mac80211: upgrade passive scan to active scan on DFS channels after beacon rx

In client mode, we can't connect to hidden SSID APs or SSIDs not advertised
in beacons on DFS channels, since we're forced to passive scan. Fix this by
sending out a probe request immediately after the first beacon, if active
scan was requested by the user.

Cc: stable@vger.kernel.org
Reported-by: Catrinel Catrinescu <cc@80211.de>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
Link: https://lore.kernel.org/r/20220420104907.36275-1-nbd@nbd.nameSigned-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/ieee80211_i.h

@@ -1148,6 +1148,9 @@ struct tpt_led_trigger {
  *	a scan complete for an aborted scan.
  * @SCAN_HW_CANCELLED: Set for our scan work function when the scan is being
  *	cancelled.
+ * @SCAN_BEACON_WAIT: Set whenever we're passive scanning because of radar/no-IR
+ *	and could send a probe request after receiving a beacon.
+ * @SCAN_BEACON_DONE: Beacon received, we can now send a probe request
  */
 enum {
 	SCAN_SW_SCANNING,
@@ -1156,6 +1159,8 @@ enum {
 	SCAN_COMPLETED,
 	SCAN_ABORTED,
 	SCAN_HW_CANCELLED,
+	SCAN_BEACON_WAIT,
+	SCAN_BEACON_DONE,
 };
 
 /**

net/mac80211/scan.c

@@ -281,6 +281,16 @@ void ieee80211_scan_rx(struct ieee80211_local *local, struct sk_buff *skb)
 	if (likely(!sdata1 && !sdata2))
 		return;
 
+	if (test_and_clear_bit(SCAN_BEACON_WAIT, &local->scanning)) {
+		/*
+		 * we were passive scanning because of radar/no-IR, but
+		 * the beacon/proberesp rx gives us an opportunity to upgrade
+		 * to active scan
+		 */
+		 set_bit(SCAN_BEACON_DONE, &local->scanning);
+		 ieee80211_queue_delayed_work(&local->hw, &local->scan_work, 0);
+	}
+
 	if (ieee80211_is_probe_resp(mgmt->frame_control)) {
 		struct cfg80211_scan_request *scan_req;
 		struct cfg80211_sched_scan_request *sched_scan_req;
@@ -787,6 +797,8 @@ static int __ieee80211_start_scan(struct ieee80211_sub_if_data *sdata,
 						IEEE80211_CHAN_RADAR)) ||
 		    !req->n_ssids) {
 			next_delay = IEEE80211_PASSIVE_CHANNEL_TIME;
+			if (req->n_ssids)
+				set_bit(SCAN_BEACON_WAIT, &local->scanning);
 		} else {
 			ieee80211_scan_state_send_probe(local, &next_delay);
 			next_delay = IEEE80211_CHANNEL_TIME;
@@ -998,6 +1010,8 @@ static void ieee80211_scan_state_set_channel(struct ieee80211_local *local,
 	    !scan_req->n_ssids) {
 		*next_delay = IEEE80211_PASSIVE_CHANNEL_TIME;
 		local->next_scan_state = SCAN_DECISION;
+		if (scan_req->n_ssids)
+			set_bit(SCAN_BEACON_WAIT, &local->scanning);
 		return;
 	}
 
@@ -1090,6 +1104,8 @@ void ieee80211_scan_work(struct work_struct *work)
 			goto out;
 	}
 
+	clear_bit(SCAN_BEACON_WAIT, &local->scanning);
+
 	/*
 	 * as long as no delay is required advance immediately
 	 * without scheduling a new work
@@ -1100,6 +1116,10 @@ void ieee80211_scan_work(struct work_struct *work)
 			goto out_complete;
 		}
 
+		if (test_and_clear_bit(SCAN_BEACON_DONE, &local->scanning) &&
+		    local->next_scan_state == SCAN_DECISION)
+			local->next_scan_state = SCAN_SEND_PROBE;
+
 		switch (local->next_scan_state) {
 		case SCAN_DECISION:
 			/* if no more bands/channels left, complete scan */