CVE-2026-89835

Summary

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.

Affected Software

VendorProductVersion RangeStatus
LinuxLinuxe65920661708b7c0f3db45c9cd5d0095034ee37f < a6573f3ffc19542de9ebc1a2b1f930fd48ba538caffected
LinuxLinuxe65920661708b7c0f3db45c9cd5d0095034ee37f < aefcec3bebdeed2bff444378122300763325ba23affected
LinuxLinuxe65920661708b7c0f3db45c9cd5d0095034ee37f < 8f3b99c50dd0da1777994ce7c7e60d39b9f60f4baffected
LinuxLinuxe65920661708b7c0f3db45c9cd5d0095034ee37f < 5cb33b00c8fbb6e8f1fa3d281c3036d5f7c7c41faffected
LinuxLinux5.12affected
LinuxLinux0 < 5.12unaffected
LinuxLinux6.12.110 <= 6.12.*unaffected
LinuxLinux6.18.51 <= 6.18.*unaffected
LinuxLinux7.2.5 <= 7.2.*unaffected
LinuxLinux7.3-rc1 <= *unaffected

Weaknesses

References