From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751984AbdBHVc0 (ORCPT ); Wed, 8 Feb 2017 16:32:26 -0500 Received: from mail-yw0-f194.google.com ([209.85.161.194]:34273 "EHLO mail-yw0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751128AbdBHVcY (ORCPT ); Wed, 8 Feb 2017 16:32:24 -0500 Date: Wed, 8 Feb 2017 15:19:07 -0500 From: Tejun Heo To: Jens Axboe , Dmitry Vyukov Cc: Andrew Morton , xiakaixu@huawei.com, Vlastimil Babka , Joe Perches , Mel Gorman , Michal Hocko , "linux-mm@kvack.org" , LKML , syzkaller Subject: [PATCH] block: fix double-free in the failure path of cgwb_bdi_init() Message-ID: <20170208201907.GC25826@htj.duckdns.org> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.7.1 (2016-10-04) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When !CONFIG_CGROUP_WRITEBACK, bdi has single bdi_writeback_congested at bdi->wb_congested. cgwb_bdi_init() allocates it with kzalloc() and doesn't do further initialization. This usually works fine as the reference count gets bumped to 1 by wb_init() and the put from wb_exit() releases it. However, when wb_init() fails, it puts the wb base ref automatically freeing the wb and the explicit kfree() in cgwb_bdi_init() error path ends up trying to free the same pointer the second time causing a double-free. Fix it by explicitly initilizing the refcnt to 1 and putting the base ref from cgwb_bdi_destroy(). Signed-off-by: Tejun Heo Reported-by: Dmitry Vyukov Fixes: a13f35e87140 ("writeback: don't embed root bdi_writeback_congested in bdi_writeback") Cc: stable@vger.kernel.org # v4.2+ --- Hello, ISTR seeing another fix for this bug but can't find it right now. If I'm imagining things, please apply this one. If not, either one is fine. Thanks. mm/backing-dev.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/mm/backing-dev.c b/mm/backing-dev.c index 3bfed5ab..61b3407 100644 --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -758,15 +758,20 @@ static int cgwb_bdi_init(struct backing_dev_info *bdi) if (!bdi->wb_congested) return -ENOMEM; + atomic_set(&bdi->wb_congested->refcnt, 1); + err = wb_init(&bdi->wb, bdi, 1, GFP_KERNEL); if (err) { - kfree(bdi->wb_congested); + wb_congested_put(bdi->wb_congested); return err; } return 0; } -static void cgwb_bdi_destroy(struct backing_dev_info *bdi) { } +static void cgwb_bdi_destroy(struct backing_dev_info *bdi) +{ + wb_congested_put(bdi->wb_congested); +} #endif /* CONFIG_CGROUP_WRITEBACK */