To generate the patch for the given code slice with a CWE-787 vulnerability, we can follow these reasoning steps:

### Step 1: Root Cause Analysis

- 1: Validate `cc->tfms_count`:
  - `cc->tfms_count` is used to allocate memory for `cc->tfms`.
  - If `cc->tfms_count` is not properly validated, it could lead to an out-of-bounds write when accessing the allocated memory.

- 2: Memory Allocation:
  - The code uses `kmalloc` to allocate memory for `cc->tfms`.
  - `kmalloc` does not initialize the allocated memory, which means it may contain arbitrary values.

- 3: Potential Vulnerability:
  - The vulnerability arises if `cc->tfms_count` is not properly validated and the allocated memory is not initialized.
  - This can lead to a buffer overflow or out-of-bounds write when accessing the allocated memory.

### Conclusion:
The vulnerable behavior in this code is a potential buffer overflow or out-of-bounds write. It occurs because the allocated memory is not initialized, and `cc->tfms_count` is not properly validated. To fix this vulnerability, we need to ensure that the allocated memory is initialized and `cc->tfms_count` is properly validated.

### Step 2: Fixing Strategy

- A common fixing strategy is to use `kzalloc` instead of `kmalloc` to allocate memory. `kzalloc` initializes the allocated memory to zero, which prevents potential buffer overflow or out-of-bounds write vulnerabilities.
- By using `kzalloc`, we can ensure that the allocated memory is initialized, which reduces the risk of buffer overflow or out-of-bounds write vulnerabilities.

### Patch:
```
<     cc->tfms = kmalloc(cc->tfms_count * sizeof(crypto_skcipher *), GFP_KERNEL);
---
>     cc->tfms = kzalloc(cc->tfms_count * sizeof(crypto_skcipher *), GFP_KERNEL);
```
Note that this patch assumes that the allocated memory should be initialized to zero. If the allocated memory needs to be initialized with a different value, a different approach may be necessary.