{"id":"CVE-2026-31656","title":"drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat","summary":"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_he…","severity":"high","cvss":7.8,"cvssVector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","cvssSource":"cna","vendor":"Linux","product":"Linux","affected":["Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 82034799c6c14b3104668878c3f3e5786f777126","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 70d3e622b10092fc483e28e57b4e8c49d9cc7f68","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 8ce44d28a84fd5e053a88b04872a89d95c0779d4","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < ca3f48c3567dd49efdc55b80029ae74659c682ee","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < a00e92bf6583d019a4fb2c2df7007e6c9b269ce7","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 2af8b200cae3fdd0e917ecc2753b28bb40c876c1","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 455d98ed527fc94eed90406f90ab2391464ca657","Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 4c71fd099513bfa8acab529b626e1f0097b76061","Linux 5.5"],"ssvc":{"exploitation":"none","automatable":"no","technicalImpact":"total","timestamp":"2026-10-16T15:11:35.318678Z"},"published":"2026-04-24","updated":"2026-10-16","sourceUpdated":"2026-10-16T15:20:19.352Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31656","references":[{"url":"https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126"},{"url":"https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68"},{"url":"https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4"},{"url":"https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682ee"},{"url":"https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7"},{"url":"https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1"},{"url":"https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657"},{"url":"https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061"}],"tags":["cve.org"],"epss":0.00117,"epssPercentile":0.01547,"ingestedAt":"2026-10-16T17:24:46.666Z","slug":"CVE-2026-31656","body":"## Overview\n\nIn 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->heartbeat.systole request.\n\nThe heartbeat worker reads engine->heartbeat.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() -> 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<4> [487.221889] Workqueue: i915-unordered engine_retire [i915]\n<4> [487.222640] RIP: 0010:refcount_warn_saturate+0x68/0xb0\n...\n<4> [487.222707] Call Trace:\n<4> [487.222711]  <TASK>\n<4> [487.222716]  intel_engine_park_heartbeat.part.0+0x6f/0x80 [i915]\n<4> [487.223115]  intel_engine_park_heartbeat+0x25/0x40 [i915]\n<4> [487.223566]  __engine_park+0xb9/0x650 [i915]\n<4> [487.223973]  ____intel_wakeref_put_last+0x2e/0xb0 [i915]\n<4> [487.224408]  __intel_wakeref_put_last+0x72/0x90 [i915]\n<4> [487.224797]  intel_context_exit_engine+0x7c/0x80 [i915]\n<4> [487.225238]  intel_context_exit+0xf1/0x1b0 [i915]\n<4> [487.225695]  i915_request_retire.part.0+0x1b9/0x530 [i915]\n<4> [487.226178]  i915_request_retire+0x1c/0x40 [i915]\n<4> [487.226625]  engine_retire+0x122/0x180 [i915]\n<4> [487.227037]  process_one_work+0x239/0x760\n<4> [487.227060]  worker_thread+0x200/0x3f0\n<4> [487.227068]  ? __pfx_worker_thread+0x10/0x10\n<4> [487.227075]  kthread+0x10d/0x150\n<4> [487.227083]  ? __pfx_kthread+0x10/0x10\n<4> [487.227092]  ret_from_fork+0x3d4/0x480\n<4> [487.227099]  ? __pfx_kthread+0x10/0x10\n<4> [487.227107]  ret_from_fork_asm+0x1a/0x30\n<4> [487.227141]  </TASK>\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)\n\n## Affected\n\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 82034799c6c14b3104668878c3f3e5786f777126`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 70d3e622b10092fc483e28e57b4e8c49d9cc7f68`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 8ce44d28a84fd5e053a88b04872a89d95c0779d4`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < ca3f48c3567dd49efdc55b80029ae74659c682ee`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < a00e92bf6583d019a4fb2c2df7007e6c9b269ce7`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 2af8b200cae3fdd0e917ecc2753b28bb40c876c1`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 455d98ed527fc94eed90406f90ab2391464ca657`\n- `Linux >= 058179e72e0956a2dfe4927db6cbe5fbfb2406aa < 4c71fd099513bfa8acab529b626e1f0097b76061`\n- `Linux 5.5`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"twilight","depthScore":43,"depthScoreParts":{"impact":42.9,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}