Patch related with Fork Bobmbing Attack

From: Anand Jahagirdar
Date: Tue Jun 12 2007 - 12:50:03 EST

Hello All
As per the discussion in the thread with subject as
Patch Related with Fork Bombing Attack on LKML, I request you for the
inclusion of my attached patch named "fork.patch".

Summery of the Patch:

This patch warns the administrator about the fork bombing attack
(whenever any user is crossing its process limit). I have used
printk_ratelimit function in this patch. This function helps to
prevent flooding of syslog and prints message as per the values set by
root user in following files:-

1) /proc/sys/kernel/printk_ratelimit:- This file contains value for,
how many times message should be printed in syslog.

2) /proc/sys/kernel/printk_ratelimit_burst: - This file contains value
for, after how much time message should be repeated.

This patch is really helpful for administrator/root user from security
point of view. They can take action against attacker by looking at
syslog messages related with fork bombing attack.

Added comments will definitely help developers.

Signed-Off-by: Anand Jahagirdar <anandjigar@xxxxxxxxx> 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;
+ }