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 9BA6ECCA482 for ; Thu, 23 Jun 2022 18:18:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236830AbiFWSSw (ORCPT ); Thu, 23 Jun 2022 14:18:52 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49272 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236977AbiFWSRh (ORCPT ); Thu, 23 Jun 2022 14:17:37 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0F169647A0; Thu, 23 Jun 2022 10:23:57 -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 671A861EA7; Thu, 23 Jun 2022 17:23:56 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2C4A8C3411B; Thu, 23 Jun 2022 17:23:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656005035; bh=09TOc/w8XVMGbpODCbGQRcCKDfQdYVC21us5zruwUnE=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=dLAi3wdpI6o/wk76CzNFfwcawJthqxmH6FqIS0zAUMQSd9T5u7wmaSFHXpKYkilof U1O7Ski0UxB6urf4MV/EnuPSnfYv2uuvxb7gVViGuR7xC0MqVca224J03a0EJ/cz8T qbdSWvWT0qRpAxd9vi9lpUFtdOrJBfVEovS5Qtkc= 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 , Ben Hutchings Subject: [PATCH 4.19 230/234] tcp: add small random increments to the source port Date: Thu, 23 Jun 2022 18:44:57 +0200 Message-Id: <20220623164349.558540381@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220623164343.042598055@linuxfoundation.org> References: <20220623164343.042598055@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: stable@vger.kernel.org From: Willy Tarreau commit ca7af0402550f9a0b3316d5f1c30904e42ed257d upstream. 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: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- net/ipv4/inet_hashtables.c | 9 +++++---- 1 file changed, 5 insertions(+), 4 deletions(-) --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -821,11 +821,12 @@ next_port: 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 */