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=-8.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 6ACFEC433E1 for ; Mon, 27 Jul 2020 11:55:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4F469206E7 for ; Mon, 27 Jul 2020 11:55:59 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728227AbgG0Lz6 (ORCPT ); Mon, 27 Jul 2020 07:55:58 -0400 Received: from mx2.suse.de ([195.135.220.15]:51710 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727088AbgG0Lz6 (ORCPT ); Mon, 27 Jul 2020 07:55:58 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 97AE5AE1C; Mon, 27 Jul 2020 11:56:07 +0000 (UTC) Received: by ds.suse.cz (Postfix, from userid 10065) id 1282EDA701; Mon, 27 Jul 2020 13:55:29 +0200 (CEST) Date: Mon, 27 Jul 2020 13:55:28 +0200 From: David Sterba To: Josef Bacik Cc: linux-btrfs@vger.kernel.org, kernel-team@fb.com Subject: Re: [PATCH][v2] btrfs: only search for left_info if there is no right_info Message-ID: <20200727115528.GJ3703@twin.jikos.cz> Reply-To: dsterba@suse.cz Mail-Followup-To: dsterba@suse.cz, Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com References: <20200722184245.19699-1-josef@toxicpanda.com> <20200722184537.19896-1-josef@toxicpanda.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200722184537.19896-1-josef@toxicpanda.com> User-Agent: Mutt/1.5.23.1-rc1 (2014-03-12) Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On Wed, Jul 22, 2020 at 02:45:37PM -0400, Josef Bacik wrote: > The CVE referenced doesn't actually trigger the problem anymore because > of the tree-checker improvements, however the underlying issue can still > happen. What was the problem? > If we find a right_info, but rb_prev() is NULL, then we're the furthest > most item in the tree currently, and there will be no left_info. > However we'll still search from offset-1, which would return right_info > again which we store in left_info. If we then free right_info we'll > have free'd left_info as well, and boom, UAF. Instead fix this check so > that if we don't have a right_info we do the search for the left_info, > otherwise left_info comes from rb_prev or is simply NULL as it should > be. > > Reference: CVE-2019-19448 > Fixes: 963030817060 ("Btrfs: use hybrid extents+bitmap rb tree for free space") > Signed-off-by: Josef Bacik > --- > v1->v2: > - Fixed the title, I had changed the fix but forgot to change the title in v1 The title still repeats what the code does and left_info or right_info are not terms that are understood without context (unlike eg. fs_info)