Re: [kernel PATCH v2 1/1] Bluetooth: hci_sync: clear workqueue before clear mgmt cmd

[Zhengping Jiang]

Hi Luiz,

> Any particular reason why you are not using hci_cmd_sync_clear
> instead?

That is a good question and we used hci_cmd_sync_clear in the first
version, but it will clear the queue and also close the timer. As a
result, when the adapter is turned on again, the timer will not
schedule any new jobs. So the option is to use hci_cmd_sync_clear and
re-initiate the queue or to write a new function which only clears the
queue.

> We also may want to move the clearing logic to
> hci_dev_close_sync since it should be equivalent to
> hci_request_cancel_all.

I actually have a question here. I saw
"drain_workqueue(hdev->workqueue)" in hci_dev_close_sync and thought
it should force clearing the cmd_sync queue. But it seems cannot
prevent the use-after-free situation.

Any suggestions to improve the solution?

Thanks,
Zhengping


On Fri, Feb 24, 2023 at 1:02 PM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:
>
> Hi Zhengping,
>
> On Fri, Feb 24, 2023 at 11:53 AM Zhengping Jiang <jiangzp@xxxxxxxxxx> wrote:
> >
> > Clear cmd_sync_work queue before clearing the mgmt cmd list to avoid
> > racing conditions which cause use-after-free.
> >
> > When powering off the adapter, the mgmt cmd list will be cleared. If a
> > work is queued in the cmd_sync_work queue at the same time, it will
> > cause the risk of use-after-free, as the cmd pointer is not checked
> > before use.
> >
> > Signed-off-by: Zhengping Jiang <jiangzp@xxxxxxxxxx>
> > ---
> >
> > Changes in v2:
> > - Add function to clear the queue without stop the timer
> >
> > Changes in v1:
> > - Clear cmd_sync_work queue before clearing the mgmt cmd list
> >
> >  net/bluetooth/hci_sync.c | 21 ++++++++++++++++++++-
> >  1 file changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/net/bluetooth/hci_sync.c b/net/bluetooth/hci_sync.c
> > index 117eedb6f709..b70365dfff0c 100644
> > --- a/net/bluetooth/hci_sync.c
> > +++ b/net/bluetooth/hci_sync.c
> > @@ -636,6 +636,23 @@ void hci_cmd_sync_init(struct hci_dev *hdev)
> >         INIT_DELAYED_WORK(&hdev->adv_instance_expire, adv_timeout_expire);
> >  }
> >
> > +static void hci_pend_cmd_sync_clear(struct hci_dev *hdev)
> > +{
> > +       struct hci_cmd_sync_work_entry *entry, *tmp;
> > +
> > +       mutex_lock(&hdev->cmd_sync_work_lock);
> > +       list_for_each_entry_safe(entry, tmp, &hdev->cmd_sync_work_list, list) {
> > +               if (entry->destroy) {
> > +                       hci_req_sync_lock(hdev);
> > +                       entry->destroy(hdev, entry->data, -ECANCELED);
> > +                       hci_req_sync_unlock(hdev);
> > +               }
> > +               list_del(&entry->list);
> > +               kfree(entry);
> > +       }
> > +       mutex_unlock(&hdev->cmd_sync_work_lock);
> > +}
> > +
> >  void hci_cmd_sync_clear(struct hci_dev *hdev)
> >  {
> >         struct hci_cmd_sync_work_entry *entry, *tmp;
> > @@ -4842,8 +4859,10 @@ int hci_dev_close_sync(struct hci_dev *hdev)
> >
> >         if (!auto_off && hdev->dev_type == HCI_PRIMARY &&
> >             !hci_dev_test_flag(hdev, HCI_USER_CHANNEL) &&
> > -           hci_dev_test_flag(hdev, HCI_MGMT))
> > +           hci_dev_test_flag(hdev, HCI_MGMT)) {
> > +               hci_pend_cmd_sync_clear(hdev);
>
> Any particular reason why you are not using hci_cmd_sync_clear
> instead? We also may want to move the clearing logic to
> hci_dev_close_sync since it should be equivalent to
> hci_request_cancel_all.
>
> >                 __mgmt_power_off(hdev);
> > +       }
> >
> >         hci_inquiry_cache_flush(hdev);
> >         hci_pend_le_actions_clear(hdev);
> > --
> > 2.39.2.722.g9855ee24e9-goog
> >
>
>
> --
> Luiz Augusto von Dentz