Re: [PATCH] Bluetooth: hci_sync: Avoid use-after-free in dbg for hci_remove_adv_monitor()

[Luiz Augusto von Dentz]

Hi Douglas,

On Fri, Jun 30, 2023 at 2:40 PM Douglas Anderson <dianders@xxxxxxxxxxxx> wrote:
>
> KASAN reports that there's a use-after-free in
> hci_remove_adv_monitor(). Trawling through the disassembly, you can
> see that the complaint is from the access in bt_dev_dbg() under the
> HCI_ADV_MONITOR_EXT_MSFT case. The problem case happens because
> msft_remove_monitor() can end up freeing the monitor
> structure. Specifically:
>   hci_remove_adv_monitor() ->
>   msft_remove_monitor() ->
>   msft_remove_monitor_sync() ->
>   msft_le_cancel_monitor_advertisement_cb() ->
>   hci_free_adv_monitor()
>
> Let's fix the problem by just stashing the relevant data when it's
> still valid.
>
> Fixes: 7cf5c2978f23 ("Bluetooth: hci_sync: Refactor remove Adv Monitor")
> Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
> ---
>
>  net/bluetooth/hci_core.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
>
> diff --git a/net/bluetooth/hci_core.c b/net/bluetooth/hci_core.c
> index 48917c68358d..dbb2043a9112 100644
> --- a/net/bluetooth/hci_core.c
> +++ b/net/bluetooth/hci_core.c
> @@ -1972,6 +1972,7 @@ static int hci_remove_adv_monitor(struct hci_dev *hdev,
>                                   struct adv_monitor *monitor)
>  {
>         int status = 0;
> +       int handle;
>
>         switch (hci_get_adv_monitor_offload_ext(hdev)) {
>         case HCI_ADV_MONITOR_EXT_NONE: /* also goes here when powered off */
> @@ -1980,9 +1981,10 @@ static int hci_remove_adv_monitor(struct hci_dev *hdev,
>                 goto free_monitor;
>
>         case HCI_ADV_MONITOR_EXT_MSFT:
> +               handle = monitor->handle;
>                 status = msft_remove_monitor(hdev, monitor);
>                 bt_dev_dbg(hdev, "%s remove monitor %d msft status %d",
> -                          hdev->name, monitor->handle, status);
> +                          hdev->name, handle, status);

Just move the call to bt_dev_dbg under msft_remove_monitor, also there
is no reason to print hdev->name since bt_dev_dbg already does that so
while at it we can probably fix this as well.

>                 break;
>         }
>
> --
> 2.41.0.255.g8b1d071c50-goog
>


-- 
Luiz Augusto von Dentz