On Mon, Mar 22, 2021 at 6:28 PM Christian Brauner <christian.brauner@xxxxxxxxxx> wrote: > > On Mon, Mar 22, 2021 at 02:44:20PM +0200, Amir Goldstein wrote: > > On Sat, Mar 20, 2021 at 2:57 PM Amir Goldstein <amir73il@xxxxxxxxx> wrote: > > > > > > > > > The code that sits in linux-next can give you pretty much a drop-in > > > > > > replacement of inotify and nothing more. See example code: > > > > > > https://github.com/amir73il/inotify-tools/commits/fanotify_name_fid > > > > > > > > > > This is really great. Thank you for doing that work this will help quite > > > > > a lot of use-cases and make things way simpler. I created a TODO to port > > > > > our path-hotplug to this once this feature lands. > > > > > > > > > > > > > FWIW, I just tried to build this branch on Ubuntu 20.04.2 with LTS kernel > > > > and there were some build issues, so rebased my branch on upstream > > > > inotify-tools to fix those build issues. > > > > > > > > I was not aware that the inotify-tools project is alive, I never intended > > > > to upstream this demo code and never created a github pull request > > > > but rebasing on upstream brought in some CI scripts, when I pushed the > > > > branch to my github it triggered some tests that reported build failures on > > > > Ubuntu 16.04 and 18.04. > > > > > > > > Anyway, there is a pre-rebase branch 'fanotify_name' and the post rebase > > > > branch 'fanotify_name_fid'. You can try whichever works for you. > > > > FYI, fixed the CI build errors on fanotify_name_fid branch. > > > > > > > > > > You can look at the test script src/test_demo.sh for usage example. > > > > Or just cd into a writable directory and run the script to see the demo. > > > > The demo determines whether to use a recursive watch or "global" > > > > watch by the uid of the user. > > > > > > > > > > > > > > > > > > If you think that is useful and you want to play with this feature I can > > > > > > > > provide a WIP branch soon. > > > > > > > > > > > > > > I would like to first play with the support for unprivileged fanotify > > > > > > > but sure, it does sound useful! > > > > > > > > > > > > Just so you have an idea what I am talking about, this is a very early > > > > > > POC branch: > > > > > > https://github.com/amir73il/linux/commits/fanotify_userns > > > > > > > > > > Thanks! I'll try to pull this and take a look next week. I hope that's > > > > > ok. > > > > > > > > > > > > > Fine. I'm curious to know what it does. > > > > Did not get to test it with userns yet :) > > > > > > Now tested FAN_MARK_FILESYSTEM watch on tmpfs mounted > > > inside userns and works fine, with two wrinkles I needed to iron: > > > > > > 1. FAN_REPORT_FID not supported on tmpfs because tmpfs has > > > zero f_fsid (easy to fix) > > > 2. open_by_handle_at() is not userns aware (can relax for > > > FS_USERNS_MOUNT fs) > > > > > > Pushed these two fixes to branch fanotify_userns. > > > > Pushed another fix to mnt refcount bug in WIP and another commit to > > add the last piece that could make fanotify usable for systemd-homed > > setup - a filesystem watch filtered by mnt_userns (not tested yet). > > Sounds interesting. > > So I'm looking and commenting on that branch a little. > One general question, when fanotify FANOTIFY_PERM_EVENTS is set fanotify > will return a file descriptor (for relevant events) referring to the > file/directory that e.g. got created. And there are no permissions > checks other than the capable(CAP_SYS_ADMIN) check when the fanotify > instance is created, right? > Correct. fanotify_init() enforces that in a few maybe not so obvious steps: 1. Either CAP_SYS_ADMIN or fid_mode (no file descriptor in event): if (!capable(CAP_SYS_ADMIN)) { /* * An unprivileged user can setup an fanotify group with * limited functionality - an unprivileged group is limited to * notification events with file handles and it cannot use * unlimited queue/marks. */ if ((flags & FANOTIFY_ADMIN_INIT_FLAGS) || !fid_mode) return -EPERM; } 2. fid_mode is not supported for high priority classes: if (fid_mode && class != FAN_CLASS_NOTIF) return -EINVAL; 3. Permission events are only allowed for high priority classes: /* * group->priority == FS_PRIO_0 == FAN_CLASS_NOTIF. These are not * allowed to set permissions events. */ ret = -EINVAL; if (mask & FANOTIFY_PERM_EVENTS && group->priority == FS_PRIO_0) You may want to look at the summary of all the limitations on unprivileged listener here: https://github.com/amir73il/man-pages/blob/fanotify_unpriv/man2/fanotify_init.2#L400 Thanks, Amir.
