{
  "affected": [
    {
      "ranges": [
        {
          "events": [
            {
              "introduced": "058179e72e0956a2dfe4927db6cbe5fbfb2406aa"
            },
            {
              "fixed": "82034799c6c14b3104668878c3f3e5786f777126"
            },
            {
              "fixed": "70d3e622b10092fc483e28e57b4e8c49d9cc7f68"
            },
            {
              "fixed": "8ce44d28a84fd5e053a88b04872a89d95c0779d4"
            },
            {
              "fixed": "ca3f48c3567dd49efdc55b80029ae74659c682ee"
            },
            {
              "fixed": "a00e92bf6583d019a4fb2c2df7007e6c9b269ce7"
            },
            {
              "fixed": "2af8b200cae3fdd0e917ecc2753b28bb40c876c1"
            },
            {
              "fixed": "455d98ed527fc94eed90406f90ab2391464ca657"
            },
            {
              "fixed": "4c71fd099513bfa8acab529b626e1f0097b76061"
            }
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "type": "GIT"
        }
      ]
    },
    {
      "package": {
        "ecosystem": "Linux",
        "name": "Kernel"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "5.5.0"
            },
            {
              "fixed": "5.10.258"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.11.0"
            },
            {
              "fixed": "5.15.203"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "5.16.0"
            },
            {
              "fixed": "6.1.169"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.2.0"
            },
            {
              "fixed": "6.6.135"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.7.0"
            },
            {
              "fixed": "6.12.82"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.13.0"
            },
            {
              "fixed": "6.18.23"
            }
          ],
          "type": "ECOSYSTEM"
        },
        {
          "events": [
            {
              "introduced": "6.19.0"
            },
            {
              "fixed": "6.19.13"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "database_specific": {
    "cna_assigner": "Linux",
    "osv_generated_from": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31656.json"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ndrm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat\n\nA use-after-free / refcount underflow is possible when the heartbeat\nworker and intel_engine_park_heartbeat() race to release the same\nengine-\u003eheartbeat.systole request.\n\nThe heartbeat worker reads engine-\u003eheartbeat.systole and calls\ni915_request_put() on it when the request is complete, but clears\nthe pointer in a separate, non-atomic step. Concurrently, a request\nretirement on another CPU can drop the engine wakeref to zero, triggering\n__engine_park() -\u003e intel_engine_park_heartbeat(). If the heartbeat\ntimer is pending at that point, cancel_delayed_work() returns true and\nintel_engine_park_heartbeat() reads the stale non-NULL systole pointer\nand calls i915_request_put() on it again, causing a refcount underflow:\n\n```\n\u003c4\u003e [487.221889] Workqueue: i915-unordered engine_retire [i915]\n\u003c4\u003e [487.222640] RIP: 0010:refcount_warn_saturate+0x68/0xb0\n...\n\u003c4\u003e [487.222707] Call Trace:\n\u003c4\u003e [487.222711]  \u003cTASK\u003e\n\u003c4\u003e [487.222716]  intel_engine_park_heartbeat.part.0+0x6f/0x80 [i915]\n\u003c4\u003e [487.223115]  intel_engine_park_heartbeat+0x25/0x40 [i915]\n\u003c4\u003e [487.223566]  __engine_park+0xb9/0x650 [i915]\n\u003c4\u003e [487.223973]  ____intel_wakeref_put_last+0x2e/0xb0 [i915]\n\u003c4\u003e [487.224408]  __intel_wakeref_put_last+0x72/0x90 [i915]\n\u003c4\u003e [487.224797]  intel_context_exit_engine+0x7c/0x80 [i915]\n\u003c4\u003e [487.225238]  intel_context_exit+0xf1/0x1b0 [i915]\n\u003c4\u003e [487.225695]  i915_request_retire.part.0+0x1b9/0x530 [i915]\n\u003c4\u003e [487.226178]  i915_request_retire+0x1c/0x40 [i915]\n\u003c4\u003e [487.226625]  engine_retire+0x122/0x180 [i915]\n\u003c4\u003e [487.227037]  process_one_work+0x239/0x760\n\u003c4\u003e [487.227060]  worker_thread+0x200/0x3f0\n\u003c4\u003e [487.227068]  ? __pfx_worker_thread+0x10/0x10\n\u003c4\u003e [487.227075]  kthread+0x10d/0x150\n\u003c4\u003e [487.227083]  ? __pfx_kthread+0x10/0x10\n\u003c4\u003e [487.227092]  ret_from_fork+0x3d4/0x480\n\u003c4\u003e [487.227099]  ? __pfx_kthread+0x10/0x10\n\u003c4\u003e [487.227107]  ret_from_fork_asm+0x1a/0x30\n\u003c4\u003e [487.227141]  \u003c/TASK\u003e\n```\n\nFix this by replacing the non-atomic pointer read + separate clear with\nxchg() in both racing paths. xchg() is a single indivisible hardware\ninstruction that atomically reads the old pointer and writes NULL. This\nguarantees only one of the two concurrent callers obtains the non-NULL\npointer and performs the put, the other gets NULL and skips it.\n\n(cherry picked from commit 13238dc0ee4f9ab8dafa2cca7295736191ae2f42)",
  "id": "CVE-2026-31656",
  "modified": "2026-07-08T05:36:28.935452610Z",
  "published": "2026-04-24T14:45:07.738Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682ee"
    },
    {
      "type": "ADVISORY",
      "url": "https://github.com/CVEProject/cvelistV5/tree/main/cves/2026/31xxx/CVE-2026-31656.json"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-31656"
    },
    {
      "type": "PACKAGE",
      "url": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"
    }
  ],
  "schema_version": "1.7.5",
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat"
}