CVE-2021-47218

In the Linux kernel, the following vulnerability has been resolved:
selinux: fix NULL-pointer dereference when hashtab allocation fails When
the hash table slot array allocation fails in hashtab_init(), h->size is
left initialized with a non-zero value, but the h->htable pointer is NULL.
This may then cause a NULL pointer dereference, since the policydb code
relies on the assumption that even after a failed hashtab_init(),
hashtab_map() and hashtab_destroy() can be safely called on it. Yet, these
detect an empty hashtab only by looking at the size. Fix this by making
sure that hashtab_init() always leaves behind a valid empty hashtab when
the allocation fails.