From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-45984][IMPORTANT] gfs2: Fix use-after-free in iomap inline data write path [ Upstream Date: Wed, 27 May 2026 18:09:36 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-45984 X-AL-KERNEL-Priority: IMPORTANT X-AL-KERNEL-Severity: IMPORTANT X-AL-KERNEL-Base-Severity: IMPORTANT X-AL-KERNEL-KPANIC: NO X-AL-KERNEL-ActionableScore: 8 X-AL-KERNEL-ActionableScore-Lower: 6 X-AL-KERNEL-Commit: 1403989d1b502f4a2c0d0b42ccf1c25748442eff List-Id: CVE: CVE-2026-45984 Priority: IMPORTANT AL-KERNEL base severity: IMPORTANT KPANIC flag: NO Patch: gfs2: Fix use-after-free in iomap inline data write path [ Upstream Commit: 1403989d1b502f4a2c0d0b42ccf1c25748442eff Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1403989d1b502f4a2c0d0b42ccf1c25748442eff Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984 Analysis date: Wed, 27 May 2026 18:09:36 -0400 ActionableScore: 8 ActionableScore lower bound: 6 Actionable bucket: Strong Important candidate / Actionable Moderate at minimum Manual review required: YES Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45984 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984 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: IMPORTANT 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-2026-45984 IMPORTANT CHECK 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-787;*CWE-664;CWE-362;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'GFS2 inline data writes can keep iomap inline_data pointing into a buffer head that is released by release_metapath() before iomap_write_end_inline() later writes to it. If reclaim frees the underlying page in between, the inline write becomes a use after free write into freed kernel memory. For the CVSS the PR:L is used because a local user with write access to an affected GFS2 file can exercise the inline data write path, although reliable triggering requires reclaim timing and specific filesystem state. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 8) MAYBE WRITE OOB DEADLOCK DISK LEAK UAF IMPROVEONLY LINUS SYZBOT - - checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=8 ActionableScoreLower=6 1. ActionableScore * Conservative score: 6 * Paranoid score: 8 * Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: 2. Signal breakdown * Local unprivileged trigger: +1. A local user with write access to an affected GFS2 filesystem can exercise the inline data write path. * Generic memory corruption, strong primitive: +2. The bug is an explicit use-after-free write detected by KASAN. * Real lifetime corruption: +1. `iomap->inline_data` points into a buffer head that was released before later write completion. * Reliable kernel crash / strong DoS: +1. The UAF write can crash the kernel under reclaim timing. * Important filesystem/storage path: +1. The bug is in GFS2 iomap inline data write handling. * Integrity impact plausible: +1. A write into freed memory can corrupt reclaimed kernel memory or filesystem metadata buffers. * Paranoid LPE plausibility: +1. UAF write in a filesystem write path may be exploitable beyond DoS, but no controlled reclaim or overwrite primitive is demonstrated. * Hard timing required: -1. Exploitation requires reclaim to free the buffer page between iomap begin and write end, and no standalone C reproducer is available. 3. Reachability analysis The issue is local and requires write access to a GFS2 file using inline data. It is not network reachable by itself. Containers may matter if untrusted workloads can write to a host GFS2 mount. Reliable exploitation depends on reclaim timing and filesystem state, but the syzbot/KASAN report confirms the lifetime bug and UAF write path. 4. Severity interpretation This is a real memory corruption issue, not only a filesystem warning or resource leak. Conservative handling is Actionable Moderate due to local trigger and timing constraints. Paranoid handling reaches Strong Important candidate because it is a UAF write in a filesystem write path, which historically can be underestimated even when a practical LPE chain is not yet demonstrated. 5. One-sentence report phrase GFS2 inline writes can retain `iomap->inline_data` pointing into a released buffer head, allowing reclaim to turn the later inline memcpy into a local use-after-free write. 6. Manual review recommendation MANUAL CHECK REQUIRED. The patch fixes an explicit KASAN-confirmed UAF write in a filesystem write path, with plausible impact beyond DoS despite timing constraints. ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: gfs2: Fix use-after-free in iomap inline data write path [ Upstream Commit: 1403989d1b502f4a2c0d0b42ccf1c25748442eff Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=1403989d1b502f4a2c0d0b42ccf1c25748442eff Changed files: fs/gfs2/bmap.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=1403989d1b502f4a2c0d0b42ccf1c25748442eff ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-45984 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-45984 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: 6 Paranoid ActionableScore: 8 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: IMPORTANT KPANIC detected for this report: NO Published priority for this report (same as in Subject): IMPORTANT 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).