* [CVE-2026-90247][MODERATE REGULAR] bpf: Fix mmap_lock leak in irq_work path [ Upstream
@ 2026-09-18 2:18 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-09-18 2:18 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-90247
Priority: MODERATE REGULAR
AL-KERNEL base severity: MODERATE
KPANIC flag: NO
Patch: bpf: Fix mmap_lock leak in irq_work path [ Upstream
Commit: a052ad5edccf5319f50ed955de4368f8318a9f20
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a052ad5edccf5319f50ed955de4368f8318a9f20
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90247
Analysis date: Thu, 17 Sep 2026 22:18:41 -0400
ActionableScore: 3
ActionableScore lower bound: 2
Actionable bucket: Borderline / manual review recommended
Manual review required: YES
Summary:
No one-sentence report phrase was found.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90247 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90247
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: YES
A detailed explanation of the methodology and priority rules is included
at the end of this message.
======================================================================
AL-KERNEL CLASSIFICATION RESULT
======================================================================
CVE-2026-90247 MODERATE https://www.kernelcve.org/list/?q=CVE-2026-90247 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:L/UI:N/S:U/C:N/I:N/A:H';CWE-362;CWE-667;*CWE-772;*CWE-833;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '5.5';DESCR 'A local denial of service can occur in the BPF mmap unlock irq_work path because nested users of the same per CPU slot can acquire two mmap_read_lock references while only one deferred mmap_read_unlock runs. This leaks a read lock and can block exit_mmap when the target mm is being torn down, causing a hung task or system availability degradation. For the CVSS the PR:L value is used because reliable triggering requires local code execution and access to BPF or perf related paths, which may be available to a local user or delegated service account depending on system policy. The issue is not network reachable and is not triggered by remote packet traffic. Impact is denial of service only based on the visible primitive, because the patch context shows a leaked lock rather than UAF, OOB access, information disclosure, or arbitrary write.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Borderline / manual review recommended (with actual score 3) YES READ LOCK DEADLOCK BPF LEAK DMAorINTERRUPT HARDWARE SYZBOT INCREASED_FROM_LOW_BASED_ON_REQUIREMANUALCHECK DECREASED_TO_MODERATEREG_BASED_ON_ACTIONABLESCORELESSTHAN4 NO NO checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=3
ActionableScoreLower=2
PrimitiveClass=CLASS_C
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=RECOMMENDED
AutoDowngradeAllowed=YES
1. ActionableScore
* Raw conservative score: 2
* Conservative score: 2. No floor or cap changed the score.
* Raw paranoid score: 3
* Paranoid score: 3. No floor or cap changed the score.
* Final recommended bucket: **Borderline / manual review recommended**::
Conservative arithmetic: +1 concrete persistent kernel lock or reference leak, +1 realistic DoS through blocked exit_mmap.
Paranoid arithmetic: conservative signals plus +1 for plausible below-host-admin local reachability through BPF or perf related paths, based on the supplied PR:L hint and common BPF tracing usage. This is not treated as proven for HostAdminRequired=NO.
2. Signal breakdown
Positive signals:
* +1 Concrete persistent kernel resource/reference leak. Two mmap_read_lock acquisitions can occur while only one deferred mmap_read_unlock runs, leaking a read lock.
* +1 Reliable local DoS. The leaked read lock can block exit_mmap and cause a hung task or system availability degradation.
* +1 Paranoid only. Local below-host-admin reachability is plausible if the relevant BPF or perf paths are available to a local user or delegated service account.
Negative or non-awarded signals:
* RealUAF not awarded. The patch shows a leaked mmap read lock, not post-free object use.
* CLASS_A or CLASS_B corruption not awarded. No UAF, OOB access, type confusion, arbitrary write, controlled reclaim, or refcount lifetime mutation is established.
* Concrete repeated release/refcount not awarded. There is no first put or release that can free an object followed by a second put or release on the same dangling reference.
* Structured stale-object leverage not awarded. The issue is slot reservation and lock accounting, not stale structured object reuse.
* Weak LPE not awarded. No exploitation primitive beyond DoS is established.
* Confidentiality and integrity signals not awarded. The patch does not show disclosure, unauthorized modification, or privilege escalation.
* Extra availability point not awarded. The hung exit_mmap consequence is the same DoS already counted.
* Remote reachability not awarded. This is not triggered by network traffic.
* BPF UAF Floor 5 not applied. This is a BPF related control-plane path, but there is no UAF and no repeated lifetime/refcount mutation.
3. Reachability analysis
The trigger is local and involves BPF or perf related execution paths that can call stack_map_get_build_id_offset or bpf_find_vma while interrupts are disabled and reuse the per CPU mmap_unlock_work slot before the first caller queues irq_work.
Host-admin-equivalent privilege is not positively established from the supplied patch alone. However, complete below-host-admin reachability is also not fully established because BPF loading, tracing, perf event use, and helper availability depend on kernel configuration, sysctls, capabilities such as CAP_BPF, CAP_PERFMON, CAP_SYS_ADMIN, and product policy. Therefore HostAdminRequired=UNKNOWN.
NamespaceScopedPrivilege=UNKNOWN. The supplied evidence does not establish that all required BPF/perf stages are available inside attacker-created namespaces.
Prior privileged setup may exist on hardened systems where unprivileged BPF is disabled or perf access is restricted. No special hardware or network exposure is required. The bug is a timing/nesting issue in irq/NMI related paths, but the scoring does not subtract for race complexity because the patch does not prove an extremely rare or one-shot condition.
4. Primitive and severity interpretation
The exact primitive is a lock accounting and reservation bug in a per CPU irq_work slot. A nested caller can acquire another mmap_read_lock before the first deferred unlock is queued, causing two read locks but only one unlock.
This is not active structured UAF and not fixed stale storage UAF. It is a CLASS_C invalid-state/resource-leak DoS primitive. The demonstrated consequence is local denial of service by blocking exit_mmap. The speculative consequence would be broader system responsiveness degradation, but no memory corruption or privilege escalation path is supported by the patch.
ImportantCandidate=NO because the established primitive is a lock leak leading to DoS, without unresolved memory corruption, ownership violation, authorization bypass, or concrete repeated lifetime/refcount mutation.
AutoDowngradeAllowed=YES because the issue is constrained to DoS based on the supplied evidence. Manual review is still recommended because it is a BPF path, syzbot-reported, and privilege reachability may vary by product configuration.
Likely operational severity is ordinary to borderline Moderate, not Important, unless external evidence later proves unprivileged reliable triggering with stronger consequences.
5. One-sentence report phrase
A local BPF mmap unlock irq_work race can leak an mmap_read_lock and block exit_mmap, causing a hung task or denial of service, with no UAF, information disclosure, arbitrary write, or privilege escalation primitive established by the patch.
6. Manual review recommendation
MANUAL CHECK RECOMMENDED
Reason: review is useful to confirm product-specific BPF/perf reachability and privilege gating, but the patch evidence supports DoS only and does not establish an Important-grade corruption primitive.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: bpf: Fix mmap_lock leak in irq_work path [ Upstream
Commit: a052ad5edccf5319f50ed955de4368f8318a9f20
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=a052ad5edccf5319f50ed955de4368f8318a9f20
Changed files:
kernel/bpf/mmap_unlock_work.h
kernel/bpf/stackmap.c
kernel/bpf/task_iter.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=a052ad5edccf5319f50ed955de4368f8318a9f20
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-90247 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-90247
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:H
The Best / paranoid CVSS vector: AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
The Best / paranoid CVSS score: 5.5
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: 2
Paranoid ActionableScore: 3
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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