Date: Thu, 4 Mar 1999 16:22:19 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Chris Costello <chris@holly.dyndns.org> Cc: Mike Tancsa <mike@sentex.net>, current@FreeBSD.ORG Subject: Re: Simple DOS against 3.x locks box solid Message-ID: <199903050022.QAA32802@apollo.backplane.com> References: <4.1.19990304073656.084804e0@granite.sentex.ca> <19990304155401.A5710@holly.dyndns.org>
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Well, 10 processes doing a find are not supposed to lockup a machine.
However, there is another potential problem with the script below ... if
the script is run as root, the find will cross mount points including
the /proc mount point. Now running xargs and random process's memory
spaces *could* certainly lockup a machine. /proc does has reentrancy
issue with multiple processes accessing it at the same time.
Try changing the 'find' to 'find -x'. If this still locks up the machine
we will have to then determine whether it occurs under 4.x as well, or
if it only occurs under 3.x.
-Matt
Matthew Dillon
<dillon@backplane.com>
:On Thu, Mar 4, 1999, Mike Tancsa put this into my mailbox:
:>
:> Is there any way to stop what is below ?
:
: Yep. Don't do it!
:
: Seriously, though, that puts a major load on the system.
:
: You have 10 process all telling the drivers to keep seeking
:about through the disks.
:
: Add /etc/login.conf restrictions if you don't want your users
:to do that.
:
:>
:>
:>
:> As posted by yk@dgtu.donetsk.ua
:> >
:> >This script freeze my 3.1-RELEASE box.
:> >I can't make any connection with my box, also from console.
:> >
:> >-------- cut here ---
:> >#! /bin/sh
:> >
:> >for j in 1 2 3 4 5 6 7 8 9 10
:> >do
:> >echo -n $j
:> >nohup sh -c 'while :; do find / -type file |xargs fgrep fticom; done'
:> >/dev/null 2>&1 &
:> >echo
:> >done
:> >--------- cut here ----
:> >
:> >--
:> >Yury V. Yaroshevsky | Donetsk State Technical University
:> >YY18-RIPE | (380 622) 356455 yk@dgtu.donetsk.ua
:> >
:> **********************************************************************
:> Mike Tancsa, Network Admin * mike@sentex.net
:> Sentex Communications Corp, * http://www.sentex.net/mike
:> Cambridge, Ontario * 01.519.651.3400
:> Canada *
:>
:>
:> To Unsubscribe: send mail to majordomo@FreeBSD.org
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:>
:
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