[PATCH] workqueue: Fix NULL pointer dereference

[PATCH] workqueue: Fix NULL pointer dereference

[Li Bin]

When queue_work() is used in irq handler, 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 irq context in current_wq_worker(), and
if in irq 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>
---
 kernel/workqueue_internal.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
index 8635417..d81cb9b 100644
--- 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_irq() && (current->flags & PF_WQ_WORKER))
 		return kthread_data(current);
 	return NULL;
 }
-- 
1.7.12.4

Re: [PATCH] workqueue: Fix NULL pointer dereference

[Tejun Heo]

On Tue, Oct 24, 2017 at 09:18:34AM +0800, Li Bin wrote:
> When queue_work() is used in irq handler, 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 irq context in current_wq_worker(), and
> if in irq 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>

Applied to wq/for-4.14-fixes.

Thanks.

-- 
tejun

Re: [PATCH] workqueue: Fix NULL pointer dereference

[Lai Jiangshan]

On Tue, Oct 24, 2017 at 9:18 AM, Li Bin <huawei.libin@huawei.com> wrote:
> When queue_work() is used in irq handler, 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!

I remember that softirq can be invoked when irq_eixt(),
and in this case the current->current_pwq is also NULL
if __queue_work() is called in the soft irq.

So in_task() might be better than !in_irq() for the fix?

> |-schedule()
> ----------------------------------------------------------------
>
> Avoid it by checking for irq context in current_wq_worker(), and
> if in irq 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>
> ---
>  kernel/workqueue_internal.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
> index 8635417..d81cb9b 100644
> --- 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_irq() && (current->flags & PF_WQ_WORKER))
>                 return kthread_data(current);
>         return NULL;
>  }
> --
> 1.7.12.4
>

Re: [PATCH] workqueue: Fix NULL pointer dereference

[Tejun Heo]

Hello,

On Thu, Oct 26, 2017 at 11:55:00PM +0800, Lai Jiangshan wrote:
> I remember that softirq can be invoked when irq_eixt(),
> and in this case the current->current_pwq is also NULL
> if __queue_work() is called in the soft irq.
> 
> So in_task() might be better than !in_irq() for the fix?

Reverted the patch for now.  Li, what do you think?

Thanks.

-- 
tejun

Re: [PATCH] workqueue: Fix NULL pointer dereference

[Li Bin]

Hi, Jiangshan

on 2017/10/26 23:55, Lai Jiangshan wrote:
> On Tue, Oct 24, 2017 at 9:18 AM, Li Bin <huawei.libin@huawei.com> wrote:

> 
> I remember that softirq can be invoked when irq_eixt(),
> and in this case the current->current_pwq is also NULL
> if __queue_work() is called in the soft irq.
> 
> So in_task() might be better than !in_irq() for the fix?
> 

Good catch, I will fix it and resend the patch.

Thanks,
Li Bin

>> |-schedule()
>> ----------------------------------------------------------------
>>
>> Avoid it by checking for irq context in current_wq_worker(), and
>> if in irq 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>
>> ---
>>  kernel/workqueue_internal.h | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/workqueue_internal.h b/kernel/workqueue_internal.h
>> index 8635417..d81cb9b 100644
>> --- 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_irq() && (current->flags & PF_WQ_WORKER))
>>                 return kthread_data(current);
>>         return NULL;
>>  }
>> --
>> 1.7.12.4
>>
> 
> .
>