* [CVE-2026-98380][MODERATE REGULAR] net/sched: reject IDR error pointers when deleting actions
@ 2026-10-10 2:19 21% AL-KERNEL
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From: AL-KERNEL @ 2026-10-10 2:19 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-98380
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: net/sched: reject IDR error pointers when deleting actions
Commit: 39b751a210bf61a374afa82749afc7a77a08bf1d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39b751a210bf61a374afa82749afc7a77a08bf1d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98380
Analysis date: Fri, 09 Oct 2026 22:19:11 -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-2026-98380 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98380
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: NO
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-98380 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-98380 CHECK WITH IMPACT FROM ORIG NN MODERATE | AEGIS IMPACT MODERATE_KPANIC AEGIS_AS=0 LEGACY=MODERATE RESULT=DIFF (independent Legacy and Aegis differ; FINAL: MODERATE, Aegis: MODERATE_KPANIC) 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-362;**CWE-476;CWE-754;BEST CVSS score: '4.7';DESCR 'A race in the traffic control action deletion path can replace a previously located action with an ERR_PTR(-EBUSY) reservation before tcf_idr_delete_index performs its second lookup. The error pointer is then treated as a valid tc_action and tcfa_bindcnt is read through an invalid address near zero, causing a general protection fault and kernel panic. For the CVSS the PR:L reflects that the attacker needs delegated traffic control privileges such as CAP_NET_ADMIN, which may be available to a service account, container root, or a user in a network namespace without full host root privileges. AC:H is used because successful triggering depends on a specific concurrent interleaving during action deletion and IDR slot reservation. The issue is not directly network reachable through packet traffic and requires local control plane operations. Impact is denial of service only because the demonstrated primitive is an invalid read from an error pointer and does not provide a UAF, OOB write, information disclosure, or controlled memory corruption.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 1) MAYBE REMOTE READ KASAN OOB NULLPTR NETWORK HARDWARE LINUS DECREASED_TO_MODERATE_REGULAR_FROM_MODERATE7_BASED_ON_GUESSCVSS_AND_CIANNH - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=1
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw conservative score: 1
* Conservative score: 1
* Raw paranoid score: 1
* Paranoid score: 1
* No floor or cap was applied.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +1 Weak or indirect corruption candidate. An IDR reservation encoded as `ERR_PTR(-EBUSY)` is incorrectly interpreted as a valid `tc_action`.
* +1 Reliable kernel crash. Reading `tcfa_bindcnt` through the error pointer produces an invalid address near `0x10` and a demonstrated kernel panic.
* -1 Hard timing requirement. The demonstrated interleaving was scheduled using a hardware execution breakpoint, providing concrete evidence that precise concurrency timing is required.
* No UAF signal. No object is shown to be accessed after its lifetime ends.
* No OOB write, repeated release, refcount mutation, controlled reclaim, arbitrary write, disclosure, or authorization bypass is established.
* No additional availability point was awarded because it would double-count the demonstrated panic.
* No remote-reachability point was awarded. The trigger uses the local traffic-control control plane rather than packet processing.
* No privilege penalty was applied because the supplied evidence does not resolve whether the complete sequence requires host-level CAP_NET_ADMIN or works with namespace-scoped authority.
* B5-R does not apply because there is no heap OOB write or retry-accumulated offset.
* B3-PENDING does not apply because no shared-backing write exists.
* B4-PENDING does not apply because no authorization decision changes from DENY to ALLOW.
3. Reachability analysis
The trigger requires concurrent traffic-control action deletion and classifier activity capable of removing the action and reserving the same IDR index. Such operations normally involve CAP_NET_ADMIN, but the supplied material does not establish which user namespace governs every required operation or whether an attacker-created network namespace supports the complete reproducer.
Accordingly, host-administrator privilege and namespace-scoped reachability remain unknown. Numeric host UID 0 is not shown to be mandatory. No packet-only or direct network trigger is established. The hardware breakpoint was a reproducer aid rather than a hardware prerequisite, but it indicates a timing-sensitive interleaving. Whether repeated ordinary operations can win the race reliably requires validation.
4. Primitive and severity interpretation
The exact primitive is a read through `ERR_PTR(-EBUSY)` after an IDR slot changes between two lookups. Adding the `tcfa_bindcnt` offset produces a near-NULL invalid address and an immediate fault.
This is not stale storage, a post-lifetime object use, or a repeated release. It is an invalid-state and invalid-pointer consumption case classified as CLASS_C. The demonstrated consequence is host kernel panic and local denial of service. No useful primitive remains after excluding the crash because the pointer value is the fixed error encoding and the operation is an atomic read rather than a write.
ImportantCandidate is NO because there is no independently useful corruption, ownership, lifetime, or security-boundary primitive. AutoDowngradeAllowed is YES because the evidence supports a constrained crash path rather than unresolved exploitation leverage. Operational severity is ordinary Moderate, subject to confirming the actual namespace and capability boundary.
5. One-sentence report phrase
A timing-sensitive race in traffic-control action deletion can cause an ERR_PTR IDR reservation to be treated as a valid action, resulting in an invalid near-NULL read and kernel panic without an established memory-corruption or privilege-escalation primitive.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Confirm whether the complete action deletion and unlocked classifier sequence is reachable with attacker-obtainable namespace-scoped CAP_NET_ADMIN and whether the race can be reproduced without debugger-assisted scheduling.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: net/sched: reject IDR error pointers when deleting actions
Commit: 39b751a210bf61a374afa82749afc7a77a08bf1d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=39b751a210bf61a374afa82749afc7a77a08bf1d
Commit description:
tcf_action_delete() drops the reference held by its lookup before calling
tcf_idr_delete_index() with the saved action index. An unlocked
classifier can remove that action and reserve the same IDR slot with
ERR_PTR(-EBUSY) in between.
tcf_idr_delete_index() only checks the lookup result for NULL. It
therefore treats the reservation as a tc_action and dereferences
tcfa_bindcnt. A hardware execution breakpoint was used to schedule the
interleaving without changing the kernel source. KASAN reported this
decoded trace:
BUG: KASAN: null-ptr-deref in tca_action_gd+0x5b9/0x1010
Read of size 4 at addr 0000000000000010 by task poc/150
Oops: general protection fault, probably for non-canonical address 0xdffffc0000000002
RIP: tca_action_gd+0x5c0/0x1010:
arch_atomic_read at arch/x86/include/asm/atomic.h:23
raw_atomic_read at include/linux/atomic/atomic-arch-fallback.h:457
atomic_read at include/linux/atomic/atomic-instrumented.h:33
tcf_idr_delete_index at net/sched/act_api.c:766
tcf_action_delete at net/sched/act_api.c:1859
tcf_del_notify at net/sched/act_api.c:2014
tca_action_gd at net/sched/act_api.c:2064
R13: 0000000000000010 R15: fffffffffffffff0
Kernel panic - not syncing: Fatal exception
R15 contains ERR_PTR(-EBUSY), and adding the tcfa_bindcnt offset produces
the address in R13. With the guard applied, the same reproducer returned
-ENOENT without a KASAN report or panic. Treat error pointers as absent
and return -ENOENT.
Fixes: 0190c1d ("net: sched: atomically check-allocate action")
Cc: [email protected]
Reported-by: Xiang Mei <[email protected]>
Signed-off-by: Weiming Shi <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
arch/x86/include/asm/atomic.h
include/linux/atomic/atomic-arch-fallback.h
include/linux/atomic/atomic-instrumented.h
net/sched/act_api.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=39b751a210bf61a374afa82749afc7a77a08bf1d
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-98380 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-98380
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: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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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