[CVE-2026-68159][IMPORTANT] libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE

[CVE-2026-68159][IMPORTANT] libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE

[AL-KERNEL]

CVE: CVE-2026-68159
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE
Commit: e36663145abd7024f0281dfb22fdef65f185845b
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e36663145abd7024f0281dfb22fdef65f185845b
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68159
Analysis date: Mon, 10 Aug 2026 10:43:09 -0400
ActionableScore: 10
ActionableScore lower bound: 8
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A malicious or compromised Ceph monitor can send an oversized pg_temp or pg_upmap OSDMap entry that is later copied into a fixed-size kernel stack array, causing a stack out-of-bounds write with reliable crash impact and plausible privilege-escalation risk.

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ABOUT THIS REPORT
======================================================================

The original Linux kernel CVE announcement for CVE-2026-68159 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68159

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: IMPORTANT
Manual review required: YES

A detailed explanation of the methodology and priority rules is included
at the end of this message.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-68159	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H';*CWE-787;CWE-121;*CWE-20;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H';BEST CVSS score: '9.8';DESCR 'A stack out of bounds write in libceph can occur because pg_temp pg_upmap and pg_upmap_items lengths decoded from an OSDMap are not bounded to CEPH_PG_MAX_SIZE before later copying into the fixed stack array ceph_osds.osds. A malicious or compromised Ceph monitor can send an OSDMap entry longer than 32 and trigger kernel memory corruption when the client calculates acting or up OSD sets. For the CVSS the PR:N is selected for the paranoid score because the attacker does not need a local account on the victim and only needs a position that can provide monitor data to the Ceph client. The issue is network reachable in Ceph deployments where monitor traffic can be controlled or tampered with, but Ceph monitor endpoints are typically inside storage or data center networks rather than exposed to the public Internet. Impact includes kernel crash and plausible privilege escalation because the primitive is a kernel stack out of bounds write, not only a warning or resource leak.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 10)	YES	REMOTE WRITE KASAN OOB NETWORK LINUS KPANIC 	NO	NO	checked

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

ActionableScore=10
ActionableScoreLower=8

## 1. ActionableScore

* Conservative score: 8
* Paranoid score: 10
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative score 8:

* Remote reachable / network-triggerable: +2. A Ceph monitor can send the malformed OSDMap to a kernel Ceph client over the normal Ceph monitor protocol.
* Generic memory corruption, strong corruption primitive: +2. The commit explicitly describes a stack out-of-bounds write into `struct ceph_osds.osds[CEPH_PG_MAX_SIZE]`.
* Weak LPE concern: +1. Kernel stack OOB write makes privilege escalation plausible, but the patch does not demonstrate target control, exploit reliability, or a concrete overwrite of a security object.
* Reliable kernel crash / strong DoS: +1. The report includes KASAN stack-out-of-bounds and a kernel BUG path.
* Confidentiality impact plausible: +1. Stack memory corruption can plausibly expose or influence sensitive kernel state in worst realistic triage terms.
* Integrity impact plausible: +1. The primitive is a kernel stack write, not only a NULL dereference or warning.
* Important filesystem/storage path: +1. The affected path is Ceph OSDMap handling used by kernel Ceph/RBD clients.
* Internal/storage-network deployment constraint: -1. Ceph monitor endpoints are usually inside storage or data-center networks, not public Internet services.

Paranoid score 10:

* Same as above, but privilege escalation plausibility is raised to +2 because the primitive is an attacker-influenced kernel stack OOB write from network-supplied OSDMap data.
* No internal-network penalty is applied in the paranoid score because the attack is still network-delivered in normal deployed Ceph environments once monitor traffic is attacker-controlled or compromised.

## 3. Reachability analysis

The trigger is a malicious or compromised Ceph monitor, or an attacker able to tamper with monitor traffic, sending an OSDMap with `pg_temp`, `pg_upmap`, or `pg_upmap_items` length greater than `CEPH_PG_MAX_SIZE`. The victim does not need to run attacker-controlled local code, so PR is effectively none from the victim perspective. This is not generally Internet-exposed, but it is realistic inside Ceph storage networks where kernel CephFS or RBD clients trust monitor endpoints.

Namespaces and containers do not materially reduce the risk if the host kernel Ceph client processes the malicious map. Local admin rights may be needed to configure a client to connect to a hostile cluster, but once a client trusts the monitor path, the malformed OSDMap is processed remotely.

Call-site confidence: high. The commit explicitly names the downstream copy into a fixed-size stack array and includes a KASAN stack-out-of-bounds trace through `ceph_pg_to_up_acting_osds()` and RBD probing.

## 4. Severity interpretation

This behaves like an Important-class kernel vulnerability, not an ordinary Moderate issue. The demonstrated primitive is a stack out-of-bounds write in kernel context from network-supplied Ceph metadata. Realistic impact is at least remote DoS against exposed Ceph clients. Theoretical worst-case impact includes privilege escalation or broader kernel compromise, but exploitability depends on stack layout, overwrite controllability, and kernel hardening.

## 5. One-sentence report phrase

A malicious or compromised Ceph monitor can send an oversized pg_temp or pg_upmap OSDMap entry that is later copied into a fixed-size kernel stack array, causing a stack out-of-bounds write with reliable crash impact and plausible privilege-escalation risk.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: this is network-delivered kernel memory corruption with an explicit stack OOB write and KASAN trace, so it should not be auto-closed even if practical exposure is usually limited to internal Ceph storage networks.

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

Patch: libceph: bound pg_{temp,upmap,upmap_items} length to CEPH_PG_MAX_SIZE
Commit: e36663145abd7024f0281dfb22fdef65f185845b
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=e36663145abd7024f0281dfb22fdef65f185845b

Commit description:

__decode_pg_temp() decodes an user-controlled length but only rejects
values large enough to overflow the allocation; it does not bound it to
CEPH_PG_MAX_SIZE. The helper backs both pg_temp and pg_upmap decoding, and
apply_upmap()/get_temp_osds() later copy the decoded list into the fixed-size
on-stack array struct ceph_osds.osds[CEPH_PG_MAX_SIZE]. A monitor that sends
an OSDMap with a pg_temp/pg_upmap entry longer than 32 thus causes a stack
out-of-bounds write.

An OSD set for a single PG can never exceed CEPH_PG_MAX_SIZE, so reject longer
entries at decode time. The bound is well below the old overflow threshold, so
it also covers the allocation-size overflow the previous check guarded against.

  BUG: KASAN: stack-out-of-bounds in ceph_pg_to_up_acting_osds
  Write of size 4 ... by task exploit
   kasan_report (mm/kasan/report.c:595)
   ceph_pg_to_up_acting_osds (net/ceph/osdmap.c:2617 net/ceph/osdmap.c:2833)
   calc_target (net/ceph/osd_client.c:1638)
   __submit_request (net/ceph/osd_client.c:2394)
   ceph_osdc_start_request (net/ceph/osd_client.c:2490)
   ceph_osdc_call (net/ceph/osd_client.c:5164)
   rbd_dev_image_probe (drivers/block/rbd.c:6899)
   do_rbd_add (drivers/block/rbd.c:7138)
   ...
  kernel BUG at net/ceph/osdmap.c:2670!

[ idryomov: do the same in __decode_pg_upmap_items() ]

Cc: stable@vger.kernel.org
Fixes: a303bb0 ("libceph: introduce and switch to decode_pg_mapping()")
Reported-by: Weiming Shi <bestswngs@gmail.com>
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Xiang Mei <xmei5@asu.edu>
Reviewed-by: Alex Markuze <amarkuze@redhat.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  mm/kasan/report.c
  net/ceph/osdmap.c
  net/ceph/osd_client.c
  drivers/block/rbd.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=e36663145abd7024f0281dfb22fdef65f185845b

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

The original Linux kernel CVE announcement for CVE-2026-68159 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68159

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:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS vector: AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 9.8

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: 8
  Paranoid ActionableScore: 10

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: IMPORTANT
KPANIC detected for this report: YES
Published priority for this report (same as in Subject): IMPORTANT

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).