drivers: nfc: nfcmrvl: fix double free bug in nfc_fw_download_done()

There are potential double free bug in nfc_fw_download_done().
The timer handler fw_dnld_timeout() and work item fw_dnld_rx_work()
could both reach in fw_dnld_over() and nfc_fw_download_done() is not
protected by any lock, which leads to double free.

The race between fw_dnld_rx_work() and fw_dnld_timeout()
can be shown as below:

   (Thread 1)               |      (Thread 2)
fw_dnld_timeout             |  fw_dnld_rx_work
                            |   fw_dnld_over
 fw_dnld_over               |    nfc_fw_download_done
  nfc_fw_download_done      |     nfc_genl_fw_download_done
   nfc_genl_fw_download_done|      nlmsg_free(msg)  //(1)
    nlmsg_free(msg) //(2)   |      ...
     ...                    |

The nlmsg_free() will deallocate sk_buff in position (1), but
nlmsg_free will be deallocated again in position (2), which
leads to double free.

This patch adds spin_lock_irq() and check in fw_dnld_over()
in order to synchronize among different threads that call
fw_dnld_over(). So the double free bug could be prevented.

Fixes: 3194c68 ("NFC: nfcmrvl: add firmware download support")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Lin Ma <linma@zju.edu.cn>

drivers/nfc/nfcmrvl/fw_dnld.c

@@ -116,7 +116,10 @@ static void fw_dnld_over(struct nfcmrvl_private *priv, u32 error)
 		nfcmrvl_chip_halt(priv);
 	}
 
-	nfc_fw_download_done(priv->ndev->nfc_dev, priv->fw_dnld.name, error);
+	spin_lock_irq(&priv->fw_dnld.lock);
+	if (dev->fw_download_in_progress)
+		nfc_fw_download_done(priv->ndev->nfc_dev, priv->fw_dnld.name, error);
+	spin_unlock_irq(&priv->fw_dnld.lock);
 }
 
 static void fw_dnld_timeout(struct timer_list *t)