### Reasoning Steps for Generating the Patch

#### Step 1: Root Cause Analysis

1. **Understanding the Code Context:**
   - The function `ethtool_get_rxfh_indir` is responsible for handling some operations related to the `ethtool` interface in a network device driver.
   - The function uses `kmalloc` to allocate memory for a structure `ethtool_rxfh_indir`.

2. **Identifying the Vulnerability:**
   - The vulnerability is identified at line 20 where `kmalloc` is used to allocate memory.
   - `kmalloc` allocates memory but does not initialize it. This means the allocated memory may contain residual data from previous allocations.

3. **Potential Issue:**
   - If the uninitialized memory is used before being explicitly initialized by the program, it can lead to undefined behavior.
   - This can result in out-of-bounds access if the uninitialized memory contains unexpected values that are used as indices or pointers.

4. **Specific CWE-787 (Out-of-bounds Write) Context:**
   - Out-of-bounds write occurs when the program writes data outside the bounds of allocated memory.
   - In this context, if the `indir` structure or its members are accessed or written to before proper initialization, it could lead to writing outside the intended memory bounds.

#### Step 2: Fixing Strategy

1. **Ensuring Memory Initialization:**
   - To prevent the use of uninitialized memory, the allocated memory should be zero-initialized.
   - This ensures that all members of the allocated structure are set to zero, preventing any undefined behavior due to residual data.

2. **Using `kzalloc` Instead of `kmalloc`:**
   - `kzalloc` is a kernel function that allocates memory and initializes it to zero.
   - By replacing `kmalloc` with `kzalloc`, we ensure that the allocated memory is zero-initialized, mitigating the risk of out-of-bounds writes due to uninitialized memory.

3. **Patch Implementation:**
   - The patch replaces the `kmalloc` call with `kzalloc` to ensure that the allocated memory is zero-initialized.

### Conclusion

The patch ensures that the allocated memory for the `indir` structure is zero-initialized, preventing any potential out-of-bounds writes due to uninitialized memory. The specific change is:

```diff
<     indir = kmalloc(full_size, GFP_USER);
---
>     indir = kzalloc(full_size, GFP_USER);
```

This change mitigates the risk of CWE-787 (Out-of-bounds Write) by ensuring that all allocated memory is initialized to zero, thus preventing any unintended behavior from residual data.