cfg80211: check wiphy driver existence for drvinfo report

When preparing ethtool drvinfo, check if wiphy driver is defined
before dereferencing it. Driver may not exist, e.g. if wiphy is
attached to a virtual platform device.
Signed-off-by: Sergey Matyukevich <sergey.matyukevich.os@quantenna.com>
Link: https://lore.kernel.org/r/20200203105644.28875-1-sergey.matyukevich.os@quantenna.comSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/wireless/ethtool.c

@@ -7,9 +7,13 @@
 void cfg80211_get_drvinfo(struct net_device *dev, struct ethtool_drvinfo *info)
 {
 	struct wireless_dev *wdev = dev->ieee80211_ptr;
+	struct device *pdev = wiphy_dev(wdev->wiphy);
 
-	strlcpy(info->driver, wiphy_dev(wdev->wiphy)->driver->name,
-		sizeof(info->driver));
+	if (pdev->driver)
+		strlcpy(info->driver, pdev->driver->name,
+			sizeof(info->driver));
+	else
+		strlcpy(info->driver, "N/A", sizeof(info->driver));
 
 	strlcpy(info->version, init_utsname()->release, sizeof(info->version));