Q: Given the following code slice:
```
1 static int __key_instantiate_and_link(struct key *key,
2 				      struct key_preparsed_payload *prep,
7 	int ret, awaken;
13 	ret = -EBUSY;
18 	if (key->state == KEY_IS_UNINSTANTIATED) {
20 		ret = key->type->instantiate(key, prep);
22 		if (ret == 0) {
43 			key_set_expiry(key, prep->expiry);```
which has a CWE-190 vulnerability at line:
```
43 			key_set_expiry(key, prep->expiry);
```
Please analyze the root cause of the vulnerability.