staging: wfx: fix potential vulnerability to spectre

array_index_nospec() should be applied after a bound check.

Fixes: 9bca45f3 ("staging: wfx: allow to send 802.11 frames")
Reported-by: kbuild test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20191011164746.2518-1-Jerome.Pouiller@silabs.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/wfx.h

@@ -13,6 +13,7 @@
 #include <linux/completion.h>
 #include <linux/workqueue.h>
 #include <linux/mutex.h>
+#include <linux/nospec.h>
 #include <net/mac80211.h>
 
 #include "bh.h"
@@ -138,6 +139,7 @@ static inline struct wfx_vif *wdev_to_wvif(struct wfx_dev *wdev, int vif_id)
 		dev_dbg(wdev->dev, "requesting non-existent vif: %d\n", vif_id);
 		return NULL;
 	}
+	vif_id = array_index_nospec(vif_id, ARRAY_SIZE(wdev->vif));
 	if (!wdev->vif[vif_id]) {
 		dev_dbg(wdev->dev, "requesting non-allocated vif: %d\n", vif_id);
 		return NULL;