[CVE-2026-80804][MODERATE REGULAR] xfs: restore nofs context unconditionally in xfs_trans_roll

[AL-KERNEL <alkernel@kernelcve.org>]

CVE: CVE-2026-80804
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: xfs: restore nofs context unconditionally in xfs_trans_roll
Commit: b09198cf90ccf296970b774beea1c1ddb260f94c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b09198cf90ccf296970b774beea1c1ddb260f94c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80804
Analysis date: Fri, 04 Sep 2026 13:21:08 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES

Summary:
An XFS transaction roll error path can fail to restore NOFS context after `__xfs_trans_commit()`, allowing filesystem reclaim under XFS inode locks and causing a circular lock dependency that can stall the system.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80804 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80804

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80804	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80804 CHECK WITH IMPACT FROM ORIG NN LOW	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-667;*CWE-833;CWE-703;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'xfs_trans_roll can return from the error path after __xfs_trans_commit without restoring the NOFS context for the new transaction. This leaves later memory allocations able to enter fs_reclaim while XFS inode locks may still be involved, creating a circular lock dependency between xfs_nondir_ilock_class and fs_reclaim. For the CVSS the PR:L value is used because a local user with write access to an affected XFS filesystem may be able to create filesystem activity that reaches transaction roll and reclaim paths, although reliable triggering depends on workload and error conditions. The issue is not network reachable. Impact is denial of service through a possible deadlock or system stall, with no supported confidentiality or integrity impact.';NO MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3)  SKIP CVE-2026-80804 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: url YES  NO NO unknown 	MAYBE	DANGER DISK INIT SIMPLEFIX ERRORPATH HARDWARE LINUS SYZBOT  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH	-	-	checked

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ACTIONABLESCORE ANALYSIS
======================================================================

ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=NO
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES

## 1. ActionableScore

* Raw conservative score: 2
* Conservative score: 2
* Raw paranoid score: 3
* Paranoid score: 3
* No floor or cap changed the score.
* Final recommended bucket: **Borderline / manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* +1 Reliable DoS / system stall: the commit describes a circular lock dependency between `xfs_nondir_ilock_class` and `fs_reclaim`, which can cause a deadlock or severe stall.
* +1 Important filesystem path: the bug is in XFS transaction rolling and NOFS context handling, which is a core filesystem transaction path.

Paranoid additional signal:

* +1 Local below-host-admin reachability: a local user with write access to an affected XFS filesystem may be able to generate filesystem activity that reaches transaction roll and reclaim paths, although the exact failing commit path is workload and state dependent.

Non-awarded signals:

* Real UAF not awarded: no stale pointer, freed object reuse, double release, or refcount-after-free primitive is established.
* Controlled corruption not awarded: the patch restores NOFS context and does not show OOB access, arbitrary write, type confusion, or object replacement.
* C/I not awarded: no confidentiality or integrity impact is supported.
* Extra availability not awarded: the same deadlock or stall is already counted as DoS.
* Race penalty not applied: this is an error-path context restoration bug with a lock dependency, not a demonstrated hard attacker-timed race.
* Concrete repeated release/refcount not applicable: no first release ending object lifetime and second lifetime mutation on the same dangling reference is shown.
* FLOOR 5 not applied: there is no UAF, no repeated lifetime mutation, and no meaningful exploitation surface beyond DoS.

## 3. Reachability analysis

The likely attacker is a local user or process that can perform filesystem operations on an affected XFS filesystem. Host administrator privilege is not positively required for ordinary filesystem activity, so `HostAdminRequired=NO`.

The complete trigger depends on reaching an `__xfs_trans_commit()` failure path inside `xfs_trans_roll()` while later allocations can enter reclaim without NOFS protection. This may require specific filesystem pressure, error conditions, or syzkaller-style workload shaping, but no special hardware or network exposure is indicated.

This is not namespace-scoped in the meaningful security sense. It is not network reachable. Prior privileged setup may exist in the form of an already mounted XFS filesystem, but that is a common system state rather than an attacker-created privileged prerequisite.

## 4. Primitive and severity interpretation

The exact primitive is an incorrect NOFS context restoration on the error path of `xfs_trans_roll()`. After `__xfs_trans_commit()` clears the NOFS flag via transaction freeing, the old code restored the context only on the success path. If the commit failed, later execution could occur without NOFS protection and allow reclaim to recurse into filesystem locking, producing a circular lock dependency.

This is best classified as `CLASS_C`: primarily invalid lock-context state leading to DoS or system stall. It is not an active structured UAF, fixed stale storage UAF, or repeated release/refcount mutation.

Demonstrated consequence is local denial of service through deadlock or lockup. Speculative privilege escalation is not supported by the patch or supplied context. `ImportantCandidate=NO` because there is no memory corruption, ownership violation, authorization bypass, or unresolved Class B lifetime primitive. `AutoDowngradeAllowed=YES` because the issue appears DoS-only and does not preserve a concrete corruption primitive requiring Important-class manual triage.

Likely operational severity is ordinary to borderline Moderate.

## 5. One-sentence report phrase

An XFS transaction roll error path can fail to restore NOFS context after `__xfs_trans_commit()`, allowing filesystem reclaim under XFS inode locks and causing a circular lock dependency that can stall the system.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Reason: no corruption primitive is established and auto-downgrade is allowed, but the issue is in a core XFS transaction path with a plausible local DoS impact, so a lightweight manual check is reasonable.

## 7. Call-site confidence

Call-site confidence: high

======================================================================
UPSTREAM PATCH SUMMARY
======================================================================

Patch: xfs: restore nofs context unconditionally in xfs_trans_roll
Commit: b09198cf90ccf296970b774beea1c1ddb260f94c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b09198cf90ccf296970b774beea1c1ddb260f94c

Commit description:

When __xfs_trans_commit() fails in xfs_trans_roll(), the NOFS context
is cleared but only restored in the success path.  This leaves the
error path without nofs protection, causing a circular lock dependency
between xfs_nondir_ilock_class and fs_reclaim:

       CPU0                    CPU1
       ----                    ----
  lock(&xfs_nondir_ilock_class);
                               lock(fs_reclaim);
                               lock(&xfs_nondir_ilock_class);
  lock(fs_reclaim);

Fix this by moving xfs_trans_set_context() before the error check so
that nofs context is always restored on the new transaction.

Reported-by: syzbot+59178abfeb0ea3f0ab20@syzkaller.appspotmail.com
Closes: https://syzkaller.appspot.com/bug?extid=59178abfeb0ea3f0ab20
Fixes: a1ca658 ("xfs: fix incorrect context handling in xfs_trans_roll")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Yun Zhou <yun.zhou@windriver.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  fs/xfs/xfs_trans.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=b09198cf90ccf296970b774beea1c1ddb260f94c

======================================================================
DETAILED REPORT METHODOLOGY
======================================================================

The original Linux kernel CVE announcement for CVE-2026-80804 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80804

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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).