static inline int proto_to_npindex(int proto)
{
	switch (proto) {
	case PPP_IP:
		return NP_IP;
	case PPP_IPV6:
		return NP_IPV6;
	case PPP_IPX:
		return NP_IPX;
	case PPP_AT:
		return NP_AT;
	case PPP_MPLS_UC:
		return NP_MPLS_UC;
	case PPP_MPLS_MC:
		return NP_MPLS_MC;
	}
	return -EINVAL;
}

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory belongs to the code that operates on the new pointer.