In late 2023, a new Linux kernel vulnerability labeled CVE-2023-52918 was discovered and patched. This issue affected the cx23885 driver, which is commonly used for certain PCI TV tuner cards and capture devices. The bug itself is related to how the driver handled video device initialization, and if left unpatched, it could cause kernel crashes — or worse, create an opportunity for attackers.
Let’s break the vulnerability down in simple terms: how it happened, what the technical details are, how it was fixed, and what you should do next. We'll also include code snippets and original references, so you can verify or dive deeper if you choose.
What is the cx23885 Driver?
First, a quick background:
The cx23885 driver is part of the Linux kernel’s media subsystem. It lets certain video capture cards (using the Conexant CX23885/7/8 PCIe bridge chips) work with your Linux system. If you are using TV or surveillance equipment on Linux, there's a good chance this driver is in play.
The Problem: cx23885_vdev_init Can Return NULL
In the kernel source, there is a helper function called cx23885_vdev_init(). Its job is to set up a "video device" — basically prepping the nuts and bolts for the device to communicate with the rest of the system. But, if the function failed, it could return a NULL pointer, which means "sorry, I couldn't give you a working device."
The real problem comes right after. Instead of checking if the returned value was NULL (meaning a failure), the code just used the pointer as if everything was fine.
Here’s the original problematic code snippet
dev = cx23885_vdev_init(dev, ...)
dev->field = some_value; // Uh-oh, dev could be NULL!
If cx23885_vdev_init() failed and returned NULL, then accessing dev->field would crash the kernel (NULL pointer dereference), and possibly open the door to further attacks.
How Was It Fixed?
The fix is simple and effective:
Always check if the pointer is NULL before using it. If it is NULL, jump to the cleanup section of the code to safely unwind and exit.
Here’s the corrected code snippet
dev = cx23885_vdev_init(dev, ...);
if (!dev)
goto fail_unwind; // Clean up and exit safely if initialization failed
dev->field = some_value; // Now safe to access
With this change, any failure during device initialization is caught right away, and the system handles it gracefully.
Why is this Important?
- Stability: A NULL pointer dereference causes a kernel panic (total OS crash), often taking your system down hard.
- Security: Savvy attackers could potentially exploit this bug to execute malicious code, especially because the kernel runs at the highest privilege level.
- Reliability: Ensures that video and TV hardware works smoothly, even if something unexpected happens while setting up devices.
Real-World Impact
While there’s no clear public exploit available at the time of writing, this type of mistake in kernel drivers has led to serious vulnerabilities before. Attackers sometimes use similar logic errors as a stepping stone for privilege escalation.
Links to References
- Official Patch Commit
- CVE-2023-52918 on NVD
- Linux Kernel Documentation for cx23885
- Linux Kernel Source for cx23885 driver
Update Your Kernel:
If you use PCI TV cards or video capture cards supported by cx23885, patch your system. Distributions will release kernel updates including this fix.
Check Your Devices:
Run lspci or look for loaded modules (lsmod | grep cx23885) to see if you’re using this driver.
Conclusion
CVE-2023-52918 is a textbook example of why checking function return values matters — especially for pointers in kernel space! Thanks to the quick response from the Linux kernel maintainers, this bug was patched, avoiding kernel crashes, and raising the security bar.
If you want your system stable and safe, make sure your kernel is up to date. Even small patches like this can make a world of difference.
Timeline
Published on: 10/22/2024 08:15:02 UTC
Last modified on: 10/24/2024 03:55:26 UTC