[CVE-2026-80806][MODERATE 7.0] ext4: don't enable DAX on new encrypted files

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

CVE: CVE-2026-80806
Priority: MODERATE 7.0
AL-KERNEL base severity: MODERATE
KPANIC flag: YES
Patch: ext4: don't enable DAX on new encrypted files
Commit: add98959b220935b243170214c787bc03044a44d
Upstream patch: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=add98959b220935b243170214c787bc03044a44d
Original CVE announcement: https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80806
Analysis date: Fri, 04 Sep 2026 13:11:23 -0400
ActionableScore: 6
ActionableScore lower bound: 5
Actionable bucket: Actionable Moderate at minimum
Manual review required: YES

Summary:
An ext4 fscrypt confidentiality issue can allow newly created encrypted files on filesystems mounted with dax always to keep S_DAX and bypass encryption, storing plaintext data despite the encrypted inode policy. For the CVSS the PR:L is used because a local user with file creation rights in an affected encrypted directory can trigger the behavior after the non default DAX configuration exists. YES REQUIRES MANUAL CHECK.

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

The original Linux kernel CVE announcement for CVE-2026-80806 is available here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80806

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.

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AL-KERNEL CLASSIFICATION RESULT
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CVE-2026-80806	MODERATE	https://www.kernelcve.org/list/?q=CVE-2026-80806 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:N';CWE-311;CWE-312;CWE-693;Other CVSS 'AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:L/A:N';BEST CVSS score: '6.3';DESCR 'A confidentiality issue in ext4 encrypted file creation can occur when the filesystem is mounted with dax always. A new encrypted regular file may incorrectly keep S_DAX because the encryption inode flag is set after the initial inode flag calculation, so DAX I/O can bypass the normal fscrypt encryption path and write plaintext data to storage. For the CVSS the PR:L is used because a local user who can create files in an affected encrypted directory can trigger the vulnerable behavior once the non default DAX configuration already exists. The issue is not network reachable and does not indicate memory corruption or kernel code execution. Impact is primarily confidentiality loss for data expected to be encrypted, with possible integrity policy impact because mount and encryption restrictions are not enforced as intended. YES REQUIRES MANUAL CHECK';YES REQUIRES MANUAL CHECK; ,and ActionableScore result is Actionable Moderate at minimum (with actual score 7)	YES	DANGER DISK INIT LINUS KPANIC  KPANIC INCREASED_TO_HIGH_BASED_ON_ACTIONABLESCOREHIGHEREQTHAN6 DECREASED_TO_MODERATE7_BASED_ON_FALSEPOSCHECKOFKP	NO	NO	checked

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ACTIONABLESCORE ANALYSIS
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ActionableScore=6
ActionableScoreLower=5

## 1. ActionableScore

* Conservative score: 5
* Paranoid score: 6
* Final recommended bucket: **Actionable Moderate at minimum**::

## 2. Signal breakdown

* Local unprivileged trigger: +1
  Once an affected ext4 filesystem is mounted with `dax=always` and an encrypted directory exists, a local user able to create files there can trigger creation of a new encrypted regular file.

* Security-boundary bypass with practical sensitive-object access: +2
  The intended fscrypt encryption boundary is bypassed because newly created encrypted files may retain `S_DAX`, causing writes to bypass encryption and reach storage as plaintext.

* Confidentiality impact plausible: +1
  Data expected to be encrypted at rest may be stored unencrypted.

* Integrity impact plausible: +1
  The filesystem violates the configured encryption policy and may create files whose storage semantics do not match the declared encrypted state.

* Important filesystem/storage path: +1
  This affects ext4 inode creation, fscrypt state, and DAX I/O behavior.

* Broad/default/common subsystem: +1
  ext4 and fscrypt are common, security-relevant storage components.

* Legacy / non-default execution mode: -1
  Practical exposure requires `dax=always` and DAX-capable storage, which is not the common default configuration.

No memory-corruption, UAF, OOB write, LPE, or network-triggered primitive is supported by the patch.

## 3. Reachability analysis

The bug is locally reachable by creating a new encrypted regular file under affected conditions. The mount option `dax=always` and DAX-capable storage normally require administrator-controlled system configuration, but the actual trigger can be a non-root user with write permission inside an encrypted directory. Containers and namespaces do not automatically make this easier unless they can access the affected mounted filesystem and create files in the encrypted tree. The path is not network reachable. Realistic exploitation depends on whether the system relies on fscrypt for confidentiality at rest on DAX-enabled ext4 storage.

## 4. Severity interpretation

This behaves like an actionable Moderate issue rather than an ordinary low-risk filesystem bug. It is not a kernel memory corruption issue and does not plausibly provide direct privilege escalation. However, it is a real encryption bypass in an important filesystem path, and the impact can matter when fscrypt is relied on to protect sensitive data at rest. The conservative score is 5 because the configuration is non-default. The paranoid score is 6 because the affected security boundary is encryption itself, and silent plaintext persistence is more serious than a simple correctness or DoS issue.

## 5. One-sentence report phrase

An ext4 fscrypt confidentiality issue can allow newly created encrypted files on filesystems mounted with dax always to keep S_DAX and bypass encryption, storing plaintext data despite the encrypted inode policy. For the CVSS the PR:L is used because a local user with file creation rights in an affected encrypted directory can trigger the behavior after the non default DAX configuration exists. YES REQUIRES MANUAL CHECK.

## 6. Manual review recommendation

MANUAL CHECK REQUIRED.

This should not be auto-closed because it is a storage encryption bypass, not merely a warning or crash. Manual review should confirm whether affected products support ext4 DAX with fscrypt, whether `dax=always` is allowed or documented, and whether encrypted user or service data could have been written as plaintext.

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

Patch: ext4: don't enable DAX on new encrypted files
Commit: add98959b220935b243170214c787bc03044a44d
Upstream URL: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=add98959b220935b243170214c787bc03044a44d

Commit description:

Currently, when a new encrypted regular file is created, the call to
ext4_set_inode_flags(inode, init=true) in __ext4_new_inode() is made
before EXT4_INODE_ENCRYPT is set.  As a result, it can set S_DAX if the
filesystem is mounted with "-o dax=always".

EXT4_INODE_ENCRYPT then actually gets set a bit later in
__ext4_new_inode(), when it calls fscrypt_set_context() which calls
ext4_set_context().  ext4_set_context() sets EXT4_INODE_ENCRYPT and
calls ext4_set_inode_flags(inode, init=false) to set S_ENCRYPTED too.

This was intended to clear S_DAX as well.  However, this was broken by
commit 043546e ("fs/ext4: Only change S_DAX on inode load").  This
causes data written to the file to bypass encryption, also causing
xfstests failures such as generic/548 (when "-o dax=always" is used).

Fix this by simplifying the flow by making __ext4_new_inode() set
EXT4_INODE_ENCRYPT earlier.  This makes it take effect in
ext4_set_inode_flags(inode, init=true), making S_DAX never be set.

Similarly, make EXT4_STATE_MAY_INLINE_DATA never be set in the first
place on new encrypted inodes.  Then it doesn't need to be cleared.

As a result of these simplifications, ext4_set_context() no longer needs
to change inode flags or state when 'handle != NULL'.  Remove that too.

Reported-by: Disha Goel <disgoel@linux.ibm.com>
Reported-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Closes: https://lore.kernel.org/r/20260723085648.1500357-1-ojaswin@linux.ibm.com
Fixes: 043546e ("fs/ext4: Only change S_DAX on inode load")
Cc: stable@vger.kernel.org
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Tested-by: Disha Goel <disgoel@linux.ibm.com>
Reviewed-by: Ojaswin Mujoo <ojaswin@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://patch.msgid.link/20260730175212.36923-1-ebiggers@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Changed files:
  fs/ext4/ialloc.c
  fs/ext4/super.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=add98959b220935b243170214c787bc03044a44d

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

The original Linux kernel CVE announcement for CVE-2026-80806 can be found here:
https://lore.kernel.org/linux-cve-announce/?q=CVE-2026-80806

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:H/I:L/A:N
  The Best / paranoid CVSS vector: AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:N
  The Best / paranoid CVSS score: 6.3

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: 6

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).