Date: Sat, 17 Jan 2004 01:57:36 -0800 (PST) From: Don Lewis <truckman@FreeBSD.org> To: rwatson@FreeBSD.org Cc: arch@FreeBSD.org Subject: Re: Signal delivery to kernel threads/processes? Message-ID: <200401170957.i0H9va7E047876@gw.catspoiler.org> In-Reply-To: <Pine.NEB.3.96L.1040116135741.94620D-100000@fledge.watson.org>
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On 16 Jan, Robert Watson wrote: > > Bill Paul raised an interesting question with me recently -- he observed > that a userspace process running with root privileges could deliver a > signal to a kthread, and that this might produce undesired behavior. I > was sure that, at some point, we had a check disallowing this, but I don't > see it in either RELENG_4 or HEAD. Do we rely on the ability to > send/receive signals to interrupt kthreads, that we know of? While the > signal delivery itself doesn't make sense, waking up a tsleep() with > PCATCH could well be useful behavior. Should a kthread have to declare if > it wants to receive interruptions? Given plans, at some point, to make > kthreads be real threads, and be part of a kernel process, that would > raise some challenges for code relying on the ability to be interrupted > with a signal in kernel space, as signals generated by kill() are > targetted at processes, not threads. > > Any thoughts? It's tempting simply to add the following to cr_cansignal() > to at least disallow sourcing the signals in userspace: > > if (p->p_flag & P_SYSTEM) > return (EPERM); > > But I don't have a broad enough view of what goes on in the kernel to > reason about what disasters this might cause if signalling is relied on. The only thing I worried about is what happens to kthreads on shutdown. It looks like this is handled by kthread_suspend() which tells the thread that it has received a SIGSTOP, but this isn't done with the normal signal delivery mechanism.
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