staging: wfx: check ssidlen and prevent an array overflow

We need to cap "ssidlen" to prevent a memcpy() overflow.

Fixes: 40115bbc ("staging: wfx: implement the rest of mac80211 API")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Jérôme Pouiller <jerome.pouiller@silabs.com>
Link: https://lore.kernel.org/r/20200424104235.GA416402@mwandaSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/wfx/sta.c

@@ -351,7 +351,9 @@ static void wfx_do_join(struct wfx_vif *wvif)
 		ssidie = ieee80211_bss_get_ie(bss, WLAN_EID_SSID);
 	if (ssidie) {
 		ssidlen = ssidie[1];
-		memcpy(ssid, &ssidie[2], ssidie[1]);
+		if (ssidlen > IEEE80211_MAX_SSID_LEN)
+			ssidlen = IEEE80211_MAX_SSID_LEN;
+		memcpy(ssid, &ssidie[2], ssidlen);
 	}
 	rcu_read_unlock();