CVE-2026-98536

CVE Details

Release Date:	2026-10-18
Impact:	Moderate	What is this?

Description

In the Linux kernel, the following vulnerability has been resolved: writeback: report a Tasks-RCU quiescent state per cgwb drain pass cleanup_offline_cgwbs_workfn() drains a dying cgwb by calling cleanup_offline_cgwb() until it returns false, with a cond_resched() between passes. On a CONFIG_PREEMPTION kernel that cond_resched() does nothing: _cond_resched() is a plain "return 0", and under PREEMPT_DYNAMIC the full and lazy modes disable it. Since commit 7dadeaa6e851 ("sched: Further restrict the preemption modes") those are the only two models on the architectures with PREEMPT_LAZY support, arm64 and x86 among them, so the drain loop never reports a Tasks-RCU quiescent state. A worker draining a cgwb with millions of attached inodes runs for minutes. On a 6.18 arm64 host in lazy mode the cgwb worker drained one dying cgroup's writeback domain for over 11 minutes. A BPF program unlink (bpf_trampoline_unlink_prog -> bpf_trampoline_update -> unregister_ftrace_direct -> ftrace_shutdown -> synchronize_rcu_tasks()) waited on that grace period while holding the trampoline mutex, 42 tasks queued behind it in D state, and the hung task detector fired at 614 s and panicked the host. Any BPF or ftrace detach during a long drain inherits the drain's length. Fix this by calling cond_resched_tasks_rcu_qs() so we do not stall out anybody who calls sycnrhonize_rcu_tasks(). We put this in a do { } while loop because if we have many small cgroups cleanup_offline_cgwb() will return false and we will never call cond_resched_tasks_rcu_qs(), creating the same problem.

See more information about CVE-2026-98536 from MITRE CVE dictionary and NIST NVD

NOTE: The following CVSS metrics and score provided are preliminary and subject to review.

CVSS v3 metrics

Base Score:	3.3
Vector String:	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L
Version:	3.1
Attack Vector:	Local
Attack Complexity:	Low
Privileges Required:	Low
User Interaction:	None
Scope:	Unchanged
Confidentiality Impact:	None
Integrity Impact:	None
Availability Impact:	Low

Errata information

Platform	Errata	Release Date
Oracle Linux version 10 (kernel-uek)	ELSA-2026-500572	2026-11-02
Oracle Linux version 8 (kernel-uek)	ELSA-2026-500574	2026-11-02
Oracle Linux version 9 (kernel-uek)	ELSA-2026-500572	2026-11-02
Oracle Linux version 9 (kernel-uek)	ELSA-2026-500574	2026-11-02