CVE-2024-27068 is a recently fixed vulnerability found in the Linux kernel's MediaTek LVTS (Low Voltage Thermal Sensor) thermal driver. This bug involves a memory leak that occurs during error handling, specifically when memory allocation fails. In this article, we’ll break down what this vulnerability means, how it arises, its potential impact, and how it was fixed—all in simple terms, with code snippets and references to help you understand.

Understanding the MediaTek LVTS Thermal Driver

The MediaTek LVTS thermal driver is part of the kernel code that manages temperature sensors on certain MediaTek hardware (mostly, smartphones and tablets). It reads hardware data to ensure your device doesn't overheat.

The file in question is:
drivers/thermal/mediatek/lvts_thermal.c

What’s the Problem? (The Vulnerability)

When the driver starts up, it needs to allocate some memory for internal use. It uses a helper function called devm_krealloc() for memory management. If devm_krealloc() fails to allocate the requested memory, the driver tries to handle the error. However, there was a bug: it did not free an earlier-allocated memory object (efuse) before exiting due to the failed reallocation.

Result?
The efuse memory chunk stayed in memory, causing a memory leak—not huge, but still wasteful and could theoretically accumulate if the function is called frequently.

Here’s (simplified) what the vulnerable part of the code looked like (before the fix)

efuse = devm_kzalloc(dev, ...); // allocate memory
if (!efuse)
    return -ENOMEM;

efuse = devm_krealloc(dev, efuse, new_size, ...); // try to reallocate
if (!efuse)
    return -ENOMEM; // ERROR: memory pointed by original efuse is leaked here!

The Fix

To avoid leaking memory, you must free any memory you’ve already allocated if a subsequent allocation fails. The patch applied does exactly that: before returning due to failed allocation, it calls a function to free efuse.

Fixed Code (Simplified)

efuse = devm_kzalloc(dev, ...);
if (!efuse)
    return -ENOMEM;

new_efuse = devm_krealloc(dev, efuse, new_size, ...);
if (!new_efuse) {
    devm_kfree(dev, efuse); // Fix: free on failure!
    return -ENOMEM;
}
efuse = new_efuse;

Can this be exploited by attackers?

- This memory leak does NOT lead directly to privilege escalation or arbitrary code execution. It's a classic "resource leak": memory gets lost if allocation fails, possibly causing gradual resource exhaustion.
- However, if an attacker could repeatedly cause this error path to trigger (perhaps by manipulating device initialization), it could lead to:

Practical Exploitation

- Difficulty: Any practical exploitation would be very hard, as it would require controlling kernel hardware interactions.
- Severity: Low, but in long-lived systems (like always-on embedded devices), even small leaks matter.

Patch Commit:

thermal/drivers/mediatek/lvts_thermal: Fix a memory leak in an error handling path

CVE Details:

CVE-2024-27068 on Mitre

Kernel Source Reference:

lvts_thermal.c (Linux mainline)

Should You Worry?

- If you maintain Mediatek devices running Linux and use upstream kernels, update to a version containing the fix.
- If you are an end user: This is mostly a concern for kernel developers and device maintainers, not for general users.

Conclusion

CVE-2024-27068 is a simple bug with a simple fix, but it's a classic example of how even small memory management mistakes in kernel drivers can cause long-term issues. Kudos to the Linux kernel team for finding and patching it quickly! Keep your kernels updated, and always handle error paths correctly in your code—even minor leaks add up.


*This post is exclusive. For further details, always check original sources and stay tuned for more vulnerability deep-dives!*

Timeline

Published on: 05/01/2024 13:15:50 UTC
Last modified on: 12/23/2024 14:25:40 UTC