In June 2024, a new vulnerability was assigned the identifier CVE-2024-56705. This vulnerability involves the memory allocation logic in the Linux kernel's media subsystem, specifically in the atomisp camera driver. If you are using Linux on certain Intel platforms, this might be relevant to you.

Let's break down what went wrong, how it was fixed, and why it matters for anyone working with kernels, drivers, or just keeping systems secure. We'll also include simplified code and links to the original discussions and fixes.

What Is atomisp and Where's the Bug?

atomisp is a driver module in the Linux kernel for Intel Atom image signal processors—basically, handling cameras on devices like some tablets and laptops. In this driver, there’s a function responsible for allocating memory for image data: ia_css_3a_statistics_allocate().

Here’s the trouble spot:
The function tries to allocate memory for something called rgby_data. But the old code didn't check if this allocation succeeded before proceeding. If the allocation failed (say, system out of memory), it would still move forward – leading to an assert failure in another function, potentially crashing the system or making it unstable.

Here's a simplified version (not full kernel code, but illustrative)

host_stats->rgby_data = kzalloc(size, GFP_KERNEL);
// No check for rgby_data being NULL

ia_css_s3a_hmem_decode(host_stats->rgby_data);
// If rgby_data is NULL, this triggers a kernel assertion or crash!

What’s wrong?
If kzalloc() can't allocate memory, it returns NULL, but the code just keeps going as if nothing happened. Later, when the system tries to use host_stats->rgby_data, it might crash or worse.

The Fix: Checking Allocation

The fix is simple and effective: Always check if your memory allocation succeeded before using the pointer.

Here’s what the patch does (simplified)

host_stats->rgby_data = kzalloc(size, GFP_KERNEL);

if (!host_stats->rgby_data) {
    // Allocation failed, handle error
    goto error;
}

// Safe to proceed with host_stats->rgby_data now

This avoids accessing a NULL pointer and prevents the crash.

Attack vector: Local.

- Risk: If an attacker could influence memory pressure or trigger this code directly, they potentially crash the system, leading to a denial of service.
- Privilege Level: Mostly impacts stability, but in theory, errors in memory handling could be used in more creative attacks, especially in complex kernel scenarios.

Exploiting the Issue

While this isn't a "remote code execution" bug, if you had access to the appropriate hardware and the means to invoke this allocation under OOM (out-of-memory) situations, you could cause the kernel to panic by provoking the assert.

Here’s how a theoretical local exploit might look in pseudo-code

// Force system into low memory state
trigger_camera_statistics_allocation();
// System crashes due to unchecked NULL pointer in old code

In reality, direct exploitation might require a custom userland application or driver interaction, but it serves as an example of why always check for allocation failures!

The official patch fixing this bug:

media: atomisp: Add check for rgby_data memory allocation failure - Patch

Kernel discussion thread:

LKML Patchwork
- Linux kernel documentation on memory allocation APIs
- CWE-401: Improper Release of Memory Before Removing Last Reference ('Memory Leak') — related to memory allocation mistakes.

Always check memory allocations.

- Use if (!ptr) after every kmalloc(), kzalloc(), or similar function in kernels and low-level code.

Conclusion

CVE-2024-56705 is a textbook example of why careful programming in kernel space is crucial. Even a missing NULL check can result in system crashes. The good news: the fix is upstream, modern kernels are patched, and you know a little more about tracking down and understanding Linux CVEs!


If you want to read more about kernel vulnerabilities or follow up on similar bugs, keep an eye on the Linux kernel mailing list and CVE Details.

Timeline

Published on: 12/28/2024 10:15:19 UTC
Last modified on: 05/04/2025 10:02:54 UTC