From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.codeaurora.org by pdx-caf-mail.web.codeaurora.org (Dovecot) with LMTP id ldhZGjVbHlvVHQAAmS7hNA ; Mon, 11 Jun 2018 11:22:19 +0000 Received: by smtp.codeaurora.org (Postfix, from userid 1000) id 26136607BB; Mon, 11 Jun 2018 11:22:19 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on pdx-caf-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham autolearn_force=no version=3.4.0 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by smtp.codeaurora.org (Postfix) with ESMTP id 91F2860792; Mon, 11 Jun 2018 11:22:18 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 smtp.codeaurora.org 91F2860792 Authentication-Results: pdx-caf-mail.web.codeaurora.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: pdx-caf-mail.web.codeaurora.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932850AbeFKLWQ (ORCPT + 19 others); Mon, 11 Jun 2018 07:22:16 -0400 Received: from mx1.redhat.com ([209.132.183.28]:55822 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932676AbeFKLWP (ORCPT ); Mon, 11 Jun 2018 07:22:15 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 3CE5A30C10F4; Mon, 11 Jun 2018 11:22:15 +0000 (UTC) Received: from [10.3.116.105] (ovpn-116-105.phx2.redhat.com [10.3.116.105]) by smtp.corp.redhat.com (Postfix) with ESMTP id 6BD7759740; Mon, 11 Jun 2018 11:22:14 +0000 (UTC) Subject: Re: [PATCH] net: thunderx: prevent concurrent data re-writing by nicvf_set_rx_mode To: David Miller , Vadim.Lomovtsev@caviumnetworks.com Cc: rric@kernel.org, sgoutham@cavium.com, linux-arm-kernel@lists.infradead.org, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, Vadim.Lomovtsev@cavium.com References: <20180608092759.28059-1-Vadim.Lomovtsev@caviumnetworks.com> <20180610.123551.885190586229525170.davem@davemloft.net> From: Dean Nelson Message-ID: <036618ae-887f-44b5-2b39-451b81191cc1@redhat.com> Date: Mon, 11 Jun 2018 06:22:14 -0500 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0 MIME-Version: 1.0 In-Reply-To: <20180610.123551.885190586229525170.davem@davemloft.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.46]); Mon, 11 Jun 2018 11:22:15 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 06/10/2018 02:35 PM, David Miller wrote: > From: Vadim Lomovtsev > Date: Fri, 8 Jun 2018 02:27:59 -0700 > >> + /* Save message data locally to prevent them from >> + * being overwritten by next ndo_set_rx_mode call(). >> + */ >> + spin_lock(&nic->rx_mode_wq_lock); >> + mode = vf_work->mode; >> + mc = vf_work->mc; >> + vf_work->mc = NULL; If I'm reading this code correctly, I believe nic->rx_mode_work.mc will have been set to NULL before the lock is dropped by nicvf_set_rx_mode_task() and acquired by nicvf_set_rx_mode(). >> + spin_unlock(&nic->rx_mode_wq_lock); > > At the moment you drop this lock, the memory behind 'mc' can be > freed up by: > >> + spin_lock(&nic->rx_mode_wq_lock); >> + kfree(nic->rx_mode_work.mc); So the kfree() will be called with a NULL pointer and quickly return. > > And you'll crash when you dereference it above via > __nicvf_set_rx_mode_task(). > I believe the call to kfree() in nicvf_set_rx_mode() is there to free up a mc_list that has been allocated by nicvf_set_rx_mode() during a previous callback to the function, one that has not yet been processed by nicvf_set_rx_mode_task(). In this way only the last 'unprocessed' callback to nicvf_set_rx_mode() gets processed should there be multiple callbacks occurring between the times the nicvf_set_rx_mode_task() runs. In my testing with this patch, this is what I see happening.