From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail.kernel.org ([198.145.29.99]:35734 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753119AbeENG6c (ORCPT ); Mon, 14 May 2018 02:58:32 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Tetsuo Handa , syzbot , weiping zhang , Jan Kara , Jens Axboe Subject: [PATCH 4.16 21/72] bdi: Fix use after free bug in debugfs_remove() Date: Mon, 14 May 2018 08:48:38 +0200 Message-Id: <20180514064823.933801155@linuxfoundation.org> In-Reply-To: <20180514064823.033169170@linuxfoundation.org> References: <20180514064823.033169170@linuxfoundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: stable-owner@vger.kernel.org List-ID: 4.16-stable review patch. If anyone has any objections, please let me know. ------------------ From: Tetsuo Handa commit f53823c18131e755905b4f654196fd2cc3953f6e upstream. syzbot is reporting use after free bug in debugfs_remove() [1]. This is because fault injection made memory allocation for debugfs_create_file() from bdi_debug_register() from bdi_register_va() fail and continued with setting WB_registered. But when debugfs_remove() is called from debugfs_remove(bdi->debug_dir) from bdi_debug_unregister() from bdi_unregister() from release_bdi() because WB_registered was set by bdi_register_va(), IS_ERR_OR_NULL(bdi->debug_dir) == false despite debugfs_remove(bdi->debug_dir) was already called from bdi_register_va(). Fix this by making IS_ERR_OR_NULL(bdi->debug_dir) == true. [1] https://syzkaller.appspot.com/bug?id=5ab4efd91a96dcea9b68104f159adf4af2a6dfc1 Signed-off-by: Tetsuo Handa Reported-by: syzbot Fixes: 97f07697932e6faf ("bdi: convert bdi_debug_register to int") Cc: weiping zhang Reviewed-by: Greg Kroah-Hartman Reviewed-by: Jan Kara Signed-off-by: Jens Axboe Signed-off-by: Greg Kroah-Hartman --- mm/backing-dev.c | 1 + 1 file changed, 1 insertion(+) --- a/mm/backing-dev.c +++ b/mm/backing-dev.c @@ -126,6 +126,7 @@ static int bdi_debug_register(struct bac bdi, &bdi_debug_stats_fops); if (!bdi->debug_stats) { debugfs_remove(bdi->debug_dir); + bdi->debug_dir = NULL; return -ENOMEM; }