net: ieee802154: forbid monitor for del llsec seclevel

This patch forbids to del llsec seclevel for monitor interfaces which we
don't support yet. Otherwise we will access llsec mib which isn't
initialized for monitors.

Reported-by: syzbot+fbf4fc11a819824e027b@syzkaller.appspotmail.com
Signed-off-by: NAlexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210405003054.256017-15-aahringo@redhat.comSigned-off-by: NStefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl802154.c

@@ -2133,6 +2133,9 @@ static int nl802154_del_llsec_seclevel(struct sk_buff *skb,
 	struct wpan_dev *wpan_dev = dev->ieee802154_ptr;
 	struct ieee802154_llsec_seclevel sl;
 
+	if (wpan_dev->iftype == NL802154_IFTYPE_MONITOR)
+		return -EOPNOTSUPP;
+
 	if (!info->attrs[NL802154_ATTR_SEC_LEVEL] ||
 	    llsec_parse_seclevel(info->attrs[NL802154_ATTR_SEC_LEVEL],
 				 &sl) < 0)