mac80211_hwsim: calculate if_combination.max_interfaces

If we just set this to 2048, and have multiple limits you
can select from, the total number might run over and cause
a warning in cfg80211. This doesn't make sense, so we just
calculate the total max_interfaces now.

Reported-by: syzbot+8f91bd563bbff230d0ee@syzkaller.appspotmail.com
Fixes: 99e3a44b ("mac80211_hwsim: allow setting iftype support")
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -2644,7 +2644,7 @@ static int mac80211_hwsim_new_radio(struct genl_info *info,
 	enum nl80211_band band;
 	const struct ieee80211_ops *ops = &mac80211_hwsim_ops;
 	struct net *net;
-	int idx;
+	int idx, i;
 	int n_limits = 0;
 
 	if (WARN_ON(param->channels > 1 && !param->use_chanctx))
@@ -2768,12 +2768,23 @@ static int mac80211_hwsim_new_radio(struct genl_info *info,
 		goto failed_hw;
 	}
 
+	data->if_combination.max_interfaces = 0;
+	for (i = 0; i < n_limits; i++)
+		data->if_combination.max_interfaces +=
+			data->if_limits[i].max;
+
 	data->if_combination.n_limits = n_limits;
-	data->if_combination.max_interfaces = 2048;
 	data->if_combination.limits = data->if_limits;
 
+	/*
+	 * If we actually were asked to support combinations,
+	 * advertise them - if there's only a single thing like
+	 * only IBSS then don't advertise it as combinations.
+	 */
+	if (data->if_combination.max_interfaces > 1) {
 		hw->wiphy->iface_combinations = &data->if_combination;
 		hw->wiphy->n_iface_combinations = 1;
+	}
 
 	if (param->ciphers) {
 		memcpy(data->ciphers, param->ciphers,