{ "schema_version": "1.6.1", "id": "RPI-CVE-2026-31656", "modified": "2026-10-09T11:39:44Z", "upstream": [ "CVE-2026-31656" ], "published": "2026-04-24T14:47:31Z", "summary": "drm/i915/gt: fix refcount underflow in intel_engine_park_heartbeat", "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->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] \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] \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)", "severity": [ { "type": "CVSS_V3", "score": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H" } ], "affected": [ { "package": { "ecosystem": "Raspberry Pi OS:12", "name": "linux" }, "versions": [ "1:6.1.47-1+rpt4" ], "ecosystem_specific": { "binaries": [ { "binary_name": "linux-image-6.1.0-rpi3-rpi-2712", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v6", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v7l", "binary_version": "1:6.1.47-1+rpt4" }, { "binary_name": "linux-image-6.1.0-rpi3-rpi-v8", "binary_version": "1:6.1.47-1+rpt4" } ] }, "database_specific": { "per_version": { "1:6.1.47-1+rpt4": { "linux_commit": "655fc658a15ae7a6f37103754adb39ba52a9a14e", "upstream_version": "6.1.47", "assessment": "commit ancestry (strak rule)", "upstream_fixed": "6.1.169", "compiled_filter": false } } } } ], "references": [ { "type": "ADVISORY", "url": "https://www.cve.org/CVERecord?id=CVE-2026-31656" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/82034799c6c14b3104668878c3f3e5786f777126" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/70d3e622b10092fc483e28e57b4e8c49d9cc7f68" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/8ce44d28a84fd5e053a88b04872a89d95c0779d4" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/ca3f48c3567dd49efdc55b80029ae74659c682ee" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/a00e92bf6583d019a4fb2c2df7007e6c9b269ce7" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/2af8b200cae3fdd0e917ecc2753b28bb40c876c1" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/455d98ed527fc94eed90406f90ab2391464ca657" }, { "type": "FIX", "url": "https://git.kernel.org/stable/c/4c71fd099513bfa8acab529b626e1f0097b76061" } ], "database_specific": { "source": "https://git.kernel.org/pub/scm/linux/security/vulns.git", "upstream_modified": "2026-08-05T13:16:28Z", "severity": { "source": "kernel CNA", "cvss_v3_score": 7.8, "cvss_v3_severity": "High", "scenario": "AV:L - The vulnerable path is reached locally through i915 DRM render ioctls such as execbuffer submission, not through network or adjacent protocols.\nAC:L - Although the bug is a race, an attacker with render access can repeatedly drive GPU request submission, heartbeat creation, completion, retirement, and engine parking to trigger it.\nPR:L - The relevant ioctl is DRM_RENDER_ALLOW and does not require CAP_SYS_ADMIN or DRM master, but the attacker needs local access to an i915 render device as an unprivileged render client.\nUI:N - No victim action is required once the attacker can issue DRM ioctls and submit GPU work.\nS:U - The impact remains within the kernel/driver security authority; this is not a VM escape or cross-scope boundary bypass.\nC:H - The stale i915_request pointer can become a use-after-free on a reused request object, and per the required kernel scoring guidance UAFs are treated as enabling high confidentiality impact.\nI:H - The double put/refcount underflow can corrupt request/fence lifetime state and create a UAF condition, which is defensibly exploitable for arbitrary kernel memory manipulation.\nA:H - The observed failure reaches refcount_warn_saturate from the engine park path and can produce a kernel warning/oops or crash; repeated triggering can deny service." } } }