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CVE-2025-38177 affects the Linux kernel's High-Speed Fair Service Curve (HFSC) queuing discipline. The hfsc_qlen_notify() function is not idempotent, making repeated notifications unsafe for callers such as fq_codel_dequeue() through qdisc_tree_reduce_backlog(). Repeated operations can inappropriately decrement the class active counter through update_vf() and attempt to remove the same eligible-tree red-black node through eltree_remove(). The flaw is associated with local denial of service. The fix guards updates with a nonzero cl->cl_nactive check and uses RB_EMPTY_NODE() and RB_CLEAR_NODE() to make node removal safe.
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A Linux kernel HFSC queueing vulnerability involving non-idempotent behavior in hfsc_qlen_notify(). The fix guards updates to active-class state and makes red-black tree node removal safe. The listed CVSS v3 score is 5.5, indicating a local, low-privilege vulnerability with high availability impact and no confidentiality or integrity impact.
A locally exploitable, low-complexity vulnerability requiring low privileges that can cause a high availability impact; confidentiality and integrity impact are rated none in the supplied CVSS v3 vector.
A Linux kernel vulnerability in the sch_hfsc component where hfsc_qlen_notify() was not idempotent, leading to an availability impact and resolved by making the function safe for repeated calls.
A Linux kernel HFSC scheduler flaw addressed by making hfsc_qlen_notify() idempotent.
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Cross-references every affected SKU, including bundled OEM variants.
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