sched_ext: Fix starvation of scx_enable() under fair-class saturation

{
  "id": "da464a445248850e127027b3879bb68dd124f65eba8b4fd2e00430f70111454a",
  "url": "https://osv.dev/vulnerability/CVE-2026-43392",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "sched_ext: Fix starvation of scx_enable() under fair-class saturation",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: sched_ext: Fix starvation of scx_enable() under fair-class saturation During scx_enable(), the READY -> ENABLED task switching loop changes the calling thread's sched_class from fair to ext. Since fair has higher priority than ext, saturating fair-class workloads can indefinitely starve the enable thread, hanging the system. This was introduced when the enable path switched from preempt_disable() to scx_bypass() which doesn't protect against fair-class starvation. Note that the original preempt_disable() protection wasn't complete either - in partial switch modes, the calling thread could still be starved after preempt_enable() as it may have been switched to ext class. Fix it by offloading the enable body to a dedicated system-wide RT (SCHED_FIFO) kthread which cannot be starved by either fair or ext class tasks. scx_enable() lazily creates the kthread on first use and passes the ops pointer through a struct scx_enable_cmd containing the kthread_work, then synchronously waits for completion. The workfn runs on a different kthread from sch->helper (which runs disable_work), so it can safely flush disable_work on the error path without deadlock.",
    "evidence": "osv:CVE-2026-43392",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
          {
            "value": "6.12.78",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.18.20",
            "evidence": "/affected/1/ranges"
          },
          {
            "value": "6.19.9",
            "evidence": "/affected/1/ranges"
          }
        ],
        "affected_versions": []
      }
    ],
    "severity": "unknown",
    "structured": {
      "id": "CVE-2026-43392",
      "aliases": [
        "CVE-2026-43392"
      ],
      "affected": [
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              "type": "GIT",
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              "type": "ECOSYSTEM",
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                  "fixed": "6.18.20"
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            "name": "Kernel",
            "ecosystem": "Linux"
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          "database_specific": {
            "source": "https://storage.googleapis.com/cve-osv-conversion/osv-output/CVE-2026-43392.json"
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      ],
      "modified": "2026-10-28T02:30:23.907110988Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/05ab9ec5dc24f234e0a2fecf3e6ff937c68f7d81",
        "https://git.kernel.org/stable/c/b06ccbabe2506fd70b9167a644978b049150224a",
        "https://git.kernel.org/stable/c/c44198f25fdfecc0ec0fe366bf8a47fe17d8e229",
        "https://git.kernel.org/stable/c/e0b14bf06393be137d3efb6a3b7cd5b4b9810a6b",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/43xxx/CVE-2026-43392.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-43392",
        "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/2026/43xxx/CVE-2026-43392.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-43392",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": null
  },
  "source_id": "core-osv",
  "document_id": 490345,
  "published_at": "2026-05-08T14:21:36.692+00:00"
}