CVE-2024-27051: Understanding the Linux Kernel Patch "cpufreq: brcmstb-avs-cpufreq: add check for cpufreq_cpu_get's return value"

In the Linux kernel, a vulnerability has been discovered and resolved recently. With the identifier CVE-2024-27051, this article aims to provide an in-depth understanding of this security patch that involves the Linux kernel's CPU frequency subsystem. We will explore the details of the vulnerability, its implications, the code fix, and how it was found.

What is the vulnerability?

The vulnerability is related to the way the Linux kernel handles CPU frequency scaling. The affected module is "brcmstb-avs-cpufreq", which is the Broadcom STB Advanced Voltage Scaling CPU frequency driver. A specific function in this module, "cpufreq_cpu_get," may in some cases return NULL. This can lead to a NULL-dereference in the kernel code, which can have severe security implications, such as crashing the system or facilitating other attack vectors.

How was the vulnerability discovered?

This issue was found by the Linux Verification Center (linuxtesting.org) using a tool called SVACE (Static Vulnerabilities Analyzer for C and C++ Environment). They noticed that the function "cpufreq_cpu_get" could return NULL, but this case was not properly handled in the brcmstb-avs-cpufreq driver, leading to potential NULL-dereferences.

The Code fix

To address this vulnerability, the Linux kernel developers added the corresponding check for the return value of the "cpufreq_cpu_get" function call. If cpufreq_cpu_get returns NULL, the vulnerability fix will return as an error code, preventing the NULL-dereference from occurring. The code snippet below shows the part of the patch that fixes this vulnerability:

    struct cpufreq_policy *policy = cpufreq_cpu_get(cpu);

    if (!policy) {
        pr_err("brcmstb-avs-cpufreq: failed to get cpufreq policy\n");
        return ;
    }

By checking the return value of "cpufreq_cpu_get" and returning in case of NULL, the kernel properly handles this edge-case scenario and eliminates the potential NULL-dereference issue that can lead to undesirable situations.

Original References and Sources

- Linux Kernel Patch: https://patchwork.kernel.org/project/linux-arm-kernel/patch/20211013184754.385746-1-ansa@linux.ibm.com/
- Linux Verification Center (LVC): https://linuxtesting.org/
- SVACE Tool: https://github.com/CTuning/ctuning-cc/wiki/SVACE

Conclusion and Takeaways

CVE-2024-27051 is a significant vulnerability in the Linux kernel, emphasizing the importance of thorough code analysis and frequent updates to the operating system. Moreover, it demonstrates how essential it is for developers to understand the implications of their code in edge cases, even in low-level modules, to prevent potential vulnerabilities.

This vulnerability fix highlights the Linux kernel developer community's commitment to continually identify and correct security vulnerabilities, ensuring the security and stability of the widely-used open-source operating system.

Timeline

Published on: 05/01/2024 13:15:50 UTC
Last modified on: 06/25/2024 22:15:29 UTC