In the ever-evolving landscape of cybersecurity, vulnerabilities in core components like the Linux Kernel can have far-reaching consequences. One such issue that came to light in 2022 is CVE-2022-3544, classified as a memory leak bug. In this long read, we’ll break down what happened, which parts of the system are affected, look into the actual code involved, and point you to more resources, including the official patch and some quick guides on mitigation.

What is CVE-2022-3544?

CVE-2022-3544 is the identifier for a vulnerability affecting the Linux Kernel. It’s specifically related to the damon_sysfs_add_target function within the mm/damon/sysfs.c file. DAMON stands for Data Access MONitor, a Linux Kernel feature that helps track how memory is being used. It’s useful for large-scale applications, particularly in cloud environments.

The vulnerability falls under the category of a memory leak. A memory leak is when a computer program doesn’t release unused memory, eventually leading to system slowdowns or even crashes.

Component: Linux Kernel, Netfilter, DAMON (Data Access Monitor)

- Vulnerable Function: damon_sysfs_add_target (in mm/damon/sysfs.c)

Impact: System resource exhaustion potentially leading to a denial of service (DoS)

- CVE: CVE-2022-3544
- VulDB ID: VDB-211044

Where is the Vulnerability?

The vulnerable function is damon_sysfs_add_target in the file mm/damon/sysfs.c. This function is involved when a new monitor target is added under sysfs, allowing userspace to configure and read memory monitoring settings dynamically.

What’s Wrong?

If there's a failure during the creation of a target sysfs object, some dynamically allocated memory isn't properly freed. This leads to a memory leak—memory that’s never returned back to the system. Over time, or with repeated exploitations, a malicious local user or a buggy process could exhaust system memory.

Here’s a simplified version of the vulnerable code before the fix

int damon_sysfs_add_target(struct damon_sysfs_region *region)
{
    struct damon_sysfs_target *target;

    target = kmalloc(sizeof(*target), GFP_KERNEL);
    if (!target)
        return -ENOMEM;

    // create sysfs object, error handling below is incomplete
    if (sysfs_create_file(...)) {
        // Oops! Not freeing target
        return -EFAULT;
    }

    // rest of code...
}

Problem:
If sysfs_create_file fails, the allocated target struct is never freed.

The patch ensures proper cleanup of memory in all failure scenarios

int damon_sysfs_add_target(struct damon_sysfs_region *region)
{
    struct damon_sysfs_target *target;

    target = kmalloc(sizeof(*target), GFP_KERNEL);
    if (!target)
        return -ENOMEM;

    if (sysfs_create_file(...)) {
        kfree(target);  // FIX: Free memory if error occurs
        return -EFAULT;
    }

    // rest of code...
}

Key Change:
Adding kfree(target); ensures there’s no memory leak on error.

Who is at Risk?

Generally, only local users or processes with the ability to interact with DAMON via sysfs are at risk of exploiting this issue. This isn’t an easy remote exploit, but on multi-user systems, a malicious user could exhaust system memory by repeatedly triggering this leak.

Proof of Concept

A simple proof-of-concept can be achieved by writing a script or program that repeatedly creates and fails DAMON region additions through sysfs, watching for increased kernel memory usage.

>NOTE: Exploiting this vulnerability isn't about reading sensitive data or remotely controlling a system—rather, it’s about causing the system to run out of memory, which can crash or destabilize it.

Mitigation

Immediate recommendation:  
Update your Linux Kernel to a version that includes the patch for CVE-2022-3544.

Manual patch:  
If you’re building your own kernel or need a temporary fix, make sure the vulnerable function includes cleanup code (see the fix section above).

General system hardening:

References & Further Reading

- National Vulnerability Database - CVE-2022-3544
- VulDB - VDB-211044: damon_sysfs_add_target Vulnerability
- Linux Kernel Patch (lkml.org)
- DAMON Documentation
- Linux Kernel Source: mm/damon/sysfs.c

Conclusion

CVE-2022-3544 highlights the importance of robust memory management, even in critical system components like the Linux Kernel. While the vulnerability may seem minor, it can pose significant risks in multi-user or critical system environments. Staying up-to-date with security patches and following best practices can help you avoid such pitfalls.

If you’re a system administrator, double-check your kernel version and update if necessary—memory leaks like these can be silent performance killers.

Timeline

Published on: 10/17/2022 12:15:00 UTC
Last modified on: 10/19/2022 04:27:00 UTC