Re: [PATCH] Bluetooth: skip invalid hci_sync_conn_complete_evt

[Desmond Cheong Zhi Xi]

On 22/7/21 10:39 pm, Marcel Holtmann wrote:
> Hi Desmond,
>
> > Syzbot reported a corrupted list in kobject_add_internal [1]. This
> > happens when multiple HCI_EV_SYNC_CONN_COMPLETE event packets with
> > status 0 are sent for the same HCI connection. This causes us to
> > register the device more than once which corrupts the kset list.
>
> and that is actually forbidden by the spec. So we need to complain loudly that such a device is misbehaving.
>
> > To fix this, in hci_sync_conn_complete_evt, we check whether we're
> > trying to process the same HCI_EV_SYNC_CONN_COMPLETE event multiple
> > times for one connection. If that's the case, the event is invalid, so
> > we skip further processing and exit.
> >
> > Link: https://syzkaller.appspot.com/bug?extid=66264bf2fd0476be7e6c [1]
> > Reported-by: syzbot+66264bf2fd0476be7e6c@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Tested-by: syzbot+66264bf2fd0476be7e6c@xxxxxxxxxxxxxxxxxxxxxxxxx
> > Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx@xxxxxxxxx>
> > ---
> > net/bluetooth/hci_event.c | 2 ++
> > 1 file changed, 2 insertions(+)
> >
> > diff --git a/net/bluetooth/hci_event.c b/net/bluetooth/hci_event.c
> > index 016b2999f219..091a92338492 100644
> > --- a/net/bluetooth/hci_event.c
> > +++ b/net/bluetooth/hci_event.c
> > @@ -4373,6 +4373,8 @@ static void hci_sync_conn_complete_evt(struct hci_dev *hdev,
> >
> > 	switch (ev->status) {
> > 	case 0x00:
> > +		if (conn->state == BT_CONNECTED)
> > +			goto unlock;  /* Already connected, event not valid */
>
> The comment has go above and be a lot more details since this is not expected behavior from valid hardware and we should add a bt_dev_err as well.

Hi Marcel,

Apologies for the delayed response.

Thanks for the feedback, I'll add more elaboration for the new check and 
add a bt_dev_err in a v2 patch.

> > 		conn->handle = __le16_to_cpu(ev->handle);
> > 		conn->state  = BT_CONNECTED;
> > 		conn->type   = ev->link_type;
>
> Regards
>
> Marcel