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SubjectRe: [PATCH 1/1] threads_max: Simple lockout prevention patch
Date
This is a resend, which was ignored before w/o comment.
A comment this time would be helpful. Thanks!

-

Simple attempt to provide a backdoor in a process lockout situation.

echo $$ > /proc/sys/kernel/su-pid allows pid to exceed the threads_max limit.
Signed-off-by: Al Boldi <a1426z@gawab.com>

---
(patch against 2.6.14)
--- kernel/fork.c.orig 2005-11-14 20:55:33.000000000 +0300
+++ kernel/fork.c 2005-11-14 20:58:25.000000000 +0300
@@ -57,6 +57,7 @@
int nr_threads; /* The idle threads do not count.. */

int max_threads; /* tunable limit on nr_threads */
+int su_pid; /* BackDoor pid to exceed limit on nr_threads */

DEFINE_PER_CPU(unsigned long, process_counts) = 0;

@@ -926,6 +927,7 @@
* to stop root fork bombs.
*/
if (nr_threads >= max_threads)
+ if (p->pid != su_pid)
goto bad_fork_cleanup_count;

if (!try_module_get(p->thread_info->exec_domain->module))

--- kernel/sysctl.c.orig 2005-11-14 20:58:45.000000000 +0300
+++ kernel/sysctl.c 2005-11-14 21:01:20.000000000 +0300
@@ -57,6 +57,7 @@
extern int sysctl_overcommit_memory;
extern int sysctl_overcommit_ratio;
extern int max_threads;
+extern int su_pid;
extern int sysrq_enabled;
extern int core_uses_pid;
extern int suid_dumpable;
@@ -509,6 +510,14 @@
.proc_handler = &proc_dointvec,
},
{
+ .ctl_name = KERN_SU_PID,
+ .procname = "su-pid",
+ .data = &su_pid,
+ .maxlen = sizeof(int),
+ .mode = 0644,
+ .proc_handler = &proc_dointvec,
+ },
+ {
.ctl_name = KERN_RANDOM,
.procname = "random",
.mode = 0555,

--- include/linux/sysctl.h.orig 2005-11-14 20:54:55.000000000 +0300
+++ include/linux/sysctl.h 2005-11-14 20:55:15.000000000 +0300
@@ -146,6 +146,7 @@
KERN_RANDOMIZE=68, /* int: randomize virtual address space */
KERN_SETUID_DUMPABLE=69, /* int: behaviour of dumps for setuid core
*/
KERN_SPIN_RETRY=70, /* int: number of spinlock retries */
+ KERN_SU_PID=71, /* int: BackDoor pid to exceed Maximum
+ /* nr of threads in the system */
};


-
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