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 40828C433EF for ; Thu, 23 Jun 2022 17:16:26 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230134AbiFWRQW (ORCPT ); Thu, 23 Jun 2022 13:16:22 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49020 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233312AbiFWRMp (ORCPT ); Thu, 23 Jun 2022 13:12:45 -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 E0FD24EF45; Thu, 23 Jun 2022 09:58:41 -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 52BA1B8248A; Thu, 23 Jun 2022 16:58:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9803CC3411B; Thu, 23 Jun 2022 16:58:38 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656003519; bh=KWIHTYBkB1oKZiqQ7+4sfDcn1nQyj2gDERCoeoco9X4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=XGMPVyb9nLvMndy39Su2YX95nqXBMG+Ai2KYjxKl2IJUo0cvfCD9iyo2+kssGjUPs dtN/iPf+fdcO8f0lAyvCkdNvtcWDZm2jY/uO/KeiHSbP/0++kOPnAeFmLPG/1KXL9x IGzZRFtwTtMYE1LHcwQka+VfeQuFpTTG4OBsSEvA= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Eric Dumazet , David Dworken , Willem de Bruijn , "David S. Miller" , Ben Hutchings Subject: [PATCH 4.9 258/264] tcp: add some entropy in __inet_hash_connect() Date: Thu, 23 Jun 2022 18:44:11 +0200 Message-Id: <20220623164351.365986967@linuxfoundation.org> X-Mailer: git-send-email 2.36.1 In-Reply-To: <20220623164344.053938039@linuxfoundation.org> References: <20220623164344.053938039@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: Eric Dumazet commit c579bd1b4021c42ae247108f1e6f73dd3f08600c upstream. Even when implementing RFC 6056 3.3.4 (Algorithm 4: Double-Hash Port Selection Algorithm), a patient attacker could still be able to collect enough state from an otherwise idle host. Idea of this patch is to inject some noise, in the cases __inet_hash_connect() found a candidate in the first attempt. This noise should not significantly reduce the collision avoidance, and should be zero if connection table is already well used. Note that this is not implementing RFC 6056 3.3.5 because we think Algorithm 5 could hurt typical workloads. Signed-off-by: Eric Dumazet Cc: David Dworken Cc: Willem de Bruijn Signed-off-by: David S. Miller Signed-off-by: Ben Hutchings Signed-off-by: Greg Kroah-Hartman --- net/ipv4/inet_hashtables.c | 5 +++++ 1 file changed, 5 insertions(+) --- a/net/ipv4/inet_hashtables.c +++ b/net/ipv4/inet_hashtables.c @@ -642,6 +642,11 @@ next_port: return -EADDRNOTAVAIL; ok: + /* If our first attempt found a candidate, skip next candidate + * in 1/16 of cases to add some noise. + */ + if (!i && !(prandom_u32() % 16)) + i = 2; WRITE_ONCE(table_perturb[index], READ_ONCE(table_perturb[index]) + i + 2); /* Head lock still held and bh's disabled */