selinux: fix overflow and 0 length allocations

Throughout the SELinux LSM, values taken from sepolicy are
used in places where length == 0 or length == <saturated>
matter, find and fix these.

Signed-off-by: William Roberts <william.c.roberts@intel.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

security/selinux/ss/conditional.c

@@ -242,6 +242,8 @@ int cond_read_bool(struct policydb *p, struct hashtab *h, void *fp)
 		goto err;
 
 	len = le32_to_cpu(buf[2]);
+	if (((len == 0) || (len == (u32)-1)))
+		goto err;
 
 	rc = -ENOMEM;
 	key = kmalloc(len + 1, GFP_KERNEL);