In early 2023, researchers discovered a critical memory leak issue in the Linux kernel within the PowerPC/pSeries architecture. Though the vulnerability—CVE-2022-48669—may sound technical and specific, it’s essential for admins and anyone running Linux on IBM POWER environments. This article breaks down what CVE-2022-48669 is, how the bug works, sample code where the problem arises, possible exploitation, and where you can find official resources and patches.

What Is CVE-2022-48669?

CVE-2022-48669 is a flaw in the Linux kernel code dealing with powerpc/pseries NUMA systems, specifically in the papr_get_attr() function. Whenever papr_get_attr() tries to reallocate memory for a buffer with krealloc, it neglects to free the original memory if the reallocation fails, leading to a potential memory leak.

Why Do Memory Leaks Matter?

Memory leaks in kernel space are dangerous because they can exhaust system memory over time or be leveraged by local attackers to degrade or destabilize the environment. While this bug is not an arbitrary code execution issue, it's still a vector for denial of service (DoS).

Where's the Problem? A Look at the Code

Let’s look at a snippet similar to the affected code in arch/powerpc/platforms/pseries/papr_scm.c:

static ssize_t papr_get_attr(struct papr_scm_priv *p, u8 *data, size_t buf_size)
{
    ssize_t rc;
    u8 *buf = kmalloc(buf_size, GFP_KERNEL);
    if (!buf)
        return -ENOMEM;

    // ... some logic ...
    buf = krealloc(buf, new_size, GFP_KERNEL);
    if (!buf)
        return -ENOMEM; // BAD: original buf is leaked here if krealloc fails

    // ... additional code ...
}

What’s Gone Wrong?

If krealloc() fails and returns NULL, the pointer to the original buffer is lost, and the memory isn’t freed. This is a classic memory leak pattern in C.

Here’s how the patch fixes CVE-2022-48669

u8 *new_buf = krealloc(buf, new_size, GFP_KERNEL);
if (!new_buf) {
    kfree(buf); // Free the original if krealloc fails!
    return -ENOMEM;
}
buf = new_buf;

The Bug Was:
Not freeing the original buffer if krealloc failed.

The Fix Is:
Assigning the result to new_buf, checking failure, and freeing buf if needed before returning.

Potential Exploit Scenario

While a user process likely can't directly trigger the memory leak unless it has access to PAPR SCM attributes (privileged IOCTLs, sysfs, etc.), a malicious system user or buggy admin scripts might repeatedly request and fail these operations, making the kernel bleed memory slowly.

Example Exploit (Pseudocode)

while true; do
    cat /sys/.../papr_scm/attr  # Or trigger via a crafted syscall
done

Over time, such a loop could exhaust kernel memory and cause the system to become sluggish or even hang.

Are You Affected?

If you’re NOT running PowerPC/pSeries or do NOT have memory-backed SCM (Storage-class memory) hardware, you’re probably safe. But if you are, and running kernel versions before the patch (December 2022/January 2023), you should update immediately.

Check Your Kernel Version:

- The bug is in mainline Linux before this commit.

Update:

- RHEL, SUSE, Ubuntu, and others have issued advisories. Use your package manager to update the kernel.

sudo dnf upgrade kernel          # Fedora / RHEL / CentOS
sudo apt update && sudo apt upgrade kernel # Debian / Ubuntu

Original Patch:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=033e76c10bb

CVE Details:

https://nvd.nist.gov/vuln/detail/CVE-2022-48669

Red Hat Advisory:

https://access.redhat.com/security/cve/CVE-2022-48669

Linux kernel source for papr_scm:

https://elixir.bootlin.com/linux/latest/source/arch/powerpc/platforms/pseries/papr_scm.c#L

TL;DR

- CVE-2022-48669 is a memory leak in PowerPC/pSeries handlers of the Linux kernel.

Malicious or buggy userspace can slowly consume kernel memory, risking DoS.

- Update your kernel if you run affected PowerPC/pSeries hardware!

Timeline

Published on: 05/01/2024 13:15:48 UTC
Last modified on: 10/29/2024 18:35:00 UTC