netlabel: validate unlabeled address and mask attribute lengths

In the Linux kernel, the following vulnerability has been resolved:

netlabel: validate unlabeled address and mask attribute lengths

netlbl_unlabel_addrinfo_get() used the address attribute length to

determine whether the attribute data could be read as an IPv4 or IPv6

address, but did not independently validate the corresponding mask

attribute length. A crafted Generic Netlink request could therefore

provide a valid IPv4/IPv6 address attribute with a shorter mask

attribute, which would later be read as a full struct in_addr or

struct in6_addr.

NLA_BINARY policy lengths are maximum lengths by default, so use

NLA_POLICY_EXACT_LEN() for the unlabeled IPv4/IPv6 address and mask

attributes. This rejects short attributes during policy validation and

also exposes the exact length requirements through policy introspection.