In the Linux kernel, a vulnerability has recently been discovered and resolved. The issue is related to the quota subsystem, specifically the flushing of the quota_release_work queue upon quota writeback. This vulnerability could potentially lead to a race condition and cause various issues within the system. In this post, we will discuss the details of the vulnerability, the code snippet affected, and the resolution process.

The vulnerability is found in the following code path, where quota writebacks are called from

freeze_super()
  sync_filesystem()
    ext4_sync_fs()
      dquot_writeback_dquots()

The issue occurs because the quota_release_work queue is not always flushed in this path. This can lead to a race condition, as outlined below:

FS freeze completes.

4. The kernel eventually tries to flush the workqueue while the FS is frozen, which hits a WARN_ON since a transaction gets started during the frozen state.

This warning originates from the following line in the code

WARN_ON(sb->s_writers.frozen == SB_FREEZE_COMPLETE);

Due to this warning, some tests, such as generic/390, might fail because of the dmesg noise. This vulnerability was detected on a powerpc machine with 15 cores.

Resolution

To resolve this issue, the quota_release_work queue must be flushed during the dquot_writeback_dquots() function, ensuring no pending work items remain after the freeze. This fix can prevent the race condition and avoid any further issues caused by this vulnerability.

The original reference for the vulnerability resolution can be found here.

Exploit Details

As of now, there are no known exploits for this specific vulnerability. However, it is essential to keep your Linux kernel up-to-date and apply any necessary patches to ensure your system's security. By staying informed on any potential vulnerabilities and their resolutions, you can minimize the risks associated with outdated software.

Conclusion

In conclusion, CVE-2024-56780 is a vulnerability in the Linux kernel related to the quota subsystem and the quota_release_work queue. By implementing the suggested resolution and flushing the workqueue during dquot_writeback_dquots(), this issue can be addressed, and the system can be protected from potential race conditions. It is essential to stay informed on any developments regarding kernel vulnerabilities and apply patches as needed to maintain a secure system environment.

Timeline

Published on: 01/08/2025 18:15:18 UTC
Last modified on: 01/09/2025 21:50:02 UTC