In the Linux kernel, the following vulnerability has been resolved: fou: Don't allow 0 for FOUATTRIPPROTO. fouudprecv() has the same problem mentioned in the previous patch. If FOUATTRIPPROTO is set to 0, skb is not freed by fouudprecv() nor "resubmit"-ted in ipprotocoldeliverrcu(). Let's forbid 0 for FOUATTR_IPPROTO.