net: ieee802154: nl-mac: fix check on panid

This patch fixes a null pointer derefence for panid handle by move the
check for the netlink variable directly before accessing them.

Reported-by: syzbot+d4c07de0144f6f63be3a@syzkaller.appspotmail.com
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210228151817.95700-4-aahringo@redhat.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>

net/ieee802154/nl-mac.c

@@ -551,9 +551,7 @@ ieee802154_llsec_parse_key_id(struct genl_info *info,
 	desc->mode = nla_get_u8(info->attrs[IEEE802154_ATTR_LLSEC_KEY_MODE]);
 
 	if (desc->mode == IEEE802154_SCF_KEY_IMPLICIT) {
-		if (!info->attrs[IEEE802154_ATTR_PAN_ID] &&
-		    !(info->attrs[IEEE802154_ATTR_SHORT_ADDR] ||
-		      info->attrs[IEEE802154_ATTR_HW_ADDR]))
+		if (!info->attrs[IEEE802154_ATTR_PAN_ID])
 			return -EINVAL;
 
 		desc->device_addr.pan_id = nla_get_shortaddr(info->attrs[IEEE802154_ATTR_PAN_ID]);
@@ -562,6 +560,9 @@ ieee802154_llsec_parse_key_id(struct genl_info *info,
 			desc->device_addr.mode = IEEE802154_ADDR_SHORT;
 			desc->device_addr.short_addr = nla_get_shortaddr(info->attrs[IEEE802154_ATTR_SHORT_ADDR]);
 		} else {
+			if (!info->attrs[IEEE802154_ATTR_HW_ADDR])
+				return -EINVAL;
+
 			desc->device_addr.mode = IEEE802154_ADDR_LONG;
 			desc->device_addr.extended_addr = nla_get_hwaddr(info->attrs[IEEE802154_ATTR_HW_ADDR]);
 		}