[CVE-2026-64464][LOW] xhci: sideband: fix ring sg table pages leak

[CVE-2026-64464][LOW] xhci: sideband: fix ring sg table pages leak

[AL-KERNEL]

CVE: CVE-2026-64464
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: xhci: sideband: fix ring sg table pages leak
Commit: 99d00a9e35e311a91d258029d5bb584377296c34
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99d00a9e35e311a91d258029d5bb584377296c34
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64464
Analysis date: Sat, 25 Jul 2026 07:40:21 -0400
ActionableScore: 1
ActionableScore lower bound: 0
Actionable bucket: Ordinary Moderate / Low-like
Manual review required: NO

Summary:
A temporary pages array in xhci_ring_to_sgtable() is leaked after successful sg_table construction, allowing repeated privileged sideband ring-buffer operations to consume kernel memory and potentially cause DoS.

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

The original Linux kernel CVE announcement for CVE-2026-64464 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64464

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.

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

CVE-2026-64464	LOW	CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H';*CWE-401;*CWE-772;**CWE-400;Other CVSS 'AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.4';DESCR 'xhci sideband leaks a temporary pages array after successful sg_table construction in xhci_ring_to_sgtable. The returned sg_table has its own scatterlist entries, so the missing free causes a resource leak rather than use after free or memory corruption. Repeated endpoint or event ring buffer requests by a sideband client can accumulate kernel memory usage and may eventually cause denial of service through memory exhaustion. For the CVSS the PR:H because reliable triggering normally requires administrative control over the xHCI sideband client or a privileged driver path. The issue is not network reachable. Impact is availability only.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate / Low-like (with actual score 1)	YES	OOB USB SIMPLEFIX LEAK ERRORPATH DMAorINTERRUPT MEMORY  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	YES	NO	checked

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

ActionableScore=1
ActionableScoreLower=0

## 1. ActionableScore

* Conservative score: 0
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate / Low-like**::

## 2. Signal breakdown

Triggered signals:

* Availability impact realistic: +1
  Repeated calls can leak kernel memory and may eventually cause memory exhaustion.

Paranoid-only interpretation:

* Reliable kernel crash / strong DoS: +1
  Only under sustained repeated triggering by a sideband client. This is not a single-shot crash primitive.

Negative signals:

* Requires admin/root/CAP_* in typical deployments: -2
  Reliable triggering appears to require privileged control of the xHCI sideband client or a privileged driver/device-management path.

* Rare AND difficult-to-reach subsystem/configuration: -1
  xHCI sideband clients are not a broad default user-facing attack surface.

Not applied:

* No generic memory corruption. The leaked object is a temporary `pages` array that is no longer needed after `sg_alloc_table_from_pages()`.
* No UAF, double-free, OOB write, arbitrary write, page-cache corruption, or lifetime corruption is shown.
* No confidentiality or integrity impact is supported.
* No remote or firmware-mediated trigger is shown.

## 3. Reachability analysis

The bug is triggered when a sideband client gets an endpoint or event ring buffer and `xhci_ring_to_sgtable()` succeeds. The path is local and device-management oriented, not network reachable. In typical deployments, an attacker would need administrative control over the relevant USB/xHCI sideband functionality or a privileged kernel driver path. Namespaces or containers do not obviously reduce the privilege requirement unless the product explicitly delegates this device-management interface to untrusted workloads.

Call-site confidence: medium. The provided patch clearly describes the allocation and missing free, but broader caller context for sideband client exposure is not included.

## 4. Severity interpretation

This behaves like a low-end resource leak / availability issue, not an Important-class kernel vulnerability. The realistic impact is memory exhaustion after repeated privileged operations. The patch does not support a memory corruption primitive, privilege escalation, information disclosure, or cross-boundary policy bypass. Paranoid scoring can count sustained memory exhaustion as stronger DoS, but the admin-gated and rare sideband path keeps it below actionable Moderate.

## 5. One-sentence report phrase

A temporary pages array in xhci_ring_to_sgtable() is leaked after successful sg_table construction, allowing repeated privileged sideband ring-buffer operations to consume kernel memory and potentially cause DoS.

## 6. Manual review recommendation

NO MANUAL CHECK NEEDED

This is a straightforward memory/resource leak with no evidence of UAF, overwrite, stale pointer use, privilege escalation, confidentiality impact, or realistic unprivileged reachability.

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

Patch: xhci: sideband: fix ring sg table pages leak
Commit: 99d00a9e35e311a91d258029d5bb584377296c34
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=99d00a9e35e311a91d258029d5bb584377296c34

Commit description:

xhci_ring_to_sgtable() allocates a temporary pages array and
uses it to build the returned sg_table with
sg_alloc_table_from_pages().

The error paths free the pages array, but the success path
returns the sg_table without freeing it. This leaks the temporary
array every time a sideband client gets an endpoint or event ring
buffer.

Free the pages array after sg_alloc_table_from_pages() succeeds.
The returned sg_table has its own scatterlist entries and does not
depend on the temporary array after construction.

Fixes: de66754 ("xhci: sideband: add initial api to register a secondary interrupter entity")
Cc: stable <stable@kernel.org>
Signed-off-by: Xu Rao <raoxu@uniontech.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://patch.msgid.link/20260703144033.483286-2-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/usb/host/xhci-sideband.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=99d00a9e35e311a91d258029d5bb584377296c34

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

The original Linux kernel CVE announcement for CVE-2026-64464 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64464

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:L/PR:H/UI:N/S:U/C:N/I:N/A:L
  The Best / paranoid CVSS vector: AV:L/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
  The Best / paranoid CVSS score: 4.4

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: 0
  Paranoid ActionableScore: 1

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).