* [CVE-2026-80856][LOW] fuse: fix invalidate lock leak on setattr writeback failure
@ 2026-09-04 17:56 21% AL-KERNEL
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From: AL-KERNEL @ 2026-09-04 17:56 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-80856
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: fuse: fix invalidate lock leak on setattr writeback failure
Commit: 8f14906ce9103ab8f2f1ebda45935a0d61b9d763
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8f14906ce9103ab8f2f1ebda45935a0d61b9d763
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80856
Analysis date: Fri, 04 Sep 2026 13:56:10 -0400
ActionableScore: 2
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80856 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80856
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-2026-80856 LOW https://www.kernelcve.org/list/?q=CVE-2026-80856 CHECK WITH IMPACT FROM ORIG NN LOW 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-667;CWE-755;*CWE-772;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A lock leak in the FUSE/DAX setattr path can occur when fuse_do_setattr takes filemap_invalidate_lock for a DAX truncate and then write_inode_now fails during writeback related mode or size changes. The function returned the error without releasing the invalidate lock, leaving a stale rwsem that can block later page faults, truncates, or similar operations on the same file. For the CVSS the PR:L value is used for the paranoid score because a local user or process with write access to an affected FUSE/DAX mount may be able to trigger the setattr path, although reliable triggering also depends on DAX being enabled and a writeback failure such as an EIO from the daemon or backend. The issue is not network reachable. Impact is denial of service through stalled file operations rather than memory corruption or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2) YES DISK LEAK NO NO 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 or process with write access to an affected FUSE or virtiofs DAX mount may trigger the setattr truncate path.
* Reliable persistent local DoS concern: +1. If the error path is reached, the leaked filemap invalidate rwsem can stall later faults or truncates on the affected file.
* Important filesystem/storage path: +1. The bug is in FUSE DAX truncate/writeback handling.
* Hard or special trigger condition: -1. Reliable triggering requires DAX truncate plus a writeback flush failure such as write_inode_now returning EIO.
* Rare/config dependent exposure: -1. The affected path depends on FUSE or virtiofs with DAX and the specific writeback failure condition.
* No memory corruption signal. The patch fixes a leaked lock, not UAF, OOB access, double free, refcount misuse, page cache corruption, or object reuse.
* No privilege escalation signal. The stale rwsem causes blocking behavior, not a demonstrated write primitive or security boundary bypass.
3. Reachability analysis
A local process can reach the vulnerable path through truncate or setattr style operations on an affected FUSE DAX file, assuming it has sufficient file permissions. Mount setup and DAX enablement are typically administrator controlled, but the actual trigger may be available to ordinary users on an already mounted filesystem. Containers or namespaces can lower practical exposure if such mounts are delegated into the container, but this still remains local and configuration dependent. The issue is not network reachable by itself.
4. Severity interpretation
This behaves like an ordinary Moderate or Low-like local denial of service. The realistic impact is a stale lock causing later file operations to block. There is no evidence in the patch of memory corruption, attacker controlled reclaim, page cache corruption, credential impact, or privilege escalation. Theoretical impact beyond DoS is not well supported.
5. One-sentence report phrase
A FUSE DAX setattr error path can leak filemap_invalidate_lock when write_inode_now fails, causing later faults or truncates on the affected file to stall and resulting in a local configuration dependent denial of service.
6. Manual review recommendation
NO MANUAL CHECK NEEDED
This can be autoclosable for practical triage because it is a constrained FUSE DAX lock leak DoS with no supported memory corruption or privilege escalation primitive.
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: fuse: fix invalidate lock leak on setattr writeback failure
Commit: 8f14906ce9103ab8f2f1ebda45935a0d61b9d763
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8f14906ce9103ab8f2f1ebda45935a0d61b9d763
Commit description:
fuse_do_setattr() takes filemap_invalidate_lock() for a DAX truncate
(fault_blocked = true) and releases it at the out:/error: labels. But
when a writeback flush is also needed, a write_inode_now() failure
returns directly and leaks the lock, so any later fault or truncate on
the file stalls on the stale rwsem.
For example, truncate(2) on a setuid file reaches fuse_do_setattr()
with both ATTR_SIZE and ATTR_MODE set:
truncate(2)
└─ do_truncate()
├─ dentry_needs_remove_privs() # S_ISUID
└─ notify_change() # KILL_SUID -> ATTR_MODE
└─ fuse_setattr() # no killpriv:
│ # ia_valid |= ATTR_MODE
└─ fuse_do_setattr()
├─ filemap_invalidate_lock() # IS_DAX && is_truncate
└─ write_inode_now() # is_wb && ATTR_MODE
└─ if (err) # e.g. daemon -> -EIO
return err # <- lock leaked
Fix this by adding an unlock label that releases the lock before
returning the error, and use it for the fuse_dax_break_layouts()
failure path as well.
Fixes: 6ae330c ("virtiofs: serialize truncate/punch_hole and dax fault path")
Cc: [email protected] # v5.10+
Signed-off-by: Baokun Li <[email protected]>
Signed-off-by: Miklos Szeredi <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
fs/fuse/dir.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=8f14906ce9103ab8f2f1ebda45935a0d61b9d763
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-80856 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80856
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:L
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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