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=-17.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,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 DD22DC4361B for ; Mon, 7 Dec 2020 08:36:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 617D12076C for ; Mon, 7 Dec 2020 08:36:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726164AbgLGIf7 (ORCPT ); Mon, 7 Dec 2020 03:35:59 -0500 Received: from mx2.suse.de ([195.135.220.15]:56574 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726141AbgLGIf7 (ORCPT ); Mon, 7 Dec 2020 03:35:59 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1607330112; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc: mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references:autocrypt:autocrypt; bh=vJgXvWoe5/CoEus2t13iaKKsQ+qQ7dxYiU8MSxUdYFw=; b=h8VrwNPwMbDUl1jyxj3iShgcxu7ak6SxMRGbF6ZbollNtRqVEbr9Kf23im6BmNRJS+vtO7 0vNNqsAYirzYRiNReAER8lsPBmnOKDfWkS2A4OPmS9KU3EVtArqtQPYv1s/P2NRRRxfJLO MZyW497OxekRWnPNGDUEqf3X1Qq5yfE= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 566AEAC90; Mon, 7 Dec 2020 08:35:12 +0000 (UTC) Subject: Re: [PATCH v4 03/53] btrfs: modify the new_root highest_objectid under a ref count To: Qu Wenruo , Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: <448e6b22-1a44-a3ac-bf91-632bd8dc9206@gmx.com> From: Nikolay Borisov Autocrypt: addr=nborisov@suse.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <448e6b22-1a44-a3ac-bf91-632bd8dc9206@gmx.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 4.12.20 г. 10:01 ч., Qu Wenruo wrote: > > > On 2020/12/4 上午2:22, Josef Bacik wrote: >> Qu pointed out a bug in one of my error handling patches, which made me >> notice that we modify the new_root->highest_objectid _after_ we've >> dropped the ref to the new_root. This could lead to a possible UAF, fix >> this by modifying the ->highest_objectid before we drop our reference to >> the new_root. >> >> Signed-off-by: Josef Bacik > > Reviewed-by: Qu Wenruo > > But found something to cleanup in the future, inlined below. >> --- >> fs/btrfs/ioctl.c | 10 ++++++---- >> 1 file changed, 6 insertions(+), 4 deletions(-) >> >> diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c >> index 703212ff50a5..f240beed4739 100644 >> --- a/fs/btrfs/ioctl.c >> +++ b/fs/btrfs/ioctl.c >> @@ -717,6 +717,12 @@ static noinline int create_subvol(struct inode *dir, >> btrfs_record_root_in_trans(trans, new_root); >> >> ret = btrfs_create_subvol_root(trans, new_root, root, new_dirid); > > Firstly, btrfs_create_subvol_root() is only called here once, and > new_dirid is always a fixed value, BTRFS_FIRST_FREE_OBJECTID. > > This means, we don't need the parameter at all. > >> + if (!ret) { >> + mutex_lock(&new_root->objectid_mutex); >> + new_root->highest_objectid = new_dirid; >> + mutex_unlock(&nBut still find something suspicious for the existing naming, inlined below.ew_root->objectid_mutex); >> + } >> + > > Secondly, new_root is a new subvolume root which just get allocated. > It looks more sane to initialize the highest_objectid inside > btrfs_get_root_ref() for new root. > > This should reduce the chance to hit such use-after-free bug completely. Actually btrfs_init_fs_root already does : 42 ret = btrfs_find_highest_objectid(root, 43 &root->highest_objectid); Where root would be the newly initialized tree so highest_objectid should already be correctly initialized. However, looking at the source of btrfs_find_highest_objectid why do we do BTRFS_FIRST_FREE_OBJECTID - 1 there?