* [CVE-2026-97549][LOW] xfs: fix under-reservation of blocks when repairing sf directories
@ 2026-09-25 15:55 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-25 15:55 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97549
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xfs: fix under-reservation of blocks when repairing sf directories
Commit: b950e84acd072ac648ace4fea53c0b1212da4b2c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b950e84acd072ac648ace4fea53c0b1212da4b2c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549
Analysis date: Fri, 25 Sep 2026 11:55:27 -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-2026-97549 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549
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-2026-97549 LOW https://www.kernelcve.org/list/?q=CVE-2026-97549 CHECK WITH IMPACT FROM ORIG NN MODERATE 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-400;CWE-682;CWE-703;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'An XFS metadata repair operation can under reserve transaction blocks when converting a shortform directory or xattr structure on filesystems where a directory or attribute block spans multiple filesystem blocks. A local actor who can invoke the XFS scrub repair path on a specially configured XFS filesystem may trigger an assertion or filesystem shutdown, causing denial of service. For the CVSS the paranoid score uses PR:L because a service account, container root, or delegated storage management context may be able to invoke the repair workflow without full host administration. The issue is not network reachable and requires a specific filesystem geometry and repair scenario. Impact is limited to availability through filesystem shutdown. No memory corruption, information disclosure, or privilege escalation primitive is indicated by the patch. NO MANUAL CHECK REQUIRED COULD BE AUTOCLOSED.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 2) YES DANGER DISK HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3 YES NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=2
PrimitiveClass=NONE
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 filesystem shutdown or strong DoS. The commit explicitly states that insufficient transaction reservation can cause an XFS filesystem shutdown.
* +1 Important filesystem and storage path. The flaw affects XFS metadata repair and transaction reservation for directory or xattr structure conversion.
Not awarded:
* No UAF, double free, stale pointer, refcount misuse, OOB access, arbitrary write, or controlled corruption is established.
* No filesystem ownership or COW violation is established. The patch corrects reservation accounting and does not show cross file modification or unauthorized data access.
* No confidentiality or integrity signal is awarded. A filesystem shutdown does not itself establish metadata corruption, disclosure, or unauthorized modification.
* No local unprivileged trigger is awarded. The supplied context shows xfs_scrub running as UID 0 but does not fully expose the capability checks for the repair ioctl.
* No host administrator penalty is applied. Host admin equivalence is likely for normal host filesystem repair workflows, but the complete authorization path is not visible in the supplied context.
* No special geometry penalty is applied. A multi filesystem block directory geometry is required, but the evidence does not establish that an attacker cannot reach such a filesystem.
* No race penalty applies. This is an accounting and reservation logic defect, not a timing race.
3. Reachability analysis
The vulnerable path is reached through the XFS metadata scrub and repair ioctl path, specifically while repairing shortform directories or xattr structures and preparing an atomic extent exchange. The supplied trace shows the operation being performed by xfs_scrub as UID 0.
A triggering filesystem requires XFS and a geometry where a directory or attribute block spans multiple filesystem blocks. Examples from the commit include a 4 KiB filesystem block with an 8 KiB directory block, or a 1 KiB filesystem block with a 4 KiB directory block.
The evidence does not establish that an ordinary unprivileged user can invoke the complete repair operation against a host XFS filesystem. It also does not establish that all required mount, repair, and metadata management operations are usable solely with attacker controlled namespace scoped privileges. Therefore HostAdminRequired and NamespaceScopedPrivilege remain UNKNOWN.
There is no network trigger, hardware prerequisite, or race requirement.
4. Primitive and severity interpretation
The exact defect is an under reservation of XFS transaction blocks. The old code assumes that conversion of a shortform directory or xattr requires one filesystem block, although the corresponding directory or attribute structure can require multiple filesystem blocks.
This is a resource accounting and filesystem transaction reservation defect. It is not a memory lifetime defect. There is no active structured stale object, no fixed stale storage, no cleanup UAF, and no second lifetime or refcount mutation.
The demonstrated consequence is an assertion warning and a possible XFS filesystem shutdown when the repair transaction lacks sufficient reserved blocks. The patch does not establish metadata overwrite, corrupted ownership, cross file modification, information disclosure, privilege escalation, or a security boundary bypass.
PrimitiveClass is NONE because no meaningful corruption, lifetime, authorization, ownership, or similar security primitive is established. ImportantCandidate is NO because the patch supported impact is filesystem availability only. AutoDowngradeAllowed is YES because no unresolved corruption or boundary primitive would be discarded by ordinary automated handling.
Operationally, this is a configuration dependent local filesystem availability issue. It should be patched as a correctness and reliability fix, but the supplied evidence does not support Important class security treatment.
5. One-sentence report phrase
An XFS metadata repair operation can under reserve transaction blocks for multi filesystem block directory or xattr structures, potentially causing an assertion or filesystem shutdown during repair.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
The patch establishes a transaction reservation accounting bug with filesystem shutdown impact only and does not establish a memory corruption, ownership violation, authorization bypass, or privilege escalation primitive.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: xfs: fix under-reservation of blocks when repairing sf directories
Commit: b950e84acd072ac648ace4fea53c0b1212da4b2c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=b950e84acd072ac648ace4fea53c0b1212da4b2c
Commit description:
Whilst running QA on XFS for-next as of 7.3-rc2 with MKFS_OPTIONS="-n
size=8192", I observed the following (trimmed) dmesg splat:
XFS: Assertion failed: args->total >= dp->i_nblocks - nblks, file: fs/xfs/libxfs/xfs_da_btree.c, line: 2387
WARNING: fs/xfs/xfs_message.c:104 at assfail+0x46/0x4a [xfs], CPU#0: xfs_scrub/1426511
CPU: 0 UID: 0 PID: 1426511 Comm: xfs_scrub Tainted: G W 7.3.0-rc2-djwx #rc2 PREEMPT(lazy) 6e418570b606a39783b0e7e7b30dc407b965f9e8
Tainted: [W]=WARN
RIP: 0010:assfail+0x46/0x4a [xfs]
RSP: 0018:ffffc900010d7890 EFLAGS: 00010246
RAX: 0000000000000000 RBX: 0000000000000000 RCX: 00000000ffffffd1
RDX: 0000000000000000 RSI: 0000000000000021 RDI: ffffffffa059fd38
RBP: 0000000000000002 R08: 0000000000000000 R09: 0000000000000000
R10: 000000000000000a R11: 000000007fffffff R12: ffffc900010d7940
R13: ffff888368d8f980 R14: ffffc900010d7a48 R15: ffffc900010d78d0
FS: 00007f445c5ce680(0000) GS:ffff8884a97ea000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f443803b9a8 CR3: 0000000107a4b000 CR4: 00000000003506f0
Call Trace:
<TASK>
xfs_da_grow_inode_int+0x2e0/0x300 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xfs_dir2_grow_inode+0x6e/0x150 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xfs_dir2_sf_to_block+0x149/0x870 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xrep_dir_swap_prep+0xe2/0x110 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xrep_dir_swap+0xfb/0x2f0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xrep_dir_rebuild_tree+0x99/0x100 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xrep_directory+0x83/0x1c0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xrep_attempt+0x4f/0x1e0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xfs_scrub_metadata+0x393/0x5b0 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xfs_ioc_scrubv_metadata+0x306/0x570 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
xfs_file_ioctl+0xa4f/0x1150 [xfs 5de2257e14108c136f11317e6bbb8ac77efd392c]
__x64_sys_ioctl+0x76/0xc0
do_syscall_64+0x7a/0x3b0
entry_SYSCALL_64_after_hwframe+0x4b/0x53
This is a consequence of commit 0fe77e5 , which added the
following assertion to xfs_da_grow_inode_int:
ASSERT(args->total >= dp->i_nblocks - nblks);
Tracing this back to xrep_dir_swap_prep, I noticed that the xfs_da_args
object that's passed to xfs_dir2_sf_to_block sets args->total to 1.
This is incorrect because mkfs set the directory block size to 8k and
the filesystem block size to 4k. In other words, args->total should be
2 here, not 1.
Dave Chinner tripped over the same problem with the same branch through
a different channel -- his test setup set the fs block size to 1k, in
which case the directory block size is still set to 4k. Here,
args->total should be 4.
Changing the assignment of args->total to sc->mp->m_dir_geo->fsbcount
makes the assertion go away, but that isn't a complete fix. In
xrep_tempexch_estimate, we also incorrectly assume that a shortform
conversion requires 1 fsblock when it should be m_dir_geo->fsbcount.
Without that, we can under-reserve space in the transaction and cause a
filesystem shutdown.
Note that the xfs_dabuf_nfsb helper will compute the correct value for
directories and xattr, so we use that instead of open-coding the logic.
Also fix xrep_xattr_swap_prep to assign args->total via xfs_dabuf_nfsb
to avoid one logic bomb if we ever support multi-fsblock attrs.
Cc: [email protected] # v6.10
Cc: [email protected]
Reported-by: [email protected]
Fixes: 629fdaf ("xfs: use atomic extent swapping to fix user file fork data")
Tripped-by: 0fe77e5 ("xfs: assert the reservation covers each da fork growth")
Signed-off-by: Darrick J. Wong <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Reviewed-by: Carlos Maiolino <[email protected]>
Signed-off-by: Carlos Maiolino <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/xfs/libxfs/xfs_da_btree.c
fs/xfs/xfs_message.c
fs/xfs/libxfs/xfs_da_btree.h
fs/xfs/scrub/attr_repair.c
fs/xfs/scrub/dir_repair.c
fs/xfs/scrub/tempfile.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=b950e84acd072ac648ace4fea53c0b1212da4b2c
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97549 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97549
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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