Security vulnerabilities can have serious consequences on your system, leading to potential data leaks or unauthorized access. This is a follow-up to a recently identified and resolved vulnerability within the Linux kernel. Specifically, the issue revolves around the jff2 filesystem and rtime decompression, which potentially corrupts memory and compromises system integrity.

This post discusses the details of the resolved vulnerability, and includes code snippets, original references, and exploit details. We'll also delve into the underlying problem and walk through the steps taken to resolve the vulnerability.

Exploit Details

The vulnerability in question is known as CVE-2024-57850, and it affects the jffs2 filesystem in the Linux kernel. Jffs2 is commonly used on flash memory devices, often found in embedded systems or routers and is a popular read-write filesystem for NAND and NOR flash memory.

The issue lies in the rtime decompression routine as it lacks proper bounds checks throughout the decompression process. This lack of proper bounds checking allows memory outside of the decompression buffer to be potentially corrupted if the compressed data is compromised. As a result, this poses a dangerous security vulnerability affecting system integrity and leaves it vulnerable to cyber attacks.

Thankfully, a recent update fixed the vulnerability by adding the required checks to prevent this failure mode.

Understanding the Code

To help illustrate the issue, here is a snippet of the original, vulnerable code in the decompress.c file:

while (cnt < cd->srclen) {
    r = cd->src[cnt++];
    if (likely(r <= maxl))
        break;
    printed += r - maxl;
}

The problem with this section of code is that the while loop does not fully check bounds during the entire decompression stage. This allows memory corruption due to the absence of a proper check.

Resolution

The core of the solution lies in adding the required bounds checks to prevent memory corruption. Here's an example of the updated, secure code that resolves CVE-2024-57850:

while (cnt < cd->srclen) {
    r = cd->src[cnt++];
    if (likely(r <= maxl))
        break;
    printed += r - maxl;
    if (unlikely(printed > destlen))
        return -EINVAL;
}

The key difference in this updated code snippet is the addition of the following check

if (unlikely(printed > destlen))
    return -EINVAL;

This prevents the memory corruption from occurring because it now validates the bounds during the entire decompression process. If the bounds checks are not met, the decompression safely exits with an error, thus mitigating the potential negative consequences on the system.

Original References

To further understand this security vulnerability and its resolution, you can consult the following references:

1. Linux kernel source: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/
2. “jffs2: Prevent rtime memory corruption”: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7e804233b6d8
3. CVE-2024-57850 Details: https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2024-57850

Conclusion

This post aimed to provide a comprehensive understanding of CVE-2024-57850 and the potential memory corruption issue within the Linux kernel with the jffs2 filesystem.

Security vulnerabilities like this can have disastrous consequences if left unpatched and exploited by threat actors. Therefore, it is crucial to regularly update your system, patching any known vulnerabilities, and keeping your environment as secure as possible.

Timeline

Published on: 01/11/2025 15:15:07 UTC
Last modified on: 03/03/2025 17:42:59 UTC