net: ieee802154: fix nl802154 add llsec key

commit 20d5fe2 upstream.

This patch fixes a nullpointer dereference if NL802154_ATTR_SEC_KEY is
not set by the user. If this is the case nl802154 will return -EINVAL.

Reported-by: syzbot+ce4e062c2d51977ddc50@syzkaller.appspotmail.com
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Link: https://lore.kernel.org/r/20210221174321.14210-3-aahringo@redhat.com
Signed-off-by: Stefan Schmidt <stefan@datenfreihafen.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

net/ieee802154/nl802154.c

@@ -1527,7 +1527,8 @@ static int nl802154_add_llsec_key(struct sk_buff *skb, struct genl_info *info)
 	struct ieee802154_llsec_key_id id = { };
 	u32 commands[NL802154_CMD_FRAME_NR_IDS / 32] = { };
 
-	if (nla_parse_nested(attrs, NL802154_KEY_ATTR_MAX,
+	if (!info->attrs[NL802154_ATTR_SEC_KEY] ||
+	    nla_parse_nested(attrs, NL802154_KEY_ATTR_MAX,
 			     info->attrs[NL802154_ATTR_SEC_KEY],
 			     nl802154_key_policy))
 		return -EINVAL;