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=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 5F01FC43381 for ; Mon, 25 Mar 2019 23:02:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3447D20830 for ; Mon, 25 Mar 2019 23:02:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730603AbfCYXCU (ORCPT ); Mon, 25 Mar 2019 19:02:20 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:56772 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726010AbfCYXCU (ORCPT ); Mon, 25 Mar 2019 19:02:20 -0400 Received: from viro by ZenIV.linux.org.uk with local (Exim 4.92 #3 (Red Hat Linux)) id 1h8Ybb-0000ti-QB; Mon, 25 Mar 2019 23:02:11 +0000 Date: Mon, 25 Mar 2019 23:02:11 +0000 From: Al Viro To: Dave Chinner Cc: Linus Torvalds , syzbot , Alexei Starovoitov , Daniel Borkmann , linux-fsdevel , Linux List Kernel Mailing , syzkaller-bugs , Jan Kara , Jaegeuk Kim , Joel Becker , Mark Fasheh Subject: Re: KASAN: use-after-free Read in path_lookupat Message-ID: <20190325230211.GR2217@ZenIV.linux.org.uk> References: <0000000000006946d2057bbd0eef@google.com> <20190325045744.GK2217@ZenIV.linux.org.uk> <20190325194332.GO2217@ZenIV.linux.org.uk> <20190325224823.GF26298@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190325224823.GF26298@dastard> 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 Tue, Mar 26, 2019 at 09:48:23AM +1100, Dave Chinner wrote: > And when it comes to VFS inode reclaim, XFS does not implement > ->evict_inode because there is nothing at the VFS level to do. > And ->destroy_inode ends up doing cleanup work (e.g. freeing on-disk > inodes) which is non-trivial, blocking work, but then still requires > the struct xfs_inode to be written back to disk before it can bei > freed. So it just gets marked "reclaimable" and background reclaim > then takes care of it from there so we avoid synchronous IO in inode > reclaim... > > This works because don't track dirty inode metadata in the VFS > writeback code (it's tracked with much more precision in the XFS log > infrastructure) and we don't write back inodes from the VFS > infrastructure, either. It's all done based on internal state > outside the VFS. > > And, because of this, the VFS cannot assume that it can free > the struct inode after calling ->destroy_inode or even use > call_rcu() to run a filesystem destructor because the filesystem > may need to do work that needs to block and that's not allowed in an > RCU callback... In Linus' patch that's what you get with non-NULL ->destroy_inode + NULL ->destroy_inode_rcu, so XFS won't be screwed by that. Said that, yes, XFS adds another fun twist there (AFAICS, it's the only in-tree filesystem that pulls that off). I would really like some comments from f2fs and ocfs2 folks, as well as Jan - he's had much more recent contact with writeback code than I have... Could somebody explain what's going on in f2fs and ocfs2 ->drop_inode()? It _should_ be just a predicate; looks like both are playing very odd games to work around writeback problems and I wonder if there's a cleaner solution for that. I can try and dig through maillist(s) archives, but I would really appreciate it if somebody could give a braindump on the issues dealt with in there...