{"id":"CVE-2026-31656","revision":"9c6fa7918dc4494491c0afd917a1d264","records":[{"revision":"9c6fa7918dc4494491c0afd917a1d264","observedAt":"2026-10-23T15:48:27.903+00:00","statement":{"source":"cve-program","id":"CVE-2026-31656","aliases":[],"title":"drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat","description":"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->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)","state":0,"publishedAt":"2026-04-24T14:45:07.738+00:00","modifiedAt":"2026-10-19T18:56:01.711+00:00","affected":[{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"unaffected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"82034799c6c14b3104668878c3f3e5786f777126\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"70d3e622b10092fc483e28e57b4e8c49d9cc7f68\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"8ce44d28a84fd5e053a88b04872a89d95c0779d4\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"ca3f48c3567dd49efdc55b80029ae74659c682ee\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"a00e92bf6583d019a4fb2c2df7007e6c9b269ce7\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"2af8b200cae3fdd0e917ecc2753b28bb40c876c1\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"455d98ed527fc94eed90406f90ab2391464ca657\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        },\n                        {\n                            \"version\": \"058179e72e0956a2dfe4927db6cbe5fbfb2406aa\",\n                            \"lessThan\": \"4c71fd099513bfa8acab529b626e1f0097b76061\",\n                            \"status\": \"affected\",\n                            \"versionType\": \"git\"\n                        }\n                    ]\n                }"},{"ecosystem":"Vendor product","name":"Linux","ranges":[],"versions":[],"rawVersionEvidence":"{\n                    \"product\": \"Linux\",\n                    \"vendor\": \"Linux\",\n                    \"defaultStatus\": \"affected\",\n                    \"repo\": \"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\n                    \"programFiles\": [\n                        \"drivers/gpu/drm/i915/gt/intel_engine_heartbeat.c\"\n                    ],\n                    \"versions\": [\n                        {\n                            \"version\": \"5.5\",\n                            \"status\": \"affected\"\n                        },\n                        {\n                            \"version\": \"0\",\n                            \"lessThan\": \"5.5\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.10.258\",\n                            \"lessThanOrEqual\": \"5.10.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"5.15.203\",\n                            \"lessThanOrEqual\": \"5.15.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.1.169\",\n                            \"lessThanOrEqual\": \"6.1.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.6.135\",\n                            \"lessThanOrEqual\": \"6.6.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.12.82\",\n                            \"lessThanOrEqual\": \"6.12.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.18.23\",\n                            \"lessThanOrEqual\": \"6.18.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"6.19.13\",\n                            \"lessThanOrEqual\": \"6.19.*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"semver\"\n                        },\n                        {\n                            \"version\": \"7.0\",\n                            \"lessThanOrEqual\": \"*\",\n                            \"status\": \"unaffected\",\n                            \"versionType\": \"original_commit_for_fix\"\n                        }\n                    ]\n                }"}],"metrics":[{"system":"CVSS 3.1","vector":"CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H","score":7.8,"severity":"HIGH"}],"references":["https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126","https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68","https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4","https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682ee","https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7","https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1","https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657","https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061"],"sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-31656","license":"CVE Program Terms of Use","key":"cve-program:CVE-2026-31656","identifiers":["CVE-2026-31656"]},"retained":false,"historicalAffected":[]}],"coverage":[]}