[CVE-2026-64312][MODERATE 7.0] crypto: pcrypt - restore callback for non-parallel fallback

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

CVE: CVE-2026-64312
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: crypto: pcrypt - restore callback for non-parallel fallback
Commit: 81ce16d938db9b88cdc231522c0358395ae8c6b5
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=81ce16d938db9b88cdc231522c0358395ae8c6b5
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64312
Analysis date: Sat, 25 Jul 2026 12:20:24 -0400
ActionableScore: 5
ActionableScore lower bound: 4
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
A pcrypt AEAD fallback bug can leave a padata completion callback installed when direct child AEAD execution is used after `padata_do_parallel()` returns `-EBUSY`, allowing asynchronous completion on an invalid request state and causing at least local DoS with possible lifetime-corruption concerns.

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

The original Linux kernel CVE announcement for CVE-2026-64312 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64312

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 7.0
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-2026-64312	MODERATE	CHECK WITH IMPACT FROM ORIG NN MODERATE	Maybe valid. Check manually. Hints by AL-KERNEL: The best (paranoid) CVSS is 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H';CWE-703;CWE-755;*CWE-664;*CWE-416;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'A callback confusion bug exists in crypto pcrypt when padata_do_parallel returns EBUSY and the code falls back to direct AEAD execution. The child AEAD request can still carry the pcrypt_aead_done callback even though the request was never enrolled in padata, so an asynchronous completion can run padata completion logic on an invalid request state. For the CVSS the PR:L is used because a local user or local process generally needs access to a pcrypt backed crypto interface or to a configured kernel consumer of this algorithm. The issue is not directly network reachable from the patch context, although network triggered use may be possible only if a system already routes attacker controlled traffic through a pcrypt based kernel crypto consumer. Impact is at least a local denial of service via crash, warning, or broken crypto request completion. In the paranoid interpretation, the callback and padata state mismatch is treated as a plausible memory lifetime or list state corruption candidate, so confidentiality and integrity impact should be reviewed manually.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 5)	YES	SIMPLEFIX LINUS  KPANIC INCREASED_TO_MODERATE7_BASED_ON_GUESSCVSS	YES	NO	checked

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

ActionableScore=5
ActionableScoreLower=4

## 1. ActionableScore

* Conservative score: **4**
* Paranoid score: **5**
* Final recommended bucket: **Actionable Moderate at minimum**

## 2. Signal breakdown

Triggered signals:

* **Local unprivileged trigger: +1**
  Potentially reachable by a local process using a pcrypt-backed crypto interface, for example through AF_ALG if the algorithm/template is available.

* **Memory corruption, weak/indirect corruption candidate: +1**
  The bug is a callback-state mismatch. The child AEAD request may carry `pcrypt_aead_done()` even though it was not enrolled in padata. This is not a demonstrated arbitrary write or controlled UAF reclaim, but it is more than pure bookkeeping.

* **Real lifetime corruption / async completion lifetime mismatch: +1**
  The wrong completion callback can run asynchronously on a request that is in the wrong padata state, creating a plausible lifetime or state-corruption hazard.

* **Reliable kernel crash / strong DoS: +1**
  A wrong async completion path can plausibly lead to warning, broken request completion, Oops, or crash.

* **Local high-control crypto API context: +1 paranoid only**
  AF_ALG and crypto request APIs can give local users relatively fine-grained control over request submission and async completion behavior, if pcrypt is exposed in the evaluated configuration.

Subtracted signals:

* **Hard or unreliable condition: -1**
  Triggering requires `padata_do_parallel()` to return `-EBUSY` and the fallback AEAD operation to complete asynchronously.

* **Configuration / exposure uncertainty: -1 conservative only**
  pcrypt must be configured and actually selected by a reachable crypto consumer. It is not a universal default hot path.

Not awarded:

* **Remote reachable: +0**
  The patch does not show direct network-triggerability.

* **Strong LPE plausibility: +0**
  No demonstrated attacker-controlled reclaim, arbitrary write, type confusion, or controlled callback target.

* **Strong generic memory corruption: +0**
  The primitive is callback/state confusion, not a proven UAF reclaim or overwrite primitive.

## 3. Reachability analysis

The most plausible trigger is a local process or local kernel consumer that can submit AEAD operations through pcrypt. If AF_ALG exposes the relevant pcrypt-backed algorithm to unprivileged users, then PR is effectively local unprivileged. If only privileged kernel configuration or a specific subsystem uses pcrypt, reachability is lower.

Namespaces do not automatically make this remote or container-escape reachable, but containerized workloads with access to AF_ALG or a crypto consumer may still be relevant. The issue is not default network packet parsing. Network-triggered use is only plausible if attacker-controlled traffic is processed by a kernel path configured to use pcrypt.

## 4. Severity interpretation

This is stronger than an ordinary Moderate correctness fix because it involves async callback confusion and request lifetime/state mismatch. Realistic demonstrated impact is most likely local DoS. The paranoid concern is that running padata completion logic for a request that was never enrolled in padata could create memory lifetime or list-state corruption, but the patch does not show a controlled overwrite or reliable privilege-escalation primitive.

Therefore this should be treated as **Actionable Moderate at minimum**, not auto-closed, but it is not a strong Important candidate without additional evidence.

## 5. One-sentence report phrase

A pcrypt AEAD fallback bug can leave a padata completion callback installed when direct child AEAD execution is used after `padata_do_parallel()` returns `-EBUSY`, allowing asynchronous completion on an invalid request state and causing at least local DoS with possible lifetime-corruption concerns.

## 6. Manual review recommendation

**MANUAL CHECK REQUIRED**

Reason: async callback confusion in crypto request handling is a plausible lifetime/state-corruption class, and the exact risk depends on call-site reachability, AF_ALG exposure, async AEAD behavior, and whether the invalid padata completion can corrupt request or list state beyond a crash.

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

Patch: crypto: pcrypt - restore callback for non-parallel fallback
Commit: 81ce16d938db9b88cdc231522c0358395ae8c6b5
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=81ce16d938db9b88cdc231522c0358395ae8c6b5

Commit description:

pcrypt installs pcrypt_aead_done() on the child AEAD request before
trying to submit it through padata.  If padata_do_parallel() returns
-EBUSY, pcrypt falls back to calling the child AEAD directly.

That fallback must not keep the padata completion callback.  Otherwise
an asynchronous completion runs pcrypt_aead_done() even though the
request was never enrolled in padata.

Restore the original request callback and callback data before calling
the child AEAD directly.  This keeps the fallback path aligned with a
direct AEAD request while leaving the parallel path unchanged.

Fixes: 662f2f1 ("crypto: pcrypt - Call crypto layer directly when padata_do_parallel() return -EBUSY")
Cc: stable@kernel.org
Reported-by: Yuan Tan <yuantan098@gmail.com>
Reported-by: Yifan Wu <yifanwucs@gmail.com>
Reported-by: Juefei Pu <tomapufckgml@gmail.com>
Reported-by: Zhengchuan Liang <zcliangcn@gmail.com>
Reported-by: Xin Liu <bird@lzu.edu.cn>
Assisted-by: Codex:gpt-5.4
Signed-off-by: Ruijie Li <ruijieli51@gmail.com>
Signed-off-by: Ren Wei <n05ec@lzu.edu.cn>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Changed files:
  crypto/pcrypt.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=81ce16d938db9b88cdc231522c0358395ae8c6b5

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

The original Linux kernel CVE announcement for CVE-2026-64312 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-64312

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:H/PR:L/UI:N/S:U/C:H/I:H/A:H
  The Best / paranoid CVSS score: 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: 4
  Paranoid ActionableScore: 5

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: YES
Published priority for this report (same as in Subject): MODERATE 7.0

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).