{
  "schema_version": "1.6.1",
  "id": "RPI-CVE-2026-74284",
  "modified": "2026-10-07T14:35:31Z",
  "upstream": [
    "CVE-2026-74284"
  ],
  "published": "2026-08-15T06:04:33Z",
  "summary": "net/sched: sch_hfsc: Don't make class passive twice",
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_hfsc: Don't make class passive twice\n\nupdate_vf() is called from two places for the same class during a single\ndequeue when the class's child qdisc (e.g. codel/fq_codel) drops its last\npackets while dequeuing:\n\n1. The child calls qdisc_tree_reduce_backlog(), which, now that the child\n   is empty, invokes hfsc_qlen_notify() -> update_vf(cl, 0, 0) and turns\n   the class passive (cl_nactive is decremented up the hierarchy).\n\n2. hfsc_dequeue() then calls update_vf(cl, qdisc_pkt_len(skb), cur_time)\n   to charge the dequeued bytes.\n\nOn the second call the class is already passive, but its child qdisc is\nstill empty, so update_vf() arms go_passive again:\n\n      if (cl->qdisc->q.qlen == 0 && cl->cl_flags & HFSC_FSC)\n              go_passive = 1;\n\nThe leaf is then skipped by the cl_nactive == 0 check inside the loop,\nwhich does not clear go_passive, so the stale go_passive propagates to the\nparent and decrements its cl_nactive a second time. A parent that still\nhas other active children is driven to cl_nactive == 0 and removed from\nthe vttree, even though those siblings are still backlogged. They are\nnever dequeued again and the qdisc stalls.\n\nFix this by only arming go_passive when the class is actually active, so an\nalready-passive class no longer triggers a second passive transition. The\nbyte accounting (cl->cl_total += len) still runs for every ancestor, so\ndequeued bytes continue to be counted exactly once.",
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  "references": [
    {
      "type": "ADVISORY",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-74284"
    },
    {
      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e"
    },
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      "type": "FIX",
      "url": "https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b"
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      "url": "https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7"
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      "url": "https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc"
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  ],
  "database_specific": {
    "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git",
    "upstream_modified": "2026-08-17T05:24:08Z"
  }
}