net/sched: sch_qfq: Fix NULL deref when deactivating inactive aggregate in qfq_reset

{
  "id": "35aefa85573029469131e5de166f3c55f6c73eec9458657def80177fccded331",
  "url": "https://osv.dev/vulnerability/CVE-2026-22976",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net/sched: sch_qfq: Fix NULL deref when deactivating inactive aggregate in qfq_reset",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net/sched: sch_qfq: Fix NULL deref when deactivating inactive aggregate in qfq_reset `qfq_class->leaf_qdisc->q.qlen > 0` does not imply that the class itself is active. Two qfq_class objects may point to the same leaf_qdisc. This happens when: 1. one QFQ qdisc is attached to the dev as the root qdisc, and 2. another QFQ qdisc is temporarily referenced (e.g., via qdisc_get() / qdisc_put()) and is pending to be destroyed, as in function tc_new_tfilter. When packets are enqueued through the root QFQ qdisc, the shared leaf_qdisc->q.qlen increases. At the same time, the second QFQ qdisc triggers qdisc_put and qdisc_destroy: the qdisc enters qfq_reset() with its own q->q.qlen == 0, but its class's leaf qdisc->q.qlen > 0. Therefore, the qfq_reset would wrongly deactivate an inactive aggregate and trigger a null-deref in qfq_deactivate_agg: [ 0.903172] BUG: kernel NULL pointer dereference, address: 0000000000000000 [ 0.903571] #PF: supervisor write access in kernel mode [ 0.903860] #PF: error_code(0x0002) - not-present page [ 0.904177] PGD 10299b067 P4D 10299b067 PUD 10299c067 PMD 0 [ 0.904502] Oops: Oops: 0002 [#1] SMP NOPTI [ 0.904737] CPU: 0 UID: 0 PID: 135 Comm: exploit Not tainted 6.19.0-rc3+ #2 NONE [ 0.905157] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.17.0-0-gb52ca86e094d-prebuilt.qemu.org 04/01/2014 [ 0.905754] RIP: 0010:qfq_deactivate_agg (include/linux/list.h:992 (discriminator 2) in",
    "evidence": "osv:CVE-2026-22976",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "5.10.248",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "5.15.198",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.1.161",
            "evidence": "/affected/1/ranges"
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            "evidence": "/affected/1/ranges"
          },
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            "value": "6.12.66",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.6",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-22976",
      "aliases": [
        "CVE-2026-22976"
      ],
      "affected": [
        {
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              "type": "GIT",
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                  "fixed": "0809c4bc06c9c961222df29f2eccfd449304056f"
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                  "fixed": "cdb24200b043438a144df501f1ebbd926bb1a2c7"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-22976.json"
          }
        },
        {
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              "type": "ECOSYSTEM",
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          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
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            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-22976.json"
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      ],
      "modified": "2026-10-28T02:30:28.746684873Z",
      "provider": "osv",
      "references": [
        "https://cert-portal.siemens.com/productcert/html/ssa-253495.html",
        "https://git.kernel.org/stable/c/0809c4bc06c9c961222df29f2eccfd449304056f",
        "https://git.kernel.org/stable/c/11bf9134613f6c71fc0ff36c5d8d33856f6ae3bb",
        "https://git.kernel.org/stable/c/43497313d0da3e12b5cfcd97aa17bf48ee663f95",
        "https://git.kernel.org/stable/c/51ffd447bc37bf1a5776b85523f51d2bc69977f6",
        "https://git.kernel.org/stable/c/6116a83ec167d3ab1390cded854d237481f41b63",
        "https://git.kernel.org/stable/c/c1d73b1480235731e35c81df70b08f4714a7d095",
        "https://git.kernel.org/stable/c/cdb24200b043438a144df501f1ebbd926bb1a2c7",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/22xxx/CVE-2026-22976.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-22976",
        "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
      ],
      "provider_metadata": {
        "cna_assigner": "Linux",
        "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/22xxx/CVE-2026-22976.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-22976",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 495461,
  "published_at": "2026-01-21T06:57:23.939+00:00"
}