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 DBE7BCCA488 for ; Thu, 23 Jun 2022 18:23:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232631AbiFWSXx (ORCPT ); Thu, 23 Jun 2022 14:23:53 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55242 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S237123AbiFWSVj (ORCPT ); Thu, 23 Jun 2022 14:21:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF9B7699BB; Thu, 23 Jun 2022 10:25:15 -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 D447761DC6; Thu, 23 Jun 2022 17:25:14 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B5F40C3411B; Thu, 23 Jun 2022 17:25:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656005114; bh=a2yASAbOJhkKvUDD8zu4yyqktGPtzXvL3oQp01bC5n4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=bw+wYo7VWJUx2eLMI71U1ZXImkei3EoOKuYhkPSZNQyqORAjAIAxXKX+q52JrJWSf 7FWYzeM0h/YRyXPepCArizrm+s9Rb7UOyGs0umE7sxF9ppN3toLrHeK6AUAcDjebV5 gMgnDoYKT8+o786f1Zpkj4Z4wA+jiZ1nuS/RhS6I= 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 5.4 06/11] tcp: add small random increments to the source port Date: Thu, 23 Jun 2022 18:45:10 +0200 Message-Id: <20220623164321.383720086@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220623164321.195163701@linuxfoundation.org> References: <20220623164321.195163701@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 Cc: 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 @@ -782,11 +782,12 @@ 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 */