CVE-2026-98818 Linux CVE debrief

Who should care

Linux kernel developers and maintainers, Linux distribution maintainers, System administrators and operators of Linux-based systems, Security teams and vulnerability management teams, Operators and administrators responsible for Linux-based infrastructure, Platform and cloud providers using Linux as a core component

Why it matters

This vulnerability can cause deadlocks in the Linux kernel's mm/slab implementation, potentially leading to system instability and hangs. Linux kernel developers, maintainers, and system administrators should assess exposure and prioritize remediation.

• Potential system hangs or freezes due to deadlocks
• Memory pressure and reclaim issues
• Scheduler and memory management instability

Technical summary

The Linux kernel's mm/slab implementation has a vulnerability that can lead to a deadlock when kfree_rcu() is called under pi_lock and attempts to allocate memory with __GFP_KSWAPD_RECLAIM. This can happen when the system is under memory pressure and kswapd is trying to reclaim memory, while a task is holding pi_lock and attempting to free memory using kfree_rcu(). The issue arises due to the potential for kfree_rcu() to be called under pi_lock, a raw spinlock in the scheduler, and its attempt to allocate memory with __GFP_KSWAPD_RECLAIM, which can wake up kswapd and lead to a deadlock. The deadlock can cause system instability and hangs.

Defensive priority

Medium

Recommended defensive actions

• Review and apply the provided patches to ensure the mm/slab implementation is updated with the fix.
• Monitor system logs for potential deadlocks related to kswapd and pi_lock.
• Consider updating to a Linux kernel version that includes the fix for this vulnerability.
• Perform a thorough review of system configurations and deployments to identify potential exposure.
• Implement compensating controls, such as enhanced monitoring and alerting, for exposed systems.
• Conduct a thorough asset inventory to identify systems that may be affected by this vulnerability.
• Track exceptions and retest remediated assets to ensure the vulnerability is fully resolved.

Evidence notes

The existence of the deadlock was verified with a modified kernel that has a lockdep map for waking up kswapd. Reproducing the issue even intentionally was not straightforward due to the rarity of the set_cpus_allowed_force() path that is called under pi_lock.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.