* [CVE-2026-97904][LOW] cpufreq: initialize policy rwsem before sysfs publication
@ 2026-09-26 20:02 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-26 20:02 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-97904
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: cpufreq: initialize policy rwsem before sysfs publication
Commit: dc11263cb05ed519758fd135fe08d611bad1f241
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc11263cb05ed519758fd135fe08d611bad1f241
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97904
Analysis date: Sat, 26 Sep 2026 16:02:57 -0400
ActionableScore: 1
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-2026-97904 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97904
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-2026-97904 LOW https://www.kernelcve.org/list/?q=CVE-2026-97904 CHECK WITH IMPACT FROM ORIG NN MODERATE 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:H';CWE-908;CWE-362;CWE-667;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:L';BEST CVSS score: '4.7';DESCR 'A race exists in the cpufreq policy creation path because the policy sysfs directory can be published before policy rwsem is initialized. A local process may access a policy sysfs attribute during this narrow window and invoke a callback that uses an uninitialized semaphore. This can cause lock malfunction or a stalled cpufreq related operation and lead to denial of service. For the CVSS the PR:L because reliable triggering requires a local process to access sysfs during policy creation. The issue is not network reachable. The base impact is limited to availability because the patch does not show a use after free out of bounds access or other memory corruption primitive. The paranoid impact uses A:H because a lock failure in CPU frequency policy handling may affect critical policy or CPU management operations.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) YES INIT SIMPLEFIX DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_GUESSCVSS_AND_CIANNH NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::
The score is unchanged because the supplied patch establishes an initialization-order race and a possible locking failure, but does not establish a memory-corruption, lifetime, authorization-bypass, information-disclosure, or integrity primitive.
2. Signal breakdown
* +1 Availability impact realistic. A sysfs callback can access `policy->rwsem` before `init_rwsem()` runs. An uninitialized read-write semaphore can cause a blocked or malfunctioning cpufreq/sysfs operation.
* +0 Local unprivileged trigger. Sysfs attributes may be readable by ordinary users, but the complete trigger also requires concurrent policy publication. The supplied evidence does not establish that an ordinary user can independently force CPU policy creation or CPU hotplug.
* +0 Reliable kernel crash or host-wide DoS. The patch does not document a panic, Oops, system-wide hang, or reliably fatal condition.
* +0 Memory corruption. No use-after-free, double-free, out-of-bounds access, invalid free, refcount misuse, or attacker-controlled write is established.
* +0 Confidentiality and integrity. No disclosure or unauthorized modification primitive is established.
* +0 Remote reachability. The vulnerable path is local sysfs access during policy creation.
* No race penalty was applied. The timing window exists, but the supplied evidence does not establish that it is exceptionally narrow, one-shot, or practically uncontrollable.
* No host-admin penalty was applied. Policy creation may be associated with privileged CPU management operations, but the complete privilege boundary is not established by the supplied patch.
3. Reachability analysis
The immediate vulnerable operation is a sysfs callback for a newly published cpufreq policy. A local process must access a policy sysfs attribute after `kobject_init_and_add()` exposes the directory but before `init_rwsem()` initializes the policy semaphore.
The complete trigger requires a concurrent cpufreq policy creation event. The patch does not show whether an ordinary unprivileged user can force this event, whether it requires CPU online or offline control, whether it occurs only during boot or driver initialization, or whether a host administrator must initiate the relevant policy lifecycle operation.
Therefore, below-host-admin reachability is not positively established, but host-admin-equivalent privilege is also not positively established. There is no supplied namespace-specific capability analysis, and no basis to conclude that the complete trigger is available in an attacker-controlled namespace.
No special hardware, firmware, boot option, sysctl, or external network input is identified as part of the issue.
4. Primitive and severity interpretation
The exact defect is publication of an active cpufreq policy sysfs object before initialization of a synchronization primitive used by policy callbacks. This is an invalid initialization-state and synchronization-order defect.
This is not a use-after-free. No object is shown to be released, freed, reused, or consumed after its lifetime ends. No repeated release or refcount mutation exists. No active structured stale-object reuse exists. The patch only moves `init_rwsem(&policy->rwsem)` before `kobject_init_and_add()`.
The demonstrated practical consequence is limited to potential incorrect locking behavior, such as a stalled sysfs access or cpufreq-related operation. A kernel crash is not demonstrated. Privilege escalation, controlled corruption, arbitrary read or write, confidentiality impact, and integrity impact remain unsupported.
The issue is classified as CLASS_C because it is an invalid-state synchronization defect with a potential denial-of-service consequence rather than a meaningful corruption or lifetime primitive.
ImportantCandidate is NO because there is no unresolved active-object UAF, memory corruption, authorization bypass, ownership violation, or security-boundary primitive. AutoDowngradeAllowed is YES because no meaningful exploitation leverage beyond an operational stall is established.
Likely operational severity is Low to ordinary Moderate. The patch should be applied through routine kernel maintenance, especially on systems where cpufreq policies are dynamically created or CPUs are frequently hotplugged, but it does not warrant Important-class handling from the available evidence.
5. One-sentence report phrase
A cpufreq policy sysfs directory could be published before its rwsem was initialized, allowing a concurrent local sysfs callback to use an uninitialized lock and potentially stall cpufreq-related operations.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Verify the affected policy sysfs callbacks and policy creation call paths to determine whether use of the uninitialized rwsem can deadlock only the accessing task or can block broader cpufreq, CPU hotplug, or system management paths.
7. Call-site confidence
Call-site confidence: medium
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: cpufreq: initialize policy rwsem before sysfs publication
Commit: dc11263cb05ed519758fd135fe08d611bad1f241
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=dc11263cb05ed519758fd135fe08d611bad1f241
Commit description:
cpufreq_policy_alloc() initializes policy->rwsem after
kobject_init_and_add() has created the policy sysfs directory and its
default attributes. A sysfs access can therefore reach a policy callback
before the semaphore has been initialized.
Initialize policy->rwsem before publishing the policy kobject so sysfs
callbacks always see an initialized semaphore.
Fixes: 2fc3384 ("cpufreq: Initialize policy->kobj while allocating policy")
Cc: All Applicable <[email protected]>
Link: https://lore.kernel.org/all/[email protected]/
Reviewed-by: Zhongqiu Han <[email protected]>
Signed-off-by: Runyu Xiao <[email protected]>
Acked-by: Viresh Kumar <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Rafael J. Wysocki <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
drivers/cpufreq/cpufreq.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=dc11263cb05ed519758fd135fe08d611bad1f241
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-97904 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-97904
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:N/A:L
The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 4.7
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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