A new vulnerability has been discovered and resolved in the Linux kernel, specifically in the 'crypto: bcm' implementation of the ahash_hmac_init function. This article will delve into the details of this vulnerability, the code involved, and the steps taken to address the issue. We will also provide links to the original references for further study.

Background

The ahash_hmac_init function's primary role in a Linux system is to provide cryptographic services, particularly in the context of hashing and message authentication. The function relies on a series of ahash_init functions, which are responsible for initializing the various cryptographic settings. However, the vulnerability lies in the possibility of the ahash_init functions failing to initialize correctly, which could lead to potential security issues if the ahash_hmac_init function continues to execute with failed settings.

CVE-2024-56681 Description and Exploit Details

The issue is caused by the absence of an error check in the ahash_hmac_init function. When ahash_init functions return an error, such as in cases of memory allocation failure, the ahash_hmac_init function continues processing as if nothing is wrong. This lack of error checking could potentially leave the system exposed to attacks that exploit this vulnerability.

Here's a code snippet of the problematic function without the fix in place

static int ahash_hmac_init(struct ahash_request *req)
{
    struct crypto_ahash *tfm = crypto_ahash_reqtfm(req);
    struct shash_desc *desc = ahash_request_ctx(req);
    desc->tfm = crypto_ahash_ctx(tfm);

    return ahash_init(req);
}

In the snippet above, you can see that the function does not properly handle the return value of ahash_init(req). If this value indicates an error, the function should also return an error code. The patched version of this code includes an error check:

static int ahash_hmac_init(struct ahash_request *req)
{
    int ret;
    struct crypto_ahash *tfm = crypto_ahash_reqtfm(req);
    struct shash_desc *desc = ahash_request_ctx(req);
    desc->tfm = crypto_ahash_ctx(tfm);

    ret = ahash_init(req);
    if (ret)
        return ret;

    return ;
}

In the corrected version, a return value ret is used to store the result of ahash_init(req). If ret is non-zero, it indicates that an error occurred, and the function returns this error code. This ensures that the ahash_hmac_init function does not continue processing with failed settings, therefore eliminating the vulnerability.

Original References

The original reference to this vulnerability can be found in the Linux kernel source code repository and mailing list:

- Linux Kernel Source Code: commit e8a712
- Linux Kernel Mailing List: patch submission

Conclusion

The discovery and resolution of vulnerabilities like CVE-2024-56681 are an ongoing process in the world of software development. By understanding and addressing these issues, we can continually improve the security and reliability of the systems we rely on every day. As always, it's essential to stay up to date with the latest patches and fixes, as well as to remain vigilant in the ongoing battle against potential cyber threats.

Timeline

Published on: 12/28/2024 10:15:09 UTC
Last modified on: 01/20/2025 06:25:49 UTC