CVE-2026-89756

Description

In the Linux kernel, the following vulnerability has been resolved: mm/migrate: report RCU-tasks quiescent states in migrate_pages_batch() migrate_pages_batch() unmaps each folio before moving it, and every unmap runs the mmu_notifier invalidate callbacks. On KVM hosts try_to_migrate() ends up in kvm_mmu_notifier_invalidate_range_start() -> tdp_mmu_zap_leafs(), which is expensive, so unmapping a large batch keeps the CPU busy for a long time. The loop already calls cond_resched(), but on PREEMPTION kernels that is a no-op, and involuntary preemption is not a Tasks-RCU quiescent state. A long batch therefore never reports a quiescent state, and the migrating task (e.g. kcompactd) becomes a Tasks-RCU holdout, stalling the Tasks-RCU grace period for minutes, which is common at Meta fleet: INFO: rcu_tasks detected stalls on tasks: 0000000055349ecc: .. nvcsw: 1157401/1157401 holdout: 1 idle_cpu: -1/56 task:kcompactd0 state:R running task Call Trace: tdp_mmu_zap_leafs tdp_mmu_next_root gfn_to_pfn_cache_invalidate_start kvm_mmu_notifier_invalidate_range_start __mmu_notifier_invalidate_range_start try_to_migrate_one try_to_migrate migrate_pages_batch migrate_pages compact_zone compact_node kcompactd kthread Use cond_resched_tasks_rcu_qs() so a quiescent state is reported even when cond_resched() does nothing. This has also been discussed at [1]

Gravité et risque d'exploitation

CVE-2026-89756 obtient un score CVSS de 0.0/10, soit une gravité non évaluée. Selon le modèle EPSS, la probabilité qu'elle soit exploitée dans les 30 prochains jours est de 0.19 %, ce qui la place devant 8.2 % des CVE référencées.

Que faire ?

• Vérifiez si Linux (versions <=6.1.*, 8315f42295d2667a7f942f154b73a86fd7cb2227, <=6.12.*, <5dc0daff0341c6baba19c38f47d299ac831d7e99, 0, 7.2.4, <4996a7bc01ef35570664854dac2530c604981039, 6.1.188, <66734981b4d3c105223a13c827c9c73be18d91ad, <=6.6.*, <efe8f86c0916f0f74eea74ae21a3b37f728c6bad, 6.6.157, <=6.18.*, <3.18, <=7.2.*, <=*, 6.18.50, <4757542649af56d894e25e30f57cd497dffad53f, 6.12.109, 3.18, <8c6d63d434ebb85c6cf3dac1e70a171b183c6614, 7.3) est présent sur votre parc.
• Appliquez le correctif ou la version corrigée indiqués dans les références de l'éditeur.
• À défaut de correctif, limitez l'exposition (filtrage réseau, désactivation du composant).
• Automatisez la détection : les agents CVE Heimdall (gratuits, open source) corrèlent l'inventaire de vos serveurs avec la base CVE.

Références

• https://git.kernel.org/stable/c/8c6d63d434ebb85c6cf3dac1e70a171b183c6614
• https://git.kernel.org/stable/c/4757542649af56d894e25e30f57cd497dffad53f
• https://git.kernel.org/stable/c/4996a7bc01ef35570664854dac2530c604981039
• https://git.kernel.org/stable/c/5dc0daff0341c6baba19c38f47d299ac831d7e99
• https://git.kernel.org/stable/c/66734981b4d3c105223a13c827c9c73be18d91ad
• https://git.kernel.org/stable/c/efe8f86c0916f0f74eea74ae21a3b37f728c6bad