Bluetooth: Fix race condition in handling NOP command

For NOP command, need to cancel work scheduled on cmd_timer,
on receiving command status or commmand complete event.

Below use case might lead to race condition multiple when NOP
commands are queued sequentially:

hci_cmd_work() {
   if (atomic_read(&hdev->cmd_cnt) {
            .
            .
            .
      atomic_dec(&hdev->cmd_cnt);
      hci_send_frame(hdev,...);
      schedule_delayed_work(&hdev->cmd_timer,...);
   }
}

On receiving event for first NOP, the work scheduled on hdev->cmd_timer
is not cancelled and second NOP is dequeued and sent to controller.

While waiting for an event for second NOP command, work scheduled on
cmd_timer for the first NOP can get scheduled, resulting in sending third
NOP command (sending back to back NOP commands). This might
cause issues at controller side (like memory overrun, controller going
unresponsive) resulting in hci tx timeouts, hardware errors etc.

The fix to this issue is to cancel the delayed work scheduled on
cmd_timer on receiving command status or command complete event for
NOP command (this patch handles NOP command same as any other SIG
command).

Signed-off-by: Kiran K <kiran.k@intel.com>
Reviewed-by: Chethan T N <chethan.tumkur.narayan@intel.com>
Reviewed-by: Srivatsa Ravishankar <ravishankar.srivatsa@intel.com>
Acked-by: Manish Mandlik <mmandlik@google.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>

net/bluetooth/hci_event.c

@@ -3311,11 +3311,9 @@ static void hci_remote_features_evt(struct hci_dev *hdev,
 	hci_dev_unlock(hdev);
 }
 
-static inline void handle_cmd_cnt_and_timer(struct hci_dev *hdev,
-					    u16 opcode, u8 ncmd)
+static inline void handle_cmd_cnt_and_timer(struct hci_dev *hdev, u8 ncmd)
 {
-	if (opcode != HCI_OP_NOP)
-		cancel_delayed_work(&hdev->cmd_timer);
+	cancel_delayed_work(&hdev->cmd_timer);
 
 	if (!test_bit(HCI_RESET, &hdev->flags)) {
 		if (ncmd) {
@@ -3690,7 +3688,7 @@ static void hci_cmd_complete_evt(struct hci_dev *hdev, struct sk_buff *skb,
 		break;
 	}
 
-	handle_cmd_cnt_and_timer(hdev, *opcode, ev->ncmd);
+	handle_cmd_cnt_and_timer(hdev, ev->ncmd);
 
 	hci_req_cmd_complete(hdev, *opcode, *status, req_complete,
 			     req_complete_skb);
@@ -3791,7 +3789,7 @@ static void hci_cmd_status_evt(struct hci_dev *hdev, struct sk_buff *skb,
 		break;
 	}
 
-	handle_cmd_cnt_and_timer(hdev, *opcode, ev->ncmd);
+	handle_cmd_cnt_and_timer(hdev, ev->ncmd);
 
 	/* Indicate request completion if the command failed. Also, if
 	 * we're not waiting for a special event and we get a success