[CVE-2026-46115][MODERATE 7.0] block: add pgmap check to biovec_phys_mergeable

[CVE-2026-46115][MODERATE 7.0] block: add pgmap check to biovec_phys_mergeable

[AL-KERNEL]

CVE: CVE-2026-46115
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: block: add pgmap check to biovec_phys_mergeable
Commit: 3d2ecbd444b01d6500671d1a582b7393943cf539
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d2ecbd444b01d6500671d1a582b7393943cf539
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46115
Analysis date: Thu, 28 May 2026 14:35:12 -0400
ActionableScore: 5
ActionableScore lower bound: 3
Actionable bucket: Actionable Moderate at minimum
Manual review required: NO

Summary:
`biovec_phys_mergeable()` could merge physically contiguous bvecs from different `dev_pagemap` owners, causing later block or DMA paths to lose correct pgmap attribution and risking storage integrity or availability issues.

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

The original Linux kernel CVE announcement for CVE-2026-46115 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46115

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: 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-2026-46115	MODERATE	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:L/I:H/A:H';*CWE-20;*CWE-664;CWE-682;CWE-668;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:L/A:H';BEST CVSS score: '6.5';DESCR 'biovec_phys_mergeable could merge physically contiguous bvec segments even when their pages belonged to different dev_pagemaps. After such a merge, later block, DMA mapping, or integrity paths may no longer recover the correct pgmap for the merged segment through page_pgmap(), which can break zone device page ownership assumptions. For the CVSS the PR:L is used because triggering requires local I/O against an already configured zone device or DAX style memory setup, but not necessarily full host administrator privileges once the device is exposed. AC:H is kept because the bug depends on physically contiguous pages from different pgmaps and a bio layout that crosses that boundary. The issue is not network reachable. Impact is mainly storage path availability and integrity risk, with only limited confidentiality concern in the paranoid model and no demonstrated arbitrary write or privilege escalation primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 4) 	MAYBE	SIMPLEFIX DMAorINTERRUPT HARDWARE  INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	-	-	checked

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

ActionableScore=5
ActionableScoreLower=3

## 1. ActionableScore

* Conservative score: **3**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger, conditional: **+1**. A local process may trigger the path through I/O if a zone device or DAX-like memory setup is already exposed.
* Weak or indirect corruption candidate: **+1 paranoid**. The bug can merge bvecs from different `dev_pagemap` owners, breaking later pgmap recovery and object ownership assumptions, but no direct overwrite primitive is shown.
* Cross-boundary ownership or policy issue: **+1 paranoid**. The core problem is loss of correct `dev_pagemap` ownership after merge.
* Integrity impact plausible: **+1**. Incorrect pgmap attribution can affect block, DMA mapping, or integrity handling.
* Availability impact realistic: **+1**. Bad merging can plausibly cause I/O failure, mapping failure, device errors, or crashes in dependent paths.
* Important filesystem/storage path: **+1**. This is in block-layer bvec merge logic used by request merge, DMA mapping, and integrity merge paths.
* Hard or special conditions: **-1**. Triggering requires physically contiguous pages from different pgmaps and a bio layout crossing that boundary.
* Configuration-dependent exposure: **-1 conservative**. Zone device memory registered in multiple pgmap chunks must be present and exposed.

## 3. Reachability analysis

The issue is local, not network reachable. It requires I/O involving zone device or DAX-style memory where pages from different `dev_pagemap` chunks can appear in the same bio and be physically contiguous. Setting up such devices is usually administrative, but once exposed, a less privileged workload may be able to issue I/O that reaches the merge path. Containers matter only if they are given access to the relevant block or DAX device.

## 4. Severity interpretation

This is best treated as **borderline to Actionable Moderate**. It is not a proven UAF, OOB write, or LPE primitive. However, it affects a sensitive block-layer ownership invariant: after merging bvecs from different pgmaps, later code cannot reliably recover the correct `dev_pagemap`. That can affect DMA or storage integrity paths, so it deserves manual review in environments using zone device memory.

## 5. One-sentence report phrase

`biovec_phys_mergeable()` could merge physically contiguous bvecs from different `dev_pagemap` owners, causing later block or DMA paths to lose correct pgmap attribution and risking storage integrity or availability issues.

## 6. Manual review recommendation

**MANUAL CHECK RECOMMENDED**

Manual review is recommended because this is an important block-layer pgmap ownership bug, although exploitation requires a specific zone-device configuration and no direct memory corruption or privilege-escalation primitive is demonstrated.

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

Patch: block: add pgmap check to biovec_phys_mergeable
Commit: 3d2ecbd444b01d6500671d1a582b7393943cf539
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3d2ecbd444b01d6500671d1a582b7393943cf539

Commit description:

biovec_phys_mergeable() is used by the request merge, DMA mapping,
and integrity merge paths to decide if two physically contiguous
bvec segments can be coalesced into one. It currently has no check
for whether the segments belong to different dev_pagemaps.

When zone device memory is registered in multiple chunks, each chunk
gets its own dev_pagemap. A single bio can legitimately contain
bvecs from different pgmaps -- iov_iter_extract_bvecs() breaks at
pgmap boundaries but the outer loop in bio_iov_iter_get_pages()
continues filling the same bio. If such bvecs are physically
contiguous, biovec_phys_mergeable() will coalesce them, making it
impossible to recover the correct pgmap for the merged segment
via page_pgmap().

Add a zone_device_pages_have_same_pgmap() check to prevent merging
bvec segments that span different pgmaps.

Fixes: 49580e6 ("block: add check when merging zone device pages")
Cc: stable@vger.kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Naman Jain <namjain@linux.microsoft.com>
Link: https://patch.msgid.link/20260410153414.4159050-2-namjain@linux.microsoft.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  block/blk.h

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=3d2ecbd444b01d6500671d1a582b7393943cf539

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

The original Linux kernel CVE announcement for CVE-2026-46115 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-46115

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:L/A:H
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:L/I:H/A:H
  The Best / paranoid CVSS score: 6.5

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: 3
  Paranoid ActionableScore: 5

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 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).