Date: Sat, 29 Sep 2001 08:43:46 -0500 From: Jonathan Lemon <jlemon@flugsvamp.com> To: Ian Dowse <iedowse@maths.tcd.ie> Cc: Jonathan Lemon <jlemon@FreeBSD.org>, cvs-committers@FreeBSD.org, cvs-all@FreeBSD.org Subject: Re: cvs commit: src/sys/kern kern_event.c Message-ID: <20010929084346.W9056@prism.flugsvamp.com> In-Reply-To: <200109291106.aa82996@salmon.maths.tcd.ie> References: <200109290600.f8T60o869371@freefall.freebsd.org> <200109291106.aa82996@salmon.maths.tcd.ie>
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On Sat, Sep 29, 2001 at 11:06:36AM +0100, Ian Dowse wrote:
> In message <200109290600.f8T60o869371@freefall.freebsd.org>, Jonathan Lemon wri
> tes:
> >jlemon 2001/09/28 23:00:50 PDT
> > MFC: r.1.28; EVFILT_TIMER.
>
> Cool, but it appears that you haven't dealt with the problem of
> timeout() allocating only from the small `callfree' list:
>
> /* Fill in the next free callout structure. */
> new = SLIST_FIRST(&callfree);
> if (new == NULL)
> /* XXX Attempt to malloc first */
> panic("timeout table full");
>
> All the other kevent filters seem to be tied to some limited/limitable
> resource (processes, file descriptors, signals) so creating an
> arbitrary number of them is not possible. With EVFILT_TIMER, there
> is no such limit, so any user can trivially run the system out of
> callouts (ncallouts is typically ~2000). Using the callout_*
> interface instead helps a lot (I sent you patches for this some
> time ago), but any user can still run the system out of kernel
> memory and fill the callout wheel with millions of timers.
>
> I really dislike seeing the addition of new ways for any local user
> to crash the system, especially in RELENG_4. Even an arbitrary
> limit set by a kern.maxkqtimersperproc sysctl, together with using
> the callout_* interface, would make this a non-issue. Maybe
> EVFILT_TIMER should be disabled in RELENG_4 for now until this
> issue is resolved?
I did hold the EVFILT_TIMER implementation out of -RELEASE for
this reason, but have since gotten several MFC requests. I'll
work on a fix for this today.
--
Jonathan
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