From mboxrd@z Thu Jan 1 00:00:00 1970 From: bqt@softjar.se (Johnny Billquist) Date: Thu, 05 Oct 2006 16:44:36 +0200 Subject: [pups] User Mode DoS Attacks (was Re: Issues of AUUGN) In-Reply-To: <4672.134.198.172.102.1160058799.squirrel@www.cs.scranton.edu> References: <4672.134.198.172.102.1160058799.squirrel@www.cs.scranton.edu> Message-ID: <45251A54.9040601@softjar.se> 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. Johnny 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 >