Based on the provided code slice and the information about the vulnerability being among CWE-457  and occurring in lines 20-22, here are five possible patches to address the issue:

Patch 1:
```
20 		kfree(io_data->to_free);
21 	ffs_free_buffer(io_data);
22 	kfree(io_data);
23 	io_data = NULL;  // Set pointer to NULL after freeing
```

Patch 2:
```
20 		kfree(io_data->to_free);
21 	ffs_free_buffer(io_data);
22 	kfree(io_data);
23 	return;  // Immediately return after freeing to prevent further use
```

Patch 3:
```
20 		kfree(io_data->to_free);
21 	ffs_free_buffer(io_data);
22 	struct ffs_io_data *temp = io_data;
23 	io_data = NULL;  // Set original pointer to NULL
24 	kfree(temp);  // Free using temporary pointer
```

Patch 4:
```
20 		if (io_data->to_free) {
21 			kfree(io_data->to_free);
22 			io_data->to_free = NULL;  // Nullify after freeing
23 		}
24 	ffs_free_buffer(io_data);
25 	kfree(io_data);
```

Patch 5:
```
20 		kfree(io_data->to_free);
21 	ffs_free_buffer(io_data);
22 	kfree(io_data);
23 	// Add a memory barrier to ensure completion of free operations
24 	smp_mb();
```