net/sched: codel: bound the dropping loop per dequeue call

{
  "id": "311ff8b6597b7b5d48d6693f078fd216f56a1cec931db2dd88c18b5eab0ddd91",
  "url": "https://osv.dev/vulnerability/CVE-2026-98427",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "net/sched: codel: bound the dropping loop per dequeue call",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: net/sched: codel: bound the dropping loop per dequeue call The CoDel control law schedules the next drop one interval/sqrt(count) after the previous drop, using the configured interval (codel_params.interval). For very small intervals the scheduled step rounds down to zero, so the dropping loop in codel_dequeue() never advances and drains the entire backlog under the qdisc lock in one call - an unprivileged user can trigger a soft lockup this way. Fix in the shared codel code used by both codel and fq_codel: 1. Make the control-law step at least 1 tick so the dropping loop always moves forward. 2. Cap the dropping loop at CODEL_MAX_DROPS_PER_DEQUEUE (256) drops per codel_dequeue() call, resyncing drop_next to now when the cap is hit: the catch-up owed to the loop grows with the idle gap and the backlog, which no interval threshold can bound. This is a deliberate behaviour change after long idle gaps. The cap applies to fq_codel (4b549a2ef4be) and the mac80211 TXQ path (fixed interval, cap only). The target sojourn delay (codel_params.target) is not validated: it does not feed the control law, so a sub-tick value is aggressive rather than deadlock-prone. Conditions to recreate the bug: - tc qdisc add dev lo root handle 1: tbf rate 1kbit burst 2kb limit 1000000 - tc qdisc add dev lo parent 1:1 handle 10: codel interval 2us target 1ms noecn limit 1000000 (same for fq_codel) - unpatched kernel: tc accepts it; a U",
    "evidence": "osv:CVE-2026-98427",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "7.2.8",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-98427",
      "aliases": [
        "CVE-2026-98427"
      ],
      "affected": [
        {
          "ranges": [
            {
              "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
              "type": "GIT",
              "events": [
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                  "introduced": "76e3cc126bb223013a6b9a0e2a51238d1ef2e409"
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                {
                  "fixed": "bacd72289d34d8c05b7de5a12448b87b6dd93878"
                },
                {
                  "fixed": "7f4a5ec6258fd7c92633ec4b0493fc51166d9398"
                }
              ]
            }
          ],
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98427.json"
          }
        },
        {
          "ranges": [
            {
              "type": "ECOSYSTEM",
              "events": [
                {
                  "introduced": "3.5.0"
                },
                {
                  "fixed": "7.2.8"
                }
              ]
            }
          ],
          "package": {
            "name": "Kernel",
            "ecosystem": "Linux"
          },
          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-98427.json"
          }
        }
      ],
      "modified": "2026-10-28T02:30:48.888498015Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/7f4a5ec6258fd7c92633ec4b0493fc51166d9398",
        "https://git.kernel.org/stable/c/bacd72289d34d8c05b7de5a12448b87b6dd93878",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/98xxx/CVE-2026-98427.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-98427",
        "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/2026/98xxx/CVE-2026-98427.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-98427",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 517196,
  "published_at": "2026-10-14T13:27:53.77+00:00"
}