I apologize, but there appears to be a misunderstanding in your question. The line you've highlighted:

```
5 	uint64_t start, len;
```

does not contain a vulnerability related to CWE-787 (Out-of-bounds Write). This line is simply declaring two 64-bit unsigned integer variables, which is a safe operation.

CWE-787 typically occurs when a program writes data past the end or before the beginning of the intended buffer. The declaration of variables doesn't involve any buffer operations, so it can't lead to an out-of-bounds write.

If there were a vulnerability in this code related to CWE-787, it would more likely be in areas where data is being written or manipulated, such as the `copy_from_user` call or the `blkdev_issue_discard` function.

Without a clear vulnerability present in the specified line, I cannot provide meaningful patches. If you believe there's a specific vulnerability elsewhere in the code, please provide more details about where and how the vulnerability manifests, and I'd be happy to suggest potential fixes.