linux-kernel - [PATCH 03/14] audit: Fix invalid wakeup in wait_for

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Date:	Thu, 29 Aug 2013 21:57:38 +0800
From:	Libin <huawei.libin@...wei.com>
To:	<akpm@...ux-foundation.org>, <tj@...nel.org>,
	<viro@...iv.linux.org.uk>, <eparis@...hat.com>,
	<tglx@...utronix.de>, <rusty@...tcorp.com.au>,
	<ebiederm@...ssion.com>, <paulmck@...ux.vnet.ibm.com>,
	<john.stultz@...aro.org>, <mingo@...hat.com>,
	<peterz@...radead.org>, <gregkh@...uxfoundation.org>
CC:	<linux-kernel@...r.kernel.org>, <lizefan@...wei.com>,
	<jovi.zhangwei@...wei.com>, <guohanjun@...wei.com>,
	<zhangdianfang@...wei.com>, <wangyijing@...wei.com>,
	<huawei.libin@...wei.com>
Subject: [PATCH 03/14] audit: Fix invalid wakeup in wait_for_auditd

If this thread is preempted at(or before) location a, and the other thread
set the condition followed with wake_up_process. After that
when this thread is re-scheduled, calling set_current_state to set itself as
state TASK_UNINTERRUPTIBLE, if it is preempted again after that and before
__set_current_state(TASK_RUNNING), it triggers the invalid wakeup problem.
----------------
wait_for_auditd()
----------------
...
//location a
set_current_state(TASK_UNINTERRUPTIBLE);
...

if (audit_backlog_limit &&
			skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
	//location b
	schedule_timeout(sleep_time);
	//location c

__set_current_state(TASK_RUNNING);
//location d
...

To solve this problem, using preempt_disable() to bound the operaion that
setting the task state and the conditions(set by the wake thread) validation.
----------------
wait_for_auditd()
----------------
...
preempt_disable();
set_current_state(TASK_UNINTERRUPTIBLE);
...

if (audit_backlog_limit &&
			skb_queue_len(&audit_skb_queue) > audit_backlog_limit) {
	preempt_enable();
	schedule_timeout(sleep_time);
	preempt_disable();
}

__set_current_state(TASK_RUNNING);
preempt_enable();
...

Signed-off-by: Libin <huawei.libin@...wei.com>
---
 kernel/audit.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/kernel/audit.c b/kernel/audit.c
index a7d1346..48d2f76 100644
--- a/kernel/audit.c
+++ b/kernel/audit.c
@@ -1060,14 +1060,19 @@ static inline void audit_get_stamp(struct audit_context *ctx,
 static void wait_for_auditd(unsigned long sleep_time)
 {
 	DECLARE_WAITQUEUE(wait, current);
+	preempt_disable();
 	set_current_state(TASK_UNINTERRUPTIBLE);
 	add_wait_queue(&audit_backlog_wait, &wait);
 
 	if (audit_backlog_limit &&
-	    skb_queue_len(&audit_skb_queue) > audit_backlog_limit)
+	    skb_queue_len(&audit_skb_queue) > audit_backlog_limit) {
+		preempt_enable();
 		schedule_timeout(sleep_time);
+		preempt_disable();
+	}
 
 	__set_current_state(TASK_RUNNING);
+	preempt_enable();
 	remove_wait_queue(&audit_backlog_wait, &wait);
 }
 
-- 
1.8.2.1


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