The Linux kernel has recently resolved a vulnerability within the comedi subsystem (a.k.a. Comedi Linux Control and Measurement Device Interface). This post will detail the vulnerability, including relevant code snippets, links to original references, and exploit information.

The Vulnerability

The vulnerability in question pertains to the comedi subsystem's handling of partial mappings during an error case. Prior to the vulnerability being resolved, if some remap_pfn_range() calls succeeded before one failed, buffer pages would still be mapped into the userspace page tables even when the buffer reference was dropped using comedi_buf_map_put(bm). This could potentially lead to a security risk as the userspace mappings would only be cleaned up later in the mmap error path.

The Fix

The developers responsible for maintaining the Linux kernel have addressed the vulnerability by explicitly flushing all mappings in the VMA on the error path during the failed remap_pfn_range() call.

The fix can be seen in commit 79a61cc3fc04 ("mm: avoid leaving partial pfn mappings around in error case"), which can be found at this link:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=79a61cc3fc04

The following code snippet demonstrates the changes made in order to address this vulnerability

/* Original problematic code */
static int comedi_buf_map_get(struct comedi_buf_map *bm,
				struct vm_area_struct *vma)
{
	[...]
	if (invalid_page_req()) {
		comedi_buf_map_put(bm);
		return -EINVAL;
	}

/* Fixed code */
static int comedi_buf_map_get(struct comedi_buf_map *bm,
				struct vm_area_struct *vma)
{
	[...]
	if (invalid_page_req()) {
		zap_vma_ptes(vma, vma->vm_start, vma->vm_end - vma->vm_start);
		comedi_buf_map_put(bm);
		return -EINVAL;
	}

Exploit Details

While this vulnerability could potentially lead to security issues, there have been no known exploits targeting this specific weakness in the Linux kernel comedi subsystem at the moment. The patch has been applied, and the vulnerability has been addressed, thus mitigating the risk of any potential exploits.

Conclusion

The CVE-2024-53148 vulnerability within the Linux kernel comedi subsystem has been effectively resolved. Users can now benefit from the increased security and proper handling of partial mappings in error cases. As always, it is crucial to keep your Linux kernel up to date with the latest patches to ensure the highest level of security.

Timeline

Published on: 12/24/2024 12:15:22 UTC
Last modified on: 01/20/2025 06:19:45 UTC