[CVE-2026-68156][IMPORTANT] libceph: refresh auth->authorizer_buf{,_len} after authorizer update

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

CVE: CVE-2026-68156
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: libceph: refresh auth->authorizer_buf{,_len} after authorizer update
Commit: 9d37aec9ffe4e743dabc3f84502e9723e17a30d4
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d37aec9ffe4e743dabc3f84502e9723e17a30d4
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68156
Analysis date: Mon, 10 Aug 2026 10:50:39 -0400
ActionableScore: 7
ActionableScore lower bound: 6
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
A stale cached Ceph authorizer buffer can survive after the underlying buffer is freed and later be copied during an msgr1 reconnect, causing a slab use after free with DoS and possible kernel heap disclosure to a Ceph peer.

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

The original Linux kernel CVE announcement for CVE-2026-68156 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68156

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-2026-68156	IMPORTANT	CHECK WITH IMPACT FROM ORIG NN IMPORTANT	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H';*CWE-416;CWE-825;*CWE-200;Other CVSS 'AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:H';BEST CVSS score: '7.4';DESCR 'A slab use after free can occur in libceph because ceph_x_update_authorizer can rebuild au buf while struct ceph_auth_handshake still caches the old authorizer_buf pointer and length. A later msgr1 reconnect can send this stale pointer through tcp_sendmsg and trigger a UAF read in _copy_from_iter, causing a kernel crash and potentially exposing stale kernel heap data to the Ceph peer. For the CVSS the PR:N is used for the paranoid score because the attacker does not need privileges on the victim host if they can act as or influence the Ceph service endpoint involved in authentication and reconnect handling. The issue is network reachable in Ceph deployments, but practical exploitation usually requires access to a Ceph storage network or a malicious compromised Ceph monitor or service rather than public Internet exposure. Impact is at least denial of service and worst case confidentiality impact from stale heap data disclosure. No direct integrity impact is assigned because the observed primitive is a UAF read during socket send, not an overwrite or control flow primitive.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)	YES	REMOTE UAF NETWORK LINUS KPANIC 	NO	NO	checked

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

ActionableScore=7
ActionableScoreLower=6

## 1. ActionableScore

* Conservative score: 6
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Remote reachable / network-triggerable: +2. The stale authorizer buffer is used during Ceph messenger reconnect and can be influenced by a Ceph peer or service-side auth ticket behavior.
* Memory corruption, weak to medium UAF primitive: +1. The concrete primitive is a stale pointer to freed `ceph_buffer` memory, but the observed access is a read/copy during send, not a write or callback dispatch.
* Real lifetime corruption: +1. `auth->authorizer_buf` can survive after `ceph_buffer_put()` frees the old buffer.
* Reliable kernel crash / strong DoS: +1. The commit explicitly reports KASAN slab-use-after-free in `_copy_from_iter()` during `tcp_sendmsg()`.
* Confidentiality impact plausible: +1. Because the freed slab buffer is copied into the outgoing TCP stream, stale kernel heap data may be disclosed to the Ceph peer.

Paranoid additional interpretation:

* Stronger UAF handling: +1 over conservative. This is a real stale pointer after free in a networked storage client path, so it should not be auto-closed as ordinary DoS even though no write primitive is shown.

Not applied:

* Privilege escalation plausible: +0. No reclaim, overwrite, callback, type confusion, refcount takeover, or control-flow primitive is shown.
* Integrity impact plausible: +0. The demonstrated operation is copying from stale memory, not corrupting kernel memory.
* Common networking core path: +0. This is networked, but it is Ceph-specific rather than a central TCP/IP receive path.
* Hard timing race penalty: 0. The bug is a stale cached pointer after rebuild, not primarily a narrow race window.

## 3. Reachability analysis

The bug is reachable by systems using kernel Ceph client authentication with msgr1 reconnect behavior. A practical attacker likely needs to control, compromise, or influence a Ceph service endpoint or storage-network path so that authorizer rebuild and reconnect happen with the stale cached pointer. No local privileges on the victim host are required in that model, but this is normally limited to Ceph storage networks rather than public Internet exposure. Containers and namespaces do not materially lower the trigger requirement unless they can mount or operate Ceph connections that reach attacker-controlled Ceph infrastructure.

Call-site confidence: medium. The patch and commit describe the downstream messenger send path and the KASAN location, but the full caller graph is not included.

## 4. Severity interpretation

This is above ordinary Moderate because it is a concrete lifetime bug with a stale freed pointer used in a network send path. Realistic impact is at least kernel crash or connection-triggered DoS, and confidentiality impact is plausible because freed kernel heap contents may be copied to the peer. It does not currently look like a strong LPE or integrity-corruption issue because the patch supports a UAF read, not an attacker-controlled write or object replacement primitive.

## 5. One-sentence report phrase

A stale cached Ceph authorizer buffer can survive after the underlying buffer is freed and later be copied during an msgr1 reconnect, causing a slab use after free with DoS and possible kernel heap disclosure to a Ceph peer.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED. This is a network-reachable lifetime UAF in a storage protocol path with plausible kernel memory disclosure, so it should not be auto-closed even if practical exploitation depends on Ceph deployment and reconnect conditions.

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

Patch: libceph: refresh auth->authorizer_buf{,_len} after authorizer update
Commit: 9d37aec9ffe4e743dabc3f84502e9723e17a30d4
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=9d37aec9ffe4e743dabc3f84502e9723e17a30d4

Commit description:

ceph_x_create_authorizer() caches au->buf->vec.iov_base and
au->buf->vec.iov_len in struct ceph_auth_handshake.  These
cached values are then used by the messenger connect code when
sending the authorizer.

ceph_x_update_authorizer() can rebuild the authorizer when a newer
service ticket is available.  If the rebuilt authorizer no longer
fits in the existing buffer, ceph_x_build_authorizer() drops its
reference to au->buf and allocates a new one.  If this is the final
reference, ceph_buffer_put() frees the old ceph_buffer and its
vec.iov_base, but auth->authorizer_buf still points at that freed
memory.

A subsequent msgr1 reconnect can therefore queue the stale pointer
and trigger a KASAN slab-use-after-free in _copy_from_iter() while
tcp_sendmsg() copies the authorizer.

Refresh auth->authorizer_buf and auth->authorizer_buf_len after a
successful authorizer rebuild so the messenger sends the current
buffer.

Cc: stable@vger.kernel.org
Fixes: 0bed9b5 ("libceph: add update_authorizer auth method")
Closes: https://lore.kernel.org/all/E378850E-106C-427B-A241-970EB2D054D7@gmail.com/
Signed-off-by: Shuangpeng Bai <shuangpeng.kernel@gmail.com>
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:
  net/ceph/auth_x.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=9d37aec9ffe4e743dabc3f84502e9723e17a30d4

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

The original Linux kernel CVE announcement for CVE-2026-68156 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68156

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:L/I:N/A:H
  The Best / paranoid CVSS vector: AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:H
  The Best / paranoid CVSS score: 7.4

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: 6
  Paranoid ActionableScore: 7

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).