{
  "affected": [
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:12",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.1.170-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:13",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.12.85-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    },
    {
      "ecosystem_specific": {
        "urgency": "not yet assigned"
      },
      "package": {
        "ecosystem": "Debian:14",
        "name": "linux"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.19.13-1"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "details": "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-\u003eheartbeat.systole request.  The heartbeat worker reads engine-\u003eheartbeat.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() -\u003e 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:  ``` \u003c4\u003e [487.221889] Workqueue: i915-unordered engine_retire [i915] \u003c4\u003e [487.222640] RIP: 0010:refcount_warn_saturate+0x68/0xb0 ... \u003c4\u003e [487.222707] Call Trace: \u003c4\u003e [487.222711]  \u003cTASK\u003e \u003c4\u003e [487.222716]  intel_engine_park_heartbeat.part.0+0x6f/0x80 [i915] \u003c4\u003e [487.223115]  intel_engine_park_heartbeat+0x25/0x40 [i915] \u003c4\u003e [487.223566]  __engine_park+0xb9/0x650 [i915] \u003c4\u003e [487.223973]  ____intel_wakeref_put_last+0x2e/0xb0 [i915] \u003c4\u003e [487.224408]  __intel_wakeref_put_last+0x72/0x90 [i915] \u003c4\u003e [487.224797]  intel_context_exit_engine+0x7c/0x80 [i915] \u003c4\u003e [487.225238]  intel_context_exit+0xf1/0x1b0 [i915] \u003c4\u003e [487.225695]  i915_request_retire.part.0+0x1b9/0x530 [i915] \u003c4\u003e [487.226178]  i915_request_retire+0x1c/0x40 [i915] \u003c4\u003e [487.226625]  engine_retire+0x122/0x180 [i915] \u003c4\u003e [487.227037]  process_one_work+0x239/0x760 \u003c4\u003e [487.227060]  worker_thread+0x200/0x3f0 \u003c4\u003e [487.227068]  ? __pfx_worker_thread+0x10/0x10 \u003c4\u003e [487.227075]  kthread+0x10d/0x150 \u003c4\u003e [487.227083]  ? __pfx_kthread+0x10/0x10 \u003c4\u003e [487.227092]  ret_from_fork+0x3d4/0x480 \u003c4\u003e [487.227099]  ? __pfx_kthread+0x10/0x10 \u003c4\u003e [487.227107]  ret_from_fork_asm+0x1a/0x30 \u003c4\u003e [487.227141]  \u003c/TASK\u003e ```  Fix this by replacing the non-atomic pointer read + separate clear with xchg() in both racing paths. xchg() is a single indivisible hardware instruction that atomically reads the old pointer and writes NULL. This guarantees only one of the two concurrent callers obtains the non-NULL pointer and performs the put, the other gets NULL and skips it.  (cherry picked from commit 13238dc0ee4f9ab8dafa2cca7295736191ae2f42)",
  "id": "DEBIAN-CVE-2026-31656",
  "modified": "2026-09-14T16:47:29.901450270Z",
  "published": "2026-04-24T15:16:45.097Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://security-tracker.debian.org/tracker/CVE-2026-31656"
    }
  ],
  "severity": [
    {
      "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
      "type": "CVSS_V3"
    }
  ],
  "upstream": [
    "CVE-2026-31656"
  ]
}