From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-98509][LOW] drm/virtio: fix memory leak of fence event on execbuffer failure Date: Sat, 24 Oct 2026 03:03:43 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-98509 X-AL-KERNEL-Priority: LOW X-AL-KERNEL-Severity: LOW X-AL-KERNEL-Base-Severity: LOW X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 2 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: 43bfe2b60c149bf6effda25f245a00509061fa15 List-Id: CVE: CVE-2026-98509 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: drm/virtio: fix memory leak of fence event on execbuffer failure Commit: 43bfe2b60c149bf6effda25f245a00509061fa15 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43bfe2b60c149bf6effda25f245a00509061fa15 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98509 Analysis date: Sat, 24 Oct 2026 03:03:43 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: Malformed virtio-gpu execbuffer requests can permanently leak a small pending fence-event allocation on post-reservation validation failures. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98509 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98509 The original announcement does not normally provide a security severity estimate, CVSS assessment, or enough information to determine whether the reported kernel bug represents a practically relevant security issue. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. It combines an autonomous classifier with LLM-assisted technical analysis and a separate ActionableScore mechanism. The purpose of this report is to prioritize Linux kernel CVEs before manual review, identify cases that require prompt investigation, and support automatic closure of issues that are unlikely to have meaningful security impact. Published priority for this report: LOW Manual review required: NO A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-98509 LOW https://www.kernelcve.org/list/?q=CVE-2026-98509 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT LOW AEGIS_AS=1 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both LOW) Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';*CWE-401;Other CVSS 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.5';DESCR 'virtio_gpu_execbuffer_ioctl can reserve a DRM fence event before validating BO handles, command data, syncobj arrays, and the input fence. A later execbuffer failure drops the out fence lacking cancellation of the pending event, permanently losing the only driver pointer to an allocation of about 96 bytes. For the CVSS the PR:L rating is used because an attacker needs local process access to the DRM render node and must issue crafted ioctls with event polling enabled for the selected ring. The demonstrated primitive is repeatable resource retention rather than UAF, OOB access, information disclosure, or arbitrary write. Base availability impact is low because each operation leaks a small object. The worst case uses A:H only if sustained repetition can realistically exhaust kernel memory. Automated impact decision path. The original SimpleNet classifier selected MODERATE. The primary LLM estimated paranoid CVSS 5.5 and the production ActionableScore returned 2 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. Recorded rule transitions were ActionableScore thresholds stage MODERATE to LOW because the ActionableScore threshold rule was applied. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. Exact triggered rule markers were DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3. The independent weaker Aegis shadow evaluated CVSS 3.3 and ActionableScore 1 with primitive class CLASS_C and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) MAYBE VIRT INIT LEAK ERRORPATH UAF HARDWARE LINUS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 PrimitiveClass=CLASS_C RealUAF=NO HostAdminRequired=NO NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES RequiresHostUID0=NO AuthorizationDecisionBypass=NO ProtectedResourceImpact=NONE B4PendingReview=NO B4PendingConfirmed=NO 1. ActionableScore * Raw base score: 2. * Conservative score: 2; no floor or cap applied. * Raw paranoid score: 2. * Paranoid score: 2; theoretical memory exhaustion is not scored without evidence of material accumulation to host-wide exhaustion. * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +1 Concrete persistent kernel resource leak: an event reserved by `drm_event_reserve_init()` becomes orphaned when later execbuffer validation fails; neither submit cleanup nor DRM-file close frees its approximately 96-byte allocation. * +1 Local unprivileged trigger: supplied evidence grounds the ioctl path in a local process with DRM render-node access rather than host-administrator powers. * No crash/strong DoS point: only kmemleak output and permanent per-operation retention are demonstrated. * No UAF, OOB access, arbitrary write, disclosure, authorization bypass, or protected-state corruption is shown. * No additional resource-exhaustion point: repeatability is plausible, but practical host-wide memory exhaustion is not established. * No hardware/configuration penalty: virtio-gpu is environment-specific, but it is not proven both rare and difficult to reach. 3. Reachability analysis A local process with access to the virtio-gpu DRM render node can select an event-polled ring and submit malformed execbuffer arguments that fail after event reservation. This supports below-host-admin reachability and does not require UID 0. Device-node access is still a deployment prerequisite. No evidence establishes namespace-scoped capabilities, special timing, or a race. 4. Primitive and severity reading The exact primitive is a repeatable, persistent kernel allocation leak caused by losing the only driver-side event pointer. It is not stale-object consumption: no post-free dereference or second lifetime mutation occurs. The shown impact is small resource retention; eventual memory-pressure DoS remains theoretical. This is CLASS_C, not an Important-preserving B5-R, B3-PENDING, or B4-PENDING case. Auto-downgrade is allowed because no unresolved corruption or security-boundary primitive remains. 5. One-sentence report phrase Malformed virtio-gpu execbuffer requests can permanently leak a small pending fence-event allocation on post-reservation validation failures. 6. Manual review advice NO MANUAL CHECK NEEDED The patch and call path establish only a bounded per-trigger resource leak without memory corruption or authorization impact. 7. Call-site confidence Call-site confidence: high ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: drm/virtio: fix memory leak of fence event on execbuffer failure Commit: 43bfe2b60c149bf6effda25f245a00509061fa15 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43bfe2b60c149bf6effda25f245a00509061fa15 Commit description: virtio_gpu_execbuffer_ioctl() reserves a DRM event with drm_event_reserve_init() when VIRTGPU_EXECBUF_RING_IDX selects a ring that userspace has enabled polling for. virtio_gpu_init_submit() does this before the BO handles, the command buffer, the syncobj arrays and the in-fence are processed, so every later error path runs with the event already pending, including plain argument validation failures such as an invalid bo_handle or an in-syncobj that carries no fence. On those paths, virtio_gpu_cleanup_submit() drops the out-fence without cancelling the event. The fence is freed without ever having been emitted, taking the only driver-side pointer to the event with it. Closing the DRM file does not help. drm_events_release() unlinks pending events but deliberately leaves the freeing to the driver's later drm_send_event(), which never runs for an orphaned event, so the allocation is leaked permanently. Found when fuzzing the virtio driver with Syzkaller: BUG: memory leak unreferenced object 0xffff88802c176e80 (size 96): comm "syz.1.367", pid 10561, jiffies 4294960122 hex dump (first 32 bytes): 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................ c8 6e 17 2c 80 88 ff ff 00 00 00 00 00 00 00 00 .n.,............ backtrace (crc e1973c6b): kmemleak_alloc_recursive include/linux/kmemleak.h:44 [inline] slab_post_alloc_hook mm/slub.c:4597 [inline] slab_alloc_node mm/slub.c:4917 [inline] __kmalloc_cache_noprof+0x49d/0x6f0 mm/slub.c:5485 _kmalloc_noprof include/linux/slab.h:988 [inline] _kzalloc_noprof include/linux/slab.h:1309 [inline] virtio_gpu_fence_event_create drivers/gpu/drm/virtio/virtgpu_submit.c:282 [inline] virtio_gpu_init_submit drivers/gpu/drm/virtio/virtgpu_submit.c:398 [inline] virtio_gpu_execbuffer_ioctl+0xbbf/0x1aa0 drivers/gpu/drm/virtio/virtgpu_submit.c:505 drm_ioctl_kernel+0x1f4/0x3e0 drivers/gpu/drm/drm_ioctl.c:817 drm_ioctl+0x5f4/0xc70 drivers/gpu/drm/drm_ioctl.c:914 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:597 [inline] __se_sys_ioctl fs/ioctl.c:583 [inline] __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x116/0x800 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f Fix by cancelling and freeing the DRM event on the execbuffer error path before dropping the fence. Clear the fence's event pointer after cancellation so it does not retain a dangling pointer. Fixes: cd7f5ca ("drm/virtio: implement context init: add virtio_gpu_fence_event") Cc: stable@vger.kernel.org Signed-off-by: Peiyang He Assisted-by: Codex:gpt-5.6-luna Signed-off-by: Dmitry Osipenko Link: https://patch.msgid.link/D320EAB5680C1411+20260908121323.2405044-1-peiyang_he@smail.nju.edu.cn Signed-off-by: Greg Kroah-Hartman Changed files: include/linux/kmemleak.h mm/slub.c include/linux/slab.h drivers/gpu/drm/virtio/virtgpu_submit.c drivers/gpu/drm/drm_ioctl.c fs/ioctl.c arch/x86/entry/syscall_64.c Diff excerpt: Not included in this email. See the upstream URL for the full patch. Full patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=43bfe2b60c149bf6effda25f245a00509061fa15 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-98509 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98509 The original CVE announcement normally does not include a security-level estimate. In particular, it may not contain a CVSS assessment, an impact level, or enough information to determine whether the reported bug is a practically relevant security issue. One purpose of this parallel CVE list is to provide that missing technical and prioritization information. The original goal of the AL-KERNEL project was to prioritize Linux kernel CVE analysis automatically before manual review. The system can also help identify non-security issues that may be suitable for automatic closure. This report was generated by AL-KERNEL, an AI-assisted Linux kernel vulnerability analysis system developed by Alexander Larkin. The first analysis stage combines an autonomous classifier with additional LLM-based analysis. The autonomous classifier runs locally on a CPU and is based on a backpropagation neural network. Together, these mechanisms produce a technical vulnerability description, identify likely weakness types, estimate CVSS severity, and provide input for ActionableScore. Two CVSS estimates are retained because incomplete kernel vulnerability information often permits more than one defensible interpretation: Conservative CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:L The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS score: 5.5 The conservative vector represents a lower-impact interpretation. The Best/paranoid vector intentionally represents a plausible upper-bound interpretation and should not automatically be treated as demonstrated real-world impact. CVSS may also need to be adjusted for a particular Linux deployment, because actual reachability, privileges, enabled kernel configuration, hardware, namespaces, exposed device nodes, and other environmental conditions can differ significantly between systems. A separate ActionableScore mechanism evaluates practical remediation urgency. Its analysis may include reachability, attack prerequisites, subsystem exposure, memory-corruption characteristics, denial-of-service reliability, and possible confidentiality, integrity, or privilege-escalation impact. Conservative ActionableScore: unknown Paranoid ActionableScore: 2 The final base severity is taken directly from the second tab-separated field of the AL-KERNEL classification result. ActionableScore does not replace or independently override that final AL-KERNEL decision, and if ActionableScore adjusted impact level of ALKERNEL, then you would see self-readable flags above like INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7. For an AL-KERNEL result of MODERATE, this report uses the following additional presentation split: ActionableScore below 5 -> MODERATE REGULAR ActionableScore 5 or more -> MODERATE 7.0 The distinction between MODERATE REGULAR and MODERATE 7.0 makes it possible to identify Moderate issues that should receive manual analysis and fixes before lower-priority MODERATE REGULAR issues. In many cases, MODERATE REGULAR fixes may wait for a later rebase or routine update. There is one override in which MODERATE REGULAR becomes MODERATE 7.0 even when the ActionableScore is below 5. When the AL-KERNEL result contains the KPANIC flag, a MODERATE result is always presented as MODERATE 7.0. The KPANIC flag selected with few regexps without usage of AI at all, so it helps to detect cases when Kernel Crash happens and similar (to filter False-Negative results from the LLM usage). KPANIC indicates that a reliable kernel crash, kernel panic, or similarly serious kernel availability impact was identified by the classification workflow. AL-KERNEL base severity for this report: LOW KPANIC detected for this report: NO Published priority for this report (same as in Subject): LOW These results are intended to support engineering triage. They are machine-generated estimates, and cases marked for manual review should be validated by a human security engineer before final disposition. For more info read docs linked from here: https://kernelcve.org/ (and you can submit you own patch there to generate such a report for non-existant CVE-id yet). Note that in many cases this AI tool selects higher severity, than real is (means you can expect Importants instead of Moderate 7.0 or Moderates 7.0 instead of regular Moderates). If you see such cases, please use reply email interface to add additional manual analyses info to this particular CVE. And please, please, let me know when you see Lows instead of Importants or Important instead of Low (because particular for such cases I need to tune this AI tool to make it better for this one and next similar). My contact email for such notifications is alexanjelausa@gmail.com (and both send reply to CVE record itself too and see "reply" button below for howto reply).