Messages in this thread Patch in this message | ![/](/images/icornerl.gif) | | Date | Sun, 17 Aug 2003 22:09:27 +0300 | From | Vladimir Kondratiev <> | Subject | [PATCH] Re: Kernel threads resource leakage |
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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); }
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