From mboxrd@z Thu Jan 1 00:00:00 1970 From: AL-KERNEL To: kernel-cve@kernelcve.org Subject: [CVE-2026-93798][LOW] btrfs: fix reloc root cleanup in merge_reloc_roots() [ Upstream Date: Thu, 24 Sep 2026 14:45:22 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-AL-KERNEL-CVE: CVE-2026-93798 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: 0 X-AL-KERNEL-ActionableScore-Lower: unknown X-AL-KERNEL-Commit: ab48583aa9948205ff9a6470e23dbff74c565e24 List-Id: CVE: CVE-2026-93798 Priority: LOW AL-KERNEL base severity: LOW KPANIC flag: NO Patch: btrfs: fix reloc root cleanup in merge_reloc_roots() [ Upstream Commit: ab48583aa9948205ff9a6470e23dbff74c565e24 Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab48583aa9948205ff9a6470e23dbff74c565e24 Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93798 Analysis date: Thu, 24 Sep 2026 14:45:22 -0400 ActionableScore: 0 ActionableScore lower bound: unknown Actionable bucket: Ordinary Moderate Manual review required: NO Summary: No one-sentence report phrase was found. ====================================================================== ABOUT THIS REPORT ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93798 is available here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93798 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-2026-93798 LOW https://www.kernelcve.org/list/?q=CVE-2026-93798 CHECK WITH IMPACT FROM ORIG NN NONE 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-667;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A race in Btrfs relocation root cleanup can expose an inconsistent combination of the reloc_root pointer and the BTRFS_ROOT_DEAD_RELOC_TREE state bit. The missing ordering allows a concurrent observer to potentially use a stale relocation root reference after the cleanup path drops its reference, creating a plausible use after free candidate. For the CVSS the PR:L is used for the paranoid score because Btrfs relocation operations may be available to a capability restricted root, delegated service account, or similarly limited local management context. The issue is not network reachable. The base impact is local denial of service through a filesystem race. In the worst case the stale pointer condition may have confidentiality and integrity impact and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) YES DISK SIMPLEFIX SKIP NO NO checked ====================================================================== ACTIONABLESCORE ANALYSIS ====================================================================== ActionableScore=0 PrimitiveClass=NONE RealUAF=NO HostAdminRequired=UNKNOWN NamespaceScopedPrivilege=UNKNOWN ImportantCandidate=NO ManualReview=NO AutoDowngradeAllowed=YES 1. ActionableScore * Raw conservative score: 0 * Conservative score: 0 * Raw paranoid score: 0 * Paranoid score: 0 * Final recommended bucket: **Ordinary Moderate**:: 2. Signal breakdown * +0 Missing memory-ordering protocol. The patch replaces a direct reloc_root NULL assignment and independent state-bit clear with clear_reloc_root, which provides the required ordering between these operations. * +0 Incorrect state-bit clearing. The old code cleared BTRFS_ROOT_DEAD_RELOC_TREE even when root did not point to the relocation root being processed. * No Real UAF signal awarded. The supplied patch does not establish that a reader dereferences reloc_root after btrfs_put_root has ended its lifetime. * No concrete repeated release or refcount mutation exists. btrfs_put_root is called once for reloc_root after the pointer relation is cleared. The patch does not show the same dangling reloc_root reference reaching a second put or refcount operation. * No crash or reliable DoS is demonstrated in the commit message or diff. * No controlled reclaim, arbitrary write, structured stale-object consumption, disclosure, integrity violation, or privilege escalation is demonstrated. * No remote reachability is established. * No privilege penalty is applied because the complete privilege boundary for Btrfs relocation is not shown. Unknown privilege requirements do not justify a negative score. 3. Reachability analysis The affected path is local Btrfs relocation cleanup in merge_reloc_roots. The supplied material does not show which users can initiate the complete relocation sequence, whether balance or relocation operations require host-admin-equivalent authority in the evaluated deployment, or whether any relevant operation can be completed from an attacker-controlled namespace. No network trigger, special hardware requirement, or prior privileged setup is established by the patch. The issue is a synchronization and state-consistency correction in filesystem relocation handling, but the supplied evidence does not establish a security-relevant attacker path. 4. Primitive and severity interpretation The patch restores an ordering invariant between root->reloc_root and BTRFS_ROOT_DEAD_RELOC_TREE. It also prevents clearing the dead relocation-tree state when the current root is not associated with the relocation root being cleaned up. This is not a demonstrated use-after-free. The term root refs in the commit refers to Btrfs root-item references and does not itself establish that the in-memory struct btrfs_root object has reached zero lifetime references. Although clear_reloc_root is intended to make concurrent observation of pointer and state-bit updates consistent, the supplied code does not establish a stale post-free dereference, a second release through a dangling reference, or a reader that consumes freed structured state. The primitive is therefore classified as NONE rather than CLASS_B. The practical consequence supported by the patch is prevention of inconsistent relocation-root state. A UAF, kernel crash, metadata corruption, or privilege escalation remains speculative and is not scored. ImportantCandidate is NO and AutoDowngradeAllowed is YES because no unresolved concrete corruption or security-boundary primitive is established. 5. One-sentence report phrase The patch restores correct ordering when clearing a Btrfs relocation root pointer and its associated state bit, preventing inconsistent relocation cleanup state without demonstrating a concrete use after free or security impact. 6. Manual review recommendation NO MANUAL CHECK NEEDED The patch fixes a synchronization and state-consistency issue, but the supplied evidence does not establish a stale post-lifetime use, crash, corruption primitive, or attacker-reachable security consequence. 7. Call-site confidence Call-site confidence: medium ====================================================================== UPSTREAM PATCH SUMMARY ====================================================================== Patch: btrfs: fix reloc root cleanup in merge_reloc_roots() [ Upstream Commit: ab48583aa9948205ff9a6470e23dbff74c565e24 Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=ab48583aa9948205ff9a6470e23dbff74c565e24 Changed files: fs/btrfs/relocation.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=ab48583aa9948205ff9a6470e23dbff74c565e24 ====================================================================== DETAILED REPORT METHODOLOGY ====================================================================== The original Linux kernel CVE announcement for CVE-2026-93798 can be found here: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93798 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: unknown Paranoid ActionableScore: 0 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).