* [CVE-2026-99158][LOW] ring-buffer: Fix false warning in ring_buffer_map_get_reader()
@ 2026-10-30 16:24 21% AL-KERNEL
0 siblings, 0 replies; 1+ results
From: AL-KERNEL @ 2026-10-30 16:24 UTC (permalink / raw)
To: kernel-cve
CVE: CVE-2026-99158
Priority: LOW
AL-KERNEL base severity: LOW
KPANIC flag: NO
Patch: ring-buffer: Fix false warning in ring_buffer_map_get_reader()
Commit: 029770f5badedc0f0ff85fc45e24785cbbee4a67
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=029770f5badedc0f0ff85fc45e24785cbbee4a67
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99158
Analysis date: Fri, 30 Oct 2026 12:24:34 -0400
ActionableScore: 0
ActionableScore lower bound: unknown
Actionable bucket: Ordinary Moderate
Manual review required: NO
Summary:
A reader/writer commit race can emit a false WARN and conditionally panic systems using `panic_on_warn`, without memory corruption or authorization impact.
======================================================================
ABOUT THIS REPORT
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99158 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99158
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-2026-99158 LOW https://www.kernelcve.org/list/?q=CVE-2026-99158 CHECK WITH IMPACT FROM ORIG NN LOW | AEGIS IMPACT LOW AEGIS_AS=0 LEGACY=LOW RESULT=SAME (final reconciliation agrees; DECISION: both 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:H';CWE-362;CWE-703;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 between the mmap ring buffer reader and a writer that is still committing events can make rb_get_reader_page return NULL after the reader catches the writer. This NULL result represents temporary lack of committed data rather than an invalid pointer or corrupted state, but ring_buffer_map_get_reader incorrectly passed it to WARN_ON. For the CVSS the PR:L reflects that an attacker needs local access to an enabled tracing ring buffer mapping or an equivalent delegated tracing interface. AC:H reflects the need to hit the writer commit timing window. The normal impact is a false kernel warning with no confidentiality or integrity effect. Availability impact is low by default, but it can become a kernel crash on systems configured with panic_on_warn. No UAF, OOB access, arbitrary write, or other memory corruption primitive is supported by the code change. Automated impact decision path. The original SimpleNet classifier selected LOW. The primary LLM estimated paranoid CVSS 4.7 and the production ActionableScore returned 0 with recommendation Ordinary Moderate. The production rules then evaluated CVSS thresholds and ActionableScore thresholds. No severity changing production threshold or specialist override was recorded. The legacy KP specialist has no review artifact for this run. The legacy FD or DH downgrade specialist has no review artifact for this run. The independent weaker Aegis shadow evaluated CVSS 0.0 and ActionableScore 0 with primitive class NONE and manual review REQUIRED. Its independently reconciled impact was LOW. The shadow agreed with the final production impact and aggregation did not change that impact. The final reported impact is LOW.';NO MANUAL CHECK; ,and ActionableScore result is Ordinary Moderate (with actual score 0) MAYBE READ WARNONLY TRACE SIMPLEFIX LEAK HARDWARE LINUS SYZBOT - - checked
======================================================================
ACTIONABLESCORE ANALYSIS
======================================================================
ActionableScore=0
PrimitiveClass=NONE
RealUAF=NO
HostAdminRequired=UNKNOWN
NamespaceScopedPrivilege=UNKNOWN
ImportantCandidate=NO
ManualReview=NO
AutoDowngradeAllowed=YES
RequiresHostUID0=UNKNOWN
AuthorizationDecisionBypass=NO
ProtectedResourceImpact=NONE
B4PendingReview=NO
B4PendingConfirmed=NO
1. ActionableScore
* Raw base score: 0.
* Conservative score: 0.
* Raw paranoid score: 0: possible panic under `panic_on_warn` +1, offset by the specifically documented narrow writer-commit timing requirement -1.
* Paranoid score: 0. No floor or cap applies.
* Final recommended bucket: **Ordinary Moderate**::
2. Signal breakdown
* +0 false warning: `rb_get_reader_page()` legitimately returns NULL when the reader catches a writer before committed length is published; no invalid dereference follows.
* Paranoid +1 possible kernel panic only when `panic_on_warn` converts the reachable `WARN_ON(!reader)` into a fatal event.
* Paranoid -1 hard timing: supplied evidence identifies a narrow reader/writer commit window and AC:H.
* No UAF, OOB access or write, stale-object use, corrupted active state, authorization bypass, disclosure, or integrity primitive is shown.
* No additional availability point: the warning and conditional panic are the same event.
* B5-R does not apply: there is no heap OOB write, retry-accumulated index, or later consumption of corrupted state.
* B3-PENDING and B4-PENDING do not apply: no shared-backing write or DENY-to-ALLOW authorization change exists.
3. Reachability analysis
The path requires local access to an enabled mmap tracing ring-buffer interface and a concurrent writer. The hints suggest delegated tracing access may suffice, but the supplied code does not establish exact credentials, host-UID requirements, capability namespace, or a complete namespace-scoped trigger. The race is timing-sensitive. Fatal impact additionally depends on administrator-configured `panic_on_warn`; no special hardware is required.
4. Primitive and severity reading
The exact defect is erroneous treatment of a valid temporary no-data result as a warning. The fix changes `WARN_ON(!reader)` to a normal NULL check and removes a redundant reader/commit-page test. There is no memory-lifetime or corruption primitive, and the NULL value is handled by `goto out` rather than dereferenced. The normal effect is log noise; conditional panic is configuration-dependent. ImportantCandidate is NO and automatic downgrade is allowed because no unresolved corruption, authorization, ownership, or trust-boundary primitive remains.
5. One-sentence report phrase
A reader/writer commit race can emit a false WARN and conditionally panic systems using `panic_on_warn`, without memory corruption or authorization impact.
6. Manual review advice
NO MANUAL CHECK NEEDED
The patch and commit directly establish a benign no-data return mishandled only by `WARN_ON`.
7. Call-site confidence
Call-site confidence: high
======================================================================
UPSTREAM PATCH SUMMARY
======================================================================
Patch: ring-buffer: Fix false warning in ring_buffer_map_get_reader()
Commit: 029770f5badedc0f0ff85fc45e24785cbbee4a67
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=029770f5badedc0f0ff85fc45e24785cbbee4a67
Commit description:
The mmap reader can warn when it catches up with a writer that is still
committing events. rb_get_reader_page() returns NULL in this case, but
ring_buffer_map_get_reader() treats that result as an error.
The initial rb_per_cpu_empty() check filters out an empty buffer, but it
does not guarantee that the next reader page has committed data. Writers
do not take reader_lock and can advance commit_page before publishing the
committed length on the new page. rb_get_reader_page() can swap to that
page, catch up with the writer and return NULL.
Handle NULL through the existing no-data exit without warning. Remove the
caller's reader_page == commit_page check as well, since the reader-page
helper already handles that case. The existing metadata update and return
path remain in place.
Cc: [email protected]
Link: https://patch.msgid.link/[email protected]
Fixes: 117c392 ("ring-buffer: Introducing ring-buffer mapping functions")
Assisted-by: Gemini:gemini-3.8-flash syzbot
Reported-by: [email protected]
Closes: https://syzkaller.appspot.com/bug?extid=de3d7f9bcc9212f3fae1
Link: https://syzkaller.appspot.com/ai_job?id=488adc18-a10e-42d2-a205-25327c38837f
Signed-off-by: Krystian Kaniewski <[email protected]>
Reviewed-by: Vincent Donnefort <[email protected]>
Signed-off-by: Steven Rostedt <[email protected]>
Signed-off-by: Greg Kroah-Hartman <[email protected]>
Changed files:
kernel/trace/ring_buffer.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=029770f5badedc0f0ff85fc45e24785cbbee4a67
======================================================================
DETAILED REPORT METHODOLOGY
======================================================================
The original Linux kernel CVE announcement for CVE-2026-99158 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-99158
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: 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 [email protected] (and both
send reply to CVE record itself too and see "reply" button below for howto reply).
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