CVE-2024-56776 - Linux Kernel Vulnerability: Avoiding Potential Dereference of Error Pointers in drm/sti

A new vulnerability has been identified and resolved in the Linux kernel, specifically in the Direct Rendering Manager / STMicroelectronics (drm/sti) subsystem. The vulnerability is marked by the Common Vulnerabilities and Exposures ID CVE-2024-56776. This vulnerability could lead to a potential dereference of error pointers in certain scenarios. In this post, we will delve into the details of this vulnerability, the fix implemented, code snippets, and original references related to the issue.

Exploit Details

The issue lies in the improper validation of return values of a particular function in the Linux kernel, drm_atomic_get_crtc_state(). This function is commonly used in the Direct Rendering Manager (DRM) subsystem. The function's return value must be checked to avoid the use of error pointers when the function fails, which could potentially lead to system instability or crashes.

Code Snippet Showing the Vulnerability

struct drm_crtc_state *crtc_state = drm_atomic_get_crtc_state(state, crtc);
if (IS_ERR(crtc_state))
	return PTR_ERR(crtc_state);

/* Reset atomic state flags for planes and CRTC */
...

As seen in the code snippet above, developers have missed the necessary check for the return value of drm_atomic_get_crtc_state(), before using the 'crtc_state' variable.

Resolution

In order to resolve this vulnerability, Linux kernel developers have implemented a fix that checks the return value of drm_atomic_get_crtc_state() to ensure the 'crtc_state' variable does not contain an error pointer. The corrected code is as follows:

struct drm_crtc_state *crtc_state;

/* Fix: Check for the return value and avoid error pointer dereference */
int ret = drm_atomic_get_crtc_state(state, crtc);
if (ret)
	return ret;

crtc_state = state->crtc_states[crtc.index];

/* Reset atomic state flags for planes and CRTC */
...

With this change, the possibility of dereferencing an error pointer is eliminated, mitigating the vulnerability.

The vulnerability was initially reported in the Linux kernel mailing list here

- [patch 1/1] drm/sti: avoid potential dereference of error pointers (https://lkml.org/lkml/2024/2/17/10)

The fix for the issue has been merged into the Linux kernel source code repository, and you can find the commit here:

- Commit in the Linux kernel repository (https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?id=9c7e9288967cb)

In Conclusion

CVE-2024-56776 is a vulnerability within the Linux kernel's drm/sti subsystem that could potentially lead to dereference of error pointers, causing system instability or crashes. By checking the return value of drm_atomic_get_crtc_state() and ensuring proper validation, the vulnerability has been mitigated. It is highly recommended that users and administrators update their Linux kernel to include the fix for this vulnerability.

Timeline

Published on: 01/08/2025 18:15:18 UTC
Last modified on: 01/09/2025 21:41:40 UTC