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Re: Shared memory DoS's
From: howie () MS COM (Howard Kaye)
Date: Mon, 19 Jul 1999 18:31:23 -0400


Tops-20 had mapped memory segments before VMS was born.  It was called
PMAP back then (for Page Map).  I don't know if it had the same
vulnerability.

Howie Kaye

"Dick St.Peters" wrote:

Mike Perry writes:

So as it turns out that it is in fact possible to create a DoS condition by
requesting a truckload of shared mem, then triggering pagefaults in the entire
shared region.

Mapped memory segments have been susceptible to this since at least
the early days of VMS, which AFAIK was the first OS to implement
mapped memory (VMS used the term "mapped section").  I ran into this
by accident no later than 1982 while doing image processing on a VMS
system.  My processes run at the lowest possible priority (equivalent
to the highest possible niceness), would effectively shut down the
system until they completed.

VMS didn't have a lot of tools for analyzing what was happening, but a
few experiments quickly showed the culprit was page faulting.  Image
processing tends to step through memory sparsely.

Sorry - I no longer have an exploit :)

--
Dick St.Peters, stpeters () NetHeaven com
Gatekeeper, NetHeaven, Saratoga Springs, NY
Saratoga/Albany/Amsterdam/BoltonLanding/Cobleskill/Greenwich/
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