[PATCH 4.13 03/33] workqueue: Fix NULL pointer dereference

[Greg Kroah-Hartman]

4.13-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Li Bin <huawei.li...@huawei.com>

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.

Reported-by: Xiaofei Tan <tanxiao...@huawei.com>
Signed-off-by: Li Bin <huawei.li...@huawei.com>
Reviewed-by: Lai Jiangshan <jiangshan...@gmail.com>
Signed-off-by: Tejun Heo <t...@kernel.org>
Fixes: 8d03ecfe4718 ("workqueue: reimplement is_chained_work() using 
current_wq_worker()")
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

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

--- a/kernel/workqueue_internal.h
+++ b/kernel/workqueue_internal.h
@@ -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;
 }