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@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.



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