In the world of open-source software, the Linux kernel has long been a landmark project, both in terms of its longevity and its adopted widespread usage. However, due to the ever-growing complexity of the codebase, vulnerabilities are sometimes inevitable.

CVE-2024-27066 is one such vulnerability that has been recently discovered and resolved. This article will discuss the details of this vulnerability, including how the vulnerability was discovered, the code snippet that needed to be fixed, the relevant documentation, and how the vulnerability can be exploited.

Vulnerability Discovery

In the Linux Kernel, a particular vulnerability has come to light under the VirtIO subsystem. The vulnerability can result in a leakage of data due to the indirect descriptor table not being properly unmapped. CVE-2024-27066 is a unique identifier assigned to this vulnerability, allowing for easier tracking and investigation.

The vulnerability resides in the following code block

  if (unlikely(vq->do_unmap)) {
                curr = id;
                for (i = ; i < state->num; i++) {
                        vring_unmap_extra_packed(vq,
                                                 &vq->packed.desc_extra[curr]);
                        curr = vq->packed.desc_extra[curr].next;
                }
  }

The issue occurs when vq->do_unmap is set to false. Due to this, the function vring_unmap_extra_packed is not called by detach_buf_packed in the relevant code, causing the indirect descriptor table to not be properly unmapped. This results in the unmap leak vulnerability.

To resolve the vulnerability, the code checks for vq->use_dma_api instead of vq->do_unmap

  if (unlikely(vq->use_dma_api)) {
                curr = id;
                for (i = ; i < state->num; i++) {
                        vring_unmap_extra_packed(vq,
                                                 &vq->packed.desc_extra[curr]);
                        curr = vq->packed.desc_extra[curr].next;
                }
  }

This alteration ensures the indirect descriptor table will be properly unmapped, thus eliminating the leakage issue. This fix synchronously updates the DMA info as well, providing a safer and smoother user experience.

References:
- Link to original vulnerability report
- Kernel documentation on VirtIO

Exploit Details

It is important to note that this bug currently does not pose a practical threat, as no known driver uses the premapped feature with indirect descriptor tables. However, an attacker who is aware of this vulnerability could still attempt to exploit it by using specially crafted malicious code or manipulated driver configurations. This would result in leaking sensitive information or potentially causing system instability.

Conclusion

CVE-2024-27066 has been successfully resolved, eliminating the unmap leak vulnerability in the Linux kernel. It is critical for developers to keep their kernel up-to-date and monitor security bulletins to protect their systems from potential threats. Thankfully, the open-source community has maintained a strong track record of addressing vulnerabilities in a timely manner, ensuring the overall security and stability of the Linux kernel.

Timeline

Published on: 05/01/2024 13:15:50 UTC
Last modified on: 12/19/2024 08:53:42 UTC