linux-kernel - Re: evading ulimits

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Date:	Sat, 23 Dec 2006 19:42:10 -0500
From:	John Richard Moser <nigelenki@...cast.net>
To:	Jan Engelhardt <jengelh@...ux01.gwdg.de>
CC:	linux-kernel@...r.kernel.org
Subject: Re: evading ulimits



Jan Engelhardt wrote:
>> I've set up some stuff on my box where /etc/security/limits.conf
>> contains the following:
>>
>> @users          soft    nproc           3072
>> @users          hard    nproc           4096
>>
>> I'm in group users, and a simple fork bomb is easily quashed by this:
>>
>> bluefox@...box:~$ :(){ :|:; };:
>> bash: fork: Resource temporarily unavailable
>> Terminated
>>
>> Oddly enough, trying this again and again yields the same results; but,
>> I can kill the box (eventually; about 1 minute in I managed to `/exec
>> killall -9 bash` from x-chat, since I couldn't get a new shell open)
>> with the below:
> 
> Note that trying to kill all shells is a race between killing them all first
> and them spawning new ones everytime. To stop fork bombs, use killall -STOP
> first, then kill them.
> 

Yes I know; the point, though, is that they should die automatically
when the process count hits 4096.  They do with the first fork bomb;
they keep growing with the second, well past what they should.
> 
> 	-`J'

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