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=-5.3 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 88373C3A59F for ; Mon, 26 Aug 2019 15:03:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5748D20874 for ; Mon, 26 Aug 2019 15:03:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732805AbfHZPDw (ORCPT ); Mon, 26 Aug 2019 11:03:52 -0400 Received: from mx2.suse.de ([195.135.220.15]:41168 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727031AbfHZPDv (ORCPT ); Mon, 26 Aug 2019 11:03:51 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id C6784B07B; Mon, 26 Aug 2019 15:03:50 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 479291E3DA1; Mon, 26 Aug 2019 17:03:50 +0200 (CEST) Date: Mon, 26 Aug 2019 17:03:50 +0200 From: Jan Kara To: "zhangyi (F)" Cc: "Theodore Y. Ts'o" , linux-ext4@vger.kernel.org, jack@suse.cz, adilger.kernel@dilger.ca Subject: Re: [PATCH v5] ext4: fix potential use after free in system zone via remount with noblock_validity Message-ID: <20190826150350.GH10614@quack2.suse.cz> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <33767946-1e6f-5165-94b3-46e2da15172f@huawei.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org 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)); Honza -- Jan Kara SUSE Labs, CR