Date: Sun, 7 Mar 1999 01:41:25 +0100
From: Michal Zalewski <lcamtuf@IDS.PL>

Linux 2.x IPC vunerability

Linux IPC implementation seems to be broken. I noticed Alan about one/two
months ago, so I believe it has been fixed in recent 2.2.x Linuxes. In
fact, any luser may consume whole memory available on system using this
simple program:

-- shmkill.c --
extern int errno;int i,d=1;char*x;main(){while(1){x=shmat(shmget(0,10000000/
d,511),0,0);if(errno){d*=10;continue;}for(i=0;i<10000000/d;i++)if(*(x+i));}}
-- eof --

Memory won't be freed even if luser's process will be killed, you have to
use ipcrm, but there could be not enough memory to run anything :-(

Under early 2.2.x, you have to run this program several times, to ensure
pages are detached (in this state, they are onwerless ;-).

The simpliest solution is to restrict for lusers IPC at all. Only a few
programs uses IPC - probably only dosemu and ShoutCast ;>

-

_______________________________________________________________________
Michal Zalewski [lcamtuf@ids.pl] [link / marchew] [dione.ids.pl SYSADM]
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Date: Mon, 8 Mar 1999 02:37:18 +0100
From: Michal Zalewski <lcamtuf@IDS.PL>

> 5. Linux 2.x IPC vunerability

As Solar Designer said, there are 'beancounter' feature (or per-user
limits, instead of per-process). Probably it will be implemented in
2.2.x kernels soon. As today, it's hard to control detached IPC pages.