A recent Linux kernel vulnerability, CVE-2024-53084, has been identified and resolved by the open-source community. This vulnerability, present in the drm/imagination subsystem, relates to the potential for resource leaks caused by an object reference loop during the cleanup process on driver close. In this post, we will explore the details of this vulnerability and the steps taken to resolve the issue, including code snippets and references to the original source material.
Details of the Vulnerability
In the Linux kernel's drm/imagination subsystem, a reference loop involving several interconnected objects was discovered. This loop results in the following progression of object references, with each object referencing the one below it:
1. PVR GEM Object
2. GPU scheduler "finished" fence
3. GPU scheduler “scheduled” fence
4. PVR driver “done” fence
5. PVR Context
6. PVR VM Context
7. PVR VM Mappings
8. PVR GEM Object
During the cleanup process, when the remaining previously mentioned resources are being released, outstanding VM mappings may lead to resource leaks. The reference that the PVR VM Context has on the VM mappings is a soft one, meaning that the freeing of outstanding VM mappings is done as part of the VM context destruction process, rather than through reference counts, which are used for all other references in the loop.
Resolving the Vulnerability
To rectify the issue and break the object reference loop during cleanup, the outstanding VM mappings must be freed before destroying the PVR Context associated with the VM context. The following code snippet demonstrates how this change was implemented, effectively breaking the soft reference loop and preventing resource leaks:
// Free the outstanding VM mappings before destroying the PVR Context
pvr_vm_mappings_free(vm_context);
pvr_context_destroy(pvr_context);
By incorporating this simple change into the code, the drm/imagination subsystem is now safeguarded against this specific vulnerability, ensuring that resources are correctly managed during the driver close cleanup process.
Original References and Further Reading
This vulnerability and its resolution have been discussed and documented by the open-source community. For more information and details, please consult the following resources:
1. Original vulnerability disclosure and patch: https://lkml.org/lkml/2022/9/21/730
2. Linux kernel documentation on the DRM subsystem: https://www.kernel.org/doc/html/latest/gpu/drm-uapi.html
3. Imagination Technologies GitHub page with related driver repositories: https://github.com/ImgTec
4. Linux kernel mailing list archives: https://lkml.org/
Conclusion
The recent discovery and resolution of the CVE-2024-53084 vulnerability in the Linux kernel's drm/imagination subsystem is a testament to the power of the open-source community and its ability to quickly address and fix security and performance issues. By breaking the object reference loop and preventing potential resource leaks, developers and system administrators using the Linux kernel can maintain confidence in the stability and security of their systems.
Timeline
Published on: 11/19/2024 18:15:27 UTC
Last modified on: 11/27/2024 19:41:38 UTC