CVE-2023-52469 - Resolving a Use-after-free Vulnerability in Linux Kernel's AMD Power Management Driver

The Linux kernel is the heart of the Linux operating system, and recently an important vulnerability has been addressed in its drivers. This post is dedicated to discussing a use-after-free bug (CVE-2023-52469) that was present in the AMD Power Management driver.

The Vulnerability

The issue was located in the Linux kernel subsystem, specifically in the drivers/amd/pm module, which deals with power management for AMD graphics devices. The problematic function was called kv_parse_power_table and manifested as a use-after-free error.

Here is a snippet of the affected code in the kv_parse_power_table function

/* allocate memory for ps if needed */
if (!adev->pm.dpm.ps)
    adev->pm.dpm.ps = kzalloc(adev->pm.dpm.num_ps * sizeof(struct kv_power_info), GFP_KERNEL);

/* if kzalloc fails, clean up and return error */
if (!adev->pm.dpm.ps) {
    kv_dpm_fini(adev);
    return -ENOMEM;
}

Cause

The issue occurs when the memory allocation (using the kzalloc function) for the ps structure held by the adev structure fails. In this case, ideally, an error should have been propagated, but instead, the control flow continues executing other functions, which later tries to access the already freed memory.

When the memory allocation for ps fails, it leads to the invocation of subsequent functions (kv_dpm_init, kv_dpm_sw_init, and kv_dpm_fini). The kv_dpm_fini function, in particular, contains a for loop that tries to access the adev->pm.dpm.ps structure. Since this structure has already been freed earlier (in kv_parse_power_table), accessing it causes a use-after-free bug.

Fixing the Vulnerability

To resolve this issue, the control flow has been improved so that, when memory allocation for ps fails, the execution will correctly propagate an error, and the memory will not be accessed after it's freed.

Here's the updated code snippet

/* allocate memory for ps if needed */
if (!adev->pm.dpm.ps)
    adev->pm.dpm.ps = kzalloc(adev->pm.dpm.num_ps * sizeof(struct kv_power_info), GFP_KERNEL);

/* if kzalloc fails, clean up and return error */
if (!adev->pm.dpm.ps) {
    kv_dpm_fini(adev);
    return -ENOMEM;
}

// Added proper handling of the error case
if (kv_dpm_init(adev) != ) {
    kv_dpm_fini(adev);
    return -EINVAL;
}

By handling the error case properly in the code, the use-after-free issue is mitigated, and the overall stability of the system is improved.

References and Additional Resources

You can find the original patch that resolved this issue in the Linux kernel source repository.

For more information on the Linux kernel and details about other security vulnerabilities, you can visit kernel.org and the National Vulnerability Database.

Conclusion

CVE-2023-52469 highlights the importance of proper memory management and error handling in software systems. By addressing the use-after-free issue in the Linux kernel, the stability and security of countless Linux-based systems around the globe have been improved. This serves as a good reminder for developers and engineers working on complex software to always be mindful of potential vulnerabilities, especially those related to memory management.

Timeline

Published on: 02/26/2024 16:27:48 UTC
Last modified on: 04/17/2024 19:00:15 UTC