[CVE-2026-80862][MODERATE 7.0] nvme-tcp: fix usage of page_frag_cache

[CVE-2026-80862][MODERATE 7.0] nvme-tcp: fix usage of page_frag_cache

[AL-KERNEL]

CVE: CVE-2026-80862
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: nvme-tcp: fix usage of page_frag_cache
Commit: d19f98c79f1b7e09e4cdf5c20d626e571e487467
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d19f98c79f1b7e09e4cdf5c20d626e571e487467
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80862
Analysis date: Fri, 04 Sep 2026 17:36:58 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum**:: Paranoid score lands in Actionable Moderate, with Important-candidate manual review justified by premature free and page refcount corruption in a storage networking path.
Manual review required: YES

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-80862 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80862

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.

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AL-KERNEL CLASSIFICATION RESULT
======================================================================

CVE-2026-80862	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80862 CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';CWE-362;*CWE-416;*CWE-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7.5';DESCR 'A race in the NVMe TCP host path can occur because page_frag_cache is used without serialization while block devices and preallocated requests are initialized in parallel. This can corrupt page reference accounting for PDU backing pages and may cause premature free, followed by warnings in skb_splice_from_iter and random kernel panic. For the CVSS the PR:N is used for the paranoid score because a malicious or compromised NVMe TCP target may influence namespace discovery and request initialization without local code execution on the victim. The issue is best treated as adjacent network reachable in storage fabric deployments rather than a public Internet bug. Impact is at least denial of service via kernel crash and in worst case may allow confidentiality or integrity impact due to memory lifetime corruption and should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE LOCK DANGER INIT SIMPLEFIX NVME NETWORK HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFDH	YES	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

1. ActionableScore
* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**:: Paranoid score lands in Actionable Moderate, with Important-candidate manual review justified by premature free and page refcount corruption in a storage networking path.

2. Signal breakdown
* Remote reachable / network-triggerable: +2. The affected host-side NVMe/TCP path can be influenced by an NVMe/TCP target during namespace discovery and request initialization, although this is adjacent storage-network exposure rather than public Internet exposure.
* Generic memory corruption: +1 conservative, +2 paranoid. Conservative treats this as weak or indirect corruption because no controlled reclaim or overwrite primitive is shown. Paranoid treats incorrect page refcounting and premature free as a strong lifetime-corruption candidate.
* Real lifetime corruption: +1. The commit explicitly states incorrect refcounting of backstore pages and premature free.
* Reliable kernel crash / strong DoS: +1. The commit reports !sendpage_ok warnings followed by possible random panic.
* Important filesystem/storage path: +1. The bug is in NVMe/TCP host request/PDU allocation during block device namespace initialization.
* Hard or unreliable race / special timing required: -1. Triggering depends on parallel block-device creation and unsynchronized page_frag_cache allocation.

Conservative total: 2 + 1 + 1 + 1 + 1 - 1 = 5.
Paranoid total: 2 + 2 + 1 + 1 + 1 - 1 = 6.

3. Reachability analysis
The most realistic attacker is a malicious or compromised NVMe/TCP target, or an attacker able to influence target behavior on the storage network after the victim host is configured to connect. No local code execution on the victim is necessarily required in that model, but the victim must be using NVMe/TCP and must reach the attacker-controlled or compromised storage endpoint. This is not a default public-facing service on most systems. It is normally deployed in storage or data-center networks. Namespace scanning and request preallocation can occur naturally during connection, discovery, recovery, or device creation, and the race becomes more plausible when multiple namespaces or queues are initialized in parallel. Namespaces and containers are not the main privilege boundary here because the vulnerable path is host kernel NVMe/TCP client code.

Call-site confidence: high for the affected allocation sites because the patch directly serializes page_frag_alloc in nvme_tcp_init_request and nvme_tcp_alloc_async_req. Call-site confidence: medium for attacker reachability because the supplied diff does not show full target-driven namespace discovery logic, but the subsystem behavior supports target-influenced parallel initialization.

4. Severity interpretation
This should not be treated as an ordinary Moderate auto-close issue. The demonstrated effect is at least host kernel DoS via warning and random panic. The more security-relevant concern is that the bug corrupts page lifetime accounting through unsynchronized page_frag_cache use, which can create premature free conditions. However, the patch does not demonstrate attacker-controlled reclaim, object replacement, arbitrary write, callback control, or a concrete LPE chain. Therefore the conservative interpretation is Actionable Moderate. The paranoid interpretation remains below clear Important unless additional evidence shows controlled reuse or privilege escalation, but it is strong enough to require manual review.

5. One-sentence report phrase
A race in the NVMe/TCP host PDU allocation path can corrupt page_frag_cache reference accounting during parallel namespace/request initialization, causing premature page free and possible host kernel panic, with exploitation most plausible from a malicious or compromised NVMe/TCP target on a storage network.

6. Manual review recommendation
MANUAL CHECK REQUIRED. The patch explicitly mentions incorrect refcounting and premature free, which makes this a lifetime-corruption candidate rather than a simple warning-only DoS, even though a practical privilege-escalation primitive is not demonstrated.

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

Patch: nvme-tcp: fix usage of page_frag_cache
Commit: d19f98c79f1b7e09e4cdf5c20d626e571e487467
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=d19f98c79f1b7e09e4cdf5c20d626e571e487467

Commit description:

nvme uses page_frag_cache to preallocate PDU for each preallocated request
of block device. Block devices are created in parallel threads,
consequently page_frag_cache is used in not thread-safe manner.
That leads to incorrect refcounting of backstore pages and premature free.

That can be catched by !sendpage_ok inside network stack:

WARNING: CPU: 7 PID: 467 at ../net/core/skbuff.c:6931 skb_splice_from_iter+0xfa/0x310.
	tcp_sendmsg_locked+0x782/0xce0
	tcp_sendmsg+0x27/0x40
	sock_sendmsg+0x8b/0xa0
	nvme_tcp_try_send_cmd_pdu+0x149/0x2a0
Then random panic may occur.

Fix that by serializing the usage of page_frag_cache.

Fixes: 4e893ca ("nvme_core: scan namespaces asynchronously")
Signed-off-by: Dmitry Bogdanov <d.bogdanov@yadro.com>
Signed-off-by: Daniel Wagner <wagi@kernel.org>
Signed-off-by: Keith Busch <kbusch@kernel.org>
[carlos.bilbao: adjust context in nvme_tcp_free_queue; branch predates
19bdb70 ("nvme-tcp: lockdep: use dynamic lockdep keys per socket
instance")]
Signed-off-by: Carlos Bilbao (Lambda) <carlos.bilbao@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  net/core/skbuff.c
  drivers/nvme/host/tcp.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=d19f98c79f1b7e09e4cdf5c20d626e571e487467

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

The original Linux kernel CVE announcement for CVE-2026-80862 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80862

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:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 7.5

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: 5
  Paranoid ActionableScore: 6

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).