[CVE-2026-72027][MODERATE 7.0] mm/compaction: handle free_pages_prepare() properly in compaction_free() commit 7da7d599b8a83271c464adfd5ef160202b470570 upstream.

[CVE-2026-72027][MODERATE 7.0] mm/compaction: handle free_pages_prepare() properly in compaction_free() commit 7da7d599b8a83271c464adfd5ef160202b470570 upstream.

[AL-KERNEL]

CVE: CVE-2026-72027
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: mm/compaction: handle free_pages_prepare() properly in compaction_free() commit 7da7d599b8a83271c464adfd5ef160202b470570 upstream.
Commit: de8577db09039d4950239b01446ab5ead9028ab4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=de8577db09039d4950239b01446ab5ead9028ab4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72027
Analysis date: Sat, 15 Aug 2026 23:32:05 -0400
ActionableScore: 7
ActionableScore lower bound: 4
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
compaction_free ignored free_pages_prepare failure and could return PageHWPoison or otherwise bad pages to the compaction free list, allowing local memory pressure to potentially cause kernel crashes or data corruption under rare bad-page conditions.

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

The original Linux kernel CVE announcement for CVE-2026-72027 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72027

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 7.0
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-2026-72027	MODERATE	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:H/I:H/A:H';CWE-252;CWE-703;*CWE-664;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:L/A:H';BEST CVSS score: '7';DESCR 'compaction_free ignored a failed free_pages_prepare result and could put a PageHWPoison or otherwise bad page back into the compaction free list. Reusing such a page can corrupt memory contents or crash the kernel because the allocator and compaction code may later treat the page as valid. For the CVSS the PR:L is selected for the paranoid score because a local unprivileged process may be able to create memory pressure and trigger compaction paths, even though reliable triggering depends on rare bad page or hardware poison conditions. The issue is not network reachable and requires local execution on the target system. Impact is at least local denial of service via kernel crash and data corruption. In a worst case it may allow broader confidentiality or integrity impact due to memory corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 6)  SKIP CVE-2026-72027 UNKNOWN SKIP The Fixes patch not applied yet, so unlikely that actual: 733aea0b3a7bba0451dfc19322665de13a5b7af4 YES  NO NO unknown 	MAYBE	DANGER INIT SIMPLEFIX LINUS KPANIC MEMORY  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	-	-	checked

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

ActionableScore=7
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: 4
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1
  A local unprivileged process can plausibly create memory pressure and indirectly exercise memory compaction paths.
* Memory corruption, weak/indirect corruption candidate: +1
  The bug can put PageHWPoison or free_page_is_bad pages back into the compaction free list, but the patch does not show attacker-controlled overwrite, reclaim, or object replacement.
* Real lifetime/page ownership corruption: +1
  A page that failed free_pages_prepare should not re-enter the free list. Reusing it violates core page lifecycle invariants.
* Broad/default/common subsystem: +1
  This is core MM compaction code, not a rare driver-only path.
* Integrity impact plausible: +1
  The commit explicitly says the failed pages might cause data corruption.
* Hard or unreliable triggering: -1
  Reliable triggering depends on rare bad-page or hardware-poison conditions.
* No attacker-controlled payload or overwrite target: -1
  The patch does not show control over the corrupted page contents or the later allocation target.

Conservative total: 4

Paranoid additional interpretation:

* Memory corruption, strong corruption primitive: +2 instead of weak +1
  In the paranoid view, reintroducing poisoned or bad pages into allocator/compaction reuse paths is treated as core memory corruption, because later kernel users may treat invalid physical memory as valid.
* Weak LPE concern: +1
  Privilege escalation is not demonstrated, but core MM data corruption can sometimes become security relevant depending on page reuse and allocator behavior.
* Confidentiality impact plausible: +1
  Worst case page reuse or stale page contents could theoretically expose data, although this is not proven by the patch.
* Availability impact realistic: +1
  Beyond a transient crash, bad page reuse can cause persistent system instability or data corruption.

Paranoid total after constraints and penalties: 7

## 3. Reachability analysis

The issue is local, not network reachable. A local process can create memory pressure and may cause compaction to run, so PR:L is the practical assumption for triage. No CAP_SYS_ADMIN or CAP_SYS_RESOURCE is inherently required just to create memory pressure, but reliable triggering also needs a failed free_pages_prepare condition such as PageHWPoison or free_page_is_bad.

Namespaces and containers can reduce but not eliminate relevance. A containerized workload may still create memory pressure, although cgroup limits and host memory policy affect whether global compaction paths are reached. The affected code is in common MM infrastructure and is normally built into general-purpose kernels.

Realistic exploitation is difficult because the attacker does not directly choose when a poisoned or bad page is encountered, nor does the patch show controlled reuse. However, the failure mode is in core page lifecycle handling and the commit explicitly warns about data corruption, so this should not be auto-closed as a simple DoS.

Call-site confidence: high, because the changed function and the immediate consequence of adding the folio back to cc->freepages are visible in the patch.

## 4. Severity interpretation

This behaves above ordinary Moderate because it is not just a warning, leak, or local assertion. The vulnerable path can recycle pages that failed validation, including PageHWPoison or otherwise bad pages, into future compaction use.

The realistic impact is local DoS and data corruption under hard-to-trigger conditions. The theoretical worst case includes broader memory corruption effects, but the patch does not demonstrate attacker-controlled reclaim, arbitrary write, type confusion, or a reliable privilege escalation primitive. Therefore, conservative handling is Borderline manual review, while paranoid handling is a Strong Important candidate / Actionable Moderate at minimum.

## 5. One-sentence report phrase

compaction_free ignored free_pages_prepare failure and could return PageHWPoison or otherwise bad pages to the compaction free list, allowing local memory pressure to potentially cause kernel crashes or data corruption under rare bad-page conditions.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the bug affects core MM page lifecycle handling and the commit explicitly mentions possible data corruption. Even though exploitation appears difficult and no concrete LPE primitive is shown, bad page reuse in allocator or compaction paths is security-relevant enough to require manual review.

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

Patch: mm/compaction: handle free_pages_prepare() properly in compaction_free() commit 7da7d599b8a83271c464adfd5ef160202b470570 upstream.
Commit: de8577db09039d4950239b01446ab5ead9028ab4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=de8577db09039d4950239b01446ab5ead9028ab4

Commit description:

free_pages_prepare() can fail but compaction_free() does not handle the
failure case.  Failed pages should not be added back to cc->freepages for
future use, since they can be either PageHWPoison or free_page_is_bad()
and might cause data corruption.

Link: https://lore.kernel.org/20260622-handle_free_pages_prepare_in_compaction_free-v1-1-fcf3b14abcf7@nvidia.com
Fixes: 733aea0b3a7b ("mm/compaction: add support for >0 order folio memory compaction.")
Signed-off-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Lance Yang <lance.yang@linux.dev>
Cc: Brendan Jackman <jackmanb@google.com>
Cc: Jiaqi Yan <jiaqiyan@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat -rw-r--r-- mm/compaction.c 7

Changed files:
  mm/compaction.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=de8577db09039d4950239b01446ab5ead9028ab4

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

The original Linux kernel CVE announcement for CVE-2026-72027 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-72027

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:L/I:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 7

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).