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

[Doug Anderson]

Hi,

On Fri, Jun 30, 2023 at 2:55 PM Luiz Augusto von Dentz
<luiz.dentz@xxxxxxxxx> wrote:
>
> 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,

Sure. I wasn't sure how much the order of the printout matters, but if
it doesn't then just putting the print first makes sense. Done in v2.

> 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.

I made that a separate patch just to keep it cleaner. I also fixed the
"add" function which has the same issue.

-Doug