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FKIE_CVE-2026-74284

Vulnerability from fkie_nvd - Published: 2026-08-15 06:22 - Updated: 2026-08-17 06:19
Severity
Summary
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.
References
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/3a49bbae676fef1ffe548971e6229ae2adeb9d10
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/66dbb13eeb2fc339f8f548a9076be4c1a94857b0
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/90b662ea25f5e83bb3b8ccec5b93ced810b92fb8
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/b2a017bfcf565721918ec7355a373911d2f2a227
416baaa9-dc9f-4396-8d5f-8c081fb06d67https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b
Impacted products
Vendor Product Version
To clipboard 

{
  "affected": [
    {
      "affectedData": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_hfsc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "a425c82ff06cda5165e0de3de8c2a445ec1f863e",
              "status": "affected",
              "version": "72c61ffbeeb8c50f6d4d70c65d3283aa1bac57a7",
              "versionType": "git"
            },
            {
              "lessThan": "fc973ecd1a079b9a87c360478542f3a56dea085b",
              "status": "affected",
              "version": "a5efc95a33bd4fcb879250852828cc58c7862970",
              "versionType": "git"
            },
            {
              "lessThan": "15720cd8fa3fc625146128f89a8e11b0449a20a7",
              "status": "affected",
              "version": "0475c85426b18eccdcb7f9fb58d8f8e9c6c58c87",
              "versionType": "git"
            },
            {
              "lessThan": "b2a017bfcf565721918ec7355a373911d2f2a227",
              "status": "affected",
              "version": "9030a91235ae4845ec71902c3e0cecfc9ed1f2df",
              "versionType": "git"
            },
            {
              "lessThan": "9221a594c72a1446137926d4c2aa04e345f798dc",
              "status": "affected",
              "version": "d06476714d2819b550e0cc39222347e2c8941c9d",
              "versionType": "git"
            },
            {
              "lessThan": "66dbb13eeb2fc339f8f548a9076be4c1a94857b0",
              "status": "affected",
              "version": "51eb3b65544c9efd6a1026889ee5fb5aa62da3bb",
              "versionType": "git"
            },
            {
              "lessThan": "3a49bbae676fef1ffe548971e6229ae2adeb9d10",
              "status": "affected",
              "version": "51eb3b65544c9efd6a1026889ee5fb5aa62da3bb",
              "versionType": "git"
            },
            {
              "lessThan": "90b662ea25f5e83bb3b8ccec5b93ced810b92fb8",
              "status": "affected",
              "version": "51eb3b65544c9efd6a1026889ee5fb5aa62da3bb",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "9a5fd5c2f4d4afdd5e405083ee53e0789ce76956",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "c1175c4ad01dbc9c979d099861fa90a754f72059",
              "versionType": "git"
            },
            {
              "lessThan": "5.10.261",
              "status": "affected",
              "version": "5.10.241",
              "versionType": "semver"
            },
            {
              "lessThan": "5.15.212",
              "status": "affected",
              "version": "5.15.190",
              "versionType": "semver"
            },
            {
              "lessThan": "6.1.178",
              "status": "affected",
              "version": "6.1.138",
              "versionType": "semver"
            },
            {
              "lessThan": "6.6.145",
              "status": "affected",
              "version": "6.6.90",
              "versionType": "semver"
            },
            {
              "lessThan": "6.12.97",
              "status": "affected",
              "version": "6.12.28",
              "versionType": "semver"
            },
            {
              "lessThan": "5.5",
              "status": "affected",
              "version": "5.4.297",
              "versionType": "semver"
            },
            {
              "lessThan": "6.15",
              "status": "affected",
              "version": "6.14.6",
              "versionType": "semver"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/sched/sch_hfsc.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.15"
            },
            {
              "lessThan": "6.15",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.10.*",
              "status": "unaffected",
              "version": "5.10.261",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "5.15.*",
              "status": "unaffected",
              "version": "5.15.212",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.1.*",
              "status": "unaffected",
              "version": "6.1.178",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.6.*",
              "status": "unaffected",
              "version": "6.6.145",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.97",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.40",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.5",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nnet/sched: sch_hfsc: Don\u0027t make class passive twice\n\nupdate_vf() is called from two places for the same class during a single\ndequeue when the class\u0027s 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() -\u003e 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-\u003eqdisc-\u003eq.qlen == 0 \u0026\u0026 cl-\u003ecl_flags \u0026 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-\u003ecl_total += len) still runs for every ancestor, so\ndequeued bytes continue to be counted exactly once."
    }
  ],
  "id": "CVE-2026-74284",
  "lastModified": "2026-08-17T06:19:22.257",
  "metrics": {},
  "published": "2026-08-15T06:22:27.903",
  "references": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/15720cd8fa3fc625146128f89a8e11b0449a20a7"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/3a49bbae676fef1ffe548971e6229ae2adeb9d10"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/66dbb13eeb2fc339f8f548a9076be4c1a94857b0"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/90b662ea25f5e83bb3b8ccec5b93ced810b92fb8"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/9221a594c72a1446137926d4c2aa04e345f798dc"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/a425c82ff06cda5165e0de3de8c2a445ec1f863e"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/b2a017bfcf565721918ec7355a373911d2f2a227"
    },
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "url": "https://git.kernel.org/stable/c/fc973ecd1a079b9a87c360478542f3a56dea085b"
    }
  ],
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
  "vulnStatus": "Received"
}



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