Subject: Re: [PATCH 3/5] v2 seccomp_filters: Enable ftrace-based system call filtering

From: Ingo Molnar <[email-masked]>
Date: Fri, 13 May 2011 15:18:00 +0200

* Peter Zijlstra <[email-masked]> wrote:

> On Fri, 2011-05-13 at 14:54 +0200, Ingo Molnar wrote:
> > I think the sanest semantics is to run all active callbacks as well.
> > 
> > For example if this is used for three stacked security policies - as if 3 LSM 
> > modules were stacked at once. We'd call all three, and we'd determine that at 
> > least one failed - and we'd return a failure. 
> 
> But that only works for boolean functions where you can return the
> multi-bit-or of the result. What if you need to return the specific
> error code.

Do you mean that one filter returns -EINVAL while the other -EACCES?

Seems like a non-problem to me, we'd return the first nonzero value.

> Also, there's bound to be other cases where people will want to employ
> this, look at all the various notifier chain muck we've got, it already
> deals with much of this -- simply because users need it.

Do you mean it would be easy to abuse it? What kind of abuse are you most 
worried about?

> Then there's the whole indirection argument, if you don't need
> indirection, its often better to not use it, I myself much prefer code
> to look like:
> 
>    foo1(bar);
>    foo2(bar);
>    foo3(bar);
> 
> Than:
> 
>    foo_notifier(bar);
> 
> Simply because its much clearer who all are involved without me having
> to grep around to see who registers for foo_notifier and wth they do
> with it. It also makes it much harder to sneak in another user, whereas
> its nearly impossible to find new notifier users.
> 
> Its also much faster, no extra memory accesses, no indirect function
> calls, no other muck.

But i suspect this question has been settled, given the fact that even pure 
observer events need and already process a chain of events? Am i missing 
something about your argument?

Thanks,

	Ingo