[CVE-2026-89552][LOW] params: fix charp corruption on allocation failure

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

CVE: CVE-2026-89552
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: params: fix charp corruption on allocation failure
Commit: 614f873268c5b172804c9af6639bd17b7e1e2359
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=614f873268c5b172804c9af6639bd17b7e1e2359
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89552
Analysis date: Sat, 12 Sep 2026 05:18:00 -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-2026-89552 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89552

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-2026-89552	LOW	https://www.kernelcve.org/list/?q=CVE-2026-89552 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-703;**CWE-476;CWE-665;Other CVSS 'AV:L/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '4.7';DESCR 'param_set_charp() updated writable charp kernel parameters in an unsafe order when slab allocation was available. The old parameter string was freed before the replacement allocation succeeded, so an ENOMEM failure could leave the global parameter pointer set to NULL. A later user of that parameter, for example zswap comparing the compressor name during setup, could dereference NULL and crash the kernel. For the CVSS the PR:L is used in the paranoid score because some systems may delegate writes to selected sysfs module parameters to service processes, but the normal deployment requires administrator rights. The issue is not network reachable and requires local access to a writable kernel parameter plus an allocation failure condition. Impact is denial of service only via kernel crash, with no supported path to information disclosure or privilege escalation.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1)	YES	DANGER NULLPTR  DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH DECREASED_TO_LOW_FROM_MODERATE_BASED_ON_ACTIONABLESCORELESSTHAN3	NO	NO	checked

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

ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=NO
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES

1. ActionableScore

* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* Final recommended bucket: **Ordinary Moderate**::

No floor or cap changed the score.

2. Signal breakdown

Positive signals:

* +1 Reliable kernel crash / strong DoS. The supplied trace shows a later NULL pointer dereference in strcmp() from zswap_setup() after param_set_charp() leaves a charp parameter as NULL on ENOMEM.

Negative signals:

* No negative privilege penalty applied. The demonstrated zswap sysfs parameter path is normally administrator controlled, but the patched helper is generic and the supplied evidence does not prove that every complete affected path requires host-admin-equivalent privilege.

Material non-awarded signals:

* Real UAF not awarded. The old string is freed and the global parameter pointer becomes NULL after failed allocation, but the demonstrated later fault is a NULL dereference, not stale post-free object use.
* Concrete repeated release/refcount not awarded. There is no visible second put/free/refcount mutation through the same dangling reference.
* Controlled reclaim not demonstrated.
* Arbitrary write not demonstrated.
* Confidentiality and integrity not awarded. The established consequence is NULL dereference and crash only.
* Extra availability point not awarded because the same crash is already counted.
* Remote reachability not established.
* Local unprivileged trigger not established.
* ImportantCandidate not set because there is no memory corruption, authorization bypass, COW/ownership violation, or unresolved Class B lifetime primitive.

3. Reachability analysis

The visible trigger is a write to a writable charp kernel parameter through sysfs, followed by an allocation failure in kmalloc_parameter(). The supplied example is zswap compressor update before zswap initialization, which is normally an administrator managed kernel parameter. However, because param_set_charp() is a generic helper and the input does not enumerate all affected parameter permissions, the complete privilege boundary is recorded as HostAdminRequired=UNKNOWN rather than definitively YES.

There is no evidence that this operation is namespace scoped. NamespaceScopedPrivilege=NO. No network trigger is present. No special hardware is required. This is not a race. The difficult condition is allocation failure, but that is a state prerequisite rather than a kernel timing race.

4. Primitive and severity interpretation

The exact primitive is unsafe update ordering for charp kernel parameters. The previous value is released before the replacement allocation succeeds. If allocation fails, the parameter value can become NULL, and a later consumer that assumes a valid string can dereference NULL.

This is CLASS_C invalid-state crash behavior. It is not active structured UAF, fixed stale storage UAF, repeated lifetime mutation, OOB access, arbitrary write, or authorization bypass. The demonstrated consequence is local denial of service via kernel crash. The speculative consequence beyond crash is weak and unsupported by the patch.

ImportantCandidate=NO because the patch supports DoS-only behavior without a concrete corruption or boundary primitive. AutoDowngradeAllowed=YES because automatic downgrade would not discard an unresolved meaningful exploitation primitive.

Likely operational severity is ordinary Moderate or Low-like depending on product policy, especially where writable kernel parameters are restricted to administrators.

5. One-sentence report phrase

param_set_charp() could leave a writable charp kernel parameter as NULL after an allocation failure, allowing a later parameter consumer such as zswap setup to hit a NULL pointer dereference and crash the kernel.

6. Manual review recommendation

NO MANUAL CHECK NEEDED

Reason: the issue is a NULL pointer dereference from invalid parameter state with no established UAF, repeated refcount mutation, authorization bypass, information disclosure, integrity impact, or remote reachability.

7. Call-site confidence

Call-site confidence: high

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

Patch: params: fix charp corruption on allocation failure
Commit: 614f873268c5b172804c9af6639bd17b7e1e2359
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=614f873268c5b172804c9af6639bd17b7e1e2359

Commit description:

param_set_charp() stores charp parameters in allocated memory after slab is
available, and releases the previous value when the parameter is updated.

The previous value is released before the replacement allocation succeeds.
If kmalloc_parameter() fails, the setter returns -ENOMEM with the parameter
left as NULL.

Failing zswap's compressor update before zswap is initialized can later
trigger:

  BUG: kernel NULL pointer dereference, address: 0000000000000000
  RIP: 0010:strcmp+0x10/0x30
  Call Trace:
    zswap_setup+0x3b1/0x490
    zswap_enabled_param_set+0x5b/0xa0
    param_attr_store+0x93/0xe0
    module_attr_store+0x1c/0x30
    kernfs_fop_write_iter+0x116/0x1f0

Allocate and copy the replacement first, then replace the parameter value
only after allocation succeeds.

Fixes: e180a6b ("param: fix charp parameters set via sysfs")
Cc: stable@vger.kernel.org
Signed-off-by: Jiacheng Yu <yujiacheng3@huawei.com>
Reviewed-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Petr Pavlu <petr.pavlu@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  kernel/params.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=614f873268c5b172804c9af6639bd17b7e1e2359

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

The original Linux kernel CVE announcement for CVE-2026-89552 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-89552

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:H/UI:N/S:U/C:N/I:N/A:H
  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 alexanjelausa@gmail.com (and both
send reply to CVE record itself too and see "reply" button below for howto reply).