* [CVE-2026-80734][LOW] btrfs: initialize inode mapping flags for cached inodes [ Upstream
@ 2026-09-03 9:32 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-03 9:32 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80734
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: btrfs: initialize inode mapping flags for cached inodes [ Upstream
Commit: 0d26249671171ab759cb4fdce673554a690fa655
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d26249671171ab759cb4fdce673554a690fa655
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80734
Analysis date: Thu, 03 Sep 2026 05:32:14 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: YES
Summary:
Btrfs cached inode reload can skip mapping flag and folio order initialization, causing later I/O to use folios smaller than the filesystem block size and potentially trigger a local kernel crash under non-default large-folio configurations.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80734 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80734
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-80734 LOW https://www.kernelcve.org/list/?q=CVE-2026-80734 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:N/I:L/A:H';CWE-665;CWE-754;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.3';DESCR 'Btrfs cached inode reload can skip initialization of inode mapping flags and minimal folio order when a delayed inode node is reused. On systems using an 8K block size with a 4K page size, the mapping can keep order 0 instead of the required order 1, so later buffered read or write paths may operate on folios smaller than the filesystem block size and hit a kernel BUG or assertion. For the CVSS the PR:L is used because a local user with access to a writable affected Btrfs filesystem may be able to drive file operations that reach the faulty inode state, although reliable triggering depends on cache eviction and a non default filesystem configuration. The issue is not network reachable. Impact is primarily local denial of service via kernel crash. A limited integrity concern is kept only in the paranoid score because wrong mapping setup can violate filesystem I/O invariants, but the patch does not show a concrete UAF, OOB write, or arbitrary write primitive.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) SKIP CVE-2026-80734 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES NO NO unknown MAYBE DANGER DISK SKIP HARDWARE INCREASED_FROM_LOW_BASED_ON_HIGHCVSSSCORE DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5 DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
## 1. ActionableScore
* Conservative score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::
## 2. Signal breakdown
* Local unprivileged trigger: +1. A local user with write access to the affected Btrfs filesystem may be able to exercise the read/write/copy_file_range paths involved.
* Memory layout invariant restoration: +1. The patch restores consistency between inode mapping flags, minimal folio order, filesystem block size, and page-cache folio sizing.
* Reliable kernel crash / strong DoS: +1. A kernel BUG/assertion is shown in the affected path, but it depends on a specific test/configuration and the assertion is noted as being added by a later patch.
* Important filesystem/storage path: +1. The bug is in Btrfs inode/page-cache/write-path initialization.
* Hard or special triggering conditions: -1. The sequence requires cached inode reuse through delayed_node, eviction/drop-cache or memory pressure, and later I/O on that inode.
* Rare/non-default configuration: -1. The described failure requires 8K block size with 4K page size and large folio support under CONFIG_BTRFS_EXPERIMENTAL.
Total: 2
## 3. Reachability analysis
The issue is local only. It is not network reachable. A normal local user may be able to contribute to triggering by creating, writing, copying, and reopening files on a writable affected Btrfs filesystem, but reliable reproduction depends on inode eviction and a non-default filesystem/page-size configuration. Namespaces do not materially turn this into a remote or cross-container issue unless the container is given access to the affected mounted Btrfs filesystem. The affected configuration is not a broad default path because the commit explicitly ties the reproducer to 8K block size, 4K page size, and experimental large folio behavior.
Call-site confidence: high, because the patch and commit message provide the relevant btrfs_read_locked_inode path and the later read/write call trace.
## 4. Severity interpretation
This behaves like an ordinary Moderate or Low-like filesystem correctness and availability issue, not an Important-class vulnerability. The realistic demonstrated impact is a local kernel BUG/assertion or crash under special Btrfs configuration and cache-reuse conditions. There is no supported UAF, OOB write, attacker-controlled overwrite, reflink/COW ownership bypass, page-cache corruption of privileged files, or privilege escalation primitive in the supplied patch context. A limited theoretical integrity concern exists because wrong folio order can violate filesystem I/O invariants, but the evidence is not strong enough to raise the actionable score.
## 5. One-sentence report phrase
Btrfs cached inode reload can skip mapping flag and folio order initialization, causing later I/O to use folios smaller than the filesystem block size and potentially trigger a local kernel crash under non-default large-folio configurations.
## 6. Manual review recommendation
NO MANUAL CHECK NEEDED. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.
The issue appears suitable for deferred handling because the score is low, the trigger conditions are narrow, and the patch does not show a concrete memory corruption, privilege escalation, or cross-file/page-cache ownership bypass primitive.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: btrfs: initialize inode mapping flags for cached inodes [ Upstream
Commit: 0d26249671171ab759cb4fdce673554a690fa655
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=0d26249671171ab759cb4fdce673554a690fa655
Changed files:
fs/btrfs/inode.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=0d26249671171ab759cb4fdce673554a690fa655
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80734 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80734
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:N/I:L/A:H
The Best / paranoid CVSS score: 5.3
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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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