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=-5.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 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 12E0FC06511 for ; Mon, 1 Jul 2019 12:40:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E10CC214AE for ; Mon, 1 Jul 2019 12:39:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728874AbfGAMj6 (ORCPT ); Mon, 1 Jul 2019 08:39:58 -0400 Received: from foss.arm.com ([217.140.110.172]:34000 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727320AbfGAMj6 (ORCPT ); Mon, 1 Jul 2019 08:39:58 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 90907344; Mon, 1 Jul 2019 05:39:57 -0700 (PDT) Received: from [10.1.197.57] (e110467-lin.cambridge.arm.com [10.1.197.57]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 043783F246; Mon, 1 Jul 2019 05:39:56 -0700 (PDT) Subject: Re: [PATCH] iommu/dma: Fix calculation overflow in __finalise_sg() To: Joerg Roedel , Nicolin Chen Cc: iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org References: <20190622043814.5003-1-nicoleotsuka@gmail.com> <20190701122158.GE8166@8bytes.org> From: Robin Murphy Message-ID: <91a389be-fd76-c87f-7613-8cc972b69685@arm.com> Date: Mon, 1 Jul 2019 13:39:55 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190701122158.GE8166@8bytes.org> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/07/2019 13:21, Joerg Roedel wrote: > On Fri, Jun 21, 2019 at 09:38:14PM -0700, Nicolin Chen wrote: >> The max_len is a u32 type variable so the calculation on the >> left hand of the last if-condition will potentially overflow >> when a cur_len gets closer to UINT_MAX -- note that there're >> drivers setting max_seg_size to UINT_MAX: >> drivers/dma/dw-edma/dw-edma-core.c:745: >> dma_set_max_seg_size(dma->dev, U32_MAX); >> drivers/dma/dma-axi-dmac.c:871: >> dma_set_max_seg_size(&pdev->dev, UINT_MAX); >> drivers/mmc/host/renesas_sdhi_internal_dmac.c:338: >> dma_set_max_seg_size(dev, 0xffffffff); >> drivers/nvme/host/pci.c:2520: >> dma_set_max_seg_size(dev->dev, 0xffffffff); >> >> So this patch just casts the cur_len in the calculation to a >> size_t type to fix the overflow issue, as it's not necessary >> to change the type of cur_len after all. >> >> Fixes: 809eac54cdd6 ("iommu/dma: Implement scatterlist segment merging") >> Cc: stable@vger.kernel.org >> Signed-off-by: Nicolin Chen > > Looks good to me, but I let Robin take a look too before I apply it, > Robin? I'll need to take a closer look at how exactly an overflow would happen here (just got back off some holiday), but my immediate thought is that if this is a real problem, then what about 32-bit builds where size_t would still overflow? Robin.