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=-3.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=no 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 49403C433DB for ; Tue, 30 Mar 2021 12:54:30 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 212FE619BD for ; Tue, 30 Mar 2021 12:54:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231933AbhC3Mx5 (ORCPT ); Tue, 30 Mar 2021 08:53:57 -0400 Received: from mail.kernel.org ([198.145.29.99]:47864 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232077AbhC3Mxk (ORCPT ); Tue, 30 Mar 2021 08:53:40 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 1170F619B1; Tue, 30 Mar 2021 12:53:38 +0000 (UTC) Date: Tue, 30 Mar 2021 14:53:36 +0200 From: Christian Brauner To: Amir Goldstein Cc: Jan Kara , linux-fsdevel , Linux API Subject: Re: [RFC][PATCH] fanotify: allow setting FAN_CREATE in mount mark mask Message-ID: <20210330125336.vj2hkgwhyrh5okee@wittgenstein> References: <20210328155624.930558-1-amir73il@gmail.com> <20210330121204.b7uto3tesqf6m7hb@wittgenstein> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-api@vger.kernel.org On Tue, Mar 30, 2021 at 03:33:23PM +0300, Amir Goldstein wrote: > On Tue, Mar 30, 2021 at 3:12 PM Christian Brauner > wrote: > > > > On Sun, Mar 28, 2021 at 06:56:24PM +0300, Amir Goldstein wrote: > > > Add a high level hook fsnotify_path_create() which is called from > > > syscall context where mount context is available, so that FAN_CREATE > > > event can be added to a mount mark mask. > > > > > > This high level hook is called in addition to fsnotify_create(), > > > fsnotify_mkdir() and fsnotify_link() hooks in vfs helpers where the mount > > > context is not available. > > > > > > In the context where fsnotify_path_create() will be called, a dentry flag > > > flag is set on the new dentry the suppress the FS_CREATE event in the vfs > > > level hooks. > > > > Ok, just to make sure this scheme would also work for overlay-style > > filesystems like ecryptfs where you possible generate two notify events: > > - in the ecryptfs layer > > - in the lower fs layer > > at least when you set a regular inode watch. > > > > If you set a mount watch you ideally would generate two events in both > > layers too, right? But afaict that wouldn't work. > > > > Say, someone creates a new link in ecryptfs the DENTRY_PATH_CREATE > > flag will be set on the new ecryptfs dentry and so no notify event will > > be generated for the ecryptfs layer again. Then ecryptfs calls > > vfs_link() to create a new dentry in the lower layer. The new dentry in > > the lower layer won't have DCACHE_PATH_CREATE set. Ok, that makes sense. > > > > But since vfs_link() doesn't have access to the mnt context itself you > > can't generate a notify event for the mount associated with the lower > > fs. This would cause people who a FAN_MARK_MOUNT watch on that lower fs > > mount to not get notified about creation events going through the > > ecryptfs layer. Is that right? Seems like this could be a problem. > > > > Not sure I follow what the problem might be. > > FAN_MARK_MOUNT subscribes to get only events that were > generated via that vfsmount - that has been that way forever. > > A listener may subscribe to (say) FAN_CREATE on a certain > mount AND also also on a specific parent directory. > > If the listener is watching the entire ecryptfs mount and the > specific lower directory where said vfs_link() happens, both > events will be reported. One from fsnotify_create_path() and > the lower from fsnotify_create(). > > If one listener is watching the ecryptfs mount and another > listener is watching the specific ecryptfs directory, both > listeners will get a single event each. They will both get > the event that is emitted from fsnotify_path_create(). > > Besides I am not sure about ecryptfs, but overlayfs uses > private mount clone for accessing lower layer, so by definition I know. That's why I was using ecryptfs as an example which doesn't do that (And I think it should be switched tbh.). It simply uses kern_path() and then stashes that path. My example probably would be something like: mount -t ext4 /dev/sdb /A 1. FAN_MARK_MOUNT(/A) mount --bind /A /B 2. FAN_MARK_MOUNT(/B) mount -t ecryptfs /B /C 3. FAN_MARK_MOUNT(/C) let's say I now do touch /unencrypted/bla I may be way off here but intuitively it seems both 1. and 2. should get a creation event but not 3., right? But with your proposal would both 1. and 2. still get a creation event? > users cannot watch the underlying overlayfs operations using > a mount mark. Also, overlayfs suppresses fsnotify events on > underlying files intentionally with FMODE_NONOTIFY. Probably ecryptfs should too? Christian