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=-13.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 22F54C43387 for ; Thu, 3 Jan 2019 08:48:18 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E7B7221479 for ; Thu, 3 Jan 2019 08:48:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730311AbfACIsQ (ORCPT ); Thu, 3 Jan 2019 03:48:16 -0500 Received: from zeniv.linux.org.uk ([195.92.253.2]:48786 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726702AbfACIsQ (ORCPT ); Thu, 3 Jan 2019 03:48:16 -0500 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.91 #2 (Red Hat Linux)) id 1geyfi-0002zp-9W; Thu, 03 Jan 2019 08:48:10 +0000 Date: Thu, 3 Jan 2019 08:48:10 +0000 From: Al Viro To: Sahitya Tummala Cc: Junxiao Bi , Joel Becker , Christoph Hellwig , linux-kernel@vger.kernel.org Subject: Re: [PATCH] configfs: Fix use-after-free when accessing sd->s_dentry Message-ID: <20190103084810.GK2217@ZenIV.linux.org.uk> References: <1546503064-12695-1-git-send-email-stummala@codeaurora.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1546503064-12695-1-git-send-email-stummala@codeaurora.org> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 03, 2019 at 01:41:04PM +0530, Sahitya Tummala wrote: > In the vfs_statx() context, during path lookup, the dentry gets > added to sd->s_dentry via configfs_attach_attr(). In the end, > vfs_statx() kills the dentry by calling path_put(), which invokes > configfs_d_iput(). Ideally, this dentry must be removed from > sd->s_dentry but it doesn't if the sd->s_count >= 3. As a result, > sd->s_dentry is holding reference to a stale dentry pointer whose > memory is already freed up. This results in use-after-free issue, > when this stale sd->s_dentry is accessed later in > configfs_readdir() path. > > This issue can be easily reproduced, by running the LTP test case - > sh fs_racer_file_list.sh /config > (https://github.com/linux-test-project/ltp/blob/master/testcases/kernel/fs/racer/fs_racer_file_list.sh) > > Signed-off-by: Sahitya Tummala > --- > fs/configfs/dir.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/fs/configfs/dir.c b/fs/configfs/dir.c > index 39843fa..a5906c5 100644 > --- a/fs/configfs/dir.c > +++ b/fs/configfs/dir.c > @@ -66,7 +66,7 @@ static void configfs_d_iput(struct dentry * dentry, > * configfs_attach_attr and set sd->s_dentry to null > * even it's still in use. > */ > - if (atomic_read(&sd->s_count) <= 2) > + if (sd->s_dentry == dentry) > sd->s_dentry = NULL; > > spin_unlock(&configfs_dirent_lock); Please, update the comment above as well - it refers the increment of sd->s_count, which becomes stale. I agree that the problem is real and the fix is sane (and that's what should've been done in the first place, back in "configfs: fix race between dentry put and lookup", which has introduced that logics).