Step 1:  CWE-787 vulnerability is an "Out-of-bounds Write" vulnerability. 

The root cause of this vulnerability is that the `memcpy` function at line 12 does not perform any bounds checking on the destination buffer `r + i`. 

In this specific case, the loop starts at `i = 3` and doubles `i` in each iteration until `i` is no longer less than `size / 2`. However, the `memcpy` function is called with `i` as the size of the data to be copied, and the destination address is `r + i`. 

If `i` exceeds `size - i` (i.e., the remaining space in the buffer), the `memcpy` function will write beyond the end of the buffer, resulting in an out-of-bounds write. This can cause undefined behavior, including crashes, data corruption, or even code execution.

To fix this vulnerability, you should ensure that the destination buffer has enough space to hold the data being copied. You can do this by changing the loop condition to `i < size - i` to ensure that `i` never exceeds the remaining space in the buffer.

Here's the corrected code:

```c
static void
fillpattern (int type, unsigned char *r, size_t size)
{
    size_t i;
    for (i = 3; i < size - i; i *= 2)
        memcpy (r + i, r, i);
}
```

Alternatively, you can also use `memmove` instead of `memcpy` to handle overlapping source and destination buffers. However, in this specific case, using `memmove` would not fix the out-of-bounds write vulnerability.
Here are the five possible patches for the vulnerability:

**Patch A**
```
<   for (i = 3; i < size / 2; i *= 2)
---
>   for (i = 3; i < size - i; i *= 2)
```
This patch ensures that the destination buffer has enough space to hold the data being copied, preventing the out-of-bounds write vulnerability.

**Patch B**
```
<   memcpy (r + i, r, i);
---
>   if (i <= size - i) {
>       memcpy (r + i, r, i);
>   } else {
>       break;
>   }
```
This patch adds a conditional check to ensure that the destination buffer has enough space before calling `memcpy`. If the buffer is too small, it breaks out of the loop to prevent the out-of-bounds write.

**Patch C**
```
<   memcpy (r + i, r, i);
---
>   size_t remaining_space = size - i;
>   if (remaining_space >= i) {
>       memcpy (r + i, r, i);
>   } else {
>       memcpy (r + i, r, remaining_space);
>   }
```
This patch calculates the remaining space in the buffer and uses it to limit the amount of data copied by `memcpy`, preventing the out-of-bounds write.

**Patch D**
```
<   for (i = 3; i < size / 2; i *= 2)
---
>   for (i = 3; i < size; i *= 2) {
>       if (i > size - i) {
>           break;
>       }
>       memcpy (r + i, r, i);
>   }
```
This patch adds a conditional check inside the loop to ensure that the destination buffer has enough space before calling `memcpy`. If the buffer is too small, it breaks out of the loop to prevent the out-of-bounds write.

**Patch E**
```
<   memcpy (r + i, r, i);
---
>   if (i + i <= size) {
>       memcpy (r + i, r, i);
>   } else {
>       memcpy (r + i, r, size - i);
>   }
```
This patch adds a conditional check to ensure that the destination buffer has enough space before calling `memcpy`. If the buffer is too small, it limits the amount of data copied to prevent the out-of-bounds write.