mac80211: disallow band-switch during CSA

If the AP advertises a band switch during CSA, we will not have
the right information to continue working with it, since it will
likely (have to) change its capabilities and we don't track any
capability changes at all. Additionally, we store e.g. supported
rates per band, and that information would become invalid.

Since this is a fringe scenario, just disconnect explicitly.
Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20201129172929.0e2327107c06.I461adb07704e056b054a4a7c29b80c95a9f56637@changeidSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/mlme.c

@@ -1417,6 +1417,17 @@ ieee80211_sta_process_chanswitch(struct ieee80211_sub_if_data *sdata,
 		return;
 	}
 
+	if (sdata->vif.bss_conf.chandef.chan->band !=
+	    csa_ie.chandef.chan->band) {
+		sdata_info(sdata,
+			   "AP %pM switches to different band (%d MHz, width:%d, CF1/2: %d/%d MHz), disconnecting\n",
+			   ifmgd->associated->bssid,
+			   csa_ie.chandef.chan->center_freq,
+			   csa_ie.chandef.width, csa_ie.chandef.center_freq1,
+			   csa_ie.chandef.center_freq2);
+		goto lock_and_drop_connection;
+	}
+
 	if (!cfg80211_chandef_usable(local->hw.wiphy, &csa_ie.chandef,
 				     IEEE80211_CHAN_DISABLED)) {
 		sdata_info(sdata,
@@ -1429,9 +1440,7 @@ ieee80211_sta_process_chanswitch(struct ieee80211_sub_if_data *sdata,
 			   csa_ie.chandef.width, csa_ie.chandef.center_freq1,
 			   csa_ie.chandef.freq1_offset,
 			   csa_ie.chandef.center_freq2);
-		ieee80211_queue_work(&local->hw,
-				     &ifmgd->csa_connection_drop_work);
-		return;
+		goto lock_and_drop_connection;
 	}
 
 	if (cfg80211_chandef_identical(&csa_ie.chandef,
@@ -1516,6 +1525,9 @@ ieee80211_sta_process_chanswitch(struct ieee80211_sub_if_data *sdata,
 			  TU_TO_EXP_TIME((csa_ie.count - 1) *
 					 cbss->beacon_interval));
 	return;
+ lock_and_drop_connection:
+	mutex_lock(&local->mtx);
+	mutex_lock(&local->chanctx_mtx);
  drop_connection:
 	/*
 	 * This is just so that the disconnect flow will know that