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SubjectRe: SIGSYS annoyance
Andy Lutomirski writes:
> On Mon, Jun 6, 2016 at 9:03 AM, Kees Cook <keescook@chromium.org> wrote:
> > On Fri, Jun 3, 2016 at 10:16 PM, Andy Lutomirski <luto@amacapital.net> wrote:
> >> https://bugzilla.mozilla.org/show_bug.cgi?id=1176099
> >>
> >> Should SIGSYS be delivered to the handler even if blocked? What, if
> >> anything, does POSIX say? All I can find is in pthread_sigmask(3p):
> >>
> >> If any of the SIGFPE, SIGILL, SIGSEGV, or SIGBUS signals are generated
> >> while they are blocked, the result is undefined, unless the signal was
> >> generated by the action of another process, or by one of the functions
> >> kill(), pthread_kill(), raise(), or sigqueue().
> >>
> >> It would be easy enough to change our behavior so that we deliver the
> >> signal even if it's blocked or to at least add a flag so that users
> >> can request that behavior.
> >
> > I had trouble following that bug. It sounded like glib just needed a
> > way to define its signal mask, and that's what they ended up
> > implementing?
> >
> > I think the current behavior is correct. SIGSYS is being generated by
> > the running process (i.e. the seccomp filter) and if it has a handler
> > but the signal is blocked, we should treat it as uncaught and kill. On
> > the other hand, it could be seen like "raise", in which case the
> > blocking should be ignored? Is there an active problem somewhere here?
> > It seems like the referenced bug has been fixed already.
>
> Agreed.
>
> It could make sense to have a new sigaction flag SA_FORCE: when set,
> if a non-default handler is installed, the signal is blocked, and the
> signal is triggered synchronously (forced), then the handler will be
> called. But that isn't specific to seccomp.

Blocking a signal is a very deliberate act. If some piece of code wants
to force-deliver it, it can unblock it first. IOW, I don't see the need
for this SA_FORCE thing.

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