The CWE-476 vulnerability at line 15 is caused by a null pointer dereference. However, in this specific code slice, the null pointer dereference is not directly visible. 

The root cause of the vulnerability lies in the fact that the `kmemdup` function at line 12 may return a null pointer if the memory allocation fails. If this happens, the `fw->img` pointer will be null.

Later, when the code tries to access `fw->len` (which is not the issue here) but potentially `fw->img` (not shown in this code slice), it will result in a null pointer dereference if `kmemdup` failed.

However, in this specific code slice, the issue is not directly visible because the code does not try to access `fw->img` after the `kmemdup` call. 

The correct analysis would be to check the code that follows this snippet to see if `fw->img` is accessed without checking if it's null. 

To fix this vulnerability, you should check the return value of `kmemdup` and handle the case where it returns null:

```c
fw->img = kmemdup(src, fw->len, GFP_KERNEL);
if (!fw->img) {
    // handle the error, e.g., return an error code or free other resources
}
```