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%3Ba=su...

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 stable@vger.kernel.org know about it.

From cef572ad9bd7f85035ba8272e5352040e8be0152 Mon Sep 17 00:00:00 2001

From: Li Bin huawei.libin@huawei.com Date: Sat, 28 Oct 2017 11:07:28 +0800 Subject: workqueue: Fix NULL pointer dereference

From: Li Bin huawei.libin@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 tanxiaofei@huawei.com Signed-off-by: Li Bin huawei.libin@huawei.com Reviewed-by: Lai Jiangshan jiangshanlai@gmail.com Signed-off-by: Tejun Heo tj@kernel.org Fixes: 8d03ecfe4718 ("workqueue: reimplement is_chained_work() using current_wq_worker()") Signed-off-by: Greg Kroah-Hartman gregkh@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; }

Patches currently in stable-queue which might be from huawei.libin@huawei.com are

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