In June 2024, a critical issue was resolved in the Linux kernel's AMD display driver (the DRM/AMD component). Identified as CVE-2024-53133, this vulnerability could cause a crash or even a double-free (a kind of memory corruption) if certain error conditions weren't handled correctly. This post dives deep into what happened, why it was risky, how it was fixed, and what it all means in plain English, with clear examples and links for further reading.

What Is CVE-2024-53133?

This vulnerability existed in the AMD Display Manager under the Linux kernel’s Direct Rendering Manager (DRM) subsystem. Its root cause was not handling memory allocation failures for the “dml” structure (Display Mode Library context) properly.

Here’s what the official commit message says:

> _In the case where a dml allocation fails for any reason, the current state's dml contexts would no longer be valid. Then subsequent calls dc_state_copy_internal would shallow copy invalid memory and if the new state was released, a double free would occur._

Translation

- "dml allocation fails": The system tries to get memory for display settings—if it can't, the data is left invalid.
- "shallow copy invalid memory": The code copies a pointer, not the data. If the pointer is not valid, bad things happen.
- "double free would occur": Freeing the same memory twice. That often leads to crashes, data loss, or security vulnerabilities.

The Risk: Why This Matters

If an attacker could cause that memory allocation to fail at just the right time (which sometimes can be triggered on purpose, or by exhausting resources), they could potentially:

Cause unpredictable memory corruption

- (In some cases) exploit it for privilege escalation (run code as the kernel, though that’s rare for this bug type)

Here’s a simplified version of how the buggy code worked before the patch

struct dc_state *new_state = kzalloc(sizeof(*new_state), GFP_KERNEL);
if (!new_state)
    return -ENOMEM;

new_state->dml = kmalloc(sizeof(*new_state->dml), GFP_KERNEL);
if (!new_state->dml)
    /* Oops! 'dml' is invalid, but code keeps running... */

// Later, copies old state into new_state, copying that bad pointer
memcpy(new_state, old_state, sizeof(*old_state));

// If later free() is called on new_state->dml, double free may occur!

What’s wrong here?: If kmalloc() for dml fails, they don’t clean up or reset the dml pointer. Later, they copy or free it not knowing it’s bad, which can double-free or crash.

The Fix

The patch bcafdc61529a48f6f06355d78eb41b3aeda5296c did:

Fixed code

new_state->dml = kmalloc(sizeof(*new_state->dml), GFP_KERNEL);
if (!new_state->dml) {
    new_state->dml = NULL;   // Mark as safe
    goto error_handling;     // Clean up, don't keep going
}

Trigger AMD display hotplug, mode set, or any action that calls the affected allocation path

3. Under unlucky timing, the system crashes or releases memory incorrectly—potentially leading to more severe kernel memory problems

Note: While exploitation for code execution is hard here, reliable root denial-of-service is possible.

How Do You Stay Safe?

1. Patch your kernel: Make sure you’re running a Linux kernel with the fix from June 2024 or later.
2. Check your vendor: If your distro or hardware vendor distributes custom kernels or drivers, ask them about CVE-2024-53133.
3. Monitor logs: Watch for AMD DRM/display driver crashes or kernel memory errors after hotplugging monitors, sleep/resume, etc.

References

- Linux Kernel Commit Fix (bcafdc61)
- Linux Kernel Mailing List Patch Discussion
- NVD Entry for CVE-2024-53133 (once published)

Final Words

CVE-2024-53133 is a perfect example of why handling out-of-memory and pointer errors in kernel modules is crucial. Even tiny mistakes can crash your system or, in rare cases, worsen into bigger security holes.

Upgrading is your best defense. If you run Linux on AMD graphics hardware — especially in environments where system uptime matters — make sure you’re protected!

*Stay safe, keep your code and drivers up to date, and always check pointers!*

*(This guide is original and simplified for clarity — feel free to share or link back!)*

Timeline

Published on: 12/04/2024 15:15:13 UTC
Last modified on: 12/11/2024 17:16:16 UTC