[PATCH V2] drivers: nfc: nfcmrvl: fix double free bug in nfcmrvl_nci_unregister_dev()

[Duoming Zhou]

There is a potential double bug in nfcmrvl usb driver between
unregister and resume operation.

The race that cause that double free bug can be shown as below:

   (FREE)                   |      (USE)
                            | nfcmrvl_resume
                            |  nfcmrvl_submit_bulk_urb
                            |   nfcmrvl_bulk_complete
                            |    nfcmrvl_nci_recv_frame
                            |     nfcmrvl_fw_dnld_recv_frame
                            |      queue_work
                            |       fw_dnld_rx_work
                            |        fw_dnld_over
                            |         release_firmware
                            |          kfree(fw); //(1)
nfcmrvl_disconnect          |
 nfcmrvl_nci_unregister_dev |
  nfcmrvl_fw_dnld_abort     |
   fw_dnld_over             |         ...
    if (priv->fw_dnld.fw)   |
    release_firmware        |
     kfree(fw); //(2)       |
     ...                    |         priv->fw_dnld.fw = NULL;

When nfcmrvl usb driver is resuming, we detach the device.
The release_firmware() will deallocate firmware in position (1),
but firmware will be deallocated again in position (2), which
leads to double free.

This patch reorders nfcmrvl_fw_dnld_deinit() before nfcmrvl_fw_dnld_abort()
in order to prevent double free bug. Because destroy_workqueue() will
not return until all work items are finished. The priv->fw_dnld.fw will
be set to NULL after work items are finished and fw_dnld_over() called by
nfcmrvl_nci_unregister_dev() will check whether priv->fw_dnld.fw is NULL.
So the double free bug could be prevented.

Signed-off-by: Duoming Zhou <duoming@xxxxxxxxxx>
---
Changes in V2:
  - Make commit message more clearer.

 drivers/nfc/nfcmrvl/main.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/nfc/nfcmrvl/main.c b/drivers/nfc/nfcmrvl/main.c
index 2fcf545012b..d8342271f50 100644
--- a/drivers/nfc/nfcmrvl/main.c
+++ b/drivers/nfc/nfcmrvl/main.c
@@ -183,11 +183,10 @@ void nfcmrvl_nci_unregister_dev(struct nfcmrvl_private *priv)
 {
 	struct nci_dev *ndev = priv->ndev;
 
+	nfcmrvl_fw_dnld_deinit(priv);
 	if (priv->ndev->nfc_dev->fw_download_in_progress)
 		nfcmrvl_fw_dnld_abort(priv);
 
-	nfcmrvl_fw_dnld_deinit(priv);
-
 	if (gpio_is_valid(priv->config.reset_n_io))
 		gpio_free(priv->config.reset_n_io);
 
-- 
2.17.1