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

[Zhengping Jiang]

Hi Luiz,

I have a question. Given that each command in the cmd_sync queue
should clean up the memory in a callback function. I was wondering if
the call to cmd_complete_rsp in __mgmt_power_off function is still
necessary? Will this always risk a race condition that cmd has been
released when the complete callback or _sync function is run?

Thanks,
Zhengping

On Fri, Feb 24, 2023 at 2:37 PM Zhengping Jiang <jiangzp@xxxxxxxxxx> wrote:
>
> 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