mac80211_hwsim: require at least one channel

Syzbot continues to try to create mac80211_hwsim radios, and
manages to pass parameters that are later checked with WARN_ON
in cfg80211 - catch another one in hwsim directly.

Reported-by: syzbot+2a12f11c306afe871c1f@syzkaller.appspotmail.com
Signed-off-by: Johannes Berg <johannes.berg@intel.com>

drivers/net/wireless/mac80211_hwsim.c

@@ -3194,6 +3194,11 @@ static int hwsim_new_radio_nl(struct sk_buff *msg, struct genl_info *info)
 	if (info->attrs[HWSIM_ATTR_CHANNELS])
 		param.channels = nla_get_u32(info->attrs[HWSIM_ATTR_CHANNELS]);
 
+	if (param.channels < 1) {
+		GENL_SET_ERR_MSG(info, "must have at least one channel");
+		return -EINVAL;
+	}
+
 	if (param.channels > CFG80211_MAX_NUM_DIFFERENT_CHANNELS) {
 		GENL_SET_ERR_MSG(info, "too many channels specified");
 		return -EINVAL;