cfg80211: fix scan crash on single-band cards

commit 58389c69150e6032504dfcd3edca6b1975c8b5bc
Author: Johannes Berg <johannes.berg@intel.com>
Date:   Mon Jul 18 18:08:35 2011 +0200

     cfg80211: allow userspace to control supported rates in scan

made single-band cards crash since it would always
access all wiphy->bands[]. Fix this and reject any
attempts in the new helper ieee80211_get_ratemask()
to do the same, rejecting rates configuration for
unsupported bands.
Reported-by: Pavel Roskin <proski@gnu.org>
Tested-by: Pavel Roskin <proski@gnu.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

net/wireless/nl80211.c

@@ -3454,7 +3454,9 @@ static int nl80211_trigger_scan(struct sk_buff *skb, struct genl_info *info)
 	}
 
 	for (i = 0; i < IEEE80211_NUM_BANDS; i++)
-		request->rates[i] = (1 << wiphy->bands[i]->n_bitrates) - 1;
+		if (wiphy->bands[i])
+			request->rates[i] =
+				(1 << wiphy->bands[i]->n_bitrates) - 1;
 
 	if (info->attrs[NL80211_ATTR_SCAN_SUPP_RATES]) {
 		nla_for_each_nested(attr,

net/wireless/scan.c

@@ -863,6 +863,7 @@ int cfg80211_wext_siwscan(struct net_device *dev,
 	}
 
 	for (i = 0; i < IEEE80211_NUM_BANDS; i++)
+		if (wiphy->bands[i])
 			creq->rates[i] = (1 << wiphy->bands[i]->n_bitrates) - 1;
 
 	rdev->scan_req = creq;

net/wireless/util.c

@@ -1013,6 +1013,9 @@ int ieee80211_get_ratemask(struct ieee80211_supported_band *sband,
 {
 	int i, j;
 
+	if (!sband)
+		return -EINVAL;
+
 	if (n_rates == 0 || n_rates > NL80211_MAX_SUPP_RATES)
 		return -EINVAL;