Step 1:  this code slice, there isn't enough information to determine a CWE-787 (Out-of-bounds Write) vulnerability directly. The line you've indicated:

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

is simply a variable declaration. It doesn't perform any operations that could lead to an out-of-bounds write. To have a CWE-787 vulnerability, we would need to see how these variables are used, particularly in writing to memory.

Without more context or code showing how `start` and `len` are used, it's not possible to reason about a potential out-of-bounds write vulnerability. The vulnerability would typically occur when these variables are used to access or modify memory locations beyond the intended bounds of an array or buffer.

If you have additional code that shows how these variables are used, particularly in memory operations, I'd be happy to analyze that for potential vulnerabilities.
You're correct that the given code slice doesn't provide enough context to definitively identify a CWE-787 vulnerability. The line you pointed out is just a variable declaration and doesn't perform any operations that could directly lead to an out-of-bounds write.

However, since the question asks for possible patches, we can propose some general improvements that could help prevent potential CWE-787 vulnerabilities if these variables are used later in the function. Here are five possible patches:

1. Add input validation:
```
<     uint64_t start, len;
---
>     uint64_t start, len;
>     if (start + len < start || start + len > bdev->bd_inode->i_size)
>         return -EINVAL;
```

2. Use size_t for len to ensure non-negative values:
```
<     uint64_t start, len;
---
>     uint64_t start;
>     size_t len;
```

3. Add upper bounds check:
```
<     uint64_t start, len;
---
>     uint64_t start, len;
>     if (len > MAX_DISCARD_LEN)
>         return -EINVAL;
```

4. Initialize variables to safe values:
```
<     uint64_t start, len;
---
>     uint64_t start = 0, len = 0;
```

5. Use a structure to encapsulate the parameters:
```
<     uint64_t start, len;
---
>     struct discard_range {
>         uint64_t start;
>         uint64_t len;
>     } range = {0};
```

These patches aim to improve the robustness of the code and prevent potential misuse of the variables that could lead to out-of-bounds writes. However, the effectiveness of these patches would depend on how these variables are used in the rest of the function, which is not shown in the provided code slice.