The Linux kernel powers the vast majority of servers, PCs, and cloud backbones. Every so often, a bug arises that's tricky—like CVE-2023-52460. This vulnerability slipped into the AMD Display Core (DC) subsystem of the Direct Rendering Manager (DRM), which is in charge of your pixels, screens, and smooth sleep/wake transitions. If you use an AMD GPU and hibernate your system, this bug could crash your machine with a NULL pointer dereference.
In this article, we'll break down what went wrong, show you how it was fixed, and walk you through the bug's details—simple and clear.
What Actually Happened?
In systems with AMD graphics and the open-source Linux driver, a user could hit a kernel panic or crash when hibernating (suspend-to-disk). This is due to the code reaching for a clk_mgr structure that was not always there (NULL), and using it without checking.
Technical Details
AMD's drm/amd/display subsystem is complex. It manages everything from display outputs to power management. Among those is an object called clk_mgr (clock manager)—which manages the GPU's display clock speeds and timings.
During the hibernate sequence, the driver assumed the source context always has a clk_mgr attached. That's not always true!
When clk_mgr was NULL, and the code tried to use it, the kernel would crash with a NULL pointer dereference. In simpler terms, the code tried to use something that wasn't there, and everything just blew up.
Here’s a simplified snippet inspired by the vulnerable section, before the patch
struct clk_mgr *clk_mgr = context->clk_mgr;
/* The code did not check if clk_mgr is NULL! */
if (clk_mgr->dml2_supported)
// do something special
If context->clk_mgr was actually NULL (which can happen in certain hibernation cases), the code above would access memory at address —resulting in a kernel crash.
Fixed Code (After the Patch)
The fix is simple: check if clk_mgr is NULL before using it.
struct clk_mgr *clk_mgr = context->clk_mgr;
if (clk_mgr && clk_mgr->dml2_supported)
// only do the special thing if clk_mgr is valid
This is a classic NULL pointer check, but its absence in kernel code is a big deal, because a bad access brings the whole system down.
Linux users running AMD GPUs, using the mainline or recent kernels.
- Machines making use of hibernate (suspend-to-disk), especially laptops and desktops with AMD graphics.
A local user could trigger this crash, possibly causing data loss (if something’s writing during the crash), but not a privilege escalation. It’s a Denial-of-Service bug at worst.
Reported: Late 2023
- Patched: The fix landed upstream on Dec 11, 2023 in this commit.
References:
- CVE-2023-52460 at MITRE
- Linux Kernel Commit dbded37f6c85 (“drm/amd/display: Fix NULL pointer dereference at hibernate”)
How To Protect Yourself
- Update your kernel. All major Linux distributions should have this fix backported. Check your distro’s security updates!
- If you compile your own kernel: Make sure you include the patch above. It’s in kernels after December 2023.
How Could an Attacker Use This?
This is not a security exploit in the typical sense. It won’t let someone run arbitrary code or take over your system.
But: a local user (or process) could script repeated hibernation to force repeated panics, resulting in a Denial-of-Service attack.
A simple PoC (Proof-of-Concept) would look like
echo disk > /sys/power/state
Or, more simply, running systemctl hibernate over and over.
If the vulnerable kernel is running, each attempt could crash the kernel unexpectedly.
Conclusion
CVE-2023-52460 is a textbook case of why all code, especially kernel code, needs NULL pointer checks. One small oversight in a deep driver routine could turn a handy feature (hibernate) into a system crasher.
Lesson: Always check for NULL, especially in system code!
Action: Update your kernel, and if you run an AMD GPU and use hibernate, make sure you're patched.
More Reading
- LKML Patch Discussion
- AMDGPU Driver Docs
- Linux Kernel CVE Tracker
Timeline
Published on: 02/23/2024 15:15:08 UTC
Last modified on: 04/30/2024 19:16:12 UTC