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 <[EMAIL PROTECTED]> 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);
