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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,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 D9C34C3A5A3 for ; Tue, 27 Aug 2019 09:20:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id ACA2D20828 for ; Tue, 27 Aug 2019 09:20:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729388AbfH0JUu (ORCPT ); Tue, 27 Aug 2019 05:20:50 -0400 Received: from szxga05-in.huawei.com ([45.249.212.191]:5221 "EHLO huawei.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725912AbfH0JUt (ORCPT ); Tue, 27 Aug 2019 05:20:49 -0400 Received: from DGGEMS409-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id B349910FF19798F531BF; Tue, 27 Aug 2019 17:20:46 +0800 (CST) Received: from [127.0.0.1] (10.177.244.145) by DGGEMS409-HUB.china.huawei.com (10.3.19.209) with Microsoft SMTP Server id 14.3.439.0; Tue, 27 Aug 2019 17:20:41 +0800 Subject: Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity To: Jan Kara References: <1565869639-105420-1-git-send-email-yi.zhang@huawei.com> <20190825034000.GE5163@mit.edu> <20190826025612.GB4918@mit.edu> <33767946-1e6f-5165-94b3-46e2da15172f@huawei.com> <20190826150350.GH10614@quack2.suse.cz> CC: "Theodore Y. Ts'o" , , From: "zhangyi (F)" Message-ID: <6874efe7-17e9-6651-0b38-22b8b8946599@huawei.com> Date: Tue, 27 Aug 2019 17:20:40 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.4.0 MIME-Version: 1.0 In-Reply-To: <20190826150350.GH10614@quack2.suse.cz> Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: 8bit X-Originating-IP: [10.177.244.145] X-CFilter-Loop: Reflected Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On 2019/8/26 23:03, Jan Kara Wrote: > On Mon 26-08-19 16:31:41, zhangyi (F) wrote: >> On 2019/8/26 10:56, Theodore Y. Ts'o Wrote: >>> I added a missing rcu_read_lock() to prevent a suspicious RCU >>> warning when CONFIG_PROVE_RCU is enabled: >>> >>> diff --git a/fs/ext4/block_validity.c b/fs/ext4/block_validity.c >>> index 003dc1dc2da3..f7bc914a74df 100644 >>> --- a/fs/ext4/block_validity.c >>> +++ b/fs/ext4/block_validity.c >>> @@ -330,11 +330,13 @@ void ext4_release_system_zone(struct super_block *sb) >>> { >>> struct ext4_system_blocks *system_blks; >>> >>> + rcu_read_lock(); >>> system_blks = rcu_dereference(EXT4_SB(sb)->system_blks); >>> rcu_assign_pointer(EXT4_SB(sb)->system_blks, NULL); >>> >>> if (system_blks) >>> call_rcu(&system_blks->rcu, ext4_destroy_system_zone); >>> + rcu_read_unlock(); >>> } >>> >>> int ext4_data_block_valid(struct ext4_sb_info *sbi, ext4_fsblk_t start_blk, >>> >> >> Hi Ted， >> Sorry about missing this warning, I think switch to use: >> system_blks = rcu_dereference_raw(EXT4_SB(sb)->system_blks); >> or >> system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, true); >> is enough to fix this waring, am I missing something? > > Proper fix for this is actually using: > > system_blks = rcu_dereference_protected(EXT4_SB(sb)->system_blks, > lockdep_is_held(&sb->s_umount)); > Totally agree, will resend the patch. Thanks, Yi.