mac80211: validate new interface's beacon intervals

As part of interface combination checking, verify any new
interface's beacon intervals. In fact, just always add the
beacon interval since that's harmless.

With this patch, mac80211 is prepared for drivers that set
the min_beacon_int_gcd parameter in interface combinations.
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

net/mac80211/cfg.c

@@ -864,6 +864,8 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 	}
 	sdata->needed_rx_chains = sdata->local->rx_chains;
 
+	sdata->vif.bss_conf.beacon_int = params->beacon_interval;
+
 	mutex_lock(&local->mtx);
 	err = ieee80211_vif_use_channel(sdata, &params->chandef,
 					IEEE80211_CHANCTX_SHARED);
@@ -894,7 +896,6 @@ static int ieee80211_start_ap(struct wiphy *wiphy, struct net_device *dev,
 					      vlan->vif.type);
 	}
 
-	sdata->vif.bss_conf.beacon_int = params->beacon_interval;
 	sdata->vif.bss_conf.dtim_period = params->dtim_period;
 	sdata->vif.bss_conf.enable_beacon = true;
 	sdata->vif.bss_conf.allow_p2p_go_ps = sdata->vif.p2p;

net/mac80211/util.c

@@ -3326,6 +3326,16 @@ int ieee80211_check_combinations(struct ieee80211_sub_if_data *sdata,
 	if (WARN_ON(iftype >= NUM_NL80211_IFTYPES))
 		return -EINVAL;
 
+	if (sdata->vif.type == NL80211_IFTYPE_AP ||
+	    sdata->vif.type == NL80211_IFTYPE_MESH_POINT) {
+		/*
+		 * always passing this is harmless, since it'll be the
+		 * same value that cfg80211 finds if it finds the same
+		 * interface ... and that's always allowed
+		 */
+		params.new_beacon_int = sdata->vif.bss_conf.beacon_int;
+	}
+
 	/* Always allow software iftypes */
 	if (local->hw.wiphy->software_iftypes & BIT(iftype)) {
 		if (radar_detect)