* [CVE-2026-97416][LOW] btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk() [ Upstream
@ 2026-09-24 18:47 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-24 18:47 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97416
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk() [ Upstream
Commit: 9740dd0c17a4be8cc47a06c5ca5293471a7e286e
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9740dd0c17a4be8cc47a06c5ca5293471a7e286e
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97416
Analysis date: Thu, 24 Sep 2026 14:47:37 -0400
ActionableScore: 2
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-2026-97416 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97416
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-2026-97416 LOW https://www.kernelcve.org/list/?q=CVE-2026-97416 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:N/A:H';**CWE-476;*CWE-20;CWE-754;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'A NULL pointer dereference can occur during Btrfs balance when a corrupted chunk tree contains a chunk item without a corresponding in memory block group. btrfs_lookup_block_group can return NULL and btrfs_may_alloc_data_chunk then dereferences the missing block group while preparing data chunk relocation, causing a kernel crash. For the CVSS the PR:L in the paranoid score covers environments where a low privileged user can provide or control a corrupted Btrfs image that is mounted and balanced by a privileged service or shared storage workflow. The issue is local and is not directly network reachable. Impact is denial of service through a kernel crash. The patch context does not provide evidence of use after free, out of bounds access, information disclosure, arbitrary write, or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES KASAN NULLPTR DISK SKIP NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 2
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Reliable kernel crash / strong DoS. The supplied trace and code directly establish a NULL pointer dereference in btrfs_may_alloc_data_chunk during Btrfs balance.
* +1 Important filesystem/storage path. The fault occurs while processing Btrfs chunk and block-group metadata during data chunk relocation.
No separate Availability point was added because the demonstrated kernel crash is already counted.
Important non-awarded signals:
* No UAF, stale post-lifetime object access, double free, or repeated refcount mutation is established.
* No out of bounds access, arbitrary write, controlled corruption, controlled reclaim, or attacker-controlled replacement is established.
* No confidentiality or integrity impact is established. The corrupted filesystem metadata causes a missing in-memory block-group lookup result and immediate NULL dereference.
* No local unprivileged trigger point was awarded. The supplied patch does not establish that an ordinary user can mount the corrupted Btrfs image and execute the complete balance operation.
* No remote reachability point was awarded. The vulnerable operation is a local Btrfs balance ioctl path.
* No filesystem ownership, reflink, COW, or cross-file permission-bypass primitive is established.
* No privilege-escalation point was awarded. A malformed image causing a crash does not provide a memory-corruption or authorization-bypass primitive.
3. Reachability analysis
The direct trigger requires a mounted Btrfs filesystem containing inconsistent metadata. Specifically, the on-disk chunk tree contains a chunk item for which no matching block-group item exists, so btrfs_lookup_block_group returns NULL during balance.
The immediate caller chain includes btrfs_ioctl_balance, so triggering normally requires access to the Btrfs balance control-plane operation. The supplied context does not show the exact capability check or whether the complete mount plus balance sequence can be performed from an attacker-controlled user namespace. Therefore HostAdminRequired and NamespaceScopedPrivilege are UNKNOWN.
A lower-privilege scenario is possible only if an attacker can provide a malformed Btrfs image to a privileged mount and balance workflow, or can operate on an already accessible Btrfs filesystem. That deployment-specific chain is not established by the patch. No special hardware, boot setting, race condition, or network access is required by the direct crash path.
4. Primitive and severity interpretation
The exact primitive is an invalid NULL pointer dereference:
btrfs_lookup_block_group returns NULL
then btrfs_may_alloc_data_chunk dereferences cache->flags
This is not an active structured-object UAF and not a fixed stale-storage lifetime issue. The missing block-group cache entry results from inconsistent filesystem metadata, and the dereference crashes before any demonstrated useful attacker-controlled memory access, write, refcount mutation, ownership violation, or semantic reinterpretation occurs.
The demonstrated consequence is local denial of service through a kernel crash during Btrfs balance. A privilege-escalation, confidentiality, integrity, or cross-filesystem ownership consequence is speculative and unsupported by the patch context.
PrimitiveClass is CLASS_C because the established behavior is crash-only invalid-state handling. ImportantCandidate is NO because there is no unresolved corruption or security-boundary primitive beyond the crash. AutoDowngradeAllowed is YES because the patch establishes a bounded NULL dereference and does not establish memory corruption, lifetime corruption, or a policy bypass.
Likely operational severity is ordinary Moderate or lower, depending on whether the affected environment permits untrusted users to supply Btrfs images to privileged maintenance workflows.
5. One-sentence report phrase
A corrupted Btrfs image can cause btrfs balance to dereference a missing block-group cache entry and crash the kernel, resulting in local denial of service.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a malformed-metadata NULL dereference with a kernel-crash consequence only. No UAF, write primitive, ownership violation, disclosure path, privilege escalation mechanism, or network reachability is demonstrated.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: btrfs: balance: fix potential bg lookup failure in btrfs_may_alloc_data_chunk() [ Upstream
Commit: 9740dd0c17a4be8cc47a06c5ca5293471a7e286e
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9740dd0c17a4be8cc47a06c5ca5293471a7e286e
Changed files:
fs/btrfs/volumes.c
fs/btrfs/ioctl.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=9740dd0c17a4be8cc47a06c5ca5293471a7e286e
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97416 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97416
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:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 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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