Patch "workqueue: Fix NULL pointer dereference" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

workqueue: Fix NULL pointer dereference

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
workqueue-fix-null-pointer-dereference.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Li Bin <[email protected]>
Date: Sat, 28 Oct 2017 11:07:28 +0800
Subject: workqueue: Fix NULL pointer dereference

From: Li Bin <[email protected]>

commit cef572ad9bd7f85035ba8272e5352040e8be0152 upstream.

When queue_work() is used in irq (not in task context), there is a potential case that trigger NULL pointer dereference.
----------------------------------------------------------------
worker_thread()
|-spin_lock_irq()
|-process_one_work()

	|-worker->current_pwq = pwq
	|-spin_unlock_irq()
	|-worker->current_func(work)
	|-spin_lock_irq()

|-worker->current_pwq = NULL
|-spin_unlock_irq()

				//interrupt here
				|-irq_handler
					|-__queue_work()
						//assuming that the wq is draining
						|-is_chained_work(wq)
							|-current_wq_worker()
							//Here, 'current' is the interrupted worker!
								|-current->current_pwq is NULL here!

|-schedule()
----------------------------------------------------------------

Avoid it by checking for task context in current_wq_worker(), and if not in task context, we shouldn't use the 'current' to check the condition.

---
 kernel/workqueue_internal.h |    3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

@@ -9,6 +9,7 @@
 
 #include <linux/workqueue.h>
 #include <linux/kthread.h>
+#include <linux/preempt.h>
 
 struct worker_pool;
 

@@ -59,7 +60,7 @@ struct worker {
  */
 static inline struct worker *current_wq_worker(void)
 {
-	if (current->flags & PF_WQ_WORKER)
+	if (in_task() && (current->flags & PF_WQ_WORKER))
 		return kthread_data(current);
 	return NULL;
 }

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/workqueue-fix-null-pointer-dereference.patch