selinux: reject a class permission count below its inherited common

In the Linux kernel, the following vulnerability has been resolved: selinux: reject a class permission count below its inherited common security_get_permissions() maps an inherited common's permissions into an array sized by the class's own permissions.nprim, but class_read() takes that nprim verbatim from the policy image and never checks that it covers the common. A class that inherits a common of N permissions while declaring a smaller nprim is accepted, and on load the common's permissions are written past the class-sized array -- an out-of-bounds heap write. Reject a class whose permission count is below its inherited common's. Well-formed policies, where the class count already includes the inherited permissions, are unaffected.