linux-kernel - Re: Patch related with Fork Bombing Atack

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Message-Id: <200706041128.35321.dhazelton@enter.net>
Date:	Mon, 4 Jun 2007 11:28:35 -0400
From:	Daniel Hazelton <dhazelton@...er.net>
To:	Jiri Kosina <jikos@...os.cz>
Cc:	Anand Jahagirdar <anandjigar@...il.com>, Nix <nix@...eri.org.uk>,
	Jens Axboe <jens.axboe@...cle.com>, security@...nel.org,
	linux-kernel@...r.kernel.org, Kedar Sovani <kedar@...amzgroup.com>
Subject: Re: Patch related with Fork Bombing Atack

On Monday 04 June 2007 10:58:41 Jiri Kosina wrote:
> On Mon, 4 Jun 2007, Anand Jahagirdar wrote:
> >            I am forwarding one improved patch related with Fork Bombing
> > Attack. This patch prints a message (only once) which alerts
> > administrator/root user about fork bombing attack. I created this patch
> > to implement my idea of informing administrator about fork bombing
> > attack on his machine only once.
> >    This patch overcomes all drawbacks of my previous patch related with
> > fork bombing attack and helps administrator. added comments will
> > definitely help developers.
> >
> > +	/*
> > +	 * following code prints a message which alerts administrator/root 		 *
> > user about fork bombing Attack +	 */
> > +	if ((atomic_read(&p->user->processes) >=
> > (p->signal->rlim	[RLIMIT_NPROC].rlim_cur - 1)) &&
> > (atomic_read(&p->user->processes) <
> > p->signal->rlim[RLIMIT_NPROC].rlim_cur)) {
>
> Did this get malformed somehow? Looks like some successive lines got
> pasted together, or something.

Seeing the lack of the '+' I think it's a mangling from not paying attention 
to the 80 column marker in the editor.

> > +        	if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
> > p->user != &root_user) { +        		printk(KERN_CRIT"User with uid %d is
> > crossing its Process limit\n",p->user->uid); +        	}
> > +	}
>
> Why not printk_ratelimit() here? Otherwise we have looped back to the
> possibility of user flooding the system logs, which has been already
> discussed in this thread, right?
>
> Also the { and } braces seem redundant.
They are. 

Here's two hints:
1) double check for hidden "word wrap" problems. A sane programmers editor 
will alert you to this, and careful checking of the patches before posting 
will also reveal them. (emacs shows a \ in the 80th column, jed puts a $ 
there, etc...)
2) when there is a potential for syslog spam - like your patch has - use 
printk_ratelimit() instead of printk(). This will throttle the output so that 
flooding the syslog is no longer possible.

DRH
ps: you patch is very difficult to apply - try using git
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