To generate the patch for the CWE-476 vulnerability, we can follow these reasoning steps:

### Step 1: Root Cause Analysis

- 1: Validate `src`:
  - The `src` pointer is used as the source of the `memcpy` operation.
  - If `src` is `NULL`, the `memcpy` operation will attempt to access memory at address 0, leading to undefined behavior.

- 2: Potential Vulnerability:
  - The vulnerability arises if `src` is `NULL`, which results in a null pointer dereference.
  - This is a classic example of a null pointer dereference vulnerability. Accessing memory through a null pointer can lead to crashes or exploitable conditions.

- 3: CWE-476:
  - CWE-476 is a null pointer dereference vulnerability.
  - In this case, the `memcpy` operation will attempt to access memory at address 0 if `src` is `NULL`, leading to a null pointer dereference.

### Conclusion:
The vulnerable behavior in this code is a null pointer dereference. It occurs because the code does not check if `src` is `NULL` before attempting to access memory through it. If `src` is `NULL`, the `memcpy` operation will lead to undefined behavior. Proper null pointer checking should be added to ensure `src` is not `NULL` before accessing memory through it.

### Step 2: Fixing Strategy

- A common fixing strategy is to add a null pointer check before accessing memory through the `src` pointer.
- This can be done by adding a condition to check if `src` is not `NULL` before performing the `memcpy` operation.

Therefore, the patch should be:
```
< 	if(dest != src) {
---
> 	if(dest != src && src != NULL) {
```
This patch adds a null pointer check to ensure that `src` is not `NULL` before attempting to access memory through it, preventing the null pointer dereference vulnerability.