2022-12-13 05:02:12

by richard clark

Subject: [PATCH] workqueue: Add a new flag to spot the potential UAF error

Currently if the user queues a new work item unintentionally
into a wq after the destroy_workqueue(wq), the work still can
be queued and scheduled without any noticeable kernel message
before the end of a RCU grace period.

As a debug-aid facility, this commit adds a new flag
__WQ_DESTROYING to spot that issue by triggering a kernel WARN
message.

Signed-off-by: Richard Clark <[email protected]>
---
include/linux/workqueue.h | 1 +
kernel/workqueue.c | 15 ++++++++++++---
2 files changed, 13 insertions(+), 3 deletions(-)

diff --git a/include/linux/workqueue.h b/include/linux/workqueue.h
index a0143dd24430..ac551b8ee7d9 100644
--- a/include/linux/workqueue.h
+++ b/include/linux/workqueue.h
@@ -335,6 +335,7 @@ enum {
*/
WQ_POWER_EFFICIENT = 1 << 7,

+ __WQ_DESTROYING = 1 << 15, /* internal: workqueue is destroying */
__WQ_DRAINING = 1 << 16, /* internal: workqueue is draining */
__WQ_ORDERED = 1 << 17, /* internal: workqueue is ordered */
__WQ_LEGACY = 1 << 18, /* internal: create*_workqueue() */
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 39060a5d0905..30dc6869b3fd 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1433,9 +1433,13 @@ static void __queue_work(int cpu, struct workqueue_struct *wq,
lockdep_assert_irqs_disabled();


- /* if draining, only works from the same workqueue are allowed */
- if (unlikely(wq->flags & __WQ_DRAINING) &&
- WARN_ON_ONCE(!is_chained_work(wq)))
+ /*
+ * For a draining wq, only works from the same workqueue are
+ * allowed. The __WQ_DESTROYING helps to spot the issue that
+ * queues a new work item to a wq after destroy_workqueue(wq).
+ */
+ if (unlikely(wq->flags & (__WQ_DESTROYING | __WQ_DRAINING)
+ && WARN_ON_ONCE(!is_chained_work(wq))))
return;
rcu_read_lock();
retry:
@@ -4414,6 +4418,11 @@ void destroy_workqueue(struct workqueue_struct *wq)
*/
workqueue_sysfs_unregister(wq);

+ /* mark the workqueue destruction is in progress */
+ mutex_lock(&wq->mutex);
+ wq->flags |= __WQ_DESTROYING;
+ mutex_unlock(&wq->mutex);
+
/* drain it before proceeding with destruction */
drain_workqueue(wq);

--
2.37.2

2022-12-14 08:02:47

by Lai Jiangshan

Subject: Re: [PATCH] workqueue: Add a new flag to spot the potential UAF error

On Tue, Dec 13, 2022 at 12:40 PM Richard Clark
<[email protected]> wrote:
>
> Currently if the user queues a new work item unintentionally
> into a wq after the destroy_workqueue(wq), the work still can
> be queued and scheduled without any noticeable kernel message
> before the end of a RCU grace period.
>
> As a debug-aid facility, this commit adds a new flag
> __WQ_DESTROYING to spot that issue by triggering a kernel WARN
> message.
>
> Signed-off-by: Richard Clark <[email protected]>

Reviewed-by: Lai Jiangshan <[email protected]>

2022-12-16 01:51:30

by richard clark

Subject: Re: [PATCH] workqueue: Add a new flag to spot the potential UAF error

Hello TJ,

On Wed, Dec 14, 2022 at 3:16 PM Lai Jiangshan <[email protected]> wrote:
>
> On Tue, Dec 13, 2022 at 12:40 PM Richard Clark
> <[email protected]> wrote:
> >
> > Currently if the user queues a new work item unintentionally
> > into a wq after the destroy_workqueue(wq), the work still can
> > be queued and scheduled without any noticeable kernel message
> > before the end of a RCU grace period.
> >
> > As a debug-aid facility, this commit adds a new flag
> > __WQ_DESTROYING to spot that issue by triggering a kernel WARN
> > message.
> >
> > Signed-off-by: Richard Clark <[email protected]>
>
> Reviewed-by: Lai Jiangshan <[email protected]>

What do I need to do for this patch next?

Thanks

2023-01-04 23:19:39

by Tejun Heo

Subject: Re: [PATCH] workqueue: Add a new flag to spot the potential UAF error

On Tue, Dec 13, 2022 at 12:39:36PM +0800, Richard Clark wrote:
> Currently if the user queues a new work item unintentionally
> into a wq after the destroy_workqueue(wq), the work still can
> be queued and scheduled without any noticeable kernel message
> before the end of a RCU grace period.
>
> As a debug-aid facility, this commit adds a new flag
> __WQ_DESTROYING to spot that issue by triggering a kernel WARN
> message.
>
> Signed-off-by: Richard Clark <[email protected]>

Applied to wq/for-6.3 w/ whitespace adjustments.

Thanks.

--
tejun