Re: [PATCH v1] Bluetooth: hci_qca: Fix double free during SSR timeout

[gubbaven]

Hi Abhishek,

On 2020-06-05 10:23, Abhishek Pandit-Subedi wrote:
> Hi,
>
> On Thu, Jun 4, 2020 at 6:59 AM Venkata Lakshmi Narayana Gubba
> <gubbaven@xxxxxxxxxxxxxx> wrote:
> > Due to race conditions between qca_hw_error and qca_controller_memdump
> > during SSR timeout,the same pointer is freed twice. Which results to
> > double free error. Now a lock is acquired while SSR state moved to 
> > timeout.
> suggestion: Change "which results to double free error" to "This
> results in a double free."
> suggestion: Change "while SSR state moved to timeout" to "when SSR
> state is changed to timeout"
[Venkata]:
Sure will update in next patchset.
> > Signed-off-by: Venkata Lakshmi Narayana Gubba 
> > <gubbaven@xxxxxxxxxxxxxx>
> > ---
> >  drivers/bluetooth/hci_qca.c | 19 ++++++++++++++-----
> >  1 file changed, 14 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/bluetooth/hci_qca.c b/drivers/bluetooth/hci_qca.c
> > index 836949d..9110775 100644
> > --- a/drivers/bluetooth/hci_qca.c
> > +++ b/drivers/bluetooth/hci_qca.c
> > @@ -983,8 +983,11 @@ static void qca_controller_memdump(struct 
> > work_struct *work)
> >         while ((skb = skb_dequeue(&qca->rx_memdump_q))) {
> >
> >                 mutex_lock(&qca->hci_memdump_lock);
> > -               /* Skip processing the received packets if timeout 
> > detected. */
> > -               if (qca->memdump_state == QCA_MEMDUMP_TIMEOUT) {
> > +               /* Skip processing the received packets if timeout 
> > detected
> > +                * or memdump collection completed.
> > +                */
> > +               if (qca->memdump_state == QCA_MEMDUMP_TIMEOUT ||
> > +                   qca->memdump_state == QCA_MEMDUMP_COLLECTED) {
> >                         mutex_unlock(&qca->hci_memdump_lock);
> >                         return;
> >                 }
> > @@ -1485,7 +1488,7 @@ static void qca_hw_error(struct hci_dev *hdev, 
> > u8 code)
> >  {
> >         struct hci_uart *hu = hci_get_drvdata(hdev);
> >         struct qca_data *qca = hu->priv;
> > -       struct qca_memdump_data *qca_memdump = qca->qca_memdump;
> > +       struct qca_memdump_data *qca_memdump = NULL;
> >         char *memdump_buf = NULL;
> >
> >         set_bit(QCA_HW_ERROR_EVENT, &qca->flags);
> > @@ -1509,9 +1512,10 @@ static void qca_hw_error(struct hci_dev *hdev, 
> > u8 code)
> >                 qca_wait_for_dump_collection(hdev);
> >         }
> >
> > +       mutex_lock(&qca->hci_memdump_lock);
> >         if (qca->memdump_state != QCA_MEMDUMP_COLLECTED) {
> >                 bt_dev_err(hu->hdev, "clearing allocated memory due to 
> > memdump timeout");
> > -               mutex_lock(&qca->hci_memdump_lock);
> > +               qca_memdump = qca->qca_memdump;
> >                 if (qca_memdump)
> >                         memdump_buf = qca_memdump->memdump_buf_head;
> >                 vfree(memdump_buf);
>
> This section of code looks a bit unclear because it's only partially
> in an if statement. Suggestion:
>   if (qca->qca_memdump) {
>     vfree(qca->qca_memdump->memdump_buf_head);
>     kfree(qca->qca_memdump);
>     qca->qca_memdump = NULL;
>   }
[Venkata]:
Sure will update in next patchset.
> > @@ -1520,8 +1524,13 @@ static void qca_hw_error(struct hci_dev *hdev, 
> > u8 code)
> >                 qca->memdump_state = QCA_MEMDUMP_TIMEOUT;
> >                 cancel_delayed_work(&qca->ctrl_memdump_timeout);
> >                 skb_queue_purge(&qca->rx_memdump_q);
> > -               mutex_unlock(&qca->hci_memdump_lock);
> > +       }
> > +       mutex_unlock(&qca->hci_memdump_lock);
> > +
> > +       if (qca->memdump_state == QCA_MEMDUMP_TIMEOUT ||
> > +           qca->memdump_state == QCA_MEMDUMP_COLLECTED) {
> >                 cancel_work_sync(&qca->ctrl_memdump_evt);
> > +               skb_queue_purge(&qca->rx_memdump_q);
> >         }
>
> Earlier in the function, you call qca_wait_for_dump_collection for
> [Idle, Collecting] so the state should be either [Timeout, Collected]
> at this branch. So, you can remove the `cancel_delayed_work` and
> `skb_queue_purge` from above and just leave it only in the bottom
> branch. Currently you're duplicating these calls unnecessarily.
>
> I don't know if we discussed this in an earlier review but I noticed
> that `qca_wait_for_dump_collection` doesn't actually pay attention to
> the return value of `wait_on_bit_timeout`. I don't have context for
> the order of calls anymore but is there a possibility for that timeout
> to complete before `qca_memdump_timeout` is called? In that case, you
> should probably set the state to timeout in
> `qca_wait_for_dump_collection` as well.
[Venkata]:
I see only skb_queue_purge is getting duplicated and will update in next 
patchset.
But cancel_delayed_work is for qca->ctrl_memdump_timeout and 
cancel_work_sync is for
qca->ctrl_memdump_evt.So these calls are not getting duplicated.

If timeout happens in qca_wait_for_dump_collection, we are setting state 
to timeout
in subsequent if block which is  if (qca->memdump_state != 
QCA_MEMDUMP_COLLECTED).
> >         clear_bit(QCA_HW_ERROR_EVENT, &qca->flags);
> > --
> > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a 
> > member
> > of Code Aurora Forum, hosted by The Linux Foundation

Regards,
Lakshmi Narayana.