High 7.8Published Apr 24, 2026

CVE-2026-31656drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat

Updated under an hour ago (2026-10-19 08:30 UTC)

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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] <TASK> <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+0x1b9/0x530 [i915] <4> [487.226178] i915_request_retire+0x1c/0x40 [i915] <4> [487.226625] engine_retire+0x122/0x180 [i915] <4> [487.227037] process_one_work+0x239/0x760 <4> [487.227060] worker_thread+0x200/0x3f0 <4> [487.227068] ? __pfx_worker_thread+0x10/0x10 <4> [487.227075] kthread+0x10d/0x150 <4> [487.227083] ? __pfx_kthread+0x10/0x10 <4> [487.227092] ret_from_fork+0x3d4/0x480 <4> [487.227099] ? __pfx_kthread+0x10/0x10 <4> [487.227107] ret_from_fork_asm+0x1a/0x30 <4> [487.227141] </TASK> ``` 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)

CVSS: 7.8 HIGH (v3.1, CNA)CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Weakness (CWE): Not given
Known exploited: Not in CISA's KEV catalog
EPSS (exploitation in the next 30 days): Not loaded for this CVE
Assigned by: Linux
NVD analysis: Modified
Record last updated: Oct 16, 2026
First seen by InfoSec Signals: Oct 9, 2026

Affected products

Affected products

Linux Linux linux:linux (from the name)	from 058179e72e0956a2dfe4927db6cbe5fbfb2406aa before 82034799c6c14b3104668878c3f3e5786f777126; 058179e72e0956a2dfe4927db6cbe5fbfb2406aa builds before 70d3e622b10092fc483e28e57b4e8c49d9cc7f68; 058179e72e0956a2dfe4927db6cbe5fbfb2406aa builds before 8ce44d28a84fd5e053a88b04872a89d95c0779d4; from 058179e72e0956a2dfe4927db6cbe5fbfb2406aa before ca3f48c3567dd49efdc55b80029ae74659c682ee; from 058179e72e0956a2dfe4927db6cbe5fbfb2406aa before a00e92bf6583d019a4fb2c2df7007e6c9b269ce7; 058179e72e0956a2dfe4927db6cbe5fbfb2406aa builds before 2af8b200cae3fdd0e917ecc2753b28bb40c876c1; 058179e72e0956a2dfe4927db6cbe5fbfb2406aa builds before 455d98ed527fc94eed90406f90ab2391464ca657; 058179e72e0956a2dfe4927db6cbe5fbfb2406aa builds before 4c71fd099513bfa8acab529b626e1f0097b76061	CNA record
linux linux_kernel linux:linux_kernel	from 5.5.1 before 5.15.203; from 5.16 before 6.1.169; from 6.2 before 6.6.135; from 6.7 before 6.12.82; from 6.13 before 6.18.23; from 6.19 before 6.19.13; 5.5; 7.0; and 6 more ranges	NVD

References

https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126
https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68patch
https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4patch
https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682eepatch
https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7patch
https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1patch
https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657patch
https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061patch

The CVE record on cve.org NVD's entry

The CVE record is authoritative. Products marked “from the name” were identified from the CNA's free-text names, not a CPE, and are matched less certainly. This product uses the NVD API but is not endorsed or certified by the NVD.