From patchwork Mon May 16 19:36:32 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Greg KH X-Patchwork-Id: 573755 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 89412C352AA for ; Mon, 16 May 2022 20:07:09 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1347593AbiEPUGL (ORCPT ); Mon, 16 May 2022 16:06:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42444 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S243872AbiEPT7D (ORCPT ); Mon, 16 May 2022 15:59:03 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1BC0317ABF; Mon, 16 May 2022 12:52:37 -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 dfw.source.kernel.org (Postfix) with ESMTPS id AB3D360AB8; Mon, 16 May 2022 19:52:36 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id AAFB4C385AA; Mon, 16 May 2022 19:52:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1652730756; bh=LRaJJ6rm2rTcuj00VtV0cAzxzyTuSvN9jZkm2Xc9noo=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=plPSUCBMjRjo5E7DA4rIZgH2N4ObuSsgWMNoLgAq3Z0B/StZUh6R0csq04IXhbgdN Ar76nYCOogh836zGFfLhdxQ6L6PVnodNhK2nR+lbSh3ciA8nB/vWWneGmJV7njau+b fgeB0xw4oCsnFey1dXwOJusyDuhjkiLEd9TXSTKw= 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 5.15 058/102] tcp: add small random increments to the source port Date: Mon, 16 May 2022 21:36:32 +0200 Message-Id: <20220516193625.662549345@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220516193623.989270214@linuxfoundation.org> References: <20220516193623.989270214@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: stable@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 81a33af8393d..573a7e66ebc8 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 */