CVE-2026-74284net/sched: sch_hfsc: Don't make class passive twice

Description

In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_hfsc: Don't make class passive twice update_vf() is called from two places for the same class during a single dequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last packets while dequeuing: 1. The child calls qdisc_tree_reduce_backlog(), which, now that the child is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns the class passive (cl_nactive is decremented up the hierarchy). 2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time) to charge the dequeued bytes. On the second call the class is already passive, but its child qdisc is still empty, so update_vf() arms go_passive again: if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC) go_passive = 1; The leaf is then skipped by the cl_nactive == 0 check inside the loop, which does not clear go_passive, so the stale go_passive propagates to the parent and decrements its cl_nactive a second time. A parent that still has other active children is driven to cl_nactive == 0 and removed from the vttree, even though those siblings are still backlogged. They are never dequeued again and the qdisc stalls. Fix this by only arming go_passive when the class is actually active, so an already-passive class no longer triggers a second passive transition. The byte accounting (cl->cl_total += len) still runs for every ancestor, so dequeued bytes continue to be counted exactly once.

Timeline

Scores

No CVSS score yet: neither the CNA, CISA nor NVD has scored this CVE. NVD status: Received.

EPSS (exploitation in 30 days)

0.22% · top 88% of all CVEs (12 Nov 2026)

CISA SSVC

Exploitation: none · Automatable: no · Technical impact: partial

The list uses the assigner's score when there is one, then CISA's, then NVD's: Not scored.

Affected products

• Linux · Linux

  • affected 72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7 – < a425c82ff06cda5165e0de3de8c2a445ec1f863e
  • affected a5efc95a33bd4fcb879250852828cc58c7862970 – < fc973ecd1a079b9a87c360478542f3a56dea085b
  • affected 0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87 – < 15720cd8fa3fc625146128f89a8e11b0449a20a7
  • affected 9030a91235ae4845ec71902c3e0cecfc9ed1f2df – < b2a017bfcf565721918ec7355a373911d2f2a227
  • affected d06476714d2819b550e0cc39222347e2c8941c9d – < 9221a594c72a1446137926d4c2aa04e345f798dc
  • affected 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb – < 66dbb13eeb2fc339f8f548a9076be4c1a94857b0
  • affected 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb – < 3a49bbae676fef1ffe548971e6229ae2adeb9d10
  • affected 51eb3b65544c9efd6a1026889ee5fb5aa62da3bb – < 90b662ea25f5e83bb3b8ccec5b93ced810b92fb8
  • affected 9a5fd5c2f4d4afdd5e405083ee53e0789ce76956
  • affected c1175c4ad01dbc9c979d099861fa90a754f72059
  • affected 5.10.241 – < 5.10.261
  • affected 5.15.190 – < 5.15.212
  • affected 6.1.138 – < 6.1.178
  • affected 6.6.90 – < 6.6.145
  • affected 6.12.28 – < 6.12.97
  • affected 5.4.297 – < 5.5
  • affected 6.14.6 – < 6.15

• Linux · Linux

  • affected 6.15
  • unaffected < 6.15
  • unaffected 5.10.261 – ≤ 5.10.*
  • unaffected 5.15.212 – ≤ 5.15.*
  • unaffected 6.1.178 – ≤ 6.1.*
  • unaffected 6.6.145 – ≤ 6.6.*
  • unaffected 6.12.97 – ≤ 6.12.*
  • unaffected 6.18.40 – ≤ 6.18.*
  • unaffected 7.1.5 – ≤ 7.1.*
  • unaffected 7.2 – ≤ *

Sources

The same CVE in the primary databases and aggregators, to check against.

• CVE.org record (opens in a new tab)
• CVE List JSON (GitHub) (opens in a new tab)
• NVD (opens in a new tab)
• FIRST EPSS (opens in a new tab)
• EUVD EUVD-2026-59431 (opens in a new tab)
• OSV.dev (opens in a new tab)
• GitHub Advisories (opens in a new tab)
• CIRCL Vulnerability-Lookup (opens in a new tab)

Badge for a README or a ticket

[![CVE-2026-74284](https://cveledger.app/badge/CVE-2026-74284.svg)](https://cveledger.app/cve/CVE-2026-74284)

Record last updated 6 Nov 2026, 17:05 UTC.