On Mon 14-03-22 11:28:23, Amir Goldstein wrote:
> On Mon, Mar 14, 2022 at 10:47 AM Jan Kara <jack@xxxxxxx> wrote:
> >
> > On Sat 12-03-22 11:22:29, Srinivas wrote:
> > > If a process calls fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_MOUNT,
> > > FAN_OPEN_PERM, 0, "/mountpoint") no other directory exclusions can be
> > > applied.
> > >
> > > However a path (file) exclusion can still be applied using
> > >
> > > fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_IGNORED_MASK |
> > > FAN_MARK_IGNORED_SURV_MODIFY, FAN_OPEN_PERM | FAN_CLOSE_WRITE, AT_FDCWD,
> > > "/tmp/fio/abc"); ===> path exclusion that works.
> > >
> > > I think the directory exclusion not working is a bug as otherwise AV
> > > solutions cant exclude directories when using FAN_MARK_MOUNT.
> > >
> > > I believe the change should be simple since we are already supporting
> > > path exclusions. So we should be able to add the same for the directory
> > > inode.
> > >
> > > 215676 – fanotify Ignoring/Excluding a Directory not working with
> > > FAN_MARK_MOUNT (kernel.org)
> >
> > Thanks for report! So I believe this should be fixed by commit 4f0b903ded
> > ("fsnotify: fix merge with parent's ignored mask") which is currently
> > sitting in my tree and will go to Linus during the merge (opening in a
> > week).
>
> Actually, in a closer look, that fix alone is not enough.
>
> With the current upstream kernel this should work to exclude events
> in a directory:
>
> fanotify_mark(fd, FAN_MARK_ADD, FAN_EVENT_ON_CHILD |
> FAN_OPEN_PERM | FAN_CLOSE_WRITE,
> AT_FDCWD, "/tmp/fio/");
> fanotify_mark(fd, FAN_MARK_ADD | FAN_MARK_IGNORED_MASK |
> FAN_MARK_IGNORED_SURV_MODIFY,
> FAN_OPEN_PERM | FAN_CLOSE_WRITE,
> AT_FDCWD, "/tmp/fio/");
>
> The first call tells fanotify that the inode mark on "/tmp/foo" is
> interested in events on children (and not only on self).
> The second call sets the ignored mark for open/close events.
>
> The fix only removed the need to include the events in the
> first call.
>
> Should we also interpret FAN_EVENT_ON_CHILD correctly
> in a call to fanotify_mark() to set an ignored mask?
> Possibly. But that has not been done yet.
> I can look into that if there is interest.
Oh, right. I forgot about the need for FAN_EVENT_ON_CHILD in the
mark->mask. It seems we can set FAN_EVENT_ON_CHILD in the ignored_mask as
well but it just gets ignored currently. So we would need to propagate it
even from ignore_mask to inode->i_fsnotify_mask. But send_to_group() would
also need to be more careful now with ignore masks and apply them from
parent only if the particular mark has FAN_EVENT_ON_CHILD in the ignore
mask. Interestingly fanotify_group_event_mask() does explicitely apply
ignore_mask from the parent regardless of FAN_EVENT_ON_CHILD flags. So
there is some inconsistency there and it would need some tweaking...
Overall I guess the functionality makes sense to me (in fact it is somewhat
surprising it is not working like that from the beginning), API-wise it is
not outright horrible, and technically it seems doable. What do you think?
> In retrospect, FAN_EVENT_ON_CHILD and FAN_ONDIR would have
> been more clear as FAN_MARK_ flags, but that's too late.
Yeah, it is like this since fanotify has been created so no real chance to
change that.
Honza
--
Jan Kara <jack@xxxxxxxx>
SUSE Labs, CR
