CVE-2025-38177

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.

This vulnerability is rated as having a Moderate impact because exploitation requires local access with network administration privileges (or an unprivileged user namespace with CAP_NET_ADMIN) to configure the Hierarchical Fair Service Curve (HFSC) queuing discipline. Under default Red Hat Enterprise Linux configurations, the HFSC packet scheduler is not utilized unless explicitly configured, limiting exposure to systems actively deploying this specialized traffic control setup. Successful exploitation could cause internal kernel state corruption, leading to a system crash and denial of service.

The CVSS score(s) listed for this vulnerability do not reflect the associated product's status, and are included for informational purposes to better understand the severity of this vulnerability.