linux-kernel - Re: [BUG][PATCH][2.6.36-rc3] fanotify: Do not ignore result of permission decisions

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Message-ID: <201010181205.34294.tvrtko.ursulin@sophos.com>
Date:	Mon, 18 Oct 2010 12:05:34 +0100
From:	Tvrtko Ursulin <tvrtko.ursulin@...hos.com>
To:	Eric Paris <eparis@...hat.com>
CC:	Andreas Gruenbacher <agruen@...e.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [BUG][PATCH][2.6.36-rc3] fanotify: Do not ignore result of permission decisions

On Friday 08 Oct 2010 17:51:00 Eric Paris wrote:
> On Fri, 2010-10-08 at 17:11 +0100, Tvrtko Ursulin wrote:
> > On Friday 08 Oct 2010 14:00:40 Andreas Gruenbacher wrote:
> > > Tvrtko,
> > >
> > > On Wednesday 08 September 2010 10:24:04 Tvrtko Ursulin wrote:
> > > >                 }
> > > >
> > > > +#ifdef CONFIG_FANOTIFY_ACCESS_PERMISSIONS
> > > > +               /* If a listener denied on a permission event we will
> > > > remember the reason +                  and run the rest with a
> > > > non-permission mask only. This allows other +
> > > > listeners to receive non-permission notifications but we do not care
> > > > +
> > > >
> > > >      about further permission checks and want to deny this event. */
> > > >      +
> > > >
> > > >             if (unlikely((res == -EPERM) && (mask &
> > > >
> > > > FS_ALL_PERM_EVENTS))) {
> > >
> > > We should probably stop processing here whenever res != 0, for any
> > > mask. (The fanotify and inotify handle_event callbacks can return
> > > -ENOMEM right now, but this doesn't seem very useful and should
> > > probably be fixed: fsnotify has no way of doing anything about
> > > -ENOMEM.
> >
> > I wasn't 100% sure of how fanotify works, or in other words can there be
> > more events in this mask after perm events are removed. If it can then
> > we should send them to other listeners. Eric?
> >
> > Also if ENOMEM, why not try sending to other listeners?
>
> No, you'll never have a PERM_EVENT and something else at the same time.
> If it's a PERM_EVENT denial we wouldn't really want to even notify
> others, since the operation won't have actually taken place (perm event
> denials should be passed all the way back up the stack)

Ok, I wasn't sure if event merging could somehow join more events on one
object into one event here.

> As to ENOMEM that's a little harder I guess.  We don't have to stop just
> because inotify got ENOMEM, but we should stop if PERM_EVENTS got an
> ENOMEM.
>
> I'd really rather not put CONFIG_FANOTIFY_ACCESS_PERMISSIONS in this
> file.  fsnotify.c should be notifier agnostic.
>
> How about just:
>
> if (unlikely(ret && (mask & ALL_PERM)))
>       return ret

Looks like it would work and on more thinking I also agree with the logic to
stop the perm chain on ENOMEM.

Tvrtko

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