CVE-2022-0854 - Understanding the Linux Kernel DMA Memory Leak (with Exploit Example)

The Linux kernel is the core of many systems, from web servers to smartphones. Occasionally, researchers discover flaws in its heart—like CVE-2022-0854, a memory leak in the DMA subsystem. This issue can expose sensitive kernel memory to unprivileged, local users.

In this post, I’ll break down what CVE-2022-0854 is, how it works, and offer a simple proof-of-concept exploit to show how a local user might read random kernel memory. You’ll also find links to the original advisories and patches for those wanting to dig deeper.

What is CVE-2022-0854?

CVE-2022-0854 is a vulnerability in the Linux kernel’s DMA (Direct Memory Access) handling. Specifically, it relates to the handling of DMA_FROM_DEVICE, which is used to transfer data from a device (like a network card) to system memory.

The flaw? When a user calls certain DMA APIs incorrectly, the kernel can accidentally “leak” chunks of memory, revealing potentially sensitive information from kernel space. A malicious local user can leverage this to see fragments of previously-used memory—credentials, tokens, keys, whatever was in that spot before.

Why Does This Happen?

Normally, when drivers or user programs interact with hardware (like a disk or network card), they use DMA to read or write data fast, bypassing most CPU intervention. When you call DMA_FROM_DEVICE, you’re telling the system: “I expect this buffer to be filled by the device.” So, the buffer needs to be initialized; otherwise, random, leftover memory may get exposed to user space unexpectedly.

If the kernel or driver doesn’t properly clear these buffers, whatever was in memory previously—a password, encryption key, kernel pointer—might still be there after the DMA operation finishes and the data is handed off to user space.

As described in the Red Hat advisory

> A memory leak flaw was found in the Linux kernel’s DMA subsystem, in the way a user calls DMA_FROM_DEVICE. This flaw allows a local user to read random memory from the kernel space.

Real-World Impact

Attackers can write a simple user-space program that makes the kernel allocate a DMA buffer (through an affected driver/interface), read whatever is left in that memory, and potentially uncover plaintext secrets. No special privileges are necessary, just the right interface to trigger the bug.

If your kernel is unpatched and exposes such DMA functionality to regular users (this is common in some embedded or testing scenarios), you’re at risk.

Exploit Example

Below is a simplified C code snippet demonstrating how an attacker might trigger this leak via /dev/dma_test—a fictional device for demonstration (replace with a real vulnerable interface):

#include <stdio.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#define LEAK_SIZE 4096

int main() {
    int fd = open("/dev/dma_test", O_RDWR);
    if (fd < ) {
        perror("open");
        return 1;
    }

    char buf[LEAK_SIZE];
    memset(buf, , LEAK_SIZE); // Not necessary for exploit, but good hygiene

    // Read from the DMA device.
    ssize_t bytes = read(fd, buf, LEAK_SIZE);
    if (bytes < ) {
        perror("read");
        close(fd);
        return 2;
    }

    // Dump what we got from the kernel
    fwrite(buf, 1, bytes, stdout);

    close(fd);
    return ;
}

Note:
- Replace /dev/dma_test with a real device node exposing DMA functionality (e.g., certain test or GPU interfaces).
- The leak happens because the driver hands back uninitialized memory, which may still have “old” kernel data.


Visual: Imagine a shared kitchen where people sometimes leave confidential notes in drawers. With this attack, you open a drawer expecting only cutlery, but occasionally find someone else’s sticky note left behind.

How to Protect Yourself

- Patch your kernel! Distributions released fixes for this issue. See Linux kernel patch for reference.
- Check for devices that expose DMA interfaces to unprivileged users and restrict or remove access if not needed.

References

- Red Hat Security Advisory - CVE-2022-0854
- Upstream Linux Kernel Patch
- CVE Record on NVD

Conclusion

CVE-2022-0854 is a classic example of how small oversights in buffer handling can lead to important leaks—even in the world’s most-used kernel. As always, patch quickly, minimize unneeded access, and stay vigilant for the quiet leaks that can turn into big headaches.

If you're interested in more technical deep dives into Linux vulnerabilities, follow this blog for regular updates. Stay safe and informed!


Disclaimer: This information is shared for educational purposes. Do not use it on systems you don’t own or have permission to test. Always adhere to responsible disclosure and ethical hacking principles.

Timeline

Published on: 03/23/2022 20:15:00 UTC
Last modified on: 07/04/2022 11:15:00 UTC