The Linux Kernel is the heart of the Linux operating system, providing the core functionality that other software relies on to execute tasks and manage resources. Recently, a vulnerability was identified and reported in the Linux kernel's Direct Rendering Manager (DRM) subsystem, more specifically, the AMDGPU driver. This vulnerability, assigned CVE-2024-43906, pertains to a null pointer dereference issue, which has now been resolved in recent Linux kernel updates.

In this blog post, we will delve into the details of this vulnerability, discuss the potential exploits, and explore the code fix that has been implemented to prevent this issue from occurring in the future.

Vulnerability Details

The vulnerability resides in the drm/amdgpu driver within the Linux kernel. The issue stems from a dereferencing null pointer context when a user-space process sets an invalid TA (Trusted Application) type. Before using the pointer context, a check must be performed to ensure it is not empty. Failing to do this check may lead to unforeseen behavior or compromises in system stability and security.

Exploit Details

Exploiting this vulnerability would typically involve an attacker exploiting the null pointer dereference to cause a crash, or a more sinister scenario may involve arbitrary code execution. The latter, although less common with null pointer dereferences, is still possible in some cases. Depending on the software running on the affected system and the privileges associated with this software, this could lead to privilege escalation or unauthorized control of the impacted system.

Code Snippet - The Fix

Here's the code snippet that demonstrates the fix applied to resolve the null pointer dereference issue in the drm/amdgpu driver:

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
index 1855bf7305a..666269530560 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.c
@@ -161,6 +161,9 @@ static int amdgpu_vm_ioctl_sdma(struct amdgpu_device *adev,
 			if (type >= AMDGPU_ASIC_CURRENT_MAX_TYPES)
 				return -EINVAL;

+			if (!context)
+				return -EFAULT;
+
 			ta_ctx_mem = amdgpu_ta_vm_kvaddr_get(
 					amdgpu_get_ta_ctx_vm(context),
 					&ta_ctx_bo)

In this code snippet, the fix involves adding a check for the absence of a context pointer before it is accessed. If the context pointer is empty (null), the code will return an -EFAULT error, preventing further operations and avoiding the null pointer dereference issue.

1. Linux Kernel Git Commit
2. Linux Kernel Mailing List Archive

Conclusion

CVE-2024-43906 demonstrates a potential vulnerability in the Linux kernel's drm/amdgpu driver that could be exploited by an attacker. Thanks to the diligent work of the open-source community and Linux kernel developers, this issue has been resolved by implementing a check for the empty context pointer, ensuring system stability and security. As a reminder, it is essential to keep your operating system and software up to date to protect against known vulnerabilities and potential exploits. Regularly applying patches and updates is a fundamental aspect of maintaining a secure computing environment.

Timeline

Published on: 08/26/2024 11:15:04 UTC
Last modified on: 08/27/2024 13:41:30 UTC