lsm: use unrcu_pointer() for current->cred in security_init()

We need to directly allocate the cred's LSM state for the initial task
when we initialize the LSM framework.  Unfortunately, this results in a
RCU related type mismatch, use the unrcu_pointer() macro to handle this
a bit more elegantly.

The explicit type casting still remains as we need to work around the
constification of current->cred in this particular case.

Reviewed-by: Xiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: pcmoore

security/lsm_init.c

@@ -467,7 +467,8 @@ int __init security_init(void)
 						    blob_sizes.lbs_inode, 0,
 						    SLAB_PANIC, NULL);
 
-	if (lsm_cred_alloc((struct cred __rcu *)current->cred, GFP_KERNEL))
+	if (lsm_cred_alloc((struct cred *)unrcu_pointer(current->cred),
+			   GFP_KERNEL))
 		panic("early LSM cred alloc failed\n");
 	if (lsm_task_alloc(current))
 		panic("early LSM task alloc failed\n");