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

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Date:   Fri, 24 Feb 2023 13:02:29 -0800
From:   Luiz Augusto von Dentz <luiz.dentz@...il.com>
To:     Zhengping Jiang <jiangzp@...gle.com>
Cc:     linux-bluetooth@...r.kernel.org, marcel@...tmann.org,
        mmandlik@...gle.com, chromeos-bluetooth-upstreaming@...omium.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        Paolo Abeni <pabeni@...hat.com>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [kernel PATCH v2 1/1] Bluetooth: hci_sync: clear workqueue before
 clear mgmt cmd

Hi Zhengping,

On Fri, Feb 24, 2023 at 11:53 AM Zhengping Jiang <jiangzp@...gle.com> 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@...gle.com>
> ---
>
> 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