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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
:> with "unsubscribe freebsd-current" in the body of the message
:> 
:
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