CVE-2023-52815: Resolving a Critical Linux Kernel Vulnerability - drm/amdgpu/vkms: Fixing a Possible Null Pointer Dereference

In today's highly connected world, security vulnerabilities in widely used software can lead to widespread exploitation if left unresolved. In this post, we'll discuss a critical vulnerability in the Linux kernel, CVE-2023-52815, that has now been resolved. The vulnerability is related to the Direct Rendering Manager (DRM) and AMD GPU Virtual Kernel Mode-Setting (VKMS) components in the Linux kernel. It can lead to a possible null pointer dereference, which could crash the system or worse, lead to privilege escalation. We'll look at the details of the exploit, related code snippets, and links to original references for a comprehensive understanding.

The Vulnerability:
The vulnerability lies within the 'drm/amdgpu/vkms' subsystem of the Linux kernel. In the function 'amdgpu_vkms_conn_get_modes()', the return value of 'drm_cvt_mode()' is assigned to the variable 'mode'. In case 'drm_cvt_mode()' fails, it will cause a NULL pointer dereference, leading to undefined behavior and potential security issues.

Code Snippet

The problematic code snippet where the assignment might lead to null pointer dereference is as follows:

static int amdgpu_vkms_conn_get_modes(struct drm_connector *connector)
{
	struct drm_crtc *crtc = amdgpu_vkms_crtc_get(connector->dev);
	struct drm_device *dev = connector->dev;
	struct drm_connector_helper_funcs *connector_funcs;
	struct videomode vm;
	struct drm_display_mode *mode;
	struct drm_cmd_test_pattern tp;
	int len = , i;

	/* ... */

	mode = drm_cvt_mode(dev, 1024, 768, 60, false, false, false);

	/* ... */
}

The Fix

To resolve this vulnerability, a check for NULL pointer is added before the dereference occurs. If 'drm_cvt_mode()' fails and returns NULL, this check will avoid potential issues and improve the overall security of the Linux kernel.

mode = drm_cvt_mode(dev, 1024, 768, 60, false, false, false);
if (!mode) {
    DRM_DEBUG_KMS("drm_cvt_mode() failed to create display mode\n");
    return -ENOMEM;
}

Original References

For more information on the vulnerability and the related fix, please refer to the following original references:

1. Linux kernel git commit: amdgpu/vkms: add a check for drm_cvt_mode failure
2. Linux kernel mailing list: PATCH drm/amdgpu/vkms: add a check for drm_cvt_mode failure

Exploit Details

Though the exploit details for CVE-2023-52815 are not publicly known yet, the vulnerable code could lead to various attacks, including denial of service (DoS), as the null pointer dereference would crash the kernel and the running system. Besides, savvy attackers could potentially leverage the vulnerability for privilege escalation attacks and gain unauthorized access to sensitive data or system resources.

Conclusion

It is crucial for the Linux kernel developers and maintainers to continuously monitor and address vulnerabilities like CVE-2023-52815 from both security and reliability perspectives. Resolving such issues in a timely manner is essential to ensure that the Linux kernel remains a robust and secure foundation for countless systems worldwide. Users and Linux distribution maintainers should ensure that they are always running the latest patched versions of the kernel to prevent any exploitation of known vulnerabilities.

Timeline

Published on: 05/21/2024 16:15:19 UTC
Last modified on: 05/24/2024 01:14:29 UTC