From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-72306][MODERATE 7.0] vduse: Fix race in vduse_dev_msg_sync and vduse_dev_read_iter Date: Sat, 15 Aug 2026 08:30:45 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-72306 X-AL-KERNEL-Priority: MODERATE 7.0 X-AL-KERNEL-Severity: MODERATE 7.0 X-AL-KERNEL-Base-Severity: MODERATE X-AL-KERNEL-KPANIC: YES X-AL-KERNEL-ActionableScore: 5 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a List-Id: CVE: CVE-2026-72306 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: vduse: Fix race in vduse_dev_msg_sync and vduse_dev_read_iter Commit: c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72306 Analysis date: Sat, 15 Aug 2026 08:30:45 -0400 ActionableScore: 5 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A local race in VDUSE message handling can leave a `vduse_dev_msg` outside both tracked lists, allowing timeout handling to perform a double `list_del()` and corrupt kernel list state, causing a kernel crash and requiring manual review for possible lifetime-corruption impact. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72306 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72306 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-2026-72306 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-362;*CWE-416;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in VDUSE message handling can leave a vduse_dev_msg outside both send_list and recv_list while vduse_dev_read_iter copies the request to userspace. If vduse_dev_msg_sync times out during this window, it can call list_del on the same message and corrupt kernel list state, leading to a kernel crash. For the CVSS the PR:L is used because reliable triggering requires local code or a local VDUSE userspace backend with access to the device interface, not full host administrator privileges in all deployments. The issue is not network reachable and is triggered through the local VDUSE control path. Impact is at least a local denial of service via kernel crash and in the paranoid case may allow confidentiality or integrity impact due to kernel list corruption or a UAF candidate, so it should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 5) YES LOCK DANGER RACE HARDWARE LINUS KPANIC YES NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=5 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 5 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local low-privilege trigger: +1. Triggering requires local access to the VDUSE userspace backend or device interface, not network access. * Memory corruption, weak/indirect corruption candidate: +1. The bug can cause double `list_del()` and kernel list corruption, but no controlled overwrite or reclaim primitive is shown. * Real lifetime corruption: +1. The patch explicitly notes that `msg` may already have been freed after malicious userspace replies and wakes the caller. * Reliable kernel crash / strong DoS: +1. The commit directly describes a double `list_del()` crash. * Privileged kernel/device-management memory corruption path: +1. The corruption occurs in VDUSE/vDPA device message handling, a trusted kernel device-management path. * Hard or unreliable race / special timing required: -1. The issue depends on a timeout racing with `copy_to_iter()` and userspace interaction. Paranoid additional signal: * Weak LPE concern: +1. Kernel list corruption plus a possible freed `msg` pointer is enough for manual review, although no attacker-controlled reclaim, callback control, or arbitrary write is demonstrated. ## 3. Reachability analysis The issue is local-only and is not network reachable. A realistic trigger requires a process that can interact with the VDUSE device backend path and influence timing around `vduse_dev_read_iter()`, message replies, and timeout handling. This is not a broadly exposed default user API on ordinary systems, but in virtualization or vDPA deployments the backend may run as a reduced-privilege service account rather than full host root. Namespaces or containerized device-backend deployments can lower the practical privilege boundary, so treating this as PR:L is reasonable for paranoid triage. Call-site confidence: high, because the patch and commit message show the affected function and the racing message lifetime/list transitions. ## 4. Severity interpretation This is more than an ordinary Moderate crash bug because the demonstrated failure is a race-driven kernel list corruption with possible freed-object lifetime semantics. The realistic demonstrated impact is local DoS through kernel crash. The theoretical escalation case is weaker: no controlled reclaim, type confusion, callback dispatch, refcount takeover, or arbitrary write is shown. Therefore the conservative score stays borderline/manual-review, while the paranoid score reaches Actionable Moderate and should not be auto-closed. ## 5. One-sentence report phrase A local race in VDUSE message handling can leave a `vduse_dev_msg` outside both tracked lists, allowing timeout handling to perform a double `list_del()` and corrupt kernel list state, causing a kernel crash and requiring manual review for possible lifetime-corruption impact. ## 6. Manual review recommendation MANUAL CHECK REQUIRED Reason: this is a race with concrete kernel list corruption and possible freed-message lifetime behavior, not merely a warning or resource leak. The known impact is DoS, but the corruption pattern is sufficiently security-relevant to require manual review. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: vduse: Fix race in vduse_dev_msg_sync and vduse_dev_read_iter Commit: c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a Commit description: There is one race case in vduse_dev_msg_sync and vduse_dev_read_iter: vduse_dev_read_iter(): lock(msg_lock); dequeue_msg(send_list); unlock(msg_lock); vduse_dev_msg_sync(): wait_timeout() finish lock(msg_lock); check msg->complete is false list_del(msg); <- double list_del() crash! To fix this case, we shall ensure vduse_msg is on send_list or recv_list outside the msg_lock critical section. Fixes: c8a6153 ("vduse: Introduce VDUSE - vDPA Device in Userspace") Cc: stable@vger.kernel.org Signed-off-by: Zhang Tianci Reviewed-by: Xie Yongji Acked-by: Jason Wang Acked-by: Eugenio Pérez Acked-by: Michael S. Tsirkin Signed-off-by: Michael S. Tsirkin Message-ID: <20260226115550.1814-3-zhangtianci.1997@bytedance.com> Signed-off-by: Greg Kroah-Hartman Changed files: drivers/vdpa/vdpa_user/vduse_dev.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=c83ad3dfa6d9953d5ce6839416bf5a1bfc50285a ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-72306 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72306 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: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: 4 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: YES 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).