A newly discovered Linux kernel vulnerability, CVE-2024-42248, threatened device stability and security in certain embedded systems. The problem surfaced in the serial driver code for the Ma35D1 chip and revolved around the improper handling of device nodes in the Device Tree.

In this post, we break down the vulnerability, examine the code, explain the potential risk, and see how kernel maintainers resolved the issue. If you work with custom Linux hardware or maintain device drivers, you’ll want to read on.

What is CVE-2024-42248?

CVE-2024-42248 is a vulnerability related to the TTY serial driver for the Ma35D1 chip in the Linux kernel.

- Vulnerable Component: drivers/tty/serial/ma35d1_serial.c
- Root Cause: The code assumes a device node exists in the Device Tree, and dereferences it without confirming. If missing, this triggers a NULL pointer dereference, which can crash the kernel.

In plain English: When a device is probed without a "serial" entry in its Device Tree, Linux shouldn't crash—yet that’s precisely what could happen.

Here’s a simplified view of what the bad code looked like

struct device_node *np = pdev->dev.of_node;
// ...
parse_serial_dt(np); // No check if 'np' is NULL!

If of_node (Device Tree node) is missing, dereferencing np leads to a NULL pointer dereference:

How It Was Fixed

The fix was elegantly simple: just check if the node exists before using it.

Here’s the relevant patch

if (!pdev->dev.of_node) {
    dev_err(&pdev->dev, "No device tree node found for serial device\n");
    return -ENODEV; // Return error instead of crashing
}

With this guard, the driver now bails out gracefully if the serial Device Tree node is missing.

Proof of Concept (Proc File)

If you want to see the problem in action, here’s a basic test outline (for educational purposes only):

Impact: System crash, loss of serial communication, potential impact to embedded products

Attackers with access to device firmware could exploit this to trigger a controlled crash. The risk is higher in embedded and custom hardware running adapted Linux kernels.

References & Original Sources

- Linux Kernel Patch Commit
- CVE Record (When available)
- Linux Kernel Documentation - Device Tree
- Detailed Patch Discussion *(Replace with actual email when known)*

How To Fix

If you maintain a kernel using the Ma35D1 serial driver, update to the latest stable release or apply the patch above.

Conclusion

CVE-2024-42248 is a textbook example of how a simple missing NULL-check can have major consequences for system reliability, especially in embedded environments. Linux kernel developers reacted quickly, and systems everywhere are safer as a result.

Stay sharp, keep your kernels updated, and remember: always check your pointers!


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Timeline

Published on: 08/07/2024 16:15:47 UTC
Last modified on: 11/05/2024 09:39:01 UTC