Step 1: The given code has a buffer overflow vulnerability in line 6 because it uses `nXDst` and `nYDst` to access elements of `pDstData`. If either of these values are large enough, they can cause the pointer arithmetic to overflow, leading to a buffer overflow.

For example, if `nXDst = INT_MAX` and `nYDst = 10`, then `&pDstData[nXDst * dstBytesPerPixel + nYDst * nDstStep]` will be calculated as:
```c
&pDstData[(INT_MAX * dstBytesPerPixel) + (10 * nDstStep)] = &pDstData[INT_MAX * 4 + 10]
```
This is a buffer overflow because `INT_MAX * 4` is a large value that exceeds the maximum capacity of an array.

The vulnerable behavior can be fixed by using safe pointer arithmetic techniques, such as checking whether the calculated index is within bounds before accessing the element at that index.

A: The patch can be done in two steps.
Step 1. The given code has a buffer overflow vulnerability in line 6 because it uses `nXDst` and `nYDst` to access elements of `pDstData`. If either of these values are large enough, they can cause the pointer arithmetic to overflow, leading to a buffer overflow.

For example, if `nXDst = INT_MAX` and `nYDst = 10`, then `&pDstData[nXDst * dstBytesPerPixel + nYDst * nDstStep]` will be calculated as:
```c
&pDstData[(INT_MAX * dstBytesPerPixel) + (10 * nDstStep)] = &pDstData[INT_MAX * 4 + 10]
```
This is a buffer overflow because `INT_MAX * 4` is a large value that exceeds the maximum capacity of an array.

The vulnerable behavior can be fixed by using safe pointer arithmetic techniques, such as checking whether the calculated index is within bounds before accessing the element at that index.

Step 2: The function `overlapping` also has the same buffer overflow vulnerability, which can be fixed in a similar way by checking the calculated indices against the upper bound of the arrays.