Messages in this thread | | | Date | Thu, 20 Nov 2008 15:52:34 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH 1/2] protect /sbin/init from unwanted signals more |
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On 11/19, Eric W. Biederman wrote: > > Roland McGrath <roland@redhat.com> writes: > > > With that, I wonder if the SIGNAL_UNKILLABLE checks in get_signal_to_deliver > > and complete_signal are needed at all. Hmm, I guess we do because this > > doesn't affect blocked signals, so they might be unblocked and delivered. > > (Note that since it doesn't affect blocked signals, this doesn't break init > > using sigwait if it wanted to.) > > Ah. That answers the question I had bouncing in the back of my head.
Even worse. The signal can be dequeued even before unblocked by the target. complete_signal() can "redirect" this signal to another thread wich doesn't block it.
> My original analysis of the situation was that we should not send blocked signals. > Treating handler != SIG_DFL as a permission check. Not as an optimization. > > Mostly because it is more consistent and uniform. > > inits today don't do anything with blocked signals.
(I guess you mean "with blocked SIG_DFL signals", otherwise this is too strong ;)
If init does exec and do not want to miss (say) SIGCHLD, the only option is to block it before exec. And right after exec the handler is SIG_DFL.
> They explicitly ignore all signals, > they don't want to deal with an enable those they do.
I do remember I had the (unrelated) bugreport which in particular showed that user-space sends SIGUSR1 to init. Usually init has a handler and does something in responce, but sometimes the handler is SIG_DFL. I don't remember the distribution, ubuntu iirc.
Yes, this perhaps means init is not perfect, but still.
> Which reminds me. I need to retest, but I had a case where I had a trivial init > that set all signal handlers to SIG_IGN so it could ignore SIGCHLD. And not > all of it's children were getting reaped automagically. Do we have a bug in > the reparenting/reaping logic?
Ah... I thought this was already fixed... shouldn't reparent_thread() check task_detached() after do_notify() ? like ptrace_exit() does.
Oleg.
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