Re: linux 2.0 PTE bug

[pedward () WEBCOM COM (pedward () WEBCOM COM)]

> Hi all,
>
> there is the program :

[SNIP of wonderful reason to set rlimits]

> The idea is to take a lot of memory. So, we map all our virtual pages,
> to force the system to allow all the pte (am talking about PC box).
> So, the process will have allocated 768 pages that will never be
> swapped (that's the crucial point).
>
> So, that's simple, you run this program as much time as you need to take
> all the memory, and the PC won't be usable anymore (for my 64Mb box,
> i need to run it about 20 times).
>
> And then, you can have a wonderful light-show with your HD-led :) (PC will
> spend its time in swapping).
>
> How to solve it ?
> Well, we could swap the pgd / pmd / pte, but i really don't know
> if it is possible or what.

The default TASK_SIZE is set in /usr/src/linux/include/asm/processor.h it is the
virtual memory maximum map size.  This in itself is not dynamically configurable
(it really has nothing to do with resources).  The main factor is RLIMIT_AS,
defined in /usr/src/linux/include/asm/resource.h, it controls how much virtual
memory that a process can map, mmap utilizes virtual memory.  You can
safely throttle people by running a program which calls setrlimit(2) with
RLIMIT_AS as the resource.  By far, 3GB is too much.

This is only a DoS if you LET it be a DoS.

> If this bug is already well know, am sorry to disturb with it.
>
> It applies only on the 2.0 kernel, for the 2.1 (soon 2.2) i don't know
> if it works, will have to read the source.
>
> Sed.
> p6mip300 () infop6 cicrp jussieu fr.

--Perry

--
Perry Harrington        System Software Engineer    zelur xuniL  ()
http://www.webcom.com  perry.harrington () webcom com  Think Blue.  /\