CVE-2025-38177: sch_hfsc: make hfsc_qlen_notify() idempotent

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.2% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2025-07-04 · updated 2026-07-30
Weakness: CWE-459

Description

In the Linux kernel, the following vulnerability has been resolved: sch_hfsc: make hfsc_qlen_notify() idempotent hfsc_qlen_notify() is not idempotent either and not friendly to its callers, like fq_codel_dequeue(). Let's make it idempotent to ease qdisc_tree_reduce_backlog() callers' life: 1. update_vf() decreases cl->cl_nactive, so we can check whether it is non-zero before calling it. 2. eltree_remove() always removes RB node cl->el_node, but we can use RB_EMPTY_NODE() + RB_CLEAR_NODE() to make it safe.

Affected products

Debian Linux: 11.0
Linux kernel: before 5.4.297; from 5.5 before 5.10.241; from 5.11 before 5.15.190; from 5.16 before 6.1.138; from 6.2 before 6.6.90; from 6.7 before 6.12.28 — fixed in 5.10.241, 5.15.190, 5.4.297, 6.1.138, 6.12.28, 6.14.6

How to fix

Upgrade to a fixed version: Linux kernel 5.10.241, 5.15.190, 5.4.297, 6.1.138. Check the vendor advisory for mitigations.

References

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