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 50478C433F5 for ; Wed, 27 Apr 2022 08:07:40 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1359310AbiD0IKr convert rfc822-to-8bit (ORCPT ); Wed, 27 Apr 2022 04:10:47 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:56422 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1354468AbiD0IKn (ORCPT ); Wed, 27 Apr 2022 04:10:43 -0400 Received: from eu-smtp-delivery-151.mimecast.com (eu-smtp-delivery-151.mimecast.com [185.58.86.151]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 59EC051E7B for ; Wed, 27 Apr 2022 01:07:33 -0700 (PDT) Received: from AcuMS.aculab.com (156.67.243.121 [156.67.243.121]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id uk-mta-261-c1VjfSuEMBeiHVaCN1aObw-1; Wed, 27 Apr 2022 09:07:30 +0100 X-MC-Unique: c1VjfSuEMBeiHVaCN1aObw-1 Received: from AcuMS.Aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) by AcuMS.aculab.com (fd9f:af1c:a25b:0:994c:f5c2:35d6:9b65) with Microsoft SMTP Server (TLS) id 15.0.1497.32; Wed, 27 Apr 2022 09:07:29 +0100 Received: from AcuMS.Aculab.com ([fe80::994c:f5c2:35d6:9b65]) by AcuMS.aculab.com ([fe80::994c:f5c2:35d6:9b65%12]) with mapi id 15.00.1497.033; Wed, 27 Apr 2022 09:07:29 +0100 From: David Laight To: 'Willy Tarreau' , "netdev@vger.kernel.org" CC: David Miller , Jakub Kicinski , "Eric Dumazet" , Moshe Kol , "Yossi Gilad" , Amit Klein , "linux-kernel@vger.kernel.org" Subject: RE: [PATCH net 6/7] tcp: increase source port perturb table to 2^16 Thread-Topic: [PATCH net 6/7] tcp: increase source port perturb table to 2^16 Thread-Index: AQHYWgPN4CV2FTUQB025UCKyP5Su7q0DZwmg Date: Wed, 27 Apr 2022 08:07:29 +0000 Message-ID: <7372f788762140d496c157813b0173e5@AcuMS.aculab.com> References: <20220427065233.2075-1-w@1wt.eu> <20220427065233.2075-7-w@1wt.eu> In-Reply-To: <20220427065233.2075-7-w@1wt.eu> Accept-Language: en-GB, en-US X-MS-Has-Attach: X-MS-TNEF-Correlator: x-ms-exchange-transport-fromentityheader: Hosted x-originating-ip: [10.202.205.107] MIME-Version: 1.0 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=C51A453 smtp.mailfrom=david.laight@aculab.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: aculab.com Content-Language: en-US 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 > Sent: 27 April 2022 07:53 > > Moshe Kol, Amit Klein, and Yossi Gilad reported being able to accurately > identify a client by forcing it to emit only 40 times more connections > than there are entries in the table_perturb[] table. The previous two > improvements consisting in resalting the secret every 10s and adding > randomness to each port selection only slightly improved the situation, > and the current value of 2^8 was too small as it's not very difficult > to make a client emit 10k connections in less than 10 seconds. > > Thus we're increasing the perturb table from 2^8 to 2^16 so that the the > same precision now requires 2.6M connections, which is more difficult in > this time frame and harder to hide as a background activity. The impact > is that the table now uses 256 kB instead of 1 kB, which could mostly > affect devices making frequent outgoing connections. However such > components usually target a small set of destinations (load balancers, > database clients, perf assessment tools), and in practice only a few > entries will be visited, like before. Increasing the table size has a bigger impact on anyone trying to get the kernel to run in a limited memory footprint. All these large tables (often hash tables) soon add up. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)