Q: Given the following code slice:
```
1 static void copy_or_link_directory(struct strbuf *src, struct strbuf *dest,
7 	struct strbuf realpath = STRBUF_INIT;```
which has a CWE-787 vulnerability at line:
```
7 	struct strbuf realpath = STRBUF_INIT;
```
Please analyze the root cause of the vulnerability.