order to add some noise in the source port selection that will make the next port less predictable. With the default port range of 32768-60999 this means a worst case reuse scenario of 14116/8=1764 connections between two consecutive uses of the same port, with an average of 14116/4.5=3137. This code was stressed at more than 800000 connections per second to a fixed target with all connections closed by the client using RSTs (worst condition) and only 2 connections failed among 13 billion, despite the hash being reseeded every 10 seconds, indicating a perfectly safe situation. Cc: Moshe Kol Cc: Yossi Gilad Cc: Amit Klein Reviewed-by: Eric Dumazet Signed-off-by: Willy Tarreau Signed-off-by: Jakub Kicinski Signed-off-by: Sasha Levin --- net/ipv4/inet_hashtables.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) diff --git a/net/ipv4/inet_hashtables.c b/net/ipv4/inet_hashtables.c index 29c701cd8312..63bb4902f018 100644 --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -833,11 +833,12 @@ int __inet_hash_connect(struct inet_timewait_death_row *death_row, return -EADDRNOTAVAIL; ok: - /* If our first attempt found a candidate, skip next candidate - * in 1/16 of cases to add some noise. + /* Here we want to add a little bit of randomness to the next source + * port that will be chosen. We use a max() with a random here so that + * on low contention the randomness is maximal and on high contention + * it may be inexistent. */ - if (!i && !(prandom_u32() % 16)) - i = 2; + i = max_t(int, i, (prandom_u32() & 7) * 2); WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2); /* Head lock still held and bh's disabled */ -- 2.35.1