drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat

{
  "id": "161ff163dd691104ecfb6b3c3b0ea17785c22277d16ff9faad54c685d3787278",
  "url": "https://osv.dev/vulnerability/CVE-2026-31656",
  "method": "structured",
  "payload": {
    "kind": "advisory",
    "title": "drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat",
    "summary": "In the Linux kernel, the following vulnerability has been resolved: drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat A use-after-free / refcount underflow is possible when the heartbeat worker and intel_engine_park_heartbeat() race to release the same engine->heartbeat.systole request. The heartbeat worker reads engine->heartbeat.systole and calls i915_request_put() on it when the request is complete, but clears the pointer in a separate, non-atomic step. Concurrently, a request retirement on another CPU can drop the engine wakeref to zero, triggering __engine_park() -> intel_engine_park_heartbeat(). If the heartbeat timer is pending at that point, cancel_delayed_work() returns true and intel_engine_park_heartbeat() reads the stale non-NULL systole pointer and calls i915_request_put() on it again, causing a refcount underflow: ``` <4> [487.221889] Workqueue: i915-unordered engine_retire [i915] <4> [487.222640] RIP: 0010:refcount_warn_saturate+0x68/0xb0 ... <4> [487.222707] Call Trace: <4> [487.222711] <4> [487.222716] intel_engine_park_heartbeat.part.0+0x6f/0x80 [i915] <4> [487.223115] intel_engine_park_heartbeat+0x25/0x40 [i915] <4> [487.223566] __engine_park+0xb9/0x650 [i915] <4> [487.223973] ____intel_wakeref_put_last+0x2e/0xb0 [i915] <4> [487.224408] __intel_wakeref_put_last+0x72/0x90 [i915] <4> [487.224797] intel_context_exit_engine+0x7c/0x80 [i915] <4> [487.225238] intel_context_exit+0xf1/0x1b0 [i915] <4> [487.225695] i915_request_retire.part.0+0x1b9/0",
    "evidence": "osv:CVE-2026-31656",
    "products": [
      {
        "name": {
          "value": "Kernel",
          "evidence": "/affected/1/package/name"
        },
        "prerequisites": [],
        "fixed_versions": [
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        "affected_versions": []
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    "severity": "high",
    "structured": {
      "id": "CVE-2026-31656",
      "aliases": [
        "CVE-2026-31656"
      ],
      "metrics": [
        {
          "type": "CVSS_V3",
          "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H"
        }
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      "modified": "2026-10-28T02:30:49.103946648Z",
      "provider": "osv",
      "references": [
        "https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1",
        "https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657",
        "https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061",
        "https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68",
        "https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126",
        "https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4",
        "https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7",
        "https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682ee",
        "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31656.json",
        "https://nvd.nist.gov/vuln/detail/CVE-2026-31656",
        "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/2026/31xxx/CVE-2026-31656.json"
      }
    },
    "related_cves": [
      {
        "value": "CVE-2026-31656",
        "evidence": "/id"
      }
    ],
    "security_relevant": true,
    "severity_evidence": "/severity/0/score"
  },
  "source_id": "core-osv",
  "document_id": 517598,
  "published_at": "2026-04-24T14:45:07.738+00:00"
}