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=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 C6C8BCA9EB9 for ; Wed, 23 Oct 2019 08:42:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A2B2D2084C for ; Wed, 23 Oct 2019 08:42:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2390444AbfJWImt (ORCPT ); Wed, 23 Oct 2019 04:42:49 -0400 Received: from szxga08-in.huawei.com ([45.249.212.255]:43742 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2390272AbfJWImt (ORCPT ); Wed, 23 Oct 2019 04:42:49 -0400 Received: from DGGEMM404-HUB.china.huawei.com (unknown [172.30.72.54]) by Forcepoint Email with ESMTP id 11C1CFFCF3A22F217689; Wed, 23 Oct 2019 16:42:45 +0800 (CST) Received: from dggeme762-chm.china.huawei.com (10.3.19.108) by DGGEMM404-HUB.china.huawei.com (10.3.20.212) with Microsoft SMTP Server (TLS) id 14.3.439.0; Wed, 23 Oct 2019 16:42:44 +0800 Received: from architecture4 (10.140.130.215) by dggeme762-chm.china.huawei.com (10.3.19.108) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA256_P256) id 15.1.1713.5; Wed, 23 Oct 2019 16:42:44 +0800 Date: Wed, 23 Oct 2019 16:45:36 +0800 From: Gao Xiang To: Chao Yu CC: Chao Yu , , Gao Xiang , Subject: Re: [PATCH v4] erofs: support superblock checksum Message-ID: <20191023084536.GA16289@architecture4> References: <20191022180620.19638-1-pratikshinde320@gmail.com> <20191023040557.230886-1-gaoxiang25@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.9.4 (2018-02-28) X-Originating-IP: [10.140.130.215] X-ClientProxiedBy: dggeme701-chm.china.huawei.com (10.1.199.97) To dggeme762-chm.china.huawei.com (10.3.19.108) X-CFilter-Loop: Reflected Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Chao, On Wed, Oct 23, 2019 at 04:15:29PM +0800, Chao Yu wrote: > Hi, Xiang, Pratik, > > On 2019/10/23 12:05, Gao Xiang wrote: > > } > > > > +static int erofs_superblock_csum_verify(struct super_block *sb, void *sbdata) > > +{ > > + struct erofs_super_block *dsb; > > + u32 expected_crc, nblocks, crc; > > + void *kaddr; > > + struct page *page; > > + int i; > > + > > + dsb = kmemdup(sbdata + EROFS_SUPER_OFFSET, > > + EROFS_BLKSIZ - EROFS_SUPER_OFFSET, GFP_KERNEL); > > + if (!dsb) > > + return -ENOMEM; > > + > > + expected_crc = le32_to_cpu(dsb->checksum); > > + nblocks = le32_to_cpu(dsb->chksum_blocks); > > Now, we try to use nblocks's value before checking its validation, I guess fuzz > test can easily make the value extreme larger, result in checking latter blocks > unnecessarily. > > IMO, we'd better > 1. check validation of superblock to make sure all fields in sb are valid > 2. use .nblocks to count and check payload blocks following sb That is quite a good point. :-) My first thought is to check the following payloads of sb (e.g, some per-fs metadata should be checked at mount time together. or for small images, check the whole image at the mount time) as well since if we introduce a new feature to some kernel version, forward compatibility needs to be considered. So it's better to make proper scalability, for this case, we have some choices: 1) limit `chksum_blocks' upbound at runtime (e.g. refuse >= 65536 blocks, totally 256M.) 2) just get rid of the whole `chksum_blocks' mess and checksum the first 4k at all, don't consider any latter scalability. Some perferred idea about this? I plan to release erofs-utils v1.0 tomorrow and hold up this feature for the next erofs-utils release, but I think we can get it ready for v5.5 since it is not quite complex feature... Thanks, Gao Xiang