panic caused by EVFILT_SIGNAL detaching in rfork()ed thread

[Igor Sysoev]

On Sat, 23 Oct 2004, Uwe Doering wrote:

> Igor Sysoev wrote:
> > Here is more correct patch to fix the panic in 4.x reported in
> > http://freebsd.rambler.ru/bsdmail/freebsd-hackers_2004/msg02732.html
> >
> > -------------------------
> > --- src/sys/kern/kern_event.c   Sun Oct 10 12:17:55 2004
> > +++ src/sys/kern/kern_event.c   Sun Oct 10 12:19:29 2004
> > @@ -794,7 +794,8 @@
> >             while (kn != NULL) {
> >                 kn0 = SLIST_NEXT(kn, kn_link);
> >                 if (kq == kn->kn_kq) {
> > -                   kn->kn_fop->f_detach(kn);
> > +                   if (!(kn->kn_status & KN_DETACHED))
> > +                       kn->kn_fop->f_detach(kn);
> >         /* XXX non-fd release of kn->kn_ptr */
> >                     knote_free(kn);
> >                     *knp = kn0;
> > -------------------------
>
> Your patch appears to be an excerpt from the fix to RELENG_5.  May I
> suggest a different approach for RELENG_4?  My reasoning is that the
> implementation of kevents differs between RELENG_4 and RELENG_5.

I agree with your patch. It is similar to my early patch, however,
I think that is more correctly to check (kn->kn_status & KN_DETACHED)
instead of !SLIST_EMPTY(&p->p_klist).

> Also, it would probably be a good idea to fix RELENG_4 swiftly (and
> possibly release a security advisory) because this flaw is certainly a
> great DoS opportunity for maliciously minded shell users ...

Yes.


Igor Sysoev
http://sysoev.ru/en/