lkml.org 
[lkml]   [2003]   [Aug]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
Date
From
Subject[PATCH] Re: Kernel threads resource leakage
I do not subscribed to the list, thus please in your reply CC me 
(vladimir.kondratiev@intel.com)

Some time ago, I reported problem WRT resource leakage in kernel_thread.
(2.4.20) To demonstrate it, I submitted program that uses /proc file to
display some info and to start/stop kernel thread. I don't want to
re-post this code again.

Finally, I found that resource leak present only if you create
kernel_thread as non-root. With my previous example, do "insmod" as
root, while perform actual thread creation/destruction (echo "+"
>/proc/kthread etc.) as non-root.

To demonstrate it better, I added to /proc 'read' procedure content of
"struct user_struct" (current->user).
It makes clear, that in this case current->user->processes do not
decremented when thread destroyed, and eventually reaches user limit
(usually 4k processes). At this point, this user can do nothing.

Problem leaves in "reparent_to_init" code in kernel/sched.c; there
current->user is simply changed to point to INIT_USER without proper
resource management.

Does it worth inclusion in 2.4.22?

Following patch fixes this bug. I verified that with this patch applied,
kernel_thread behaves properly.

--- kernel/sched.c.orig 2003-08-17 20:12:14.000000000 +0300
+++ kernel/sched.c 2003-08-17 21:21:08.000000000 +0300
@@ -1274,8 +1274,16 @@
this_task->cap_permitted = CAP_FULL_SET;
this_task->keep_capabilities = 0;
memcpy(this_task->rlim, init_task.rlim, sizeof(*(this_task->rlim)));
- this_task->user = INIT_USER;
-
+ if (this_task->uid) { /* not root? switch user */
+ struct user_struct *old_user = this_task->user,
+ *new_user = INIT_USER;
+ this_task->uid = 0;
+ this_task->user = new_user;
+ atomic_inc(&new_user->__count);
+ atomic_inc(&new_user->processes);
+ atomic_dec(&old_user->processes);
+ free_uid(old_user);
+ }
spin_unlock(&runqueue_lock);
write_unlock_irq(&tasklist_lock);
}

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 13:47    [W:0.031 / U:0.412 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site