[pups] User Mode DoS Attacks (was Re: Issues of AUUGN)

Johnny Billquist bqt at softjar.se
Fri Oct 6 00:44:36 AEST 2006

Back in those days, there didn't exist any process limits, except for 
system wide ones... :-)

Another fun exercise that actually hurts systems today, but didn't hurt 
much back then, are programs that allocate a large chunk of memory and 
hit on a single address on each page repetedly.

Talk about thrashing the memory system... :-) But on the PDP-11, you 
don't use demand paging, nor can you allocate that much memory.


Bill Gunshannon wrote:
>>>But you'd need kernel mode for that; this is a DoS attack (one of the
>>>first?) launched by a user.
>>The userland DoS I remember:
>>main() {
>>	while(1)
>>		fork();
> Typical "Rabbit Program".
>>And in fact I tried it once on the 11/45 I had access to. Not pretty.
>>It can be made less disastrous by judicious addition of a wait(); call.
>>--Milo, wondering how contemporary UNIX will deal with such
>>pathological behavior....
> Not necessarily pathological.  I have students do it all the time
> in the early parts of the Operating Systems Course.  The only one
> it denies service to on contemorary UNIX is the individual who does
> it.  Process limits are by user, not by system.
> bill

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