Re: Patch related with Fork Bombing Atack

[Anand Jahagirdar]

Hello All
           I am forwarding one more improved patch related with fork
bombing attack. I have used printk_ratelimit function in my patch
and it works rellly well. it prints message as per printk_ratelimit
values stored in /proc/sys/kernel/printk_ratelimit
and /proc/sys/kernel/printk_ratelimit_burst.
root can set printk_ratelimit values(such as how many times message
should be repeated ,after how much time message should repeat) by
making changes in the above 2 mentioned files.
      this patch will never flood syslog anymore and will definitely
help administrator by informing him about fork bombing attack.
       added comments will help developers.

Regards,
Anand

On 6/4/07, Daniel Hazelton <dhazelton@xxxxxxxxx> wrote:
> 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
Index: root/Desktop/a1/linux-2.6.17.tar.bz2_FILES/linux-2.6.17/kernel/fork.c
===================================================================
--- root.orig/Desktop/a1/linux-2.6.17.tar.bz2_FILES/linux-2.6.17/kernel/fork.c	2007-06-05 19:16:28.000000000 +0530
+++ root/Desktop/a1/linux-2.6.17.tar.bz2_FILES/linux-2.6.17/kernel/fork.c	2007-06-05 19:18:07.000000000 +0530
@@ -958,11 +958,18 @@
 	retval = -EAGAIN;
 	
 
+	/*
+         * following code does not allow Non Root User to cross its process
+         * limit. it alerts administrator about fork bombing attack and prevents
+         * it.
+         */
 	if (atomic_read(&p->user->processes) >= p->signal->rlim[RLIMIT_NPROC].rlim_cur) 
 		if (!capable(CAP_SYS_ADMIN) && !capable(CAP_SYS_RESOURCE) &&
-				p->user != &root_user) 
-	
+				p->user != &root_user) {
+			if (printk_ratelimit())
+                                printk(KERN_CRIT"User with uid %d is crossing its process limit\n",p->user->uid);
 			goto bad_fork_free;
+		}
 				
 
 	atomic_inc(&p->user->__count);