mac80211: connect with HT20 if HT40 is not permitted

Some changes to fix issues with HT40 APs in Korea
and follow-up changes to allow using HT40 even if
the local regulatory database disallows it caused
issues with iwlwifi (and could cause issues with
other devices); iwlwifi firmware would assert if
you tried to connect to an AP that has an invalid
configuration (e.g. using HT40- on channel 140.)

Fix this, while avoiding the "Korean AP" issue by
disabling HT40 and advertising HT20 to the AP
when connecting.

Cc: stable@vger.kernel.org [3.6]
Reported-by: Florian Reitmeir <florian@reitmeir.org>
Tested-by: Florian Reitmeir <florian@reitmeir.org>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -3099,24 +3099,34 @@ static int ieee80211_prep_channel(struct ieee80211_sub_if_data *sdata,
 				   ht_cfreq, ht_oper->primary_chan,
 				   cbss->channel->band);
 			ht_oper = NULL;
+		} else {
+			channel_type = NL80211_CHAN_HT20;
 		}
 	}
 
-	if (ht_oper) {
-		channel_type = NL80211_CHAN_HT20;
+	if (ht_oper && sband->ht_cap.cap & IEEE80211_HT_CAP_SUP_WIDTH_20_40) {
+		/*
+		 * cfg80211 already verified that the channel itself can
+		 * be used, but it didn't check that we can do the right
+		 * HT type, so do that here as well. If HT40 isn't allowed
+		 * on this channel, disable 40 MHz operation.
+		 */
 
-		if (sband->ht_cap.cap & IEEE80211_HT_CAP_SUP_WIDTH_20_40) {
-			switch (ht_oper->ht_param &
-					IEEE80211_HT_PARAM_CHA_SEC_OFFSET) {
+		switch (ht_oper->ht_param & IEEE80211_HT_PARAM_CHA_SEC_OFFSET) {
 		case IEEE80211_HT_PARAM_CHA_SEC_ABOVE:
+			if (cbss->channel->flags & IEEE80211_CHAN_NO_HT40PLUS)
+				ifmgd->flags |= IEEE80211_STA_DISABLE_40MHZ;
+			else
 				channel_type = NL80211_CHAN_HT40PLUS;
 			break;
 		case IEEE80211_HT_PARAM_CHA_SEC_BELOW:
+			if (cbss->channel->flags & IEEE80211_CHAN_NO_HT40MINUS)
+				ifmgd->flags |= IEEE80211_STA_DISABLE_40MHZ;
+			else
 				channel_type = NL80211_CHAN_HT40MINUS;
 			break;
 		}
 	}
-	}
 
 	if (!ieee80211_set_channel_type(local, sdata, channel_type)) {
 		/* can only fail due to HT40+/- mismatch */