CVE-2026-89835

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.

• https://git.kernel.org/stable/c/22760e3e9cecbddc475edc91600787abf407a302
• https://git.kernel.org/stable/c/54196bcfde998fb37009f50e0ef16498f651f0f9
• https://git.kernel.org/stable/c/5cb33b00c8fbb6e8f1fa3d281c3036d5f7c7c41f
• https://git.kernel.org/stable/c/8f3b99c50dd0da1777994ce7c7e60d39b9f60f4b
• https://git.kernel.org/stable/c/a6573f3ffc19542de9ebc1a2b1f930fd48ba538c
• https://git.kernel.org/stable/c/aefcec3bebdeed2bff444378122300763325ba23