From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-64474][LOW] vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc Date: Sat, 25 Jul 2026 08:09:06 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-64474 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: 8e872c07e40d51a66dee7b280a23a460a2e1e3fa List-Id: CVE: CVE-2026-64474 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc Commit: 8e872c07e40d51a66dee7b280a23a460a2e1e3fa Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e872c07e40d51a66dee7b280a23a460a2e1e3fa Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474 Analysis date: Sat, 25 Jul 2026 08:09:06 -0400 ActionableScore: 2 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate / Low-like Manual review required: NO Summary: A local process with VFIO migration control access can trigger an infinite loop in vfio_mig_get_next_state on blocked PRE_COPY transitions, causing a soft lockup or kernel panic, but the issue is not network reachable and does not show memory corruption or privilege escalation. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64474 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474 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-2026-64474 LOW CHECK WITH IMPACT FROM ORIG NN MODERATE 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-835;**CWE-400;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'vfio_mig_get_next_state can enter an infinite loop when a blocked migration transition resolves to VFIO_DEVICE_STATE_ERROR and the skip loop keeps following the ERROR sentinel back to itself. A local process with access to the VFIO device migration control path can trigger this through transitions such as STOP_COPY to PRE_COPY or STOP_COPY to PRE_COPY_P2P on a precopy capable device. For the CVSS the PR:L is used because the attacker needs local access to a VFIO device or a VM manager context with migration control, but full host root is not necessarily required when VFIO access is delegated. The issue is not network reachable and does not provide a memory corruption primitive. Impact is denial of service through a soft lockup or kernel panic when softlockup_panic is enabled.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES DEADLOCK DANGER SIMPLEFIX HARDWARE DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=2 ## 1. ActionableScore * Conservative score: 2 * Paranoid score: 2 * Final recommended bucket: **Ordinary Moderate / Low-like**:: ## 2. Signal breakdown Triggered signals: * Local delegated trigger: +1 A local process with access to VFIO migration controls can request the problematic state transition. This is not generally remote and not broadly unprivileged, but VFIO access may be delegated to a VM manager or non-root service account. * Reliable kernel crash / strong DoS: +1 The blocked transition can cause an infinite loop while holding the driver state mutex, leading to soft lockup and possibly panic when softlockup_panic is enabled. Not triggered: * Remote reachable: +0 No network packet or remote protocol path is involved. * Memory corruption: +0 The patch fixes an infinite loop on the VFIO_DEVICE_STATE_ERROR sentinel. There is no UAF, OOB access, double free, refcount misuse, stale pointer reuse, or arbitrary write primitive. * Privilege escalation plausible: +0 No LPE primitive is indicated. The issue is DoS-only. * Confidentiality / Integrity: +0 No information disclosure or data modification path is shown. * Rare configuration penalty: 0 VFIO migration and precopy-capable devices are not universal, but this is still a normal VFIO control path for affected deployments, so I would not strongly penalize it. ## 3. Reachability analysis The bug can be triggered by a local actor that can operate the VFIO device migration state machine, typically a VM manager such as QEMU or a process with delegated VFIO device access. Full host root is not always required in practical deployments, but generic unprivileged local users usually do not have this access by default. Namespaces and containers may matter if VFIO device access is delegated into a container or service context, but this does not become a normal unprivileged namespace attack. The path is not network reachable. Realistic exploitation requires an affected VFIO migration-capable device and a transition such as STOP_COPY to PRE_COPY or STOP_COPY to PRE_COPY_P2P on a precopy-capable setup. ## 4. Severity interpretation This behaves like an ordinary Moderate / Low-like kernel DoS issue, not an Important-class vulnerability. The realistic impact is a local denial of service through soft lockup or panic in configurations where VFIO migration is available and softlockup_panic may convert the lockup into a crash. There is no demonstrated memory corruption, no security boundary bypass, no sensitive-object access, and no privilege escalation primitive. Theoretical severity should not be raised solely because the affected code is in VFIO or because the loop runs in kernel context. ## 5. One-sentence report phrase A local process with VFIO migration control access can trigger an infinite loop in vfio_mig_get_next_state on blocked PRE_COPY transitions, causing a soft lockup or kernel panic, but the issue is not network reachable and does not show memory corruption or privilege escalation. ## 6. Manual review recommendation NO MANUAL CHECK NEEDED This can be handled as a DoS-only VFIO state-machine bug unless the evaluated product delegates VFIO migration controls to untrusted tenants or exposes a specific virtualization management path that makes triggering unusually easy. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vfio: prevent infinite loop in vfio_mig_get_next_state() on blocked arc Commit: 8e872c07e40d51a66dee7b280a23a460a2e1e3fa Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8e872c07e40d51a66dee7b280a23a460a2e1e3fa Commit description: vfio_mig_get_next_state() walks vfio_from_fsm_table[] one step at a time, looping to skip optional states the device does not support until *next_fsm is supported. A blocked transition is encoded as VFIO_DEVICE_STATE_ERROR, which the trailing return reports as -EINVAL. The skip loop does not account for the ERROR sentinel. state_flags_table[ERROR] is ~0U and vfio_from_fsm_table[ERROR][*] is ERROR, so once *next_fsm becomes ERROR the loop condition stays true and *next_fsm never changes. The blocked arcs STOP_COPY -> PRE_COPY and STOP_COPY -> PRE_COPY_P2P map to ERROR yet pass the support check on a precopy-capable device, causing the loop to spin forever while holding the driver state mutex. This can result in a soft lockup, and a panic with softlockup_panic set. Terminate the skip loop on the ERROR sentinel so a blocked transition falls through to the existing return and reports -EINVAL. Fixes: 4db5260 ("vfio: Extend the device migration protocol with PRE_COPY") Reported-by: Yuhao Jiang Cc: stable@vger.kernel.org Signed-off-by: Junrui Luo Reviewed-by: Kevin Tian Reviewed-by: Jason Gunthorpe Link: https://lore.kernel.org/r/SYBPR01MB7881290BBDE79B61AE6A017FAF122@SYBPR01MB7881.ausprd01.prod.outlook.com Signed-off-by: Alex Williamson Signed-off-by: Greg Kroah-Hartman Changed files: drivers/vfio/vfio_main.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=8e872c07e40d51a66dee7b280a23a460a2e1e3fa ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-64474 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64474 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:L/UI:N/S:U/C:N/I:N/A:H 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).