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Date:   Tue, 09 Jun 2020 21:25:15 +0530
From:   gubbaven@codeaurora.org
To:     Abhishek Pandit-Subedi <abhishekpandit@chromium.org>
Cc:     Marcel Holtmann <marcel@holtmann.org>,
        Johan Hedberg <johan.hedberg@gmail.com>,
        Matthias Kaehlcke <mka@chromium.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Bluez mailing list <linux-bluetooth@vger.kernel.org>,
        robh@kernel.org, hemantg@codeaurora.org,
        linux-arm-msm@vger.kernel.org, bgodavar@codeaurora.org,
        Claire Chang <tientzu@chromium.org>,
        Sean Paul <seanpaul@chromium.org>, rjliao@codeaurora.org,
        Yoni Shavit <yshavit@google.com>
Subject: Re: [PATCH v1] Bluetooth: hci_qca: Fix double free during SSR timeout
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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@codeaurora.org> 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@codeaurora.org>
>> ---
>>  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.