5 Oct
2006
5 Oct
'06
7:46 p.m.
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();
}
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....
--
Milo Velimirović
University of Wisconsin - La Crosse
La Crosse, Wisconsin 54601 USA
43 48 48 N 91 13 53 W
--
There's a reason Dennis Ritchie and Ken Thompson have been awarded
the U.S. National Medal of Technology (1998) and are fellows of the
Computer History Museum Online. Dave Cutler hasn't and isn't.
"You are not expected to understand this."
5 Oct
5 Oct
8:33 p.m.
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();
}
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
--
Bill Gunshannon | de-moc-ra-cy (di mok' ra see) n. Three wolves
bill(a)cs.scranton.edu | and a sheep voting on what's for dinner.
University of Scranton |
Scranton, Pennsylvania | #include <std.disclaimer.h>
8:44 p.m.
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:
Typical "Rabbit Program".
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();
} 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
8:51 p.m.
(oops, sent it off-list - sorry, Milo!)
On Thu, 2006-10-05 at 08:46 -0500, Milo Velimirovic wrote:
Speaking for Linux, quite badly, though there are some patches that
allow you to limit forks per user. There's even a bash version,
":(){ :|:& };:", which will infinitely fork off bash processes. (It
defines a function calling itself in the background, and then
immediately launches it)
The max number of processes is not so much a problem as the fact that
they are all draining the system resources. Besides, one is likely to
run out of memory before one hits the max process number in Linux
anyway.
- Tore Sinding Bekkedal
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();
}
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....
6661
days inactive
6661
days old
3 comments
4 participants
participants (4)
-
Bill Gunshannon -
Johnny Billquist -
Milo Velimirovic -
Tore Sinding Bekkedal