[CVE-2026-53154][LOW] mm/hugetlb: restore reservation on error in hugetlb folio copy paths

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

CVE: CVE-2026-53154
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: mm/hugetlb: restore reservation on error in hugetlb folio copy paths
Commit: 8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53154
Analysis date: Thu, 25 Jun 2026 05:17:13 -0400
ActionableScore: 2
ActionableScore lower bound: 1
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A hugetlb reservation accounting bug can leak a per VMA reserve map entry after a failed hugepage copy, causing later faults on previously reserved addresses to fail with SIGBUS under hugetlb pool pressure.

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

The original Linux kernel CVE announcement for CVE-2026-53154 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53154

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-53154	LOW	CHECK	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-772;CWE-404;**CWE-400;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 hugetlb reservation accounting bug can occur when alloc_hugetlb_folio consumes a VMA reservation and copy_user_large_folio() later fails on the error path. The folio itself is released, but the per VMA reserve map entry remains marked as consumed, so a later fault on the same reserved address may follow the no reservation path and can deliver SIGBUS under hugetlb pool pressure. The most practical trigger is local use of private hugetlb mappings with UFFDIO_COPY resubmission when the copy fails, for example due to a hwpoisoned source page. The fork time CoW path is much less common because it also needs a pinned hugetlb anonymous folio and a failing source copy. For the CVSS the PR:L is used because a local user or process must be able to create and operate the relevant hugetlb mapping and userfaultfd style workflow, while full administrator privileges are not necessarily required in all deployments. The issue is not network reachable. Impact is denial of service through failed huge page faults and SIGBUS rather than information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 2)	YES	OOB LEAK ERRORPATH MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=2
ActionableScoreLower=1

## 1. ActionableScore

* Conservative score: 1
* Paranoid score: 2
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

* Local unprivileged trigger: +1. A local process may trigger the affected paths if it can create and operate private hugetlb mappings and relevant UFFDIO_COPY or fork CoW workflows.
* Availability impact realistic: +1 in paranoid scoring only. The visible effect is SIGBUS on a later fault for an address that was previously reserved, especially under hugetlb pool pressure.
* Hard or special condition required: -1. The practical path requires hugetlb reservations, copy_user_large_folio failure, and often hwpoison or a rare pinned hugetlb anonymous page condition.
* Rare and difficult-to-reach configuration: -1 in conservative scoring. hugetlb plus userfaultfd resubmission or the fork-time pinned-page path is not a common default application path.
* No memory corruption signal. The patch restores reservation accounting and does not show UAF, OOB access, stale pointer use, arbitrary write, or page-cache corruption.
* No privilege escalation signal. The failure mode is reservation loss followed by SIGBUS, not credential, object lifetime, or permission-boundary corruption.

## 3. Reachability analysis

A local user or local workload with access to hugetlb mappings is the realistic trigger. Full root is not necessarily required in all deployments, but hugepage availability and userfaultfd policy can restrict practical reachability. Containers may expose this only if hugetlb resources and userfaultfd-like workflows are delegated. The path is not network reachable. Exploitation conditions are specific and mostly produce workload-local denial of service rather than host compromise.

## 4. Severity interpretation

This behaves like an ordinary Moderate or Low-like resource accounting bug. The theoretical impact is denial of service through failed hugepage faults and SIGBUS. There is no realistic evidence of memory corruption, information disclosure, integrity impact, or privilege escalation from the patch context. The paranoid score is only slightly higher because repeated failures under hugetlb pressure could have broader workload availability impact.

## 5. One-sentence report phrase

A hugetlb reservation accounting bug can leak a per VMA reserve map entry after a failed hugepage copy, causing later faults on previously reserved addresses to fail with SIGBUS under hugetlb pool pressure.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This can be handled as a low-priority resource accounting DoS issue because the patch shows no memory corruption primitive, no security-boundary bypass, no remote reachability, and no plausible privilege escalation path.

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

Patch: mm/hugetlb: restore reservation on error in hugetlb folio copy paths
Commit: 8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38

Commit description:

Two sites in mm/hugetlb.c allocate a hugetlb folio via
alloc_hugetlb_folio() (consuming a VMA reservation) and then call
copy_user_large_folio(), which became int-returning in commit 1cb9dc4
("mm: hwpoison: support recovery from HugePage copy-on-write faults") and
can now fail (e.g.  -EHWPOISON on a hwpoisoned source page).  On the
failure path, folio_put() restores the global hugetlb pool count through
free_huge_folio(), but the per-VMA reservation map entry is left marked
consumed:

  - hugetlb_mfill_atomic_pte() resubmission path (UFFDIO_COPY)
  - copy_hugetlb_page_range() fork-time CoW path when
    hugetlb_try_dup_anon_rmap() fails (rare: pinned hugetlb anon
    folio under fork)

User-visible effect: on UFFDIO_COPY into a private hugetlb VMA where the
resubmission copy fails, the reservation for that address is leaked from
the VMA's reserve map.  A subsequent fault at the same address takes the
no-reservation path, and under hugetlb pool pressure the task is SIGBUSed
at an address it had previously reserved.  The fork-time CoW path leaks
the same way in the child VMA's reserve map, though it requires the much
rarer combination of pinned hugetlb anon page + hwpoisoned source.

Add the missing restore_reserve_on_error() call before folio_put() on both
error paths.

Link: https://lore.kernel.org/20260520044912.6751-1-devnexen@gmail.com
Fixes: 1cb9dc4 ("mm: hwpoison: support recovery from HugePage copy-on-write faults")
Signed-off-by: David Carlier <devnexen@gmail.com>
Reviewed-by: Muchun Song <muchun.song@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Mina Almasry <almasrymina@google.com>
Cc: Muchun Song <muchun.song@linux.dev>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: yuehaibing <yuehaibing@huawei.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/hugetlb.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=8d6e1dd3ad1340cd8b6d554b7aa93d8f0a1c6d38

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

The original Linux kernel CVE announcement for CVE-2026-53154 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-53154

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: 1
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).