[CVE-2026-68147][IMPORTANT] fscrypt: Avoid dynamic allocation in fscrypt_get_devices()

[CVE-2026-68147][IMPORTANT] fscrypt: Avoid dynamic allocation in fscrypt_get_devices()

[AL-KERNEL]

CVE: CVE-2026-68147
Priority: IMPORTANT
AL-KERNEL base severity: IMPORTANT
KPANIC flag: YES
Patch: fscrypt: Avoid dynamic allocation in fscrypt_get_devices()
Commit: 4462ac3d90e897dda52ce4b6af2d526ddae835a8
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4462ac3d90e897dda52ce4b6af2d526ddae835a8
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68147
Analysis date: Mon, 10 Aug 2026 19:40:41 -0400
ActionableScore: 7
ActionableScore lower bound: 5
Actionable bucket: Strong Important candidate / Actionable Moderate at minimum
Manual review required: YES

Summary:
fscrypt_destroy_inline_crypt_key() could free a blk_crypto_key without evicting it from all block devices after fscrypt_get_devices() allocation failure, leaving stale block-crypto references and creating a local use-after-free risk under fscrypt inline-encryption workloads.

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ABOUT THIS REPORT
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The original Linux kernel CVE announcement for CVE-2026-68147 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68147

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-2026-68147	IMPORTANT	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-416;CWE-252;CWE-755;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H';BEST CVSS score: '7';DESCR 'fscrypt_destroy_inline_crypt_key() could free and zeroize a blk_crypto_key without first evicting it from all block devices when fscrypt_get_devices() failed under memory pressure or direct reclaim. This leaves block crypto state with a stale reference to freed key memory and creates a use-after-free condition. For the CVSS the PR:L is used because a local unprivileged user may be able to exercise encrypted file operations and memory pressure on a system where fscrypt inline encryption is enabled, while reliable triggering depends on filesystem configuration and reclaim timing. The issue is not network reachable. Impact is at least local denial of service via kernel crash and in the paranoid interpretation may allow confidentiality or integrity impact because the bug class is use-after-free in kernel memory.';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Strong Important candidate / Actionable Moderate at minimum (with actual score 7)  SKIP CVE-2026-68147 UNKNOWN SKIP No affected files built, so skip this CVE NO  - - unknown 	MAYBE	DISK INIT NOMEMCHK UAF HARDWARE LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN7	-	-	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=7
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 7
* Final recommended bucket: **Strong Important candidate / Actionable Moderate at minimum**::

## 2. Signal breakdown

Conservative signals:

* Local unprivileged trigger: +1. A local user may be able to exercise fscrypt encrypted file operations and trigger inode eviction on a system using fscrypt inline encryption.
* Generic memory corruption: +2. The commit explicitly states that skipping blk_crypto_evict_key() before freeing blk_crypto_key causes a use-after-free.
* Real lifetime corruption: +1. This is a stale lifetime/reference issue involving blk_crypto_key and block-device crypto state.
* Important filesystem/storage path: +1. The affected path is fscrypt inline encryption and blk-crypto key lifecycle management.
* Hard or unreliable condition: -1. Reliable triggering depends on allocation failure under memory pressure or direct reclaim, plus a suitable fscrypt inline-encryption setup.

Paranoid additional signals:

* Weak LPE concern: +1. The primitive is a kernel UAF involving a security-sensitive crypto key object, but the patch does not show controlled reclaim, overwrite, callback control, or type confusion.
* Confidentiality impact plausible: +1. In the paranoid interpretation, stale crypto-key state could theoretically affect key material handling or adjacent reused memory.
* Integrity impact plausible: +1. In the paranoid interpretation, stale key references in block crypto state could theoretically affect encrypted I/O correctness or reused kernel memory.

Not counted:

* Remote reachable: +0. No network path.
* Strong LPE plausibility: +0. No demonstrated attacker-controlled reclaim, arbitrary write, callback dispatch, or reliable object replacement.
* Availability impact separate bonus: +0. DoS is plausible, but not double-counted beyond the memory-lifetime issue.

Call-site confidence: high. The patch includes fscrypt_get_devices() callers in select, prepare, and destroy paths, including the exact destroy path that skipped eviction on allocation failure.

## 3. Reachability analysis

The trigger is local. A user needs access to workloads that create, use, and evict fscrypt inline-encryption keys, most plausibly on f2fs or another filesystem using blk-crypto inline encryption. The vulnerable destroy path can be reached during inode eviction, and the problematic failure case is allocation failure in fscrypt_get_devices(), especially under direct reclaim.

Namespaces and containers may matter only if the container can access a mounted encrypted filesystem and generate relevant file lifecycle pressure. This does not require full host root in all deployments, but it does require a configured fscrypt inline-encryption environment. The path is not remotely reachable and is not a generic default server exposure.

## 4. Severity interpretation

This is at least an Actionable Moderate because the patch fixes an explicitly described kernel use-after-free in a storage crypto key lifetime path. Realistic exploitation evidence points most clearly to local DoS or unsafe stale key state under memory pressure. The Important-class concern is paranoid but defensible because the affected object is a freed kernel crypto key object that may remain referenced by block crypto state.

This should not be auto-closed as an ordinary Moderate resource-allocation cleanup. The allocation failure is not just an ENOMEM handling bug. It changes whether blk_crypto_evict_key() is called before freeing the key.

## 5. One-sentence report phrase

fscrypt_destroy_inline_crypt_key() could free a blk_crypto_key without evicting it from all block devices after fscrypt_get_devices() allocation failure, leaving stale block-crypto references and creating a local use-after-free risk under fscrypt inline-encryption workloads.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED

Reason: the commit explicitly identifies a use-after-free in kernel storage crypto key lifetime handling. Conservative impact is local DoS, but the stale key reference and security-sensitive object type make this a manual-review candidate for possible confidentiality, integrity, or privilege-escalation implications.

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

Patch: fscrypt: Avoid dynamic allocation in fscrypt_get_devices()
Commit: 4462ac3d90e897dda52ce4b6af2d526ddae835a8
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=4462ac3d90e897dda52ce4b6af2d526ddae835a8

Commit description:

When a blk_crypto_key starts being used or is evicted, fs/crypto/ calls
fscrypt_get_devices() to get the filesystem's list of block devices,
then iterates over them and calls blk_crypto_config_supported(),
blk_crypto_start_using_key(), or blk_crypto_evict_key() on each one.

Currently, the block device pointers are placed in a dynamically
allocated array.  This dynamic allocation is problematic because:

- It can fail, especially at the fscrypt_destroy_inline_crypt_key() call
  site when it's invoked for inode eviction under direct reclaim.

- fscrypt_destroy_inline_crypt_key() doesn't handle the failure.  It
  just zeroizes and frees the blk_crypto_key without calling
  blk_crypto_evict_key().  That causes a use-after-free.

For now, let's fix this in the straightforward and easily-backportable
way by switching to an on-stack array.  Currently the fscrypt
multi-device functionality is used only by f2fs, which has a hardcoded
limit of 8 block devices.  An on-stack array works fine for that.

(Of course, this solution won't scale up to large number of block
devices.  For that we'd need a different solution, like moving the block
device iteration into the filesystem.  Or in the case of btrfs, which
will only support blk-crypto-fallback, we should make it just call
blk-crypto-fallback directly, so the block devices won't be needed.)

Fixes: 22e9947 ("fscrypt: stop holding extra request_queue references")
Cc: stable@vger.kernel.org
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://sashiko.dev/#/patchset/20260713023708.9245-1-ebiggers%40kernel.org
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260719055602.78828-1-ebiggers@kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  fs/crypto/inline_crypt.c
  fs/f2fs/super.c
  include/linux/fscrypt.h

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=4462ac3d90e897dda52ce4b6af2d526ddae835a8

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

The original Linux kernel CVE announcement for CVE-2026-68147 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-68147

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: 5
  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).