From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-74721][MODERATE 7.0] accel/amxdna: Fix page-insertion errors in amdxdna_insert_pages() [ Upstream Date: Sat, 22 Aug 2026 13:57:01 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-74721 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: 7 X-AL-KERNEL-ActionableScore-Lower: 4 X-AL-KERNEL-Commit: 1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 List-Id: CVE: CVE-2026-74721 Priority: MODERATE 7.0 AL-KERNEL base severity: MODERATE KPANIC flag: YES Patch: accel/amxdna: Fix page-insertion errors in amdxdna_insert_pages() [ Upstream Commit: 1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74721 Analysis date: Sat, 22 Aug 2026 13:57:01 -0400 ActionableScore: 7 ActionableScore lower bound: 4 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: A local reference lifetime bug in amdxdna_insert_pages() can prematurely close VMA backed GEM resources during mmap error handling, causing a later double close and refcount underflow with at least kernel crash impact and possible UAF based privilege escalation concern. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74721 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74721 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-2026-74721 MODERATE CHECK WITH IMPACT FROM ORIG NN IMPORTANT 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-911;*CWE-672;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'A reference lifetime bug in amdxdna_insert_pages() can release VMA backed resources before the mmap syscall has returned. The failing error paths manually call vm_ops close while the VMA remains alive, dropping shmem pages_pin_count and the GEM object reference that backs the mapping. When the process later unmaps the range, normal VMA teardown can call close again and produce a refcount underflow, which is a use after free candidate rather than a simple warning. For the CVSS the PR:L is used because a local user or service with access to the amdxdna DRM accel device can trigger mmap related paths without full administrator privileges. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid case may allow confidentiality and integrity impact due to memory lifetime corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6) SKIP CVE-2026-74721 UNKNOWN SKIP No affected files built, so skip this CVE NO - - unknown MAYBE READ OOB ERRORPATH KPANIC MEMORY KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=7 ActionableScoreLower=4 ## 1. ActionableScore * Conservative score: 4 * Paranoid score: 7 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: ## 2. Signal breakdown Conservative signals: * Local unprivileged trigger: +1. A local user or service with access to the amdxdna DRM accel device can plausibly reach the mmap path. * Memory corruption, weak or indirect corruption candidate: +1. The patch describes premature resource release and later refcount underflow, but no demonstrated reclaim or controlled overwrite. * Real lifetime corruption: +1. Manual `vm_ops->close()` drops shmem pin count and GEM object reference while the VMA is still alive. * Reliable kernel crash / strong DoS: +1. Refcount underflow or double close can realistically crash or destabilize the kernel. * Hard or special error path required: -1. Triggering depends on page insertion or fault error paths. * Rare hardware or device specific exposure: -1. Requires amdxdna hardware and driver exposure. Paranoid additional signals: * Memory corruption, strong corruption primitive: +2 instead of weak +1. The described double close and refcount underflow can become a UAF style lifetime bug. * Privilege escalation plausible: +2. Not proven, but local GEM/VMA lifetime corruption can be a credible LPE candidate if object reuse is controllable. * Confidentiality impact plausible: +1. Paranoid case assumes memory lifetime corruption may expose kernel or cross object data. * Integrity impact plausible: +1. Paranoid case assumes refcount lifetime corruption may allow object state corruption. Call-site confidence: medium. The patch includes the failing helper and explains the caller relationship with `amdxdna_gem_obj_mmap()`, HMM notifier cleanup, VMA lifetime, and later VMA teardown, but not the full caller body. ## 3. Reachability analysis The issue is local, not network reachable. The likely attacker is a local user or containerized service that can open the amdxdna accel DRM device and invoke mmap related GEM object paths. Full root is not inherently required if the device node is exposed through normal render or accel permissions, but practical reachability depends on udev policy and hardware availability. Namespaces may matter if the device node is passed into a container, because a reduced privilege container process could still exercise the driver path. The trigger is not default on all systems because it requires AMD XDNA hardware, the amdxdna driver, and a hard page insertion or page fault failure path. ## 4. Severity interpretation This is above an ordinary Moderate correctness bug because the patch fixes real VMA and GEM object lifetime corruption, not just a warning or leak. The realistic impact is local DoS through refcount underflow or kernel crash. The Important class concern is based on the paranoid interpretation that premature release of a VMA backed GEM object followed by a second close can create a UAF candidate. There is no demonstrated arbitrary write, controlled reclaim, or public exploit path in the supplied material, so the conservative score remains borderline. Manual review is still warranted because local driver mmap lifetime bugs have historically produced underestimated privilege escalation risk. ## 5. One-sentence report phrase A local reference lifetime bug in amdxdna_insert_pages() can prematurely close VMA backed GEM resources during mmap error handling, causing a later double close and refcount underflow with at least kernel crash impact and possible UAF based privilege escalation concern. ## 6. Manual review recommendation MANUAL CHECK REQUIRED This should not be auto-closed because the bug is a local lifetime corruption issue with refcount underflow on a still-live VMA and a plausible UAF path, even though practical exploitation beyond DoS is not demonstrated. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: accel/amxdna: Fix page-insertion errors in amdxdna_insert_pages() [ Upstream Commit: 1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 Changed files: drivers/accel/amdxdna/amdxdna_gem.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=1501e4d07c6fee0d50531a0d1cb2be01a63e6e75 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-74721 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74721 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:L/I:L/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: 7 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).