From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74481][MODERATE 7.0] mm/page_reporting: use system_freezable_wq to fix UAF during suspend Date: Sat, 15 Aug 2026 14:01:55 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74481 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 3 X-AL-KERNEL-Commit: f978048326570047e8216e81a67f9c71ef2bb1b1 List-Id: CVE: CVE-2026-74481 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: NO Patch: mm/page_reporting: use system_freezable_wq to fix UAF during suspend Commit: f978048326570047e8216e81a67f9c71ef2bb1b1 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f978048326570047e8216e81a67f9c71ef2bb1b1 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74481 Analysis date: Sat, 15 Aug 2026 14:01:55 -0400 ActionableScore: 5 ActionableScore lower bound: 3 Actionable bucket: Actionable Moderate at minimum Manual review required: YES Summary: A UAF in mm page reporting during suspend or hibernation can let unfrozen page reporting work access virtio_balloon virtqueues after device teardown, causing a kernel crash and requiring manual review due to real kernel lifetime corruption. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74481 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74481 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: MODERATE 7.0 Manual review required: YES A detailed explanation of the methodology and priority rules is included at the end of this message. ====================================================================== AL-KERNEL CLASSIFICATION RESULT ====================================================================== CVE-2026-74481 MODERATE CHECK WITH IMPACT FROM ORIG NN LOW Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';*CWE-416;CWE-362;*CWE-672;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A use-after-free can occur in mm page reporting during suspend or hibernation because page_reporting_process was queued on system_wq, which is not freezable, and can continue running while virtio_balloon removes virtqueues. If memory freeing or shrinker activity returns pages to the buddy allocator during the PM freeze window, page reporting may call virtballoon_free_page_report on deleted virtqueues and crash in virtqueue_add_split. For the CVSS the PR:L is used for the paranoid score because a local user or guest service may be able to create memory churn and interact with suspend or hibernation policy, although reliable triggering depends on platform power management behavior. The issue is not network reachable and is local to the guest or host where page reporting and virtio_balloon are enabled. Impact is at least local denial of service via kernel crash and in the worst case may allow confidentiality or integrity impact due to UAF based memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) YES OOB DANGER INIT UAF KERNEL_PANIC_PLUS_UAF HARDWARE MEMORY DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=3 ## 1. ActionableScore * Conservative score: **3** * Paranoid score: **5** * Final recommended bucket: **Actionable Moderate at minimum** ## 2. Signal breakdown Conservative signals: * Memory corruption, weak primitive: **+1**. The commit explicitly describes a UAF on deleted virtqueues, but the shown failure is a GPF/crash and there is no demonstrated reclaim, object replacement, write-after-free, callback control, or arbitrary write. * Real lifetime corruption: **+1**. The bug is a real lifetime mismatch between PM freezer ordering, page reporting work, and virtqueue teardown. * Reliable kernel crash / strong DoS: **+1**. The trace shows a crash in `virtqueue_add_split()` via `virtballoon_free_page_report()` and the issue was reproduced through suspend/resume stress testing. * Hard or unreliable race / special timing required: **-1**. Triggering requires the PM freeze window plus page freeing or shrinker activity while virtqueues are being deleted. * Requires admin/root/system PM control in typical deployments: **-1**. Full `-2` is not used because local users or services may influence memory pressure and some systems expose suspend through policy-controlled desktop or service paths. Conservative total: **3** Paranoid additional signals: * Local unprivileged trigger contribution: **+1**. A local user may be able to create memory churn while a suspend or hibernation operation is initiated by system policy, even if they cannot directly control all PM steps. * Privileged kernel/device-management memory corruption path: **+1**. The UAF occurs in virtio/virtqueue device-management state during PM teardown, which is a trusted kernel/device boundary. * Broad virtualization relevance: **+1**. `virtio_balloon` and page reporting are relevant in virtualized/cloud environments, though not universal. Paranoid total after timing/privilege constraints: **5** Call-site confidence: **high**. The commit message provides the direct call path from `page_reporting_process()` to `virtballoon_free_page_report()` and the crash site in `virtqueue_add_split()`. ## 3. Reachability analysis The issue is local and not network reachable. Realistic triggering requires page reporting with a driver such as `virtio_balloon`, plus S3 suspend or S4 hibernation where the PM freezer runs while virtqueues are deleted. In typical server or VM deployments, initiating suspend/hibernate is privileged or controlled by system policy, so conservative reachability is not fully unprivileged. However, a local user or guest workload may help trigger the vulnerable window by creating memory churn and free-page activity during a policy-driven suspend or hibernation cycle. Namespaces and containers do not obviously make this directly reachable unless a container or service can influence host or guest PM state. The path is configuration dependent, but not obscure in virtualized environments that use virtio balloon page reporting. ## 4. Severity interpretation This is more than an ordinary low-priority DoS because the patch fixes a real UAF in kernel device lifetime handling. The realistic demonstrated impact is a local kernel crash during suspend or hibernation. Theoretical privilege escalation is not strongly supported because the patch and trace do not show attacker-controlled reclaim, controlled reuse, type confusion, callback hijack, or write-after-free. Therefore, conservative handling is **borderline/manual-review Moderate**, while paranoid handling is **Actionable Moderate at minimum** due to real UAF plus device lifetime corruption in a virtualization-relevant path. ## 5. One-sentence report phrase A UAF in mm page reporting during suspend or hibernation can let unfrozen page reporting work access virtio_balloon virtqueues after device teardown, causing a kernel crash and requiring manual review due to real kernel lifetime corruption. ## 6. Manual review recommendation **MANUAL CHECK REQUIRED** Reason: the bug is an explicit UAF in a kernel device lifetime path. The demonstrated effect is DoS, but the lifetime corruption occurs on virtqueue state during PM teardown, so it should not be auto-closed without manual validation of exploitability and deployment exposure. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: mm/page_reporting: use system_freezable_wq to fix UAF during suspend Commit: f978048326570047e8216e81a67f9c71ef2bb1b1 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=f978048326570047e8216e81a67f9c71ef2bb1b1 Commit description: During PM freeze (e.g. S3 suspend or S4 hibernation), device drivers like virtio_balloon reset their underlying virtio devices and delete their virtqueues via vdev->config->del_vqs(). However, page reporting work (page_reporting_process) was scheduled on the global system_wq. Because system_wq lacks the WQ_FREEZABLE flag, the PM freezer skips it, leaving page_reporting_process active during suspend. If pages are freed into the buddy allocator while suspending (for example, when core MM invokes the balloon shrinker during S4 hibernation image saving), page reporting triggers virtballoon_free_page_report() on deleted virtqueues, resulting in a Use-After-Free / General Protection Fault: [ 196.795226] general protection fault, probably for non-canonical address 0xaa1436fe70dae6df: 0000 [#1] SMP NOPTI [ 196.825967] Workqueue: events page_reporting_process [ 196.831038] RIP: 0010:virtqueue_add_split+0x233/0x4c0 [virtio_ring] [ 196.927073] virtballoon_free_page_report+0x3a/0xe0 [virtio_balloon] [ 196.946943] page_reporting_process+0x370/0x4f0 Fix this by switching page reporting work to system_freezable_wq. This ensures that the PM freezer pauses page_reporting_process before device drivers destroy their reporting virtqueues. Because the reporting worker is frozen, memory reclamation/freeing (e.g. via shrinker execution) can safely return pages to MM during freeze without triggering unfrozen reporting work on deleted virtqueues. This aligns with the driver's existing design. The comment in virtballoon_freeze() states: /* * The workqueue is already frozen by the PM core before this * function is called. */ Testing: I have verified these fixes using Google’s virtualization infrastructure by running continuous suspend/resume iterations (40+ cycles) while churning memory using stress-ng (`stress-ng --vm 4 --vm-bytes 60% --timeout 1`) to constantly create free pages for the buddy allocator. We also set the `page_reporting_order` parameter to 0 to make the page reporting worker highly sensitive, forcing it to pick up any 4K free pages. This confirmed that the UAF crashes are no longer reproducible. Link: https://lore.kernel.org/20260721005603.1710551-1-linkl@google.com Fixes: 36e66c5 ("mm: introduce Reported pages") Signed-off-by: Link Lin Suggested-by: David Hildenbrand (Arm) Suggested-by: Michael S. Tsirkin Acked-by: David Rientjes Acked-by: David Hildenbrand (Arm) Acked-by: Michael S. Tsirkin Cc: Alexander Duyck Cc: Greg Thelen Cc: James Houghton Cc: Jason Wang Cc: Jiaqi Yan Cc: Vlastimil Babka Cc: Xuan Zhuo Cc: Signed-off-by: Andrew Morton Signed-off-by: Greg Kroah-Hartman Changed files: mm/page_reporting.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=f978048326570047e8216e81a67f9c71ef2bb1b1 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74481 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74481 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:H/PR:H/UI:N/S:U/C:N/I:N/A:H The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H The Best / paranoid CVSS score: 7 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: 3 Paranoid ActionableScore: 5 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: MODERATE KPANIC detected for this report: NO Published priority for this report (same as in Subject): MODERATE 7.0 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).