* [CVE-2026-97551][MODERATE REGULAR] xfs: initialise args->total for parent pointer updates
@ 2026-09-25 18:41 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-25 18:41 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97551
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xfs: initialise args->total for parent pointer updates
Commit: 9ad85bce62cadfdf4242f6e6bbff2a52e51d30f1
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ad85bce62cadfdf4242f6e6bbff2a52e51d30f1
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97551
Analysis date: Fri, 25 Sep 2026 14:41:11 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97551 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97551
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 REGULAR
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-2026-97551 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-97551 CHECK WITH IMPACT FROM ORIG NN MODERATE Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H';CWE-191;CWE-682;**CWE-400;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'An integer underflow in XFS parent pointer updates occurs because args total is initially zero and attr fork growth subtracts a reservation value from it. The wrapped value can bypass a free space availability check and, when allocation reaches an allocation group with zero available blocks, an ENOSPC error can escalate into an XFS filesystem shutdown. For the CVSS the PR:L value is used because a local user with write access to a suitable directory can potentially trigger parent pointer updates without administrative filesystem control. Reliable triggering also requires an XFS filesystem with parent pointers enabled, attribute fork growth, and a specific low free space allocation group state. The issue is not network reachable. Impact is denial of service for the affected filesystem. No memory corruption, information disclosure, integrity impact, or privilege escalation primitive is demonstrated by the patch.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES DISK SIMPLEFIX LINUS YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* Final recommended bucket: **Borderline / manual review recommended**::
Conservative arithmetic: +1 local unprivileged trigger, +1 filesystem shutdown, +1 important filesystem path, -1 unusual parent pointer filesystem feature requiring prior privileged filesystem setup.
Paranoid arithmetic: conservative 2, plus +1 because a user with write access may be able to influence sustained filesystem space pressure and allocation conditions sufficiently to make the zero-free-block AG condition practically reachable.
2. Signal breakdown
* +1 Local unprivileged trigger. A user with write permission to a directory on an already mounted affected XFS filesystem can perform namespace operations that invoke parent pointer add or replace handling. The user does not need filesystem administration at trigger time.
* +1 Reliable kernel availability impact. The supplied commit explicitly states that the invalid reservation accounting can cause `-ENOSPC` to be escalated by `xfs_defer_finish_noroll()` into an XFS filesystem shutdown.
* +1 Important filesystem path. The defect is in XFS metadata and attribute-fork reservation handling during parent pointer updates. The resulting shutdown affects availability of the mounted filesystem.
* -1 Unusual and preconfigured feature requirement. The vulnerable path requires an XFS filesystem formatted and mounted with parent pointer support, plus an attr-fork growth operation. Enabling and deploying this filesystem feature is normally prior administrative setup.
Paranoid-only signal:
* +1 Plausible attacker influence over allocation pressure. A local writer may be able to consume filesystem capacity and repeatedly perform allowed directory operations, making the required allocation failure state more practical than a purely accidental one. This does not establish metadata corruption or privilege escalation.
Important non-awarded signals:
* No real UAF, stale-object use, double release, refcount mutation, OOB access, arbitrary write, or controlled corruption is established.
* No confidentiality impact is established. The wrapped reservation value is used for allocation accounting and no disclosure path is shown.
* No integrity impact is established. The demonstrated result is allocation failure and filesystem shutdown, not persistent metadata corruption or unauthorized modification.
* No privilege escalation or authorization bypass is established.
* No remote reachability is established. The vulnerable operation is reached through local filesystem activity.
* No race penalty applies. The failure follows deterministic arithmetic and allocation-state conditions rather than a timing race.
* No additional availability point is awarded because the filesystem shutdown is the same consequence already counted as the strong DoS signal.
3. Reachability analysis
The evaluated attacker is an ordinary local user who already has write access to a directory on an affected mounted XFS filesystem. Parent pointer add or replace operations can be reached through normal filesystem namespace activity, but only where the administrator has previously created an XFS filesystem with the parent pointer feature enabled.
Host-admin-equivalent privilege is not required for the runtime trigger once such a filesystem is available, therefore `HostAdminRequired=NO`. This is not a namespace-specific capability path. User namespaces do not by themselves create or format the required host XFS filesystem feature, and the supplied evidence does not establish that the complete setup and trigger can be performed inside an attacker-controlled namespace. Therefore `NamespaceScopedPrivilege=UNKNOWN`.
The trigger additionally requires attribute-fork growth and allocation in an allocation group with zero available blocks. The supplied evidence establishes this condition but does not establish that every local user can reliably select a particular allocation group. The conservative score therefore retains the feature/configuration limitation. The paranoid score treats filesystem filling and repeated allowed operations as a plausible way to make the condition operationally relevant.
No special hardware, network listener, firmware input, boot option, or race window is involved.
4. Primitive and severity interpretation
The exact defect is an unsigned integer underflow in `args->total`. `xfs_parent_da_args_init()` starts from zeroed memory, while `xfs_da_grow_inode_int()` subtracts a reservation amount from the zero value. This wraps the `xfs_extlen_t` value and defeats the intended free-space availability check.
This is not a memory corruption primitive. The patch-supported consequence is an invalid reservation/accounting state which can reach an `-ENOSPC` path that forces an XFS filesystem shutdown. There is no active stale object, fixed stale storage, UAF, refcount operation, cleanup lifetime bug, or attacker-controlled post-free state.
PrimitiveClass is `NONE` because the patch establishes an arithmetic and allocation-accounting logic flaw, not a corruption, ownership, authorization, or lifetime primitive. The demonstrated impact is filesystem-level denial of service. A theoretical possibility of filesystem metadata corruption is not supported by the supplied patch or call-path description and is not scored.
`ImportantCandidate=NO` because no meaningful exploitation leverage beyond filesystem shutdown is established. `AutoDowngradeAllowed=YES` because the issue is a constrained local DoS condition with no unresolved kernel memory-corruption or security-boundary primitive. Manual review remains recommended to verify product exposure, especially whether affected XFS parent pointer filesystems are deployed and whether untrusted users can fill or heavily manipulate them.
Likely operational severity is ordinary Moderate or lower in environments where parent pointers are not enabled. It becomes more actionable for shared systems that deploy the feature and permit untrusted users to consume substantial filesystem space.
5. One-sentence report phrase
An integer underflow in XFS parent pointer attribute-fork reservation accounting can bypass a free-space check and cause an XFS filesystem shutdown when allocation reaches an empty allocation group, resulting in local denial of service.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Verify whether XFS parent pointer support is enabled on deployed filesystems and whether untrusted local users can perform parent pointer updates while creating sustained low-free-space allocation conditions.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfs: initialise args->total for parent pointer updates
Commit: 9ad85bce62cadfdf4242f6e6bbff2a52e51d30f1
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9ad85bce62cadfdf4242f6e6bbff2a52e51d30f1
Commit description:
xfs_parent_da_args_init() builds an xfs_da_args from a zeroed
xfs_parent_args (kmem_cache_zalloc), leaving args->total == 0.
xfs_da_grow_inode_int() treats that field as a running block reservation
and subtracts from it; because it is an xfs_extlen_t (uint32_t), the
first attr-fork growth wraps it to ~0U. That defeats the free-space
check in xfs_alloc_space_available(), and when it coincides with an AG
that has exactly zero available blocks the allocation is clamped to
maxlen 0 and returns -ENOSPC, which xfs_defer_finish_noroll() escalates
to a filesystem shutdown.
Set args->total the way the log recovery path does
(xfs_attri_recover_work(), xfs_attr_item.c:706), in the add and replace
paths that can grow the fork. Removals and lookups never grow it, so
they leave the field alone, matching that switch.
Fixes: b7c62d9 ("xfs: parent pointer attribute creation")
Cc: [email protected] # v6.10
Signed-off-by: Javier Tia <[email protected]>
Reviewed-by: Darrick J. Wong <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
[ Backported to 6.12.y and 6.18.y, whose fs/xfs/libxfs/xfs_parent.c are
byte-identical. These trees queue the operation with
xfs_attr_defer_add() instead of calling xfs_attr_setname() and
xfs_attr_replacename() directly, and spell the inode number
child->i_ino rather than I_INO(child), so the upstream hunks do not
apply as-is. The defect is unchanged: xfs_attr_defer_add() stores a
pointer to this same xfs_da_args, and xfs_attr_finish_item() resets
only args->trans, so the zeroed total still reaches
xfs_da_grow_inode_int(). The assignment therefore goes in the same
place, before the operation is queued. xfs_attr_calc_size() needs no
new include: it is declared in xfs_attr.h, which xfs_parent.c already
includes. ]
Signed-off-by: Javier Tia <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/xfs/libxfs/xfs_parent.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=9ad85bce62cadfdf4242f6e6bbff2a52e51d30f1
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97551 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97551
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:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 2
Paranoid ActionableScore: 3
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: NO
Published priority for this report (same as in Subject): MODERATE REGULAR
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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