* [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage
@ 2022-04-12 13:46 Tetsuo Handa
2022-04-12 22:18 ` Tetsuo Handa
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2022-04-12 13:46 UTC (permalink / raw)
To: Md. Haris Iqbal, Jack Wang; +Cc: Jens Axboe, linux-block
Flushing system-wide workqueues is dangerous and will be forbidden.
Since system_long_wq is used only inside rnbd_destroy_sessions(),
let's use list_head than creating a local workqueue for tracking
work_struct to flush.
Link: https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
---
Notice: This patch is only compile tested. Please test before applying.
drivers/block/rnbd/rnbd-clt.c | 5 ++++-
drivers/block/rnbd/rnbd-clt.h | 1 +
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
index b66e8840b94b..b14e7c15133e 100644
--- a/drivers/block/rnbd/rnbd-clt.c
+++ b/drivers/block/rnbd/rnbd-clt.c
@@ -1730,6 +1730,7 @@ static void rnbd_destroy_sessions(void)
{
struct rnbd_clt_session *sess, *sn;
struct rnbd_clt_dev *dev, *tn;
+ LIST_HEAD(list);
/* Firstly forbid access through sysfs interface */
rnbd_clt_destroy_sysfs_files();
@@ -1762,11 +1763,13 @@ static void rnbd_destroy_sessions(void)
*/
INIT_WORK(&dev->unmap_on_rmmod_work, unmap_device_work);
queue_work(system_long_wq, &dev->unmap_on_rmmod_work);
+ list_add_tail(&dev->unmap_on_rmmod_list, &list);
}
rnbd_clt_put_sess(sess);
}
/* Wait for all scheduled unmap works */
- flush_workqueue(system_long_wq);
+ list_for_each_entry(dev, &list, unmap_on_rmmod_list)
+ flush_work(&dev->unmap_on_rmmod_work);
WARN_ON(!list_empty(&sess_list));
}
diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h
index 2e2e8c4a85c1..a6d704abda61 100644
--- a/drivers/block/rnbd/rnbd-clt.h
+++ b/drivers/block/rnbd/rnbd-clt.h
@@ -136,6 +136,7 @@ struct rnbd_clt_dev {
char *blk_symlink_name;
refcount_t refcount;
struct work_struct unmap_on_rmmod_work;
+ struct list_head unmap_on_rmmod_list;
};
/* rnbd-clt.c */
--
2.32.0
^ permalink raw reply related [flat|nested] 5+ messages in thread
* Re: [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage
2022-04-12 13:46 [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage Tetsuo Handa
@ 2022-04-12 22:18 ` Tetsuo Handa
2022-04-13 5:21 ` Jinpu Wang
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2022-04-12 22:18 UTC (permalink / raw)
To: Md. Haris Iqbal, Jack Wang; +Cc: Jens Axboe, linux-block
On 2022/04/12 22:46, Tetsuo Handa wrote:
> Flushing system-wide workqueues is dangerous and will be forbidden.
>
> Since system_long_wq is used only inside rnbd_destroy_sessions(),
> let's use list_head than creating a local workqueue for tracking
> work_struct to flush.
>
> Link: https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
>
> Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> ---
> Notice: This patch is only compile tested. Please test before applying.
>
> drivers/block/rnbd/rnbd-clt.c | 5 ++++-
> drivers/block/rnbd/rnbd-clt.h | 1 +
> 2 files changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> index b66e8840b94b..b14e7c15133e 100644
> --- a/drivers/block/rnbd/rnbd-clt.c
> +++ b/drivers/block/rnbd/rnbd-clt.c
> @@ -1730,6 +1730,7 @@ static void rnbd_destroy_sessions(void)
> {
> struct rnbd_clt_session *sess, *sn;
> struct rnbd_clt_dev *dev, *tn;
> + LIST_HEAD(list);
>
> /* Firstly forbid access through sysfs interface */
> rnbd_clt_destroy_sysfs_files();
> @@ -1762,11 +1763,13 @@ static void rnbd_destroy_sessions(void)
> */
> INIT_WORK(&dev->unmap_on_rmmod_work, unmap_device_work);
> queue_work(system_long_wq, &dev->unmap_on_rmmod_work);
> + list_add_tail(&dev->unmap_on_rmmod_list, &list);
> }
> rnbd_clt_put_sess(sess);
> }
> /* Wait for all scheduled unmap works */
> - flush_workqueue(system_long_wq);
> + list_for_each_entry(dev, &list, unmap_on_rmmod_list)
> + flush_work(&dev->unmap_on_rmmod_work);
Since kfree(dev) might be called from unmap_device_work(), this seems unsafe.
We need rnbd_clt_get_dev() before queue_work() and rnbd_clt_put_dev() after flush_work()
in order to make dev->unmap_on_rmmod_list traversal safe...
> WARN_ON(!list_empty(&sess_list));
> }
>
> diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h
> index 2e2e8c4a85c1..a6d704abda61 100644
> --- a/drivers/block/rnbd/rnbd-clt.h
> +++ b/drivers/block/rnbd/rnbd-clt.h
> @@ -136,6 +136,7 @@ struct rnbd_clt_dev {
> char *blk_symlink_name;
> refcount_t refcount;
> struct work_struct unmap_on_rmmod_work;
> + struct list_head unmap_on_rmmod_list;
> };
>
> /* rnbd-clt.c */
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage
2022-04-12 22:18 ` Tetsuo Handa
@ 2022-04-13 5:21 ` Jinpu Wang
2022-04-13 5:30 ` Tetsuo Handa
0 siblings, 1 reply; 5+ messages in thread
From: Jinpu Wang @ 2022-04-13 5:21 UTC (permalink / raw)
To: Tetsuo Handa; +Cc: Md. Haris Iqbal, Jens Axboe, linux-block
Hi Tetsuo,
On Wed, Apr 13, 2022 at 12:18 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2022/04/12 22:46, Tetsuo Handa wrote:
> > Flushing system-wide workqueues is dangerous and will be forbidden.
> >
> > Since system_long_wq is used only inside rnbd_destroy_sessions(),
> > let's use list_head than creating a local workqueue for tracking
> > work_struct to flush.
> >
> > Link: https://lkml.kernel.org/r/49925af7-78a8-a3dd-bce6-cfc02e1a9236@I-love.SAKURA.ne.jp
> >
> > Signed-off-by: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
> > ---
> > Notice: This patch is only compile tested. Please test before applying.
> >
> > drivers/block/rnbd/rnbd-clt.c | 5 ++++-
> > drivers/block/rnbd/rnbd-clt.h | 1 +
> > 2 files changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/block/rnbd/rnbd-clt.c b/drivers/block/rnbd/rnbd-clt.c
> > index b66e8840b94b..b14e7c15133e 100644
> > --- a/drivers/block/rnbd/rnbd-clt.c
> > +++ b/drivers/block/rnbd/rnbd-clt.c
> > @@ -1730,6 +1730,7 @@ static void rnbd_destroy_sessions(void)
> > {
> > struct rnbd_clt_session *sess, *sn;
> > struct rnbd_clt_dev *dev, *tn;
> > + LIST_HEAD(list);
> >
> > /* Firstly forbid access through sysfs interface */
> > rnbd_clt_destroy_sysfs_files();
> > @@ -1762,11 +1763,13 @@ static void rnbd_destroy_sessions(void)
> > */
> > INIT_WORK(&dev->unmap_on_rmmod_work, unmap_device_work);
> > queue_work(system_long_wq, &dev->unmap_on_rmmod_work);
> > + list_add_tail(&dev->unmap_on_rmmod_list, &list);
> > }
> > rnbd_clt_put_sess(sess);
> > }
> > /* Wait for all scheduled unmap works */
> > - flush_workqueue(system_long_wq);
> > + list_for_each_entry(dev, &list, unmap_on_rmmod_list)
> > + flush_work(&dev->unmap_on_rmmod_work);
>
> Since kfree(dev) might be called from unmap_device_work(), this seems unsafe.
> We need rnbd_clt_get_dev() before queue_work() and rnbd_clt_put_dev() after flush_work()
> in order to make dev->unmap_on_rmmod_list traversal safe...
you are right, unmap_device_work could free the dev structure, lead to UAF.
simply add rnbd_clt_get_dev and put_dev will lead to following WARN_ON
to be triggered.
>
> > WARN_ON(!list_empty(&sess_list));
> > }
I feel the simple approach is to replace the gloable system_long_wq
with a local workqueue for rnbd_client.
Thanks!
> >
> > diff --git a/drivers/block/rnbd/rnbd-clt.h b/drivers/block/rnbd/rnbd-clt.h
> > index 2e2e8c4a85c1..a6d704abda61 100644
> > --- a/drivers/block/rnbd/rnbd-clt.h
> > +++ b/drivers/block/rnbd/rnbd-clt.h
> > @@ -136,6 +136,7 @@ struct rnbd_clt_dev {
> > char *blk_symlink_name;
> > refcount_t refcount;
> > struct work_struct unmap_on_rmmod_work;
> > + struct list_head unmap_on_rmmod_list;
> > };
> >
> > /* rnbd-clt.c */
>
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage
2022-04-13 5:21 ` Jinpu Wang
@ 2022-04-13 5:30 ` Tetsuo Handa
2022-04-13 6:40 ` Jinpu Wang
0 siblings, 1 reply; 5+ messages in thread
From: Tetsuo Handa @ 2022-04-13 5:30 UTC (permalink / raw)
To: Jinpu Wang; +Cc: Md. Haris Iqbal, Jens Axboe, linux-block
On 2022/04/13 14:21, Jinpu Wang wrote:
> I feel the simple approach is to replace the global system_long_wq
> with a local workqueue for rnbd_client.
OK. Please post a patch.
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage
2022-04-13 5:30 ` Tetsuo Handa
@ 2022-04-13 6:40 ` Jinpu Wang
0 siblings, 0 replies; 5+ messages in thread
From: Jinpu Wang @ 2022-04-13 6:40 UTC (permalink / raw)
To: Tetsuo Handa; +Cc: Md. Haris Iqbal, Jens Axboe, linux-block
On Wed, Apr 13, 2022 at 7:31 AM Tetsuo Handa
<penguin-kernel@i-love.sakura.ne.jp> wrote:
>
> On 2022/04/13 14:21, Jinpu Wang wrote:
> > I feel the simple approach is to replace the global system_long_wq
> > with a local workqueue for rnbd_client.
>
> OK. Please post a patch.
Will do, thanks!
^ permalink raw reply [flat|nested] 5+ messages in thread
end of thread, other threads:[~2022-04-13 6:40 UTC | newest]
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2022-04-12 13:46 [PATCH] block/rnbd: client: avoid flush_workqueue(system_long_wq) usage Tetsuo Handa
2022-04-12 22:18 ` Tetsuo Handa
2022-04-13 5:21 ` Jinpu Wang
2022-04-13 5:30 ` Tetsuo Handa
2022-04-13 6:40 ` Jinpu Wang
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