CVE-2026-89835

/// Technical description

In the Linux kernel, the following vulnerability has been resolved:

f2fs: avoid NULL checkpoint thread access in sysfs

checkpoint_merge can be enabled even when no checkpoint merge thread is

running. A read-only mount is one case: f2fs does not start

f2fs_issue_ckpt there, but ckpt_thread_ioprio is still writable through

sysfs.

The ckpt_thread_ioprio store path updates the saved ioprio value and,

when checkpoint_merge is enabled, calls set_task_ioprio() for the

checkpoint thread. If cprc->f2fs_issue_ckpt is NULL, that dereferences a

NULL task pointer.

Protect ckpt_thread_ioprio sysfs writes with s_umount as well, so the

checkpoint thread cannot disappear under the store path while updating

its ioprio.

/// Remediation

Check the references section for vendor advisories, patches, and mitigation guidance. If immediate patching is not possible, review the CVSS vector to understand the attack surface and apply compensating controls such as network segmentation or access restrictions.

/// References