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SubjectRe: Very large font size crashing X Font Server and Grounding Server to a Halt (was: remote DoS in Mozilla 1.0)
On Thu, Jun 13, 2002 at 09:44:33AM +0800, Federico Sevilla III wrote:
> From: Federico Sevilla III <jijo@free.net.ph>
> To: BugTraq Mailing List <bugtraq@securityfocus.com>,
> Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
>
> (Note: bug originally posted on BugTraq, this response is cross-posted to
> the LKML because of the way the server hosting the X font server ground to
> a halt.)

It really is nothing new. (Besides of XFree86's Type1 engine calling
abort() when it does not like to do something ..)
...
> Suggestions on how to work around this on multiple levels would definitely
> be appreciated. I'll be starting by removing the X font server from our
> file and authentication server onto some high-powered workstation, but I'm
> sure this won't be enough, and knowing that a user process like xfs-daemon
> can drag the Linux kernel down to knees is not very comforting. :(

ANY very big program with active working set larger than memory size
has problems at Linux / Linux has problems handling it. Indeed the
problem is _not_ new, nor trivial to solve efficiently. The ultimate
situation is called "trashing", where a program to proceed a page of
code needs to be moved into memory, and to make room for that, some
other program page must be moved out.. What makes the issue more
difficult is that the memory is used for lots and lots of different
kinds of buffers and caches as well, and playing a balancing act on
them all is quite difficult.

This is recurring topic at linux-kernel list, and has its own
list called linux-mm (not at vger, though.)

Others may have different views on the issue, but I think that:
2.0: fairly tolerable OOM/trashing behaviour
2.2: got worse
2.4.early: rather terrible
2.4.late: improved somewhat, roughly in par with 2.2

> --> Jijo
> - --
> Federico Sevilla III : <http://jijo.free.net.ph/>
...
> Please read the FAQ at http://www.tux.org/lkml/

/Matti Aarnio
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