[CVE-2026-93206][LOW] PCI/proc: Use file_ns_capable() when checking config space read access

[CVE-2026-93206][LOW] PCI/proc: Use file_ns_capable() when checking config space read access

[AL-KERNEL]

CVE: CVE-2026-93206
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: PCI/proc: Use file_ns_capable() when checking config space read access
Commit: 8a3a54aa3e65ed76f8560a387243a7738ae0cb1c
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a3a54aa3e65ed76f8560a387243a7738ae0cb1c
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93206
Analysis date: Thu, 24 Sep 2026 12:10:51 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO

Summary:
No one-sentence report phrase was found.

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

The original Linux kernel CVE announcement for CVE-2026-93206 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93206

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-2026-93206	LOW	https://www.kernelcve.org/list/?q=CVE-2026-93206 CHECK WITH IMPACT FROM ORIG NN LOW	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N';CWE-863;CWE-269;CWE-284;BEST CVSS score: '0';DESCR 'PCI procfs config space read authorization was evaluated against the credentials of the process performing read instead of the credentials stored when the file was opened. This created behavior inconsistent with sysfs when a PCI config space file descriptor was passed between processes. For the CVSS the PR:L value reflects a local unprivileged process that may provide a file descriptor to a separate privileged reader. The privileged reader already has CAP_SYS_ADMIN and can read the same PCI configuration space directly. No kernel memory disclosure write primitive privilege escalation or denial of service is demonstrated. Impact is C:N I:N A:N.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0)	YES	INIT HARDWARE LINUS 	NO	NO	checked

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

ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 0
* Conservative score: 0
* Raw paranoid score: 0
* Paranoid score: 0
* Final recommended bucket: **Ordinary Moderate**::

2. Signal breakdown

* +0 No kernel memory corruption, UAF, stale lifetime use, OOB access, refcount mutation, crash, or resource-exhaustion primitive is established.
* +0 No local-unprivileged trigger is established for a meaningful security consequence. The described behavior requires a separate more privileged task to perform the read.
* +0 No concrete authorization-boundary bypass is awarded. Before the patch, the expanded PCI configuration range is returned only when the current reader has CAP_SYS_ADMIN. Such a reader already has the authority to access the same PCI configuration information directly.
* +0 No protected resource theft, information disclosure to the unprivileged file opener, or privilege escalation is established. The patch does not show that an unprivileged sender of a descriptor receives data read by the privileged task.
* +0 No remote reachability is established.
* +0 No confidentiality or integrity signal is awarded. Reading PCI configuration space by an already CAP_SYS_ADMIN privileged process is not evidence of unauthorized disclosure or modification.
* +0 No security-state lifetime mismatch is present. This is credential selection for an open file descriptor, not a teardown or object-lifetime condition.
* +0 No capability penalty is applied because the complete attacker-controlled chain is not established. CAP_SYS_ADMIN is required for the process whose open credentials grant expanded access, but it is unclear whether an attacker can cause a privileged reader to disclose the result.

3. Reachability analysis

The affected operation is a local read of a PCI procfs configuration-space file. Before the patch, `proc_bus_pci_read()` evaluated `capable(CAP_SYS_ADMIN)` against the task executing `read()`. Therefore, a CAP_SYS_ADMIN process reading an FD originally opened by an unprivileged process could obtain the complete PCI configuration range.

The patch changes this to `file_ns_capable(file, &init_user_ns, CAP_SYS_ADMIN)`, making authorization depend on the credentials saved in `file->f_cred` at open time. This matches sysfs behavior and treats a privilegedly opened FD as an intentional delegated capability when passed to another process.

A meaningful attacker chain is not supplied. In particular, there is no evidence that an unprivileged process can force a CAP_SYS_ADMIN process to read an attacker-provided FD and return the additional configuration bytes across a protected boundary. The relevant capability check explicitly targets `init_user_ns`, but the complete privilege and descriptor-passing scenario is not sufficiently established to classify the vulnerable operation as namespace-scoped.

4. Primitive and severity interpretation

The primitive is an authorization-semantics inconsistency between procfs and sysfs PCI configuration reads. It is not a memory-safety defect and does not establish a meaningful attacker-side ALLOW-versus-DENY security-boundary bypass.

The pre-patch code allowed a privileged reader to receive expanded config-space data through an FD opened by a less privileged process. However, that privileged reader already possessed `CAP_SYS_ADMIN` and could read the same information independently. The post-patch behavior intentionally allows an unprivileged reader to use a descriptor that was opened by a privileged process, because access is delegated at FD-open time.

No protected PCI configuration data is shown to cross from the privileged reader back to the unprivileged opener. No write path, device reconfiguration, privilege escalation, host escape, or denial of service follows from the patch context. Therefore this is `PrimitiveClass=NONE`, not a Class A authorization vulnerability.

`ImportantCandidate=NO` because no practical security consequence beyond inconsistent descriptor credential semantics is established. `AutoDowngradeAllowed=YES` because neither a concrete corruption primitive nor a meaningful unresolved authorization bypass remains.

5. One-sentence report phrase

The patch aligns procfs PCI configuration read authorization with sysfs by using the credentials captured when the file descriptor was opened, and no independent privilege escalation, disclosure, or denial of service consequence is established.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

The supplied patch documents interface-consistency and FD capability-delegation semantics, but does not establish an attacker-controlled path to protected data, privileged functionality, kernel corruption, or availability impact.

7. Call-site confidence

Call-site confidence: medium

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

Patch: PCI/proc: Use file_ns_capable() when checking config space read access
Commit: 8a3a54aa3e65ed76f8560a387243a7738ae0cb1c
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=8a3a54aa3e65ed76f8560a387243a7738ae0cb1c

Commit description:

proc_bus_pci_read() decides how much of the config space is readable based
on capable(CAP_SYS_ADMIN), which checks the credentials of the task calling
read(), not the credentials of the process that opened the file.

The sysfs equivalent, pci_read_config(), has checked the credentials of the
opening process since commit de139a3 ("pci: check caps from sysfs file
open to read device dependent config space"), so a privileged process can
open the config space file and pass the file descriptor to an unprivileged
process (for example, a process running a KVM guest with an assigned
device), which can then read the entire config space.  The check was
subsequently routed through the LSM framework in commit 47970b1 ("pci:
use security_capable() when checking capablities during config space read")
and converted to the dedicated helper in commit ab0fa82 ("pci-sysfs:
use proper file capability helper function").

Thus, the two interfaces check the same capability against different
credentials.  Checking the credentials of the task calling read() makes the
outcome depend on who reads rather than who opened, so the restriction is
bypassed whenever a more privileged process reads through the descriptor.
Checking the credentials recorded in file->f_cred settles the decision at
open() time and ties it to the file, where it cannot change with the
caller.

Use file_ns_capable() to check CAP_SYS_ADMIN against the credentials in
effect when the file was opened, bringing the procfs interface in line with
the sysfs behaviour.

As a result, a file descriptor opened by a privileged process and passed to
an unprivileged one now allows the entire config space to be read through
procfs, matching sysfs.

Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Cc: stable@vger.kernel.org
Link: https://patch.msgid.link/20260720204145.1500105-1-kwilczynski@kernel.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  drivers/pci/proc.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=8a3a54aa3e65ed76f8560a387243a7738ae0cb1c

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

The original Linux kernel CVE announcement for CVE-2026-93206 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-93206

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: Not available
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:N
  The Best / paranoid CVSS score: 0

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: unknown
  Paranoid ActionableScore: 0

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).