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SubjectRe: [PATCH v9 3/4] seccomp: add a return code to trap to userspace
On Sun, Dec 02, 2018 at 11:26:50PM -0600, Serge E. Hallyn wrote:
> On Sun, Dec 02, 2018 at 08:28:26PM -0700, Tycho Andersen wrote:
> > +struct seccomp_knotif {
> > + /* The struct pid of the task whose filter triggered the notification */
> > + struct task_struct *task;
> > +
> > + /* The "cookie" for this request; this is unique for this filter. */
> > + u64 id;
> > +
> > + /*
> > + * The seccomp data. This pointer is valid the entire time this
> > + * notification is active, since it comes from __seccomp_filter which
>
> define 'active' - is a notification in state REPLIED still active?

Yes,

> Actually while looking at that, I came to wondering - when are knotifs
> freed? Seems like only during seccomp_notify_release(), i.e. when the
> tracing task stops polling for events? Is that going to be a problem?
> Or am I misreading this?

they're stack allocated in do_user_notification(). So "active" in this
sense really means "somewhere in do_user_notification()".

> > + if (ret == 0 && copy_to_user(buf, &unotif, sizeof(unotif))) {
> > + ret = -EFAULT;
> > +
> > + /*
> > + * Userspace screwed up. To make sure that we keep this
> > + * notification alive, let's reset it back to INIT. It
>
> Is keeping the notification alive the right thing to do?
>
> If userspace has messed up in something this touchy, it seems unlikely
> that it'll to better if we give it a do-over... I'm not sure whether
> killing the whole thing (victim and tracer) is the right thing or not.

I suppose we could do that too. I just didn't want to get into a
situation where the notification is lost and the task is stuck because
userspace screwed up here.

Tycho

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