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=-2.5 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_MUTT 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 E0BC1C43381 for ; Wed, 27 Mar 2019 19:00:06 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BC7D8206B7 for ; Wed, 27 Mar 2019 19:00:06 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389977AbfC0TAA (ORCPT ); Wed, 27 Mar 2019 15:00:00 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:33030 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2389673AbfC0S77 (ORCPT ); Wed, 27 Mar 2019 14:59:59 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1h9Dm8-00060f-HR; Wed, 27 Mar 2019 18:59:48 +0000 Date: Wed, 27 Mar 2019 18:59:48 +0000 From: Al Viro To: Jan Kara Cc: Mark Fasheh , Dave Chinner , Linus Torvalds , syzbot , Alexei Starovoitov , Daniel Borkmann , linux-fsdevel , Linux List Kernel Mailing , syzkaller-bugs , Jaegeuk Kim , Joel Becker Subject: Re: KASAN: use-after-free Read in path_lookupat Message-ID: <20190327185948.GC2217@ZenIV.linux.org.uk> References: <0000000000006946d2057bbd0eef@google.com> <20190325045744.GK2217@ZenIV.linux.org.uk> <20190325194332.GO2217@ZenIV.linux.org.uk> <20190325224823.GF26298@dastard> <20190325230211.GR2217@ZenIV.linux.org.uk> <20190326041509.GZ2217@ZenIV.linux.org.uk> <20190327165831.GB6742@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190327165831.GB6742@quack2.suse.cz> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Mar 27, 2019 at 05:58:31PM +0100, Jan Kara wrote: > On Tue 26-03-19 04:15:10, Al Viro wrote: > > On Mon, Mar 25, 2019 at 08:18:25PM -0700, Mark Fasheh wrote: > > > > > Hey Al, > > > > > > It's been a while since I've looked at that bit of code but it looks like > > > Ocfs2 is syncing the inode to disk and disposing of it's memory > > > representation (which would include the cluster locks held) so that other > > > nodes get a chance to delete the potentially orphaned inode. In Ocfs2 we > > > won't delete an inode if it exists in another nodes cache. > > > > Wait a sec - what's the reason for forcing that write_inode_now(); why > > doesn't the normal mechanism work? I'm afraid I still don't get it - > > we do wait for writeback in evict_inode(), or the local filesystems > > wouldn't work. > > I'm just guessing here but they don't want an inode cached once its last > dentry goes away (it makes cluster wide synchronization easier for them and > they do play tricks with cluster lock on dentries). Sure, but that's as simple as "return 1 from ->drop_inode()". > There is some info in > 513e2dae9422 "ocfs2: flush inode data to disk and free inode when i_count > becomes zero" which adds this ocfs2_drop_inode() implementation. So when > the last inode reference is dropped, they want to flush any dirty data to > disk and evict the inode. But AFAICT they should be fine with flushing the > inode from their ->evict_inode method. I_FREEING just stops the flusher > thread from touching the inode but explicit writeback through > write_inode_now(inode, 1) should go through just fine. Umm... Why is that write_inode_now() needed in either place? I agree that moving it to ->evict_inode() ought to be safe, but what makes it necessary in the first place? Put it another way, what dirties the data and/or metadata without marking it dirty?