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 X-Spam-Level: X-Spam-Status: No, score=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 71F9DC433E0 for ; Mon, 28 Dec 2020 22:57:43 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3A2A7222F9 for ; Mon, 28 Dec 2020 22:57:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732295AbgL1W4e (ORCPT ); Mon, 28 Dec 2020 17:56:34 -0500 Received: from shards.monkeyblade.net ([23.128.96.9]:44328 "EHLO mail.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729696AbgL1WwJ (ORCPT ); Mon, 28 Dec 2020 17:52:09 -0500 Received: from localhost (unknown [IPv6:2601:601:9f00:477::3d5]) by mail.monkeyblade.net (Postfix) with ESMTPSA id AC5C04CE686D1; Mon, 28 Dec 2020 14:51:28 -0800 (PST) Date: Mon, 28 Dec 2020 14:51:28 -0800 (PST) Message-Id: <20201228.145128.1498314185351532341.davem@davemloft.net> To: weichen.chen@linux.alibaba.com Cc: eric.dumazet@gmail.com, kuba@kernel.org, splendidsky.cwc@alibaba-inc.com, yanxu.zw@alibaba-inc.com, dsahern@kernel.org, liuhangbin@gmail.com, roopa@cumulusnetworks.com, jdike@akamai.com, nikolay@cumulusnetworks.com, lirongqing@baidu.com, mrv@mojatatu.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v4] net: neighbor: fix a crash caused by mod zero From: David Miller In-Reply-To: <20201225054448.73256-1-weichen.chen@linux.alibaba.com> References: <20201225054448.73256-1-weichen.chen@linux.alibaba.com> X-Mailer: Mew version 6.8 on Emacs 27.1 Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit X-Greylist: Sender succeeded SMTP AUTH, not delayed by milter-greylist-4.6.2 (mail.monkeyblade.net [0.0.0.0]); Mon, 28 Dec 2020 14:51:29 -0800 (PST) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: weichenchen Date: Fri, 25 Dec 2020 13:44:45 +0800 > pneigh_enqueue() tries to obtain a random delay by mod > NEIGH_VAR(p, PROXY_DELAY). However, NEIGH_VAR(p, PROXY_DELAY) > migth be zero at that point because someone could write zero > to /proc/sys/net/ipv4/neigh/[device]/proxy_delay after the > callers check it. > > This patch uses prandom_u32_max() to get a random delay instead > which avoids potential division by zero. > > Signed-off-by: weichenchen > --- > V4: > - Use prandom_u32_max() to get a random delay in > pneigh_enqueue(). > V3: > - Callers need to pass the delay time to pneigh_enqueue() > now and they should guarantee it is not zero. > - Use READ_ONCE() to read NEIGH_VAR(p, PROXY_DELAY) in both > of the existing callers of pneigh_enqueue() and then pass > it to pneigh_enqueue(). > V2: > - Use READ_ONCE() to prevent the complier from re-reading > NEIGH_VAR(p, PROXY_DELAY). > - Give a hint to the complier that delay <= 0 is unlikely > to happen. > > V4 is quite concise and works well. > Thanks for Eric's and Jakub's advice. Applied and queued up for -stable, thanks.