[CVE-2026-74626][MODERATE REGULAR] NTB: ntb_netdev: Preserve RX queue depth on allocation failure

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

CVE: CVE-2026-74626
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: NTB: ntb_netdev: Preserve RX queue depth on allocation failure
Commit: 755fd7843f300d724caceabdf9bb13adc8701540
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=755fd7843f300d724caceabdf9bb13adc8701540
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74626
Analysis date: Sat, 22 Aug 2026 14:13:08 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Ordinary Moderate / Borderline manual review recommended
Manual review required: YES

Summary:
ntb_netdev can lose RX queue entries when skb replacement allocation fails after packet delivery, allowing repeated allocation failures from an NTB peer traffic path to stall receive traffic on the NTB virtual Ethernet interface.

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

The original Linux kernel CVE announcement for CVE-2026-74626 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74626

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 REGULAR
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-2026-74626	MODERATE	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H';**CWE-400;CWE-754;*CWE-664;Other CVSS 'AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '5.3';DESCR 'ntb_netdev can lose RX queue entries when skb replacement allocation fails after the received skb has already been handed to the network stack. Repeated allocation failures can drain the RX queue while the interface remains up, causing receive traffic to stall on the NTB virtual ethernet link. For the CVSS the PR:N is used because a peer that can transmit on the NTB link does not need credentials on the victim system. The issue is adjacent reachable rather than Internet reachable because NTB normally requires a directly connected peer or tightly coupled hardware environment. Impact is denial of service for receive traffic. No confidentiality or integrity impact is supported because the bug is a resource handling failure without evidence of UAF, OOB access, or an arbitrary write primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Borderline manual review recommended (with actual score 3)	YES	SIMPLEFIX NETWORK SKB HARDWARE PACKET  DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN5	NO	NO	checked

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

ActionableScore=3
ActionableScoreLower=2

## 1. ActionableScore

* Conservative score: 2
* Paranoid score: 3
* Final recommended bucket: **Ordinary Moderate / Borderline manual review recommended**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The affected path processes traffic from an NTB peer, but this is adjacent or hardware-coupled reachability, not Internet remote reachability.
* Reliable strong DoS: +1. Repeated allocation failures can drain the RX queue and stall receive traffic while the interface remains up.
* Availability impact realistic: +1. The stall can persist because ntb_netdev has no retry refill path.
* Hard or unreliable condition: -1. Triggering requires skb allocation failures or memory pressure at the right time.
* Rare and difficult-to-reach subsystem/configuration: -1. NTB virtual Ethernet requires NTB hardware or a tightly coupled peer environment.

Paranoid adjustment:

* Paranoid score removes the rare-subsystem penalty for environments where NTB is actually deployed and treats the receive stall as operationally significant for the NTB link.

No memory corruption signals apply. The patch shows resource handling and queue-depth loss, not UAF, OOB access, double free, type confusion, arbitrary write, or page-cache/shared-page corruption.

## 3. Reachability analysis

A peer able to transmit over the NTB virtual Ethernet link can influence the RX path without credentials on the victim host. This is best treated as adjacent reachability rather than general network exposure. Ordinary remote Internet attackers cannot normally reach this path unless the NTB peer or topology exposes it indirectly.

Namespaces and containers do not materially lower privileges for triggering from the peer side, because the relevant input is received traffic on the NTB link. Local users on the victim generally need the ability to create memory pressure or control the NTB interface to make the condition reliable. The path is not broadly default-exposed and depends on NTB hardware and ntb_netdev deployment.

## 4. Severity interpretation

This behaves like an ordinary Moderate availability issue, with borderline manual-review value for systems that rely on NTB networking. The realistic impact is receive-side DoS on the NTB virtual Ethernet interface. There is no supported confidentiality or integrity impact, and no evidence of practical privilege escalation or kernel memory corruption.

## 5. One-sentence report phrase

ntb_netdev can lose RX queue entries when skb replacement allocation fails after packet delivery, allowing repeated allocation failures from an NTB peer traffic path to stall receive traffic on the NTB virtual Ethernet interface.

## 6. Manual review recommendation

MANUAL CHECK RECOMMENDED

Manual review is recommended because the issue is externally influenceable from an NTB peer and can cause a persistent receive stall in affected deployments. It is not Important-class by default because exploitation depends on memory pressure and NTB-specific exposure, and the patch does not support memory corruption or privilege escalation.

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

Patch: NTB: ntb_netdev: Preserve RX queue depth on allocation failure
Commit: 755fd7843f300d724caceabdf9bb13adc8701540
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=755fd7843f300d724caceabdf9bb13adc8701540

Commit description:

ntb_netdev_rx_handler() hands the received skb to the network stack
before allocating its replacement. If the allocation fails, nothing is
reposted. Every failure therefore takes one buffer out of the RX queue
while the interface remains up, and enough failures eventually stall
reception.

A retry path could refill the queue later, but ntb_netdev has none.
Allocate the replacement first instead. If that fails, drop the packet
and repost the same skb. This keeps the queue full and lets packet
delivery resume as soon as memory is available again.

Fixes: 548c237 ("net: Add support for NTB virtual ethernet device")
Cc: stable@vger.kernel.org
Signed-off-by: Koichiro Den <den@valinux.co.jp>
Reviewed-by: Dave Jiang <dave.jiang@intel.com>
Link: https://patch.msgid.link/20260806032537.3526498-1-den@valinux.co.jp
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/net/ntb_netdev.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=755fd7843f300d724caceabdf9bb13adc8701540

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

The original Linux kernel CVE announcement for CVE-2026-74626 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-74626

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:L
  The Best / paranoid CVSS vector: AV:A/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 5.3

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: 2
  Paranoid ActionableScore: 3

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 REGULAR

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).